New to this system.  What rifle-length buffer weight (A2 fixed stock) is optimal for 550 - 600 ROF? The stock 5.2 oz rifle-length buffer seems way too fast at 800-900.    I saw that the Kynshot RB5001 is 8.3 oz, so does anyone have experience with this?  The Kynshot RB5000HP works perfectly in my carbine length systems and keep the ROF in the 600 range.

I have the rifle length hydraulic buffer in my Colt M16a1.
I am running a Brownell's 20 inch chrome lined 1/7 pencil barrel mated to an old Colt A2 upper, along with the original A1 stock.
It does slow down rate of fire by a noticeable amount.
Unfortunately, I can't give you any data as I don't have an electronic shot timer.
Am currently down South for the winter but plan on buying one and documenting the difference between the standard rifle and hydraulic buffers when I return in March.

RCA

Keep an eye out for one of the old Colt LMG buffers and the "green spring" that went with it.  They aren't exactly common, but they do surface for sale once in a while.  For a fixed stock gun, they will give you the RPM you desire.  The old AAC rate reducer come close to that, but they are even harder to find nowadays.  Everybody wants to run collapsing stocks, so there are relatively few options available today for the fixed stock configuration.

I did test a rifle buffer Kynshot but can't find the data right now.  I also have an AAC rate reducer but I don't use them any more as I would rather tune by controlling the gas / dwell time instead.

Basically, you could have two configurations that have the same cyclic rate but one is achieved by throwing mass at it and it will not be as smooth.
Yeah.  I don't see the point of using a fixed stock anymore unless you just want the rigidity...so many collapsible stock options and I can get in the low 500's with my collapsible stock configurations as documented on my site here:
https://c3junkie.com/?page_id=1403





With the fat gas tube, you are approaching and maybe even exceeding the volume of a standard rifle length gas tube.
I did this for the Mid gas tube here:


I also made custom rifle length large volume but don't have that data handy.

This is all taking it to the extreme.
Pictures below are using a standard gas tube:

Of course, given all the fantastic info Amphibian has accumulated for the shorter stocks, it would probably be easier to just stick a spacer in the fixed stock to reduce the internal length to use the components for the collapsible one.

Great info!  Yes, I use the Kynshots in my carbine tubes and Maxim shorty tubes with my other systems (5.5" AR9s, 7.5" AR47, 10.5" 556, and 7.5" 300AAC).  I'm able to get the ROF in the 550- 600 range consistently with them.  This is a special 'retro' build project, and I'm trying to make it look and feel like the Original M16A2  - with the fixed A2 stock and rifle length buffer.  

Perfect!  I have had great experiences with all of the Kynshot products on my carbine tube systems.  I think I will go ahead and purchase one of these.  Were there any other side effects (negative or positive) with the Kynshot?

Note--
I was able to noticeably reduce the ROF by swapping 2 of the steel rifle-length buffer weights with Tungsten weights.  I effectively raised the stock buffer weight to 7.2 oz from the OEM 5.2 oz.  When I got home, I decided to swap out one more weight, and now it sits at 7.8 oz.  I'll test again and report back. Kynshot lists the rifle length buffer weight at 8.3 oz, so I think anything in between 5.2 and 8.3 is going to have a reducing effect on the ROF.  

Great info!  Yes, I use the Kynshots in my carbine tubes and Maxim shorty tubes with my other systems (5.5" AR9s, 7.5" AR47, 10.5" 556, and 7.5" 300AAC).  I'm able to get the ROF in the 550- 600 range consistently with them.  This is a special 'retro' build project, and I'm trying to make it look and feel like the Original M16A2  - with the fixed A2 stock and rifle length buffer.  

Suggestion--
Instead of the 4 quarters, I would suggest trying the Kynshot spacer.  It does kind of the same thing, but it gets inserted in front of the buffer instead of behind the springs like the quarters are (https://www.kynshot.com/products/our-products/r15015098-spacer-weight-29/).  Also, I have used the Tubbs flatwires before, but I have had much better success with the Wilson Flatwires because they have a little wider diameter for a wider variety of buffers.

Note--
I was able to noticeably reduce the ROF by swapping 2 of the steel rifle-length buffer weights with Tungsten weights.  I effectively raised the stock buffer weight to 7.2 oz from the OEM 5.2 oz.  When I got home, I decided to swap out one more weight, and now it sits at 7.8 oz.  I'll test again and report back.

