I have been running a Colt-system, 9mm franken-AR SBR for years. It has always been reasonably satisfactory, if bouncy (as blowback guns tend to be). However, with PCC action shooting matches on the rise, I wanted to revisit the gun with a view to making it more competitive.

A few weeks back VLTOR, who sponsor our local 3-Gun matches, were kind enough to send me one of their new A5H4 buffers for testing. This thing looks like a regular CAR buffer on Viagra - substantially extended in length. I understand it is intended to be used with an AR15-A2 buffer spring, and is somewhat heavier than a regular 9mm buffer (6.83oz vs. 5.5oz). The idea is that, in an AR15/9mm with carbine buffer tube, it will shorten the bolt stroke so that the bolt bottoms out just past the bolt catch engagement point. A lot of folks like this because it reduces the chance of breaking their lower receiver or bolt catch if they have the last round bolt hold open feature. However, I was told that a side effect of the design is that it seems to make the gun feel significantly flatter shooting and less bouncy. I am not a believer in "feelz" alone, so I decided to do what I hope is an objective test.

As a baseline, I used a regular 9mm buffer from Rock River Armory with a CAR buffer spring. In addition to the A5H4 buffer/A2 spring, I also tested the 9mm buffer + CAR spring with a spacer ~0.7" long... a stack of quarters in the back of the buffer tube, which is a common red neck modification used to shorten  the buffer stroke and reduce the chances of breaking the AR15/9 bolt catch. The gun was my AR15/9 with 10” barrel and a red dot sight.



I set up a simple course of fire with two 8” steel plates at 15 yards distance, spaced 3 yards apart. The shooter would be timed as they shot each plate twice; I recorded the split time for the double taps on each plate and the total time for the course of fire. I used two shooters of different ability levels – my son (a quick 19 years old) and me (a slow old guy). Typical run times for the whole exercise were in the 1.5-2.1 second range, timed with a shot timer of course. We did 10 replicates of each condition (excluding any runs with misses etc.). I have posted a video of the test on YouTube.

I used conventional statistical methods to draw conclusions, notably a “t-test” to determine significance of performance differences. Here is the data summary




Here are my conclusions...

SHOOTER #1 (the young gun): Compared with the 9mm buffer alone and the 9mm buffer + spacer, the TOTAL RUN TIMES were significantly faster, and the SPLIT TIMES (times between shot 1 and 2 in each "double tap") were significantly more consistent with the VLTOR A5H4 buffer.

SHOOTER #2 (the old man): Compared with the 9mm buffer alone, the TOTAL RUN TIMES and the SPLIT TIMES were significantly faster with the VLTOR A5H4 buffer, and equally so with the 9mm + spacer configuration.

BOTTOM LINE: The data suggests that VLTOR A5H4 buffer can significantly improve shot-to-shot time in a practical shooting course of fire, and that the primary way it achieves this is by shortening the buffer stroke, with the increased weight perhaps contributing more to the consistency of the cadence rather than the raw speed. For sure the VLTOR buffer made the rifle feel like it was shooting flatter (as did the spacer added to the 9mm buffer), and performance was clearly superior compared with the 9mm buffer alone.

An existing gun could certainly be modified to get much of this same effect by simply dropping a stack of quarters (or similar spacer) in the back of the buffer tube, but for a new build I would go the VLTOR route as it is a cleaner and likely better solution at comparable cost to a regular buffer setup.

I have to admit, these findings are not what I expected – I would have thought having the buffer NOT hit the back of the buffer tube would be smoother (which is my experience with open bolt submachine guns), but the data is very clear otherwise when it comes to the AR15/9mm.

All this testing was done with Metalform 32-round Colt-pattern magazines and round nose FMJ minor power factor ammo. One aspect to be checked is whether feeding reliability is impacted with the shorter stroke (such as when running higher-capacity magazines, lead bullets or hollow points, etc.). So far I see no evidence of this, but it is something I will play with in the future as time allows.

please keep the information coming... my PCC is 16" and am currently playing with an A1 stock and tube so I can experiment with heavier rifle buffers... currently  with a piece of 1/2" brass with a couple of turns of plastic electricians tape to keep it from rattling... around 6.2oz...my NFA lower came with a polymer bumper for the carbine buffer, and as I tried the heavier buffers I had on hand (H1 and ST T2), the shake decreased, so went for the rifle buffer for additional space... may try filling one with lead shot.... for a comp, a 3 port with 3 porpoise holes from GuntecUSA but I get less scope movement with it clocked to 11 o'clock rather than 1 as I do with my Miculek on my 5.56 game gun...currently shooting Bayou 135s with WSF,,, haven't put them over a chronograph yet.... 900+ fps out of my G34..., may have to try some 115s and keep them ID'd with a different color polymer.... regards

I used an A5H4 with a rifle spring in a carbine tube when I built mine about 1 1/2 yrs ago. I have probably put 1500-2000 consevatively. I used a 8.5 CMMG barrel and ASC mags.

When I first started, the ASC mags had a very thick coating on them, so first time out I think my 20rds had 1-2 FTE/FTF. I have since found a tutorial on here about cleaning up the coating in the feed lip area with a small file or emery cloth.

Since that first time out I have shot WIn White box, Rem UMC Bulk, Federal Bulk, Prvi Partisan, Tulammo, Perfecta, all with not problems. I have shot some of the oddball Win White box hollow points with no problem. A box of Isreali nato stuff a coworker gave me(very hot!!). I even had a bag of probably 150-200 rds of misc carry ammo(115s to147s, and everything in between)from Golden Sabers, Hydrashoks varieties in reg, +p, and +p+, and Gold Dots, again assorted power, which all fired fine. All cycled, fed and ejected, and fired fine. Even in mixed mags.

Now, I do have one exception. I got 50 rds of Win PDX-1 hollow points from a buddy, not sure if the 124+p or the 147s, but every single round was either a FTF or and FTE, or a combination there of. I literally ran all 50rds and could not get 2 shots of without a problem. Can't explain why it had an issue, but it did. I tried mixing some in with the other hollow points, same thing. Had empties end up facing backwards in the action, facing sideways, rounds kicked straight up with an empty underneath. Never could explain it, just haven't bought anymore.

So I am sold on the A5H4 set up!!


Edit- Oh, and I have had zero issues with bolt catch breakage and have had nearly 100% BHO(I don't recall any time it didn't lock open, but I am sure there has been 1-2).

relative stacked length of an NFA modular bolt, 6.2oz rifle buffer (mine has 1/2" diameter brass slug), NFA bumper (.775") in an A1 stock...

I wonder how this system would perform in full auto?

I'm looking at the A5H2, A5H4 or a hydraulic buffer (all with appropriate spring).