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My first SBR and have some questions


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Planning on filling out my paperwork here in the next couple days. 

I have some questions on what to expect to “tune” the rifle. I haven’t really made up my mind on what barrel length yet but it’s going to be .223 for my first upper. 

what have you guys ran into to “tune” your rifle to 

Make you work reliably?  Heard that gas and buffer systems have caused issues. Do most guys run regular carbine buffer and springs? Also, what size gas block are most guys running?

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A complete upper from a reputable manufacturer like BCM should not need to be tuned for reliability. If you’re putting together the upper yourself a 11.5 barrel with carbine length gas has a very good reputation for reliability. You can add an adjustable gas block if you plan to shoot suppressed. A 10.5 will normally run just fine too but that 1” equates to a much shorter dwell time which can result in reliability issues. A heavier (h2,h3) buffer and blue sprinco spring can help with reliability by slowing the carrier speed. If building the lower now, go with the a vltor a5 buffer system.

I have a 13” mid-gas (cut down from 16”) with a 0.076 gas port. The first time I shot it, I had several failures to eject. I believe it was unlocking early and the carrier speed felt very fast. This was with a regular carbine spring and h1 buffer.

I swapped to h2 buffer and blue sprinco spring and it has been good to go. However, I decided to order a vltor a5 tube and their a5h3 buffer for the lower because I feel the 13” mid gas is right on the edge of reliability and the a5 should help increase dwell time and smooth out the carrier (plus, waiting on suppressor and will eventually get a 10.5-11.5 upper)

Sent from my iPhone using Tapatalk

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  • 1 month later...

+1 on the 11.5" barrel.  But feel free to make up your own mind based on ballistics lost and what range you're wanting to use this for.  And what you are using it for :) Everything has a tradeoff.


I've had zero reliability issues with built uppers in this range - with no adjustable gas I'd play with H2 buffers and experiment adding or subtracting one tungsten weight. i have a cheaper H3 and standard carbine buffer I use for tuning so you can effectively build everything from standard to H3 and shoot, watch your brass ejection piles.  I'm a big fan of adjustable blocks, even cheaper ones like the seekins that have a set and forget mentality, but I understand a lot of folks are hardcore against them on antyhing that needs to be 100% failproof every time. 


So much variety out there with different manufacturer's, but with the ability to change buffer weight and adjust gas I've never not had a .223 run well. If you really want one more step up grab the JP silent capture with adjustable weights and springs, but that's going to add a couple hundred bucks onto your rig.  That system plus adjustable gas is pretty killer, and I love how smooth it is.

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