There were some flattop uppers for sale on the EE and someone asked the question, "Do these have m4 feed ramps"?  What's an m4 feed ramp, and why should/shouldn't I want one?

M4 feed ramps are extended feedramps......for a semi auto it really isn't necessary, it's more of a benifit for a select fire weapon.

Thanks

Here's a pic, by Troy, which shows M4 feed ramp cuts:
[img]http://photos.ar15.com/WS_Content/ImageGallery/Attachments/DownloadAttach.asp?sAccountUnq=2775&iGalleryUnq=160&iImageUnq=10626[/img]

Mike

Please explain how a full auto benefits from extended feed ramps and a semi auto does not.  I fail to see a difference in how they would function in one and would in the other.

In other words I am calling you out as propogating some BS that you heard someone else say and I dont believe it.  Please give a detailed and scientific explanation of how it helps the full auto and not the semi auto.

Thanks.

Fire up the Dremel tool, if you want some.

During full auto fire the carbine operates much faster than in semi auto,so in full auto the feedramps are more relevant for reliable operation,I just think its a way for colt to make their M4 more unique because they are the only ones who have the patent to do this on production rifles and also colt is the only company with the contract to supply the SOPMOD carbine M4A1 to the military,so I think its more about uniqueness than functionality,if it was an improvement the new flat top full size rifles now being supplied to the marines and 3rd INF DIV by FN would have this improvement and they dont,so to me its only relevant for full auto carbines,"maybe"

Seems to me that if there's an advantage to the extended feed ramps, it would be just as much a benefit in semi as in select fire.  The process of stripping a round out of the magazine and chambering it is identical regardless of how fast the weapon is being fired.  The time from when one round is fired until the next one is chambered is the same in semi or full auto fire.

In short, I am calling [bs].

And the reason why the FN uppers wouldn't have them is that Colt still holds the patent on them, so you'll only see them on M4's made by Colt.

My old Colt SP1 has them...this should be standard on all new AR's

To ESWANSON yes it is identical to how it strips a round but im talking speed wise the cyclic rate for a weapon funtioning full auto is a lot faster than one firing semi no matter how fast you pull the trigger you wont duplicate that speed in semi auto,so in full auto the carrier strips rounds faster plus the fact, a carbine because of its shorter gas tube operates faster and under more stress than a full size rifle that stress doubles when you add the full auto function in,if its such an advancement why is no other manufacturer other than colt doing it so next time read the thread right I am talking how fast it strips a round not the manner in witch it strips a round.So the time in wich it does this during these functions is different how could the time be the same if operating in fullauto is faster than semi auto in other words I think what your saying is BTBS thats BIG TIME B###SH##.so think CYCLIC RATE

My recently purchased RRA CAR UTE has the "M4" feedramps...this whole "Colt holds the patent" I suspect, is more [b]BS[/b] (right along w/ "only full-autos benefit from M4 feedramps")

Actually, Colt does hold a patent on the ramps, but they hold it only for one reason; TO STOP FN FROM USING IT.
They don't give a damn about the commercial aftermarket. That's not where the big bucks are.  The whole deal, I suspect with the connivence of some of the Army procurment people, was to come up with a "thing" to put on the M4, that would ensure that FN couldn't steal that contract from them; they same way FN took the M16A2 work away.

Re the ramps themselves, if your AR s feeding ammo with no hangups or glitches, deepening the ramps is a waste of time.  When one of my ARs started catching the bullet noses at the bottom of the ramp after I swapped two uppers and lowers around, I did a modified (less deep than the M4) mod on the bottom of the ramp and problem went away.

In the words of the Prophet;  "If it ain't broke, don't fix it" [:D]

If you don't know the answer, just make something up.  Yeah, that's the ticket.

