10.5 AR-15 build question

[roadcarver]

I just built an AR-15 upper with a 10.5” barrel. I am reusing a lower that I had for a Windham MPC that had a 15.7” barrel.

I notice that the brass case mouth gets dinged quite a bit after it gets ejected. Is this caused by wrong spring or buffer weight? What is the recommended buffer and spring for a 10.5” build?

I am using factory Remington 55gr 223 ammo.

 

[*MALICE*]

Being that it's a 10.5, it's probably overgassed (they often are). Ultimately, if the rifle is functioning correctly, and you don't really care about the condition of the brass, you don't really have to do anything.

Some people might advocate a heavier spring or buffer, but in my experience, by the time overgassing is 'severe' enough that you're entertaining correcting it, a heavier buffer is unlikely to do much (heavier buffers were intended to reduce carrier bounce in full auto rifles, not correct overgassing). You're just adding more reciprocating mass and the money is probably better spent towards an adjustable gas block.

Adjustable gas blocks are great because you can tune your rifle to the ideal amount of gas, or use it to tune to different ammo (for example, if you're running very light reloads you can open the the screw, or if you are running hot 5.56 pressure ammo, dial it back). Better to control the overgassing at the source than trying to band-aid it further down the system.

 

[roadcarver]

Thanks! Didn’t know about adjustable gas blocks for ar-15’s. I will look into it.

I reload and case mouth are not bothering me but just making sure I am not doing anything wrong.

Being that it's a 10.5, it's probably overgassed (they often are). Ultimately, if the rifle is functioning correctly, and you don't really care about the condition of the brass, you don't really have to do anything.

Some people might advocate a heavier spring or buffer, but in my experience, by the time overgassing is 'severe' enough that you're entertaining correcting it, a heavier buffer is unlikely to do much (heavier buffers were intended to reduce carrier bounce in full auto rifles, not correct overgassing). You're just adding more reciprocating mass and the money is probably better spent towards an adjustable gas block.

Adjustable gas blocks are great because you can tune your rifle to the ideal amount of gas, or use it to tune to different ammo (for example, if you're running very light reloads you can open the the screw, or if you are running hot 5.56 pressure ammo, dial it back). Better to control the overgassing at the source than trying to band-aid it further down the system.

 

[*MALICE*]

if the rounds you're reloading are causing the overgassing, you could always try loading them lighter. Would cost you less in powder and in parts......

 

[FoxAlpha]

I run an H buffer in my 10.3" SBR and haven't noticed any issues with brass or over gassing. Wasn't by choice it was just what I had when I built the rifle. While I agree, adjustable gas blocks work well, more SBR's run without them and just use heavier buffers to resolve the issue. I find adjustable gas blocks more dinkin around than I prefer. It's a gun after all, not a custom tuned race car. In my opinion atleast.

 

[roadcarver]

What is the weight of your H buffer? I've gone with an H2 buffer by TNA.

I run an H buffer in my 10.3" SBR and haven't noticed any issues with brass or over gassing. Wasn't by choice it was just what I had when I built the rifle. While I agree, adjustable gas blocks work well, more SBR's run without them and just use heavier buffers to resolve the issue. I find adjustable gas blocks more dinkin around than I prefer. It's a gun after all, not a custom tuned race car. In my opinion atleast.

 

[Reaper of the apocalypse]

I ran into something similar with my 11.5" SBR build at first. After research, I decided to run an H2 buffer, this is what happened:
With American eagle ammo, it was great. However, I ran some steel cased MFS which isn't as hot as American made ammo, and I could feel the difference. The rifle cycled just enough to chamber another round, however it cycled slowly and I could feel the buffer bounce in the tube. Also, it didn't cycle rear enough and it didn't lock back on an empty mag.
After that, I switched to an H1 buffer and my problems disappeared. With American made ammo, there wasn't any easily noticable increase in recoil or fast cycling.

So I recommend an H1, as most versatile for SBRs. But you'll have to test different types yourself.