The reason I mention quarters is that everyone has access to them and easily tuneable by adding/removing.  For permanent usage, I make my own spacers out of Delrin on my lathe and not everyone has a lathe.  I have the Kynshot spacers too but prefer not to add reciprocating mass for anything gas operated or delayed blowback.

Funny...the same manufacturer that makes the flat wire for Wilson Combat also makes them for Tubb.  I presume maybe different specifications though.

You've definitely got the right tools for tuning.  The Kynshot spacers have come in very handy to give some extra weight on the 9mm systems.  Without going to the A5 tube and staying with a carbine length tube, my AR9s have the Kak heavy tungsten internal weight installed in the bolt.  This extra mass with the Kynshot RB5000HP + the Kynshot spacer put the entire mass at around 23.5 ounces, and makes for very smooth blowback.  I worked with Blowback9 on one of his build examples on his wordpress site, and in his testing, the optimum AR9 weight was in the 22 - 24 ounce range.  The Kynshot hydraulics make this a pretty nice SBR system.

On this Retro M16 build, it sounds like the Kynshot rifle buffer will be a good way to lower the ROF, and I really appreciate all your posted test results.

Here is some helpful comparison info on the Tubbs vs the Wilson flatwire springs:
https://blowback9.wordpress.com/2023/03/03/flat-wire-spring-comparison/

Yes, very familiar with Blowback9's work.  In fact, he reached out to me early on in his testing saying something to the effect that he didn't see much difference using the hydraulic buffers until trying the flat springs which I have been running for years before he tried them.  So his work backed up the results I had already obtained but my focus is on full auto delayed blowback setups while he is more focused on semi auto straight blowback.  I did try his GRSin full auto and it is quite nice but I personally don't like all that reciprocating mass.  It is still not MP5 smooth.  You still have considerable 'muzzle dip' with all the reciprocating mass that straight blowback setups have.

I would put my tuned CMMG RDB setup used w/ a .40SW bolt instead of a 9mm bolt for increased delay in conjunction with my fixed ejector to be just as smooth as an MP5 but with a much nicer cyclic rate than the MP5.  That setup is also using a flat spring and Kynshot hydraulic as documented on my site: https://c3junkie.com/?page_id=280

I don't know if you are familiar with the Ferfrans RRS but that thing will drop the cyclic rate also.
I had an RB5007 in the picture below.
This is all w/o increasing reciprocating mass but I personally felt the cadence was off using this mechanical sear trip delay.

That's a ton of good work.  Thanks for documenting.  My usage is much more casual, and the full-auto is really the poor-man's version with the 3 pos FRTs and Hoffman's Super Safeties (NAGR Member).  I've been super happy with the results on the 11.5" MCX Virtus and the 5.5" 300aac Rattler.  With the PMM bar, the ROF is just right on both at about 600 RPM's.  Luckily, the only way to increase/decrease is to adjust the gas since there is no buffer to work with.  Throw a can on, and they increase by about 300 RPMs.  I have not tried decreasing the gas withe the can on.  I was just too excited that it worked so well with no tweaking.

Ohh......binary / FRT's will always run slower than true FA.

The binaries are slower, but not the 3 pos FRT's and definitely not the Hoffman Tactical Super Safeties.  The SS is slightly faster than both the F/A and the FRT, because there is a little less resistance on the bolt. The FRT and F/A are about the same in ROF given the same buffer weights.  They both have about the same amount of drag on the bolt.  There's a pretty active group that keeps logs of this information and comparisons between them.  The SS is the current king of ROF.  

https://www.youtube.com/watch?v=QDQEdQLxBn8

https://www.youtube.com/watch?v=ut-WKgVd_ow

I watched those videos and it sounded like different buffers are used in each setup so not apples to apples.
So what other data do you have that shows how the 3 POS FRT's and Hoffmans are faster?  I will also say, I have no first hand experience with either and assumed they worked just like the binaries.  
Is there another website like mine that has documented these rates with shot timers that calculate the cyclic rate and the same buffers are used in both setups?  Not being a smartass, just wanted to know.

What do you mean by 'king of ROF'?  In speed?  Like high speed?  I definitely do NOT want high speed.  I like a rate in the 600's but it must be a smooth 600 not a bouncy one with a lot of reciprocating mass to achieve that rate.