I have M4 ramps on two of my colts.  My buddy was having trouble with his new bushmaster.  Occasionally like several rounds out of every mag would FTF, some of the rounds that failed to feed had their bullets shoved back into the case.  It took a while for the lightbulb to click on but when i looked it did not have m4 ramps and there were little spots of copper at the bottom of the ramps where the projectile tips hit.  I added the ramps and last weekend dumped a mag (his mag, his  ammo) through it as fast as i could with no hiccup.  I'm so impressed i will be doing the same thing to my built bushmaster which occasionally has a feeding problem.   It doesn't seem your so much adding a ramp as adding clearance, at least from this one experience.  I have .jpgs if anyone wants to see what i'm talking about.  I'm really not sure why this topic always causes such heated exchanges.  It doesn't hurt anything so do it if it makes you happy, if you don't believe in it or don't have a problem..then don't.

M4 feed ramps are available on Armalite, Bushmaster, Colt, Diemaco, DPMS, LMT, and RRA uppers. And are easily added to any others.

I am a big believer in adding your our ramps (Dremel).  

Here is some info for my fellow ramp-adders.  You are placing the ramps in the wrong location.  Even Colt is putting the ramps in the wrong location.

The wrong way is to make the ramps follow the same direction as the oem cut in the extension.  This is wrong.

To understand, take your upper off.  Remove the carrier.  Open the ejection dust cover.  Place upper back onto lower (without carrier).  Place a mage with ammo in it.  (Safety says you should be wearing saftey glasses when playing with live ammo).  Now look inside thru the the ejection port.  

You will see that the bullet will try to impact in a direction that is running straight downward from the feedramp.  The way Colt and other home-jobs do it, the ramps are too far left and right (outward bound).  The ammo is being feed from directly below, not from the left or right (outward bound).

Therefore, when adding your Dremel cuts, hold the Dremel at an angle pointing straight down into the mag-well direction.  The ammo is coming from the mag-well direction, not from the left or right.

Below is an illustration.  The red lines show the wrong angle for the cuts.  The blue lines show the correct angle that the feedramps should be cut.

[img]http://pic2.picturetrail.com/VOL33/1216349/2303971/27862763.jpg[/img]

I called bushmaster when the new feed ramp first came on the scene they dont do it to production guns the reason I was told is that colt has the patent and they would be sued over it they wouldnt even do it on a custom order basis,the other manufactures I dont know about but bushmaster said no.

Cyclic rate changes in FA? WTF?
Think about it guys. In semi-auto, the round is fired, the case is ejected as the bolt moves rearward, it then strips a new round, and loads it into the barrel. Then Repeat.
In Full Auto, it does the exact same thing, the only difference is that the auto sear is much faster then your finger.
The Bolt moves no faster during FA than in Semi-auto.
So what are the REAL reasons to have this mod? Well, go shooting, and pull on the magwell. Pull it rearward from the bottom. This causes the rounds seated to be angled downward. This increases the chances that when the bolt comes to chamber it, it will jam it nose first into the front of the receiver.
All your out of spec magazines which the lips are bent up, and weak springs will benefit from this mod.
Other reasons are some of the newer heavier bullet loads, or hollow point ammo which has a tendancy to get hung up on the flat tip of the bullet.
The ONLY way FA is different than SEMI is the high amount of rounds being fired. This causes fouling which will happen the same as in semi, and heat which causes metal to expand in most cases.
Expanding metal can be controlled with "loose" tolerances and lubrication (hense the term fighting battle rifle.) This is where your Colt and Bushmaster M26 surpasses a precision machined Les Baer. Loose tollerances allow for dirt, fouling, metal expanse and so on. Your trade off for reliability is accuracy.
If you want to adjust the cyclic rate of your full auto, or semi for that matter, you can change the size of the gas port on the barrel, change to a different gas tube, change the bolt and/or carrier to a different weight, change the recoil buffer weight, recoil spring weight, use one of those new fangled pnuematic buffers, change to a different lubricant, fire the weapon at different temperatures, adjust the loads being fired, barrel length, different gas rings... I'm sure there are more.
IMO, get the ramps, they truely do increase reliability.
-Steve

g35,

I see what you are saying but I don't agree that the way the M4 cuts are implented by Colt, DPMS, Armalite, etc. is wrong.  If you look at the pic below you can see that the bullet tip will go on to the ramp slightly above where the receiver cut is.  It will still go straight up into the chamber and I can't see where it would misdirected or cause any issues.

