Checked the buffer tube per instructions, and it does not appear it was (or now is) preloading.  I wasn't meaning to criticize others, and my wording sucked describing my process.  Sorry about that.  I'm pretty sure, in my case, the biggest difference is the forward side charging handle on the FM uppers and the leverage it provides by charging with an extend arm.  (I checked, and while I got a decent handshake, I'm not a secret farrier.  I do admit, nailing furs to people's feet sounds fun.)  I tried charging it when I woke up in the middle of the night, to see how my sleepy-hands handled charging, and they were reliable.

I kinda went down a rabbit hole trying to make the charging as hard as I had anticipated.  The point where it became really hard was my upper with a kaw/faxon bbl upper (not fully broken in yet -- chamber is a hair tight), dry cleaned to remove lube, a round chambered, with a new fully loaded glock magazine in the well.    I couldn't reliably cycle on my first attempt in anything resembling a normal position.  (The upper with the FM bbl was still reliably cyclable under similar conditions.)  I played around with much of this while watching tv, until suddenly every charge was getting harder... and I realized my right index finger was red and swelling up from the repeated charging.  Mighta over done it.

It was stated to me directly from an employee at Maxim Defense. It wasn’t made clear exactly what parts but certainly part or parts from the assembly come from Germany if I’m remembering correctly. My assumption is the critical dimension and hardened parts but that’s just speculation. Maybe it’s just the parts concerning the patent mentioned previously.

So, I got curious, and I found the Swiss patent to see if there was anything interesting in there -- mostly curious about the design diagrams as my German's a little rusty.

Swiss patent for Wyssen Defence AG RDB system

US Patent for Wyssen RDB system

It's not that different.

Compared to both/either patents, the Maxim system uses a different spring configuration than the diagrams (Fig 1-3, 7), and a different profile for the "short" contour sleeve than Fig 7 for their CQB version.

In the patent drawings -- Swiss and US -- there is a second, wider diameter spring at the base instead of a plastic bumper.  The short-sleeved version extends this outer spring and removes the spring tight to the shaft.

That extra spring at the end of the compression would slightly stiffen the compression at the back of the cycle and thus store extra energy.  Upon moving forward, for the first inch (or so), the diagrams have the 2 springs imparting energy on buffer/bolt increasing the energy released in that period.  (This is the exact opposite of the compression order for Dead Foot Arms MCS springs, which I find interesting.)  More energy released, more acceleration during that period.  Faster bolt means lower cycle time, right?  I wonder why this was changed for production.  Would this have any effect on gas issues, or are the gas issues inherent to the cycle speed/delay while the chamber is opening?


Regarding location of manufactured of parts, I'd be curious if overseas sourcing was part of the contract to use the patented technology, and if there's any relation to which parts are modified from the patent diagrams.
---
ETA link for US patent

Ordered a carbine version for a PSA AR-V MP5 knockoff build. See how long it takes to ship.

Thanks for linking those very interesting. They both still have the hard polymer stop at the end of travel it seems. The larger spring at the end may be just to cushion that hard stop?  

I got mine in the mail and opened it up. Everything looks well made. It was also completely dry no lube no grease on bearings. Shout out to Tim at Maxim for everything!  Now I just need to get it installed and put some rounds out. I don’t have anything too fancy just a 16” mostly Angstadt parts gun that feeds from Glock mags. Also have a lower that feeds from Colt mags so I’d be interested to see if that makes any difference. Bolt is cut for either magazine and the rifle has run flawlessly with a 9mm 7 point something ounce buffer, standard carbine spring, and 9mm spacer at the bottom of the tube making it a “short stroke” setup. LRBHO does not function but it runs well and has mild recoil probably mostly due to the overall weight of the rifle.

Is the consensus that the “pre load” needs to be such that when the upper and lower are together the bolt needs to just be resting but not actively engaging the recoil assembly?

That seems to make the most sense.  If it's pre-loaded, then you're not getting the full effect of the delay mechanism, so you're extracting the case too fast & the bolt is going to transfer more energy to the buffer tube when it stops.

If there's a gap, then the bolt is again extracting the case too fast before hitting the buffer, leading to a possible case failure.

I present the proof of concept of the MaxBreaker.  I took an ambi charging handle, attached an aluminum plate via bolts to the right side paddle.  That plate pushes on the tang as the charging handle's right side is pulled.  The length of the charging handle becomes a lever, and its length determines the force multiplication, so a longer handle makes this easier.  At a rough estimation this prototype about doubles the force applied to the paddle as it applies it against the tang.  This force then pushes the handle back, retracting the bolt through the "hard" part of the charge.

This charging handle that comes with holes is United Defense or Presma design.  (Presma Ambi Charging Hadle on Optics Planet, United Defense Ambi Charge Handle at Davidson Defense.)  The bolts and washers and nuts are nothing special.  The aluminum plate was a piece of scrap -- a flat heat sink out of some electronic item I scrapped.







And this is the displacement from just the lever pull:

Refining the shape and hole placement would increase this several hundredths.