No, I understand where you are coming from.  It was a mystery to me too until about 3 years ago.  I went through all the iterations of Hyperfires, Franklin BFS, and then Fostech, but none were what I was looking for.  Then I found out about the RareBreed triggers, and a whole new sub-world opened up.  Then everyone hit the brakes last year when the Alphabet guys started tracking WOT buyers which was basically a copy of the Rarebreed and the Alamo (Graves) triggers and sending out letters for purchasers to turn in their triggers.  

Rare Breed's President got together with the NAGR and got a permanent injunction filed, so that if you are a member of NAGR, the alphabeters are not even allowed to talk with you or send any correspondence to you about FRTs.  Now power users are starting to post more empirical numbers and not worry about getting into trouble - kinda like the pistol braces.

That's the FRT story in a nutshell.

Tim Hoffman is a brilliant 20 something year old that has been developing similar forced reset type engineering wonders for the last few years and has his own company, Hoffman Tactical.  There has been a huge patent infringement case between Rare Breed, Alamo (Graves) and WOT (Big Daddy) that has made everyone kinda sick of all of them, and Tim hates patents so he released the simple STL files for his Super Safety publicly so anyone can print them - or have them printed.  Many people got these printed in 316L and 17-4 steel in China, and now there are several that print them here in the US.

The Super Safety design is still kinda new, so people are just now starting to share their empirical data publicly.  If you send me a DM, I'll send you the forums.  By King of the Rate of Fire, I mean that using the same exact upper and lower springs/weights, the Full Auto (not burst) M16 is right about the same ROF as a 3 position RareBreed - so 600 rpms on the M16 will be almost exactly 600 rpms with a Rare Breed.  The data that I have seen (and experienced) show that the Super Safety with the same 7.5" barrel, same H4 carbine buffer, same Wilson Combat flatwire spring, same gas setting on the AGB - the SS will be slightly faster than the FRT (which is the same speed as the M16).  This was reproduced with can on as well.  

9mm had similar results - same 5.5" barrel, same upper, same lower, same RB5000HP Buffer + Kynshot spacer.  The SS was slightly faster than the FRT. Add a can, and increase the speed by about 300 RPMs.

HK416D - Crazy results with an FRT.  900 rpms without a can using a heavy 7.5 ounce buffer in a carbine buffer 1200 with a can!  I told the guy that he needs an A5 tube at least and add a spacer.  He really needs about 11 - 12 oz to slow that down to a nice 600 or so.  No tests were done with the Super Safety on the HK.

***MCX Virtus and Rattler - Solid results with the FRT, and a nice 500 - 600 ROF with no can.  The SS doesn't work in these piston systems, because it requires a bolt opening instead of a trip bar.

Ok.  Thanks for the info.  Was never that interested since I have FAs and the triggers you mentioned I think are still banned in my state.  

I am working on a new delayed blowback 9mm setup that will function with a RR / RDIAS / RLL and presume FRT which is why I was a little curious.

Very interested!  AR9s are my favorite past time.  What are the specs you have so far?  

My next project was going to be something with Scorpion or maybe MP5 mags.  My current favorite is a Spikes Colt Mag dedicated system with a Macon 5.5" barrel with 1/2x28 threads for my 6" Titanium Form 1.  I'm thinking about moving to a Q taper mount and adding a Rearden muzzle device since that's what the rest of rifle caliber systems are using.  It's running right at 550 with no can.  

I think New Frontier, Wraithworks and Lingle are some of the few making the Scorpion AR lowers so far.  New Frontier pulled their Scorpion lower for now, but expect to release Gen 2 that fixes a few things soon.

I don't really want to go into all the specifics till I have some parts delivered and complete some testing. I like 3 lug myself but only with the old school Bixler mount which doesn't use any o-rings or springs to wear out and mounts rock solid vs the spring loaded push turn 3 lug mounts.  On top of that you can buy quality 3 lugs adapters for like $30 these days and no exposed threads that could be damaged if dropped.

I just ordered a Tubb Lightweight to see how it performs with the 9mm and 556.  I reviewed Blowback9's specs on it again, and I'm surprised I hadn't tried it.

The Tubb LW spring was initially marketed as their 300BLK spring but I was also using it for 9mm.  I think it is too weak to reliably strip rounds for 556.  For 9mm, I typically see around a 50RPM decrease w/ the LW spring vs 556 spring.