[img]http://a2.cpimg.com/image/AA/BB/20163242-27d3-02000180-.jpg[/img]



stevenb,

That's one of the best explainations of why the M4 feed ramps help in reliability.  It's very simliar to why people throat a 1911 to increase it's reliability.  

I was told that it aided in reliability with special rounds which I suppose would be heavier weight bullets. The semi and full auto thing was made up.  

My turn-- they do it because they can't seem to keep the barrel extension from protruding into the upper, thus the nose of the bullets snag underneath the OD of the extension, so they blend the material (ramp) so the bullet does not snag... like throating a 1911 to feed SWC reliably.


IBTL

To STEVENB how can you say the bolt moves at the same speed if I fire 50 rounds in a minute in semi auto,and dump 2 mags full auto in about 10 seconds how are they moving at the same speed ?the carrierdoes move faster as it feeds and ejects as the auto sear trips the hammer the hammer cant strike until the bolt is closed so the carrier has to move just as fast to keep up with the hammer droping.If you dont want rounds to nose dive use a quality spring and a green follower the ramps seem to be a waste for a mag related problem.Thats why we give a wack to the mag before we seat so the rounds are against the back of the magazine and they will feed right,and as far as cyclic rate I use a heavy buffer,Im not into having gas ports in the barrel modified larger and thats only recomended for barrels under 14.5 so you wont get short stroking because the barrel is so short you lose gas pressure to quick.So the moral of the story good maintenence and good mags, I have 30k+ rounds out of my preban  bushy never had that type of malfunction I also use wolf springs in my mags,and the brit mags give more clearence where rounds are stripped than GI aluminums and I have gone more than 2000 rounds at a time without a malfunction my post ban bushy so far no malfunctions in 10k rounds,The israelis have been using 653 carbines for 30 years in the desert and those work fine no hokey modification is a substitute for good working mags,good maintenece and in proper repair,If rounds are nose diving replace the mag,spring or follower if that dont work send the rifle back to the factory unless these problems are ocuring on home built rifles then the problem could be out of spec parts or receivers,ive seen mags seat to deep on some rifles put together piece by piece.And ive never had hollow points hang up and I fire alot of wolf,if that happend id polish the ramps like on my 1911,and when you start messing with changing bolt or carrier weight,your asking for trouble throwing the weapon out of spec like the gas port if you make it larger on a carbine you increase pressure,cyclic rate and operating stress wich leads to accelerated parts wear as far as changing spring weight,when the army or marines change the spec I will to,colt only did the feed ramps so no one can copy them,after 38 years no one has done this until now and then you have people saying the feed ramp cuts are wrong,so its like the the colt modification is good but its cut wrong,So military M4A1s have this angle but its wrong its like a rep at bushmaster said"If you want entertainment have beer and go to ar15.com and read some of the info you get on the threads,no one seems to have more problems with their ARs than people here,with all this info thats here some of you guys should be working for colt so you can tell them and the military this or that is wrong modify this modify that maybe all this modifying,using inferior parts,springs what have you is the problem.

Wow that's got to be the longest sentence i've ever seen!  Do you talk that way too 927?