--- Earlier thoughts on this concept

Re levered charging handle:  How hard would it be to design a charging handle that pushes against the back of the upper receiver tang that's over the charging handle?  A milspec handle has the whole right side available to put a pivot point for a lever into.  A lever similar to QD throw levers could start in a forward pointing position along the side of the receiver, then rotate about 90° until lines up to pull the handle.  Ambi charging handles could accomplish the same feat from either or both sides... or with precise enough machining, I think the ideal would be for both levers to have gear teeth and push a small piston into the tang.

ETA displacement picture

Nice.  Could we do something similar w/ a side charging handle?

Oh I kind of like the cammed charging handle, it is needed with the larger cal H&K roller guns. Cleaver idea.

Now for my review, mine that I ordered in july just came in. I put it in the tube and it might be preloaded a little. I did unscrew the buffer tube 1 turn but there is a gap between the bolt and buffer face. I screwed it back in and test shot it. It is much better than the 7.5 oz buffer than was in it, but it seems like bolt speed is higher. This would not surprise me as mp5 bolt speeds are fast as well, and I use colt/uzi style mags and if they can keep up with 1200 rpm on a mini uzi I think it will be fine.

I do need to test more than the 30 rounds I put thru it, I will also unscrew the buffer tube and shim the back on the inside of the tube to eliminate the gap and retest. Total it got 30 rounds fired thru it, 10 by me 20 by two others.

Oh cocking force is a lot higher but not OMG high. I also found playing with it that mortaring it on my leg made charging it a lot easier.

Rather than screwing in the tube, anyone tried closing the gap w/ quarters?

Quarters, washers, shims, etc. Whatever that is handy and the right thickness.

QC10's cut-out handle -- no
NFA/Spartan/Gibbz Gen 2 -- Maybe, but it would require a pivot point, probably by drilling into the charging handle.  The charging handle sits a bit lower than the rail, so a lever can't both sit flat against the charging handle and push against the picatinny rail.  I don't have the tools, materials, or expertise to do that and know I wouldn't mess it up.  These handles sit farther from the body of the receiver, so any lever mounted on them would have a pivot point further from the body.  To gain a mechanical advantage, the manipulated end of the lever would have to be proportionally further away from the pivot point than the contact point on the receiver.  I worry the lever would be cumbersomely large.  But I think it's possible.
Gibbz Gen 3 handle -- Less likely.  With the latch in the handle, there's less space to mount anything, but there are a couple of roll pins in it that, depending on the internals, possibly be replaced with a slightly wider hardened bolt, and that could be used as a pivot point...  I don't actually have one of these to even look at.
Foxtrot Mike forward chargers, Gen 1 Handle -- I don't know how strong the fiberglass material of the charging handle is in regards to mounting a lever.  But, there's plenty of material to work with.  These ride high enough that a lever might be able to smoothly push against part of the picatinny rail.  The one problem with this handle is it's only held in by friction, and a lever might slowly work the charging handle loose.
Foxtrot Mike forward chargers, Gen 2 Handle -- Probably not, but I don't yet have a gen 2 handle, so it's hard to say.  It'd be harder to get the angle right on a lever with the charging handle coming out at an inclined or declined angle instead of horizontal.
FM forward chargers, paratrooper handle -- This was where I started with the idea, seeing the folding paratrooper handle.  I think something could be done with it.  I believe the paratrooper handle is steel, making it more viable to drill through and mount a lever on.  I have one of these coming, and will see what I think think with it in my hands.

Those are the side chargers that I can speak to.

It would be possible to make a bulky, unwieldy rail-mounted lever to do the same thing to side chargers that couldn't easily be modified, but I see that as an untenable, if functional, solution.

The elegance of using the charging handle is that the lever is already there, and the plate I added is mechanically one piece with the paddle it's attached to.  If someone, say Maxim, wanted to use a solution like this, there's a good chance that all they need to redesign is one part of an ambi-charging handle: left or right paddle.  (Paddle length and location of pivot point/roll pin will make some models more suitable for this purpose than others.  I know manufacturing and IP involve more hurdles than design.)  I admit this with sadness, as I'm no fan of rear charging.

Some other thoughts on those receivers and charging the Maxim system:
The milspec handle and the QC10 handles have the same issue: the latch is a thin horizontal piece of metal that protrudes from the face of the charging handle, and more force is transferred along that thin part of the handle than the surface it protrudes from.  Additionally, both have a spring that exerts force into the finger.  Neither are comfortable on the charging finger.  The ambi charging handle and FM charging handle (along with the NFA/Spartan side charger) have broad, uninterrupted surfaces for the fingers to rest on.  The NFA/Spartan/Gibbz Gen 2 additionally uses a ball detent that exerts no force parallel to the charging action once it is unlatched -- every other charging method I tried has a small spring imparting an imposing force on part or all of the charging finger(s) through the entire charge.

