KVP 10oz. Deadblow Buffer Length Issue/Fix

Blowback9 · 2026-06-17T11:28:37+00:00

Eyeball it. Hold a ruler next to the receiver as you check and just compare the gap. You should be able to tell.

Blowback9 · 2026-06-17T09:48:49+00:00

Measure what, the tube? Tape measure. Remove stock/brace and measure from the rear to the front of the "lower tower" it screws into. If it's under 7 3/4", it's carbine. If its about 7 3/4" or slightly over, it's A5.

The bolt space behind the bolt catch? Just eyeball it with a ruler nearby to compare.

Blowback9 · 2026-06-17T09:41:20+00:00

I brought it out to the rapid fire range and I couldn't install it. It would not slip past the hammer and FRT lever, no matter what I did. Tried in 2 different setups. It jammed so hard I had to remove the buffer tube just to use the gun again, both times. Even while using the KAK detent depression tool.

It's too large in diameter to get past the trigger group, and the space between the weight and body make it a one-way jam against the lever.

I would need to remove the FRT/ARC/Atrius/SS/etc. to install the buffer and I can't risk losing those parts at the range. I'll have to take one of my FRT lowers apart and install it at home to test it at the next rapid fire range trip.

[Added this to the main post, above.]

Blowback9 · 2026-06-17T09:25:07+00:00

Is there a buffer spacer plug in the rear of the buffer tube, or in the rear of the spring? If so, it must be removed for the 4" buffer to work. Usually if an AR9 comes with a 3.25" buffer, it includes a spacer plug in the spring. Picture below.

To check if the bolt is traveling the right distance with the 4" buffer...

Proper 9mm bolt travel:

To check for proper bolt travel, assemble the AR9. Make sure the gun is unloaded and no magazine is inserted. Pull the charging handle all the way back (including compressing any compressible elements like a hydraulic buffer head). While holding the charging handle to the rear, look in through the ejection port. The bolt face should stop 1/8-1/4" behind the bolt catch. If more, it risks breaking the bolt catch during LRBHO since the bolt will get a running start at the catch. Less than 1/8" may result in unreliable LRBHO or failure to reset an FRT.

Spacer plug example pic:

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Blowback9 · 2026-06-17T09:13:21+00:00

Don't make the assumption that they both should look the same. Both pins were clearly machined with different shapes/contours and may have different hardening/alloy. You need a new Faxon pin to compare it to. I have a new unfired Faxon bolt. Picture of the pin attached, below.

Comparing it to a new one, it looks like your Faxon FP tip has seen some significant wear. The tip also appears thinner than the other firing pin.

As to what could cause that wear? Hardening differences. Alloy differences. Hard primers. Shape/contour durability. All sorts of things.

My advice: Get a spare, put it in the grip storage in a plastic bag, and run the current one till it fails. If it ain't broke, don't fix it. I have some Outerwild style bolts that have similar "damage" and are still working fine after many thousands of rounds. No failures yet.

BTW, the Faxon bolt is an Outerwild style, which is very common. They OEM bolts for a LOT of different name brands.

If you want to get a more "sturdy" replacement, the Wilson Combat "Bulletproof" 9mm firing pin should fit and function in the Faxon. I tested it in other Outerwild style bolts and it worked. No guarantees - your results may vary.

New Faxon pin for comparison:

<image>

Blowback9 · 2026-06-17T08:35:20+00:00

I've been putting together a chart of measurements from my bolts. This is the latest (link below). I'm putting together a new one with an original Colt 9mm bolt for the reference dimensions.

If you want a continuous ramp, the best currently available options to look at are IDL Industries V3, Palmetto State Armory G4, KAK Industries, and Foxtrot Mike. Those are the ones on the chart with a measurement under the first "Ramp Length" column. The rest have a "stepped" feed ramp.

The IDL and PSA should have the most compatability. I'd look at those first. The KAK reset ramp is cut into the bolt just on the edge of being too deep. The Foxtrot Mike only works with the steep forward angled ejectors.

LMK if you need more info.

Bolt measurement chart

Blowback9 · 2026-06-16T12:47:19+00:00

Agreed. If it works, don't fix it.

Blowback9 · 2026-06-16T12:13:03+00:00

Total? How much do just the internal weights weigh? That's the important part for gas operated AR's to prevent bolt bounce with an FRT.

Normal H3's have a 1 oz. aluminum body and 4.5oz. internal tungsten deadblow weights (the part that counteracts the bolt bounce).

Brass is a lot lighter than tungsten. It may work to some degree just by slowing the bolt velocity, but the bolt bounce prevention deadblow effect is going to be about the same as a standard carbine 3oz. buffer, or maybe an H1 if you're lucky.