The Marine Corps did the type classification testing for the replacement of our old M3A1 Greaseguns in the mid-80's.  This new weapon was thus called the "M4".  It was our handle, not Colt's, but Colt picked it up and ran with it as our subsequent M4 Carbine procurement program failed year after year thereafter (1987-1991).
The feed ramps were applied after the original M4's failed in the Cold Chamber at APG during Developmental Testing (DT).  With the new ramps, they passed CW functioning, but interestingly picked up cyclic rate in hot and temporate.  So if the feed ramps increase the cyclic rate, they are doing something to reduce the time it takes rounds to ramp-up into the chamber.
I like the anaolgies above to "ramping M1911's".  I hardly know any M1911 shooters who don't ramp their guns, even if they never shoot wad-cutters or big-face hollow points.  Its a confidence thing.
Caution, be carefull of "still pictures" that "show" what's about to happen when the bolt moves forward to strip and ramp-up the next round.  At 750+ rpm of the M4 Carbine, lots of things are happening very fast.  And in full auto, many of these moving parts are "recovering" or "re-bounding" from their last pulse and not all may be poised properly for the next (feeding) step.  
Take the magazine follower for example, with only 2 or 3 rounds on top of it near the end of a 10-round burst, it may be bouncing downwards as the bolt impacts against the next round to be fed.  In other words, that next round may not be resting neatly under the magazine feed lips under gentle spring pressure waiting patiently to be rammed forward.
This also helps explain why semi's only probably don't need this modification, as well as rifles limited to 3-round bursts.
ColdBlue sends...

To cold blue ,now that makes sense.To CURT,man im always forgetting to puntuate,maybe I have a future as an auctioneere,going ounce,going t
twice."bang"I ended the sentence with a period.
[buttkick]

If the bolt and carrier are moving faster in full auto than in semi, why does the brass land in the same spot reguardless of the mode of fire (discounting weapon rise and/or sweep due to recoil)?
I don't think there is a man alive that can beat the cyclic rate of a semi-automatic. There are a few who get close, but the fact that the weapon cycles at .13333 seconds at a rate of 450 rounds per minute. 450 RPM (rounds per minute)/60 seconds = 7.5 rounds per second/100 miliseconds = .13333. I'm lucky if I can pull the trigger 3 or 4 times a second in my ar-15. I assure you, it is waiting on me. [;)]
Try to push a stop watch timer as fast as you can and see how quickly you can do it. Back when I was in school, I hovered around .18 seconds to start then stop it on a average day.
Now throw in recoil, and a much heavier control opposed to the very light stop watch button. Not to mention the greater distance in travel for the trigger opposed to the watch button. The only delay in the m16 is the autosear, if it wasn't for it, the rate would be even higher in the theoretical 450rpm model I gave. But then you'd encounter slam fires due to the hammer riding against the carrier.

I completely agree with you that the ramps would be considered a bandaid to fix a problem that shouldn't exist. Similar to the idea of putting Water Wetter in your overheating car.

BUT, in the era of dwindling high capacity magazines, you are strong armed into keeping worn magazines. The green followers are a definate enhancement, and attribute to reliability.
The ramps are no replacement for proper cleaning and lubrication. But, if you are pushing reliability as far as possible, then it is a worthy upgrade.
-Steve

I would say the brass deflector on the receiver has more to do with landing the brass in the same place because no matter how fast brass is ejecting it hits the deflector wich slows the momentum  and usually lands the brass  in the same spot,all im saying is and the best ive been able to do is firing as fast as I can while reasonably aiming is 30 rounds in about 35 seconds on full auto an M16 can dump a mag in 3 seconds,so im just saying in fullauto it "the carrier "seems to operate faster I would think this is due to the auto sear coming into play tripping the hammer because in this mode if im correct the disconector makes no contact on the hammer  or the trigger sear for that matter,to me it just makes sense that it goes faster because its firing faster.