Greater surface area of the charging handle greatly decreases the pressure on the charging finger, and that makes me think an NFA side charger with the ball detent instead of the latching lever should shine here.  The NFA handle has more surface area, no protruding latch, and like the QC10 benefits from leverage of being about 6" forward of the rear charging handle.  The more surface area there is to spread the force over, the more comfortable because less pressure, and the easier on the fingers it is to pull.  Of all four, using both sides of the rear ambi charging handle was the most comfortable for my hand, dividing the force between my index and middle finger, but it felt like my arm muscles were straining more than with the FM forward chargers.  The FM forward side chargers felt like less work on the arms, but harder on the fingers as the surface area is around half that of the ambi charging handle, and only 1 finger fits.  Gloves made the pressure on my finger much more tolerable.

Anyone able to link to the Law tactical/Maxim RDB adapter mentioned earlier? I looked only to find one for a couple of other manufacturers. Nothing mentioned for the Maxim RDB. I built my wife a shorty backpack AR-V that uses a law folder. Unfortunately, the law and RDB are not compatible.

https://www.anarchyoutdoors.com/tactical-folding-bolt-carrier-extension/

Thank @Droppoint

Has anyone tried the Devil Dog Hard Charger with the Maxim RDB? I saw someone mentioned it but didn’t see if anyone used With the RDB. I’m going to order either the RDB or go with the Gentle Recoil System for my 8” JP-GMR15. I figure if I go with the RDB I’d likely want the LevAr or the Devil Dog. I’ve read and reread this thread twice. Still can’t make up my mind on what to go with.

Thanks HD I looked at this one but it was OOS and didn't mention compatibility with the Maxim RDB. When it comes back in stock I'll grab one.

Thanks.

It works, but in mine LRBHO stopped working for some reason.  I don't know if the little bit of mass from the adapter was the cause (slight shortstroke?), or something else.

Got mine last week and finally put it in my (almost complete) build.  

I have an FM 10" side charging upper and no buttstock and that thing is 'resistant' to charging.  I'll be on the farm this weekend shooting it.

I installed mine and also had to turn my buffer tube out 1 turn so it wouldn’t preload.
I’m using a Tecwell tac latch L, which is the largest charging handle I’ve found, and I can get 4 fingers on it pull it back.
I wear a thin work glove on my weak hand which reduces the felt pressure on my fingers and I don’t have to worry about snagging a fingernail
https://techwellusa.com/advanced-ambi-arc-l-charging-handle-for-ar-platform-223.html

That thing is huge:

@Malfero - what charging handle do you have for your FM?  Rear, forward side gen 1 (polymer/fiberglass?), forward side gen 2 (angled steel handle), or paratrooper(folding)?



I have a decently performing prototype of the MaxBreaker rear charging handler.  I flubbed some of the angles and cut one piece a bit shorter than I should have, so there's still room for improvement.  

There's still some of the higher force portion of charging remaining after the lever finishes acting, but it is negligible compared to what it was with this ambi charging handle previously.


The screw attaching to the nut with the washer goes through a short slot, not a round hole, allowing the left lever piece to rotate around the outermost screw.


A side by side image of the charging handle latched, and with the paddles depressed/latch fully open.  The difference is about 0.120".  The amount of displacement requiring the increased force is about 0.150" (that's a very rough measurement).  So, there's a small period of the increased resistance remaining, but most isn't felt at full strength.


The MaxBreaker, installed.  I do intend on flipping those other screws upside down so their screw heads are up, but it's easier to work on this way.




Rear / underside view


edit: typo fix

This is some brilliant work!

Forward charging Gen(?).  The handle itself is a small plastic nub slightly angled up.  I do have the folding paratrooper handle and plan on installing it this weekend.

When I go to charge, as long as I immediately jerk the handle back it'll charge with little issue.  If you start pulling it back, realize it's hard to pull then add more force, add some more force etc, that's when it's hard.

That's the same way my NFA side charger works. Might be hard to snatch a standard charging handle the same way.

Got the RDB Carbine assembly finally. Ordered June 13 direct from Maxim. Received on Sept 13. 13 weeks. Yikes. But glad it finally got here.

Went to install it on a mostly Angstadt Arms 16” rifle - purchased assembled upper and lower when they were running really good sales a year ago or so. I had a 7.5oz extended buffer with a 9mm spacer and a standard carbine spring in it to produce a sort of “short stroke” setup. Shot it quite a bit with little cleaning and never had issues with reliability accuracy or recoil.

Went to install the RDB and realized the buffer tube had an overly thick bottom end. The very rear most round portion of the buffer tube was way thicker than other tubes and would not allow the RDB to go in without being almost entirely unthreaded from the receiver.

My only spare receiver extension / buffer tube was an A5 length. So with the above mentioned Colt style 9mm spacer (apparently this is used so that a normal carbine buffer can be installed with this spacer at the bottom of the tube to prevent over-travel of the bolt / buffer) it installed perfectly with plenty of thread engagement into the receiver. There is zero preload and zero free space between the bolt and RDB when everything is installed and closed. Just a note - because the bolt / carrier is not retained by a closed ejection port cover and the RDB is not retained by the buffer retainer pin and spring everything just sort of wants to slide out when taking the rifle down. Not a big deal but instead of pivoting the upper and lower apart as I normally would I just separate them  while keeping the bolt and buffer retained with my hands.

