AR Cycling Issue - Subsonic 240 Suppressed & Unsuppressed

[Dutchninja]

I will be doing some more testing to see what the issue is but I'm working through some CB subsonic load development and am having some cycling issues with my SBR in 300 blackout. (AAC manufacture barrel) Subsonic rounds will cycle fine without my suppressor but as soon as I put my can on, I start getting FTF. (round is picked up but jams half way)

I have made the same ammo using different powder (5744) and do not have any issues feeding unsuppressed and suppressed using the same boolit, cases, primers, OAL, mag, and gun. I've also tested the same ammo in my 16.5 with carbine gas system with no issues. The SBR gun also feeds other subs and supers without issue.

Problem rounds are using 10.0g A1680. Other strange thing is i swear i saw a flash of unburnt powder out the ejection port. I've heard of issues with sub rounds without a can on but not the other way around. Anyone experience this? Is the gun unlocking and pushing excessive gas back? Initial thoughts?

[runfiverun]

sounds like a powder timing issue.
if your seeing stuff from the ejection port your powder is on the slow end.
check your cases and see if they are being stretched a bit, that would tell you if they are being extracted while still under pressure.
compare them to the cases from the other powder.

[Dutchninja]

No ejector swipes or excessive length gained. It's not over pressure but I'm thinking overgassed right now.

[Gtek]

Install can and close your adjustable gas block to off, single round in mag and fire, BCG should not move. Open one click, fire, repeat one click steps until bolt locks open. Then take off can and I bet bolt will not lock back. One or two clicks north of just locking is usually happy land (WITH THAT CONFIGURATION). All the variables that can be induced into this little round, powder, gas system, orifice, powder, bullet weight, buffer weight, BCG type (style). Can be a finicky little booger, Welcome to the show!

[Dutchninja]

For anyone that cares. Brought a ton of other mags to check function after making a bunch more rounds. Several brands of GI mags, Magpul 20's and 30s, etc. The only ones it was choking on was the magpul 30 round ones. I'm thinking it doesn't have enough spring pressure because the 20 round mags functioned without issue. Even tried the original Carbine buffer as well as an H1 and H2 buffer and everything worked except in the 30s. strange.

[Gtek]

Well that is the second one in a week. Friend bought a new SW and said it was jamming. Saw the cartridges, pushing bullets hard angle in neck (30 PMAGS). He tried Mil 30's and Brownell's aluminum 20's, not a hiccup. Hmmmmmm!

[Moonie]

My preference for the 300 BO is Lancer, I've had issues with 30 round Magpul's as well. The latest version are supposed to be better but the Lancers have been 100% for me with all proper length rounds.