If the brass deflector was the the deciding factor in where the brass lands, then it wouldn't change depending on if your extractor spring is weak or over-powering.
You mentioned that it takes you 35 seconds to dump 30 rounds. That's aprox. 1 round per second. You also mentioned you were aiming between shots. In FA, none of this takes place.
The bolt and carrier has to cycle at a specific speed so it doesn't short stroke or over-power the recoil buffer and spring.
When you get a chance, have someone fire the AR, and position yourself on the right side so you can see into the ejection port. Careful not to be in the way of brass though. Attempt to physically see the bolt and carrier move. To me, it is just a blur, and it is ready to fire again.
The autosear actually slows down the hammer from falling in full auto mode so the hammer isn't riding against the back of the bolt carrier and firing pin as it strips a round off of the magazine and chambers it. If the hammer is pressed against the firing pin during this fall, there is a chance it will slamfire. I've read reports in which the autosear was not working, and it caused the weapon to slamfire multiple times, and fired until it was out of ammo.
In semi, the hammer is locked back in the position to drop each time the bolt cycles.
This super high cyclic rate is excellent in 3 round burst at short range, like a cqd rifle. Basically, you get 3 rounds in a small area in half a second beforfe recoil can dramatically effect your accuracy. Plus it won't burn up all your ammo. For 3 round burst, I prefer a high cyclic rate. That way recoil has the least effect on my 3 expended rounds. That way they stay close together in cqd ranges. It gives you a lot of firepower on tap.
Just remember, the same amount of gas enters the upper receiver reguardless of if you are shooting semi or FA. It all comes down to how fast you can move your finger, and how fast the internal parts of the disconnector takes to fall.
Not trying to talking down to you or anything just sharing some info. [:)]
-Steve

Full auto does not make the weapon cycle faster nor does it have anything to do with reliablity from a feeding/ejecting stand point.  The carrier moves at the exact same rate both fore and aft during both the only difference is the downtime between shots.  So you may ask does that increased downtime make a difference?  No it does not.  Watch some slow motion footage of a full auto firing.  Especially a full auto pistol which has an astronomical rate of fire.  The hammer falling is the big lull and the magazine is fully seated under the bolt by the time the hammer falls.

Please let me repeat the CYCLIC RATE HAS NOTHING TO DO WITH THE SPPED OF THE CARRIER MOVING BACK AND FORTH.  The difference is the lull between cycles.  This lul does not have an effect on load/extract/eject sequence.

No offence taken steve or devl its just weird,I figured larger fire volume would make the carrier cycle faster,so does anything as far as components operate faster or is it the lul in the hammer falling like devl said that dictates the rate of fire.

I don't get it. If I go from my 14.5 inch upper to my 10.5 inch upper in full auto there is an obvious increase in the rate of fire. If the carrier is traveling the same speed with both how can that be? There should be the same down time with both uppers in FA.

Easiest way to find bolt carrier velocity or debate at what speed it travels?


Simply argue that carrier velocity is a direct result of gas port pressures.    If gas port pressures are the same in full auto fire as with in semiauto fire, carrier velocity will be equal.


Look at the difference between a 20inch M16 and a 14.5 inch M4, port pressures ARE NOT equal and there is a clear cut difference between full auto cyclic rates between the two due to port pressures.   One with the greater port pressure is the one with greater cyclic rate, ofcourse it helps that there are some changes in buffer weights spring weights.    Still, the difference is obvious.


Rules of physics still apply here.   Probably the rule that fits best is something along the lines of conservation of energy.    A body at rest prefers to stay at rest while a body in motion prefers to stay in motion.     On the motionless bolt carrier, a certain amount of force(in this case exerted by the gas pressure) is going to deliver a consistent and repeatable amount of acceleration to the bolt/carrier.    Going the other way(literally) when the bolt carrier is being accelerated by the spring/buffer group, it is again going to be placing a certain force on the carrier that presents consistent results.

Whether it's in full auto or semiauto, these forces will be the same.


That's where we need to make sure to not overlook the obvious, just how long is that gas tube folks?    Various things are acting together here to either make port pressures go up or down.    With longer 20 inch barrels the gasses have more volume within the barrel to expand and drop in pressure before those gasses get to act on the carrier, extending away from the chamber pressures are dropping significantly.    Compare to a 14.5 inch barrel where the gas port has moved closer to the chamber a significant distance, gas port pressures have effectively increased compared to that of a 20inch barrel.   It is not unreasonable to expect a change in the rate of fire when those forces begin to act on the carrier group.