Next the only bad part - it is EXTREMELY DIFFICULT to charge the rifle. It’s just a tad easier to charge when there is a round chambered already. The RDB came completely dry so I greased the ball bearings with some Geiselle 0000 thin grease and it didn’t seem to do much. If someone picked this thing up and didn’t know what was going on they would probably think it’s seized and broken. Between myself and two other young healthy active males we all agree it’s horrible to charge the rifle.

Now the good part - it’s super soft recoiling. Between the weight of the rifle (old Aimpoint Comp M4 on top) and the RDB it shoots softer than an MP5. I will definitely be leaving this in and hopefully it will either wear in a bit or I will get better at charging it. I might even consider getting one of those camming charging handles eventually when I find one on sale.

I've been contemplating charging handle locations a lot since this product came out.  The difference in difficulty of a charging handle at different locations depends is more than leverage; it also depends on which muscle groups of the user are stronger and what position their body is in.  You'd think we all are in the same position to use a charging handle, and for a rear charging handle, the angle of your elbow is gonna be pretty similar if you are short or tall.  But when that charging handle moves forward, and the elbow opens, it changes body position, and alters the kinematics of using the charging handle.  This happens at different rates depending on arm length.  Body size changes the advantage you get with forward charging handles.  

For an extreme example, for a shorter person an FM charging handle (located 14" forward of the rear charging handle position) pull can utilize shoulder muscles as the arm approaches full extension.  A taller person, whose elbow is still significantly bent cannot provide much help from the shoulder muscles to an arm in a contracted position.

The further forward the charging handle is, the greater kinematic advantage the larger muscle groups in the upper arm have (bicep, primarily, in this case).  



@Droppoint -- thanks for the compliment.  I appreciate the digital force readings you have on your blowback9.wordpress.com article and your methodical approach to gathering data and documenting.  The math in the image below is based on your numbers.

Here's a sketch of another style handle that's next up on my fabrication list to deal with the Maxim's charging force wall.  This one will be a standard charging handle (non ambi) and rely on the thumb and finger pinching together as added leverage.  So, more advantageous for those that have a strong grip... and also potentially problematic with the testing method of pulling the charging handles with paracord.



ETA: The other advantage to this it allows the thumb muscles to help retract the charging handle, and usually the thumb muscles contribute nothing to the rearward force.  The thumb is also the strongest digit on the hand, by far.

By the time you go to a Foxtrot Mike upper & their Paratrooper folding charging handle, you're right @ $500 in the upper.

*smh*

I'm not meaning to advocate for getting an FM upper, nor would necessarily be beneficial -- I was just illustrating changes to which muscle groups are used to complete the charging action as the handle position changes.  (Other factors may make FM a bad choice for someone.)  I also am not advocating getting an AK instead of an AR. The FM is just a clear example of how it changes.

An incomplete side charging upper receiver usually runs $200-$300, and there's still barrel, bolt and handguard to go.  I haven't run across much for inexpensive side charging upper receivers in general.

As I said above, the charging difficulties of this RDB buffer system have made me think about how we go about using charging handles -- the body physics -- more than I ever have before.  At least I think I said that up there.  It's more information to digest than a suggestion of a definitive solution or course of action.

No, I appreciate the math.  The cheapest route to a side charging upper is a Dremel, a tap, and a lot of oil.  My FIL used his mill, of course, but he was much happier w/ his side charger AR.

The problem of difficulty cocking a device of the configuration discussed here was resolved around 1100 with the invention of the crossbow stirrup.

MHO, YMMV, etc.  Be well.

I just adjusted the buffer tube to stop the preload. It then had enough slop that the recoil system rattled when I shook the rifle. So I started looking at items I had around to use as a spacer, well it turns out a penny is about one turn worth of threads. So I started digging further and found my bag of 5/8 muzzle devise shims. The thickest one was perfect. I can see the the bolt slightly push back on the buffer face when it closes but then returns to full forward once closed all the way, no rattle, no preload.

Cocking force feels the same as when it was preloaded, so I will give it another test in a few weeks when I can get to the range.

I think the statement that preloading it makes a big difference needs some clarification and investigation.

Below is the force vs displacement chart from the patent for this device.  The graph is labelled N for Newtons (force) and mm for millimeters (distance).  Our force measurement is in pounds, and we use inches for distance. The shape of the graph stays the same, whatever your units are.



Work = Force x Distance
By reducing the distance the bolt travels in the higher force portion of the chart (essentially shifting your starting point on the graph above from the vertical axis to a point on the line slightly right), the amount of force needed to break through is not decreased at all -- in fact, the starting force INCREASES slightly, unless the preload overcomes the entire higher force portion of the cycle -- and that is very roughly about 0.150".  What is decreased is the amount of energy (work) that is absorbed by the spring system both in this portion and overall, making the system less effective, and decreased is the distance & time (presuming the same force pulling) that a higher force must be applied.