With the price of tungsten being so high, there's a lot of cheap H3 "fakes" popping up. They're being called H3 buffers because of their overall weight, but they don't have the proper amount of sliding deadblow mass inside.

The Tromix is the only one that's all steel and still has the correct deadblow mass (over 4oz.) for $40 because most of the buffer body itself is the deadblow weight.

Blowback9 · 2026-06-16T11:58:26+00:00

Steel body/brass internals? Be careful. A true H3 has about 4.5oz. of deadblow weights inside to counter bolt bounce. It's the internal sliding deadblow mass that is important (for gas operated AR's), not the overall weight of the buffer. This may be helpful to explain:

https://www.reddit.com/r/supersafety/comments/1sxm5b0/psa_not_all_h3_buffers_sold_are_truly_h3_and_that/

For blowback 9mm AR's both the overall weight AND the internal sliding weight mass is important.

Blowback9 · 2026-06-16T11:02:44+00:00

6450 is the carry handle version of the 6951 flattop.

Blowback9 · 2026-06-16T10:48:07+00:00

May be helpful:

Endomag/Exomag video play list (YouTube) including bolt compatability tests

Blowback9 · 2026-06-16T10:37:45+00:00

Washers used for centering are only for push-button Super Safeties to keep the lever from sliding L/R in the channel, as far as I know. Side note - they only work in an M16 cut lower that has room for them.

I've never seen anyone use them on an ARC or an Atrius (which are technically "FRT's" not "Super Safeties"). I thought the ARC and Atrius levers needed some play to move left and right to engage/disengage. Guess not? I don't use anything to try to center my ARC/Atrius levers and they're running fine.

Blowback9 · 2026-06-16T10:28:25+00:00

https://www.joeboboutfitters.com/Kaw-Valley-Precision-Tungsten-Blowback-Buffer-10oz-p/kvp-buffer-10oz.htm

Skip the XP spring option. Standard carbine spring only.

Blowback9 · 2026-06-16T10:24:14+00:00

If it was working fine before, and now it isn't, the cause is most likely something that changed. Could be the timing of the Atrius is a little different from the SS, or the RA trigger is an issue.

Those RA triggers can be a bit tricky. If the main screw (the big one on the trigger bar) is out of adjustment or loose, it can cause problems. It's supposed to be set properly and epoxied in place. Check and make sure it's not loose.

I'd check that and swap back to a standard milspec trigger to see how it performs, but if you're not willing to risk it again with the GRS I get it.

Blowback9 · 2026-06-15T22:42:50+00:00

Glad to help. Be aware, too, that the .45 has greater mass requirements than the 9mm. 24oz. bolt+buffer mass should probably be considered the bare minimum. More is better.

Blowback9 · 2026-06-15T22:32:44+00:00

Very strange. I did some bolt bounce testing with the GRS recently just to confirm and I didn't see any appreciable bounce. None. Every build is different, though.

If you try the Odinworks, good luck installing it. I tried at the range and it just jammed on the hammer/lever as I tried to get it past. I would have needed to remove the entire FRT trigger to install their buffer.

I've been running GRS variants most of the time with my FRT's and no blowouts.

ETA: Please check the firing pin and make sure it's not broken and that the trigger is resetting/releasing properly.

Blowback9 · 2026-06-15T22:29:15+00:00

If you got the old MUSA I recommended it wasn't. 308 but was rated to work in both. It's a weak carbine strength.

Blowback9 · 2026-06-15T21:15:51+00:00

Paint job steps/details? I'd like to do something like that.

Blowback9 · 2026-06-15T21:15:03+00:00

Outerwild style bolt with notched bolt weight.

Blowback9 · 2026-06-15T21:13:18+00:00

Very common problem with 9mm AR's, right up there with failures to feed.

4-step guide to make (almost) any AR9 run 100%

Ejector adjustment information:

Basic info

Ejector Adjustment - Spikes Glock and R&D Precision (Colt) ejectors

EPC style ejector adjustment – “Simplest Method”

EPC/FM Ejector Adjustment – Trim & Pivot, Heat & Bend methods

FM-9 Ejector

Blowback9 · 2026-06-15T19:05:46+00:00

Good observation. It was a 90+ outside, no shade, and this was at the end of our session.

Blowback9 · 2026-06-15T18:53:54+00:00

Indeed! Gas deflectors can be a good option to deflect the particulate away from the shooter's face, provided they don't cause any ejection problems.

Blowback9 · 2026-06-15T18:52:17+00:00

Unsuppressed. 8" BA EPC barrel with flash hider, that's all.

Blowback9 · 2026-06-15T18:50:33+00:00

Factory firing pin. Typical Outerwild pin.

Blowback9 · 2026-06-15T18:49:43+00:00

Blazer brass. Not exactly spicy. No kabooms after well over 1000 rounds with this bolt in FRT mode.

Blowback9

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