Okay folks, Mr. Science is taking a break from his keyboard to go get some food.

A 10.5" barrel has a faster cyclic rate and faster moving bolt carrier because of one reason...

The 10.5" barrel has a larger gas port and has more force pushing it in a shorter period of time.  The same thing happens when you go from a 20" to a carbine because of the gas port location.

Still, flipping a selector lever does not change the speed the carrier moves.  The speed at which the carrier moves is ONLY altered by weight of the carrier, weight of the buffer, strength of the spring, location of the gas port and size of the gas port.

Also using hotter ammo will speed it up too as will use of a sound suppressor which increases the pressure in the gas tube.  The selector lever changes none of these variables.

M4 feed ramps improve the loading of ammo in carbines with weak mags due to the spring failing to get the bullet up for the bolt fast enough or because it feeds low due to a tilted mag or poor feed lip angles.  Semi vs. full auto has nothing to do with it.

I looked once for a patent on the feed ramps and could not find one.  I was able to find the patent on the M4 handguards.  It runs out in a year or two.

Colt does have the "Techical Data Package" for the M4, but that only has to do with military procurement and does not effect civilian sales.

Agreed, figure I had to quote you just to get it posted within this thread atleast one more time.    DRILL it into their heads.  YEAH, that's it!!!   :)

Anybody have some detailed info. in how to add these to the upper and barrel w/ a dremel?

Maybe w/ some pics?

you don't want to go "bubba basement gunsmithing" on a AR with a dremel drill.......the chances of fuckin' up your upper is a real likelyhood. but hey it isn't my rifle, so knock yourself out

Sssshhh...
Don't tell the secret.  That's how some of us get through life.

I love this place.  It's just like one of my wife's family reunions!

I wouldn't do a bubba job on it because it will remove the anodized part of the receiver.
-Steve

Although I do not have a link for you, I can tell you that I have read that using a dremel to route out your own feedramps will destroy the parkerizing applied to the upper; this makes sense to me.

So, I have opted for the "if it ain't broke, don't fix it" option.  IF I experience FTF problems, with good mags, I may look into sending the upper to a reliable guy to put in the ramps and re-parkerize the upper ([red]will Kurt of KKF do this?[/red]); in fact, I may do this if it is cheap, just for the LCF.

(That's the [b]L[/b]ook [b]C[/b]ool [b]F[/b]actor.)

huh, I could of sworn I read on here numerous times about guys doing it themselves.

I think I'll wait and see if I have any FTF.

I've got an RRA upper/BM barrel combo.

Kurt Wala of KKF does the feedramps for $35 bucks.  The fact that anodization is removed from your upper reciever means very little.  If a bullet hits low and you dont have the feedramp, the bullet impacting the lower receiver below the feedramp will scratch off the anodization anyway. If you remove the parkerization from the barrel extension you can apply cold blue to the feed ramp to protect them and the aluminum will be touched up with Alumi Black and even Kurt uses the Alumi Black on his feed ramp cut.  I think its funny how you guys are always talking about the problems caused by removing the anodization from the upper receiver.  Please direct me to a post where someone on this board has had issues because they cut in M4 feed ramps.  Oh wait, you can't because there are none. [:)]

putting in a feedramp, that nobody will see......how is that a "cool factor"? unless you're going to go around with your AR opened up saying to folks...."ohh look at my feed ramps" truthfully nobody will really care about your extended feedramps.

That statement was meant to be tounge-in-cheek; only you would know they were there, and it would be a nice, cozy feeling [sex]

That having been said, I'm sending an upper to Kurt.  I don't trust myself with a dremel on a brand-spankin' new upper.

Ok so the M4 feed ramps are actually cut into the upper, not the barrel.

Does anyone know if the new Bushys have them?

Great thread, I've learned a couple new things [:)]