So a small preloading doesn't reduce the necessary force, but it does decrease how long it must be applied before it gets easier.

A milspec buffer tube is 16 threads per inch, or .0625" per thread.  A quarter is about .069".  A penny is about .0598".   If your system is preloaded, and you back out your buffer tube one full turn, and add a quarter spacer, the amount of preload just increased.  (-.625"+.69" = .065")  If you backed it out and put a penny in, your preload only decreases 0.0027" -- about a 1.8% preload.   (0.0027/0.150 =   0.0018)

Thinner shims than coins are a good choice to solve preloading.

An unindexed pistol buffer tube shines over a standard carbine buffer in this situation.  Without an index, you can just slowly screw the tube back in, then tighten the castle nut when the extension meets resistance as the buffer system contacts the rear of the bolt/carrier.

A couple thousandths shouldn't make a difference, but a several hundredths will, which a full turn is.  This might give some extra insight when figuring out how to deal with a preloading situation.

I'd like to add the caveat that my .150" for the higher-resistance segment is a very rough number, but that in no way changes the math above relating to coinage and thread pitch -- just the % preload calculation.


@SecondAmend -- are you sure the best charging aid wasn't the cranequin from slightly later?  I also see more potential for adding a geared handle to an AR rail.

edits: some phrasing edits for clarity

The mil-spec based MaxBreaker.  This version utilizes a lever and the thumb for additional charging force at a mechanical advantage.


A rear view, showing the stop for the lever, so it doesn't fly around.  This model gets in the way of his MBUS folding down in the rearmost 2 positions on the rail.  (Many BUIS should be unaffected.)


And an update to the Ambi MaxBreaker-- it is even more effective with some changes to the bolt, nut, and washer placement.


I have more pictures in the MaxBreaker and MaxBreaker Ambi imgur Gallery for anyone that is interested.

I know these aren't the prettiest, both designs work well.  I think it would be cool if others could benefit from these designs, but I'm uncertain how to proceed.  I could do an instructional writeup -- these mods can be done with materials found in most hardware stores, and the following tools: a coping saw, Phillips head screwdriver, needle nose pliers, drill, and sandpaper and/or files.  Or I could buy some materials and make some replicas of these home-brews to sell ... it seems tedious, and not a high enough quality product for what I'd have to charge to make it worth my while.  (I'm not out to make money on this, but it wouldn't make me cry.)  Or I could pitch the idea to a company, possibly right to Maxim, who could refine the engineering and manufacture them properly.  Or I could just be happy I have multiple solutions for myself.

Heck, nobody but me has tried using these yet.  I should really find someone else to try these out and give me feedback.

Thoughts?

It's clever, but additional leverage on a side or forward charging handle will probably be more beneficial.

ETA:  you're rapidly becoming my favorite noob - graphs and math, who knew?

My carbine buffer length system arrived today, and I have one immediate reaction: the CQB buffer length version I've been working with is easier to charge.  Not massively easier, but I can feel a difference.  (I don't currently have appropriate scale to get an accurate measurement.)  Every part of the charging cycle on the carbine length version feels more difficult to me, but also smoother than the CQB length version.  (The doubling-up of the CQB's spring at full compression I think is responsible for the last part.)

I don't have a scale to test them side by side, but I'll do a bit more subjective testing, get some side-by side pictures, and update with those.

ETA:



So, that QC10 receiver with the skeletonized side charging handle/latch -- just tie a piece of paracord on there, and clutch the other end, pulled taut, between your teeth.    I tried to take a picture, but ran out of hands.  You can make up the rest of how that completely serious suggestion at a charging method goes.  

But more seriously, I'm gonna see if I can figure something out for some side chargers, too.  The rear charging handle solutions just jumped out at me immediately and I had several extras lying around to experiment with--not the case with side charging handles/side charging uppers.

I'm likely to make an attempt at FM forward handles next.  I have FMP 16" and 10" uppers, and have 2 polymer reversible side (left or right) handles (gen 1), one aluminum reversible paratrooper handle (left or right), and one steel (MIM) 4-position (left-up, right-up, left-down, right-down) handle (gen 2) to work with.  I also have a 2nd paratrooper handle coming.  (Why?  While  FMP sells theirs (in stock) on their web store for $49, for some reason Optics Planet (backorder) sells the kit for only $13, and thus for $13 I don't have to worry about it if I mess one up experimenting.)

Just got back from the outdoor range and did a pile of tests/experiments.  Now that it's cooling off I should be able to get out more often.

Tested to see if adding round count changes pull force for initial charging.

Used a digital force meter/paracord to measure charging force (hammer cocked). My Maxim unit had about 200 rounds on it so far.  No preload.
At start--------: took 3 measurements, average 29.4lbs.
+100 rounds: took 3 measurements, average 31.3lbs.
+200 rounds: took 3 measurements, average 28.8lbs.

