Looking to put together a 5.56 pistol build

[cbickel]

I have a few lonely stripped lowers, and was thinking of a ~10.5”. PSA has a few build kits that are really cheap. Also thinking of a bcm 11”. This is my first <16” build. What do I need to know with gas systems/buffers to insure a reliable shooter?

 

[Hop]

Short barrels = high pressures = very high bcg speeds. They often outrun the bolt catch &/or the magazine follower spring then fail to lock back on the last round. A bolt with the o-ring extractor mod + a heavier buffer might be a good idea. I use a Spikes ST-T3 in my BCM 11.5". I can't remember what's in my DD MK18 but it doesn't like to lock back on the last round either. I probably need to swap in a heavier buffer.

 

[bwframe]

I may have just gotten lucky with my 300BLK pistol build?

I was gonna plan it out and throw bigger money at it, but last minute bought a PSA 8 1/2 upper with Midwest rail on sale. Same on the lower parts, gonna build from scratch, but next week PSA put their lower kit on sale with the PDW brace I wanted, at barely more than I could buy the brace alone.

I put a Geissele trigger into my stripped lower with everything else PSA kits. A few hundred rounds down the pipe, pretty much like a sewing machine.

 

[Hop]

300BLK easily runs with short barrels. Different powder burn rates & pressure curves than 5.56mm.

 

[bwframe]

300BLK easily runs with short barrels. Different powder burn rates & pressure curves than 5.56mm.

Thanks for the explanation!

I've considered a few different 5.56 pistol uppers that I've run across in the classifieds and on sale from companies. What do I need to look out for to best attempt to remove my 300BLK upper and replace it with the 5.56 upper in the field?

 

[ol' poke]

Thanks for the explanation!

I've considered a few different 5.56 pistol uppers that I've run across in the classifieds and on sale from companies. What do I need to look out for to best attempt to remove my 300BLK upper and replace it with the 5.56 upper in the field?

#1 concern would be to not mix up your magazines! Other than that, sprint/bugger may be swapped as needed.

 

[Hop]

sprint/bugger LOL Did you get auto-corrected?

I've got two lowers (SBR & pistol) & 3 short barrel uppers (8.5" 300BLK, 10.3" 5.56, 11.5" 5.56) to swap around. Different sized gas ports cause different pressures + I have a suppressor. It's hard to say what will work for you. My best advise would be to get several buffer weights & maybe some Sprinco springs to fine tune your lower to your upper. Short 5.56 barrels have less dwell time so manufacturers tend to over size the gas ports to make them run. Suppress one of those barrels and your bolt speed goes way up & can cause all kinds of issues. The only way to tune is by playing with the spring constant & buffer weights.

Tactical Springs & Machine Gunners Lube
https://www.spikestactical.com/collections/lower-parts/spikes-tactical-tungsten-buffer/

 

[MCgrease08]

I use a KAK Shockwave Blade and tube and I've found that a standard carbine buffer spring and weight works fine paired with my 11.5" BCM upper. I can't recall any issues with the bolt not locking back, but as Hop mentioned, it can be an issue with some pistols.

 

[cbhausen]

I’m doing a 300 Blackout build right now which will run suppressed with a Dead Air Sandman–S. I used this kit:

https://palmettostatearmory.com/psa...ild-kit-vortex-sparc-ar-1x-red-dot-scope.html

with this upper:

https://palmettostatearmory.com/psa...de-7-lightweight-m-lok-upper-with-bcg-ch.html

From what I understand I’d stay away from a 1:8 twist and go with a 1:7 if running suppressed with 220 grain projectiles. There have been some internet reports of baffle strikes with unstabilized projectiles in shorter-length / longer-twist barrels.

 

[Tyler-The-Piker]

I just went out this morning and my new 10.5" 1:7 barrel did quite well at 25-50yds with the 62gr M855

ETA:
...although I think I still need a good linear compensator

 

[tcecil88]

When I built my 7.5" pistol it was overgassed to the point of being obnoxious. The rounds ejected to 1:00 and the pistol just felt like it was beating itself to death. I installed a Seekins adjustable gas block and a Armaspec SRS H2 Buffer assembly. After installing these parts and installing an A2 type flash suppressor, the pistol runs very smooth and is much more pleasant to shoot.

 

[cbickel]

Thanks for the feedback everyone!