A question for all the AR guru's.
I'm putting a carbine stock on my 18" SPR. It has a rifle length gas system and I've currently been using an A2 stock and buffer. What weight buffer should I use with this setup? I am thinking using an H buffer
Theoretically, shouldn't the longer gas system result in less impulse
The only large scale data point I know of for rifles with carbine stocks are the Canadian C7 variants that use that. A search on those yielded some different answers on buffer weights, but the only source I've seen that I trust has first-hand knowledge on the issue said the chose H2. There's a few threads at M4C about it, if you use "C7A2" as a search term it will help weed things out (using "buffer" as a search term at M4 is kind of like doing a Google search for "the").
However that's with a 20" barrel, so there's a bit more dwell time to work with than on your 18". And I assume that in an 18" SPR build you might be running .223 pressure precision loads vs. some of the hotter 5.56 stuff. Backing off to the H for those reasons might make it a good starting point. It may work with an H2 (or only work when clean and freshly lubed, etc), and it may end up needing a C to be reliable with everything. Ultimately you're not going to know for sure till you try it.
--Josh
“Formerly we suffered from crimes; now we suffer from laws.” - Tacitus.
I'd start with an H2, though an H has a fine chance of working. I'd fret over function, first, but yes, a rifle-length gas system isn't as likely to be overgassed the way a carbine-length system often may be. It's one among many reasons why somebody came up with the mid-length system, and some with their own unique longer-than-carbine-length systems, and they have been noted to be of lesser perceived recoil than carbine-length.
On the "practical" side of the house, the conventional wisdom is to use the heaviest buffer you can (to keep the cyclic rate of the bolt down) that allows the weapon to function reliably (without short-stroking); reduced perceived recoil is a happy fringe benefit, not a goal. A competitor'd likely have a different view on whether reduced recoil on a .223/5.56 system is a worthwhile primary goal or not....
You'll not know for sure until you try it out for yourself. I have a carbine-length Noveske that shoots softer than any middie I've tried, all using an H buffer, which is NOT how things are supposed to be....
See weights, below.
H3 is 5.6oz
I just finished test firing my SPR build with a rainier arms 18" ultra-match rifle length gas barrel on Saturday. The gas port measures close to .098. Incidentally I ran it with an H2 buffer with my lighter .223 reloads and it locked the bolt back with no problems and ejected consistently at about 3 o'clock. I'm sticking with the H2.
Side note: The barrel is made from a shilen blank with ratchet rifling. I'm very pleased with the quality. I had some moa and sub-moa groups with mixed headstamps, no load development, and an ALG QMS (mil spec 5lb) trigger. I can't wait to see what it will do with a tuned load or some black hills match ammo.
This paired with the fact that H2 is .2 oz different than Rifle which is what you've been using. I'd say stick with the same weight. However I use an H in my Midlength and it runs (get ready for it) flawlessly (Did your toes curl?) and I shoot Wolf only.Originally Posted by EMC
ETA: Flawless being 4,500 rounds conservatively of weaker .223 Rem out of a 5.56 barrel, with an H Buffer, 16" barrel, and M16 BCG. With maybe 3 malfunctions related to feeding in D&H mags with GI followers in the first hundred rounds. Changing the followers to Magpul Anti Tilt Followers resolved the issue and other than a single stuck case with Wolf, I've had no issues cleaning the chamber every 500 rounds.
My 12.5 SBR by BCM shipped with an H, I'm going to shoot it first and see what the ejection pattern and function looks like before I change anything. I'll probably load 1 round in a mag and fire to see if it locks back a couple of times just to verify.
Last edited by BWT; 08-13-2013 at 10:49 AM.
From my past reading I take it that much of the problem for the .mil is getting the guns to run on full auto, which isn't a consideration for most people.
My two data points are that I have seen two 20" rifles in my life with carbine stock assemblies installed, one mine and one a friend's. Mine was an a2 style upper, my friend's an M16a1 upper on a CAR-15 lower. Both ran fine, and we used the standard buffers because back then there wasn't anything else. This was the days that were pre flat top uppers, M4s, etc.
It's also my understanding that even if you were to replicate the exact weight of a rifle buffer in your carbine extension, the result would still be different due to the different spring rate, spring length, and the way the weights in the shorter length buffer move during recoil.
Thanks for all the help guys (I really appreciate you dumbing down the m4.net data for me). I try and stay out of the carbine forums as they tend to be huge time sinks for me and it is hard to filter out the white noise, I usually leave the forums in a worse mood than when I started.
I'll order an H2 buffer with my next "Montezuma Iowa Care Package." If the goblins come before then, I'll just have to hope the H1 buffer works.
Given the chart above, the H2 looks to be pretty much the equivalent to the rifle buffer so barring the spring rates being drastically different, should work just fine. I've had zero issues with the rifle buffer and stock.
My experience is about the same.
I took my first carbine course with a 20" Bushmaster upper on a CAR lower with the standard buffer. Ammo was my reloads which were put together with 1970's era H4895 under a 55 grain bullet loaded in the middle of the charts. 400ish rounds without an issue but if I were to do it again, knowing what I know now, I would play with a heavier buffer.
-Seconds Count. Misses Don't-
I am told that this;
http://www.vltor.com/emod-a5.html
Is the best way to go if you want to spend the money and do it right the first time.
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