I know it's not a lot, but it looks to me like round count probably doesn't have that much of an effect, if any...  People saying it "gets easier" after shooting a while may be just getting used to the charging force.

How does it do with a suppressor?

Fired 10 subsonic rounds with 9.4oz. buffer, 10 subsonic rounds with Maxim.  5.5" barrel, Octane suppressor.

No noticable difference in sound/smokeyness to me.  Both were a bit smokey as expected.  If there was a sound difference, I didn't notice it, but I'm not a suppressor connoisseur, either.

Warning: This post is all physics and agreeing with Droppoint.

I think you're right.  "Breaking in" typically would be smoothing metal surfaces and remove sharp edges to reduce friction.  Springs that "break in" are bad springs.   This system's resistance isn't based on friction and doesn't have sharp edges in need of smoothing (unless one was improperly finished), so "breaking in" should have negligible effect.  But, I'll break down the forces and mechanics I can see at play, because I like to think about physics.  If I miss anything pertinent, or there's more to add, anyone please point it out.  This is how I think about things.

First, in physics there are 2 laws of conservation (Newtonian physics) which apply to my physics explanation below.  Conservation of momentum (an object in motion will stay in motion and an object at rest will stay at rest, unless acted upon by an outside force), and conservation of energy (energy can be neither created, nor destroyed, only transferred).  There is no analogue for force or pressure.

In the RDB system the rearward force of the bolt is opposed by creating a mechanical advantage for the spring pushing forward, multiplying its force through the angles that the rollers contact the two parts of the buffer.  Before free rearward travel of the bolt/buffer combination is achieved, some of the buffer's energy is diverted directly into to the gun (recoil).  In a direct blowback system, the point when energy is directly transferred to the gun is when when the buffer hits the back of the tube.  (The spring applies force to the back of the buffer tube, and therefore the whole gun, with force equal to that applied to the buffer + bolt.)




Nope Maxim didn't use the second spring.

In the image above, from the right side the bolt pushes on the pusher piece (3) , and that pushes on the the rollers (10).  That all happens with the force being directed straight rearward.

But the rollers push against the guide rod and control piece (the next moving part) at angles.  According to the patent, the face of the control piece (2) that the rollers contact should be at least 45°.  This angle determines how great the mechanical advantage the RDB has when pushing on the bolt.  Changing the angle of the pocket on the guide rod is not feasible, because that would allow the chamber to open start opening immediately, defeating one of the stated purposes of the device: to keep the chamber shut longer.  The more vertical that angle where the rollers contact the control piece, the faster that roller pops out of the pocket in the guide rod.  The more horizontal that angle, the further the control piece must move before the pusher piece can move freely.  (If the angle were too low, I'd expect binding issues may occur, but that's a different mental rabbit hole.)

While it is unlocking, the horizontal portion of the force applied by the rollers to the guide rod is transferred through the guide rod straight to the back of the buffer tube, moving the entire gun.  This energy transfer is part of the recoil when cycling, and when charging it is force diverted into whatever part of your body is holding the firearm.  The forces that push toward the center of the guide rod from the rollers cancel out and the guide rod doesn't move radially, and doesn't collapse in on itself because it's sturdy metal.  No movement means no work is done and no significant* energy is transferred radially.  (*There is a negligible amount of heat generated from the friction of the contact of parts.)

To Droppoint's suggestion that people are "getting used to it", a large part of a charging action is balancing the force your body exerts on the gun with the force your hand exerts on the charging handle.  The charging action with this device is different enough from standard practice that there is some training of muscles to have the right timing to push back firmly enough when charging.  This is the very definition of "getting used to it".  While this won't make it possible for those not strong enough to charge the Maxim RDB to suddenly be able to, it would make the experience repeatable and feel smoother for those already able.   I think Droppoint's right, and physics agrees.

But, continuing on with the physics...

The force applied by the rollers to the control piece is likewise divided.  Some is directed radially outward from all rollers, and those forces cancel out and the control piece doesn't expand outward on account of being sturdy metal.  Again no movement radially means no work done and no energy transferred in that direction.  The rest, a fraction of the force applied to the rollers initially, is transferred horizontally to the pusher piece, pushing it rearward.

Finally, the pusher piece moves rearward and transfers its energy to the spring as the spring compresses.  

Once out of the pockets in the guide rod, the rollers, control piece, and pusher piece function as a single piece and moves freely rearward.  I could go into breaking down the forces and energy transfer here, but it's a lot easier and accurate enough to say that once free of the pockets, those rollers act like the ball bearings that they are...and ball bearings are used to reduce friction.  Energy is transferred to the spring from the buffer + bolt without too much lost energy from the buffer system at this point.

If the bolt and buffer haven't reached a stop before they reach the bumper at the rear, any remaining energy and momentum are transferred into the gun: more recoil.

