I know this basic topic has been covered before and diagnosed as an overgas issue. What I’ve been able to find in a search for the resolve is that it is usually inferior uppers with too large of a barrel gas port hole…
Here is my issue:
I have a BCM 14.5" Mid-length upper on a LMT Lower, A JP Buffer spring and an H2 Buffer (I think a DPMS… its what was in stock at my local gun shop), Magpul Gen 2 Mags (pretty new, I wouldn’t expect weak springs in them). If I put an empty mag in and charge the handle, the bolt locks back, every time. If I load a magazine and fire it the bolt does not lock back maybe 33% of the time after the last round is fired. I don’t know how big the gas port in the barrel is (its under a fixed front sight), but I am assuming that being a BCM it should be GTG. I tried to call BCM and see what their thoughts are, but it has been difficult to get somebody on the phone.
I’m thinking maybe a heavier buffer to get me through my next gun classes in a couple of weeks, but I would like to fix the problem instead of compensate for it.
Any thoughts??? Thank you in advance for your help.
What MarkM said. I have a PSA 14.7" barrel that barely cycles with anything other than 5.56 and I run an H in it unsuppressed. With the Saker I can bump it up to an H2 but it’s barely on the cusp of locking back on the last round with anything other than 5.56.
The port on a BCM 14.5 middy is less than .080" It’s either .076 or .078… but in any case it’s an H1 buffer port unless you have an expansion chambered muzzle device like the Mod 1 Gunfighter or a Battle comp.
Even then, I sacrifice a little smoothness (which there’s plenty to borrow from) for a more reliabiltiy with less than 5.56 pressure match ammo.
Thanks for the quick replies guys, I knew MarkM would be able to tell me how to handle it. I guess I should have mentioned in my original post that I do have the Mod1 Gunfighter Comp, and was shooting PMC .225 (55 grain) through it. On its maiden voyage to the range I shot 20 rounds of the same PMC .223, 20 rounds of M193 & 20 rounds of M885 through it with no problems, but the 2nd time out is when I encountered the issues.
I bought the JP spring from Brownell’s, thinking it would be an upgrade… Lesson learned I guess. FWIW, I’d gladly sacrifice some smoothness for reliability any day… I’m sure I’m not the only one!
Aftermarket stuff like that only complicated the diagnosis when something isn’t right. PMC 55 grain comes in various loadings it seems. Some quite mild… some a little hotter. People post all kinds of different chrono data with that stuff. It’s not bad stuff… but some of it can be weak.
They are. I’ve run an H4 buffer and had it fire 8 rounds and lock back just to test… but with an odd burning powder, it can short stroke on a much lighter buffer too.
I also run a BCM 14.5" Middy , I currently run H w/ SpringCo Blue spring, I have used a H2 with the blue spring just to test, and all of them have run fine even with basic PMC.
Also just to check, what BCG do you have?? It is not some really light weight modified carrier is it??