Friction exists in this system, but it's negligible compared to the mechanical disadvantage and diversion of force into the guide rod.  Breaking-in shouldn't have a major effect unless friction was a primary factor in the forces at play in the RDB system, and it isn't.

(Today was just one of those days I needed a distraction, like thinking about and writing up this...)

Stealing yer picture:



So, my favorite 23'r, help me understand what's happening here, b/c I find delayed blowback systems inherently difficult to understand:

You're saying the large spring at the base of the unit in the patent drawing ended up not being used, is that correct?

In battery, the bearings (#10) are found in the recesses in the guide rod (#9), with the pusher piece (#3) fully forward, pushing the actual bolt (not seen) into battery with a live round in the chamber.

This raises questions for me - what pushes the bearings into those recesses, since the recoil spring (#8) is only pushing on the delay mass (#2)?  Ah - I see.  As the action is going into battery, the bearings (#10) are in the recesses between the pusher piece (#3) and the delay mass (#2).  Once the bolt goes home, the pusher piece (#3) is at its further extent forward, exposing the recesses (#9) in the guide rod (#7).  The recoil spring (#8) continues to push the delay mass (#2) forward, forcing the bearings (#10) into the recesses (#9).

On firing, the pusher piece (#3) moves rearward, which forces the bearings (#10) out of the recesses (#9), which accelerates the delay mass (#2) rearward at a higher velocity than the pusher piece (#3) and the bolt.  This accelerated movement of the delay mass (#2) multiplies the effective mass of the buffer, causing the delay.  Once the delay mass (#2) is pushed far enough by the bearings (#10) for the bearings to completely emerge from the recesses (#9), the delay effect stops, and the entire mechanism simply acts as additional mass to the blowback bolt, the bolt pushing on the pusher piece (#3), which pushes on the bearings (#10), which pushes on the delay mass (#2), which is resisted by the recoil spring (#8).

Am I anywhere near correct?  The differential speeds of roller and lever delayed blowback systems is always confusing to me.  Gas-delayed blowback is so much simpler.  

Wow. Thanks for taking the time to write this all up.  Good read!

Everything you wrote seemed spot on except for this.  The mass accelerating plays a minimal role.  Forces are transferred at angles which divert the force in other directions.  Some goes to recoil, some goes to moving the ball bearings outward, and some is just force applying pressure, but doing no work.

To see the effect, at every part where force is transferred between parts, divide the force pushing at a non-90° angle into two components: a force perpendicular to the surface, and one parallel.  The spring pushing forward transfers force forward and inward to the rollers.  The force pushing back into the rollers from the bolt is directed rearward, inward, and outward.  Only the parallel portion of a force does work on a mass.  The force vector components moving parallel to a mass do no work.  Other than moving the ball bearings in/out of battery, almost no energy is transferred in an inward/outward manner (compared to the energy transferred parallel to the guide rod).  

The red force vector is the pusher piece applying force to the roller.  This is representative of the moments after firing.

That force is transferred to the next set of surfaces from the roller.  (I have the force divided equally between the control piece and guide rod, but I'm sure the ratio is more complicated.  The concept, however, is solid.)  The red force vector is the portion that is parallel to the guide rod at all points.  The yellow boxes are just guides for dividing the force into parallel and perpendicular components relative to the surface they are contacting.

The blue force vector components are parallel to bearing surfaces, and do no work (and transfer no energy).  The green force vector components indicate the force components perpendicular to the surface that do work (and therefore transfer energy).  

You can see how that red force vector shrinks (from right to left) as force is diverted in other directions.


So what pushes the ball in and out of the pocket?  For every action, there is an equal and opposite reaction.  The guide rod pushes the roller outward with a force equal and opposite to the purple force vector pushing in on it.  The spring applying force from left to right has its force applied at an angle to the roller, and thus actively pushes the roller back down into the pocket.  If the angle where the roller meets the control piece were reduced (flatter), more force from the spring will be diverted into pushing the bearing inward.  

I'll see about making another force vector diagram later showing the force coming from the spring in another separate image when I have more time later.

This is where the RDB differs from "direct blowback" in terms of dominant factors.  

In direct blowback the dominant resistance is the mass of the bolt+carrier resisting change in motion, whether this is opening the chamber, transferring force to the spring or slamming the chamber shut.

In Maxim's RDB, until those bearings get out of the pocket in the guide rod, the dominant force is the spring pushing forward.  The parts could have a near 0 weight, but as long as their shape and hardness were correct, the delay would be almost exactly the same.

Also, here's the diagram of the system out of pocket:


Once out of pocket, the transfer of force from the control piece to the bearings and then to the pusher piece (or in the reverse direction) is much closer to linear than when in battery.  While there is some friction between the bearings and the surface it touches, this is very low largely because the bearing surfaces are tiny and have low coefficients of friction to start with.  Plus lube.


I kinda got to wondering: why shape the outsideof the control piece the way they did?  Once the RDB system is freely rolling along the rod, I'd have thought a full-bore pusher piece with extra mass might be beneficial as mass starts become a more important factor at this point.  I really should tear apart the CQB and the carbine length RDB systems side by side and answer a few questions, including:
How different are the springs?
What's the weight difference between the control pieces in each?
Are there any other differences besides the guide rod length & spring recess (not the roller pockets), control piece length/mass, and spring?

edit: typo; may be more

eta credit where due: The black and white diagrams aren't mine strictly speaking, but are fair use -- I pulled them from the Wyssen Defence AG patent document.  The force line diagrams are all my own addition.

Ah cheers, thanks for clearing that up.  I'm confusing lever delay w/ roller delay, I thought they were more similar.

Just some analysis and correlation of one chunk of data to some others.

Glad its appreciated.  A lot more fun that saying "huh, so that's how this works" to myself.

Just saw this was released.  Don't know if it would helping charging with the Maxim or not.

https://noveske.com/products/noveske-love-handle/

I don't think it gives any mechanical advantage other than having larger handles.

Just got my PSA AR-V MP5 poor man's copy done and have the Maxim buffer in it. With the PRI large handle gas buster charging handle, it is not that hard to charge. It was stiff at first but that was only because the charging handle was rubbing so badly in the upper.  Now that I hand cycled it a bunch of times it is getting smoother. Now to get to the range and give it a test run.

I will apologize in advance but this whole thread is a disappointment. I have followed since the beginning.
I love my blowback AR9 and anything that could make it shoot closer to my AR22 has my interest.
I was going to get a CMMG RDB kit a couple years ago but held off due to the extractor spring issue.  
Then when I heard about this product I was excited cause I can still use my bolt and barrel.
But the hard to charge aspect and the attempts to overcome this glaring defect is a bummer.
Im not sure how maxim decided to put out this product knowing how hard it is to charge.
Based on all the posts here there is no way I am going to get it.
I shouldnt have to mount a lever to the charging handle just to rack it.
Hopefully Maxim can improve the design.

I can understand if someone wants to keep an original style upper, but as I stated before, an NFA style side charger makes charging much easier. If I didn't have a side charger, I wouldn't like the effort either. Yeah, I tried a standard one.

I had the side charger before these became available and liked it better that the standard top mount already.

100% my take as well.  Honesty I don't have any problem with my existing setup, but thought this could be the bee's knees.  I don't run against the clock so dot bounce isn't a big deal and I don't find the recoil with the 21.5 ounces of reciprocatiing mass in my current build to be bothersome.  My AR-9 is the queen of the range every time I bring it with, everybody loves it.  I think I would just try a heavier dead blow buffer before investing in the Maxim, but I appreciate thier efforts.  Perhaps there is room for improvement.

You're right, you shouldn't have to mount a lever.  Neither should I.  Maxim should be producing a modified charging handle, or contracting someone else to.  I know it sounds arrogant to declare that, but I'm that confident in this solution.  

I have two questions:
1) Why are the attempts to overcome the charging issue a bummer?  I get the charging difficulties being a bummer, but the innovation that follows, too?
2) Would you be interested in the Maxim RDB System if you could buy, or it came with a charging handle that fully addressed the charging difficulty?

I ask because, with my Ambi MaxBreaker charging handle modification, I can charge the cqb version of this with only my pinkie finger.  No special way of holding or pulling handle are necessary.  (I can not do this with other charging handles with this RDB.) It's slightly harder on the carbine length version, but not by much.

Video of me charging Maxim RDB equipped AR with Ambi MaxBreaker using only pinkie finger

(If it seems like my hand is a hair shaky, know that I have some tendon damage in that hand and wrist.  The underhand hold is for visibility only and it strains those tendons more than the 3rd charge that's overhand.)

I have on backorder a scale for measuring the force pulling on the handle.  Once it arrives, I'll get numbers to back this up.

I designed and made this with on-hand scrap, spare bolts/nuts/washers, a drill press, a Dremel, and hand tools in two afternoons.  What happens when a similar idea meets a production design and team with commercial equipment?  If anything, "the attempts to overcome this glaring defect", should be a sign that this product is just a redesigned charging handle away from working fine.  Producing a charging handle with an altered design is WAY easier than redesigning this whole system, right?  (If machining aluminum is easier than steel, and the mechanics of a compound lever are simpler than that of 5 ball bearings rolling up a constantly changing slope while sandwiched between 2 moving parts with different velocities and a static central rod, then I propose the answer is "yes".)  This type of solution should be relatively inexpensive to get to production compared to altering the design and production of their product.  As I believe was been pointed out above, a charging handle having a levered action is a solution previously used in other firearms to overcome a substantially similar design issue.

*grumbling*

I'm gonna put to together an e-mail to Maxim and pitch my idea.  Worst they can do is say they're uninterested, right?

Naw, the worst they could do would be to patent your idea and tell you to pound sand

Believe it or not, it would bother me less than them shooting the idea down, me finding no way to get it out there, and nothing coming of it besides me having my functioning prototype.  Or them buying rights to it and never developing it.