300blk

[Pokulski-Blatz]

I have tried 125gr and 208gr subsonic rounds with the exact same results.

[inline 6]

Yeah, I missed that. I think this is a possible culprit and when I brought this up to the board a while back I didnt get the anwser that CJ is giving now. Maybe I worded it differently back then I cant remember to be honest but this is the same problem I was having and Cj basically said that for that short of barrel and shooting subs they need to be 220g.

[inline 6]

this was CJ's response to my initial problem that was not worded an clearly as the OP's....

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What kind of ammo was this? 208gr is right on the edge of what will or won't cycle subsonic. Of course it all depends on the barrel and gas port, but my experience is 190gr won't cycle period. Sometimes I can get 208's to cycle, sometimes I can't. 220+ is usually a guaranteed thing. If these were hand loaded you need to put it in front of a chrono and make sure it's squeezing all the pressure you can. It's a lot more susceptible when they are lower weights like that. A 220 gr will cycle as slow as 850fps on the other hand.

[likeitfast55]

Thanks, I had someone else tell me the very same thing. I am surmising that the heaver bullet is slower due to weight and thus greater gas pressure for the carrier to cycle properly.
I will get some 220's and try that as well as different carriers. So 220 cycles, how about with a can on it?

[inline 6]

I never got around to firing that upper with a can as I sold it off for another caliber. It was so close to functioning properly as it would shoot fine for a couple rounds then have a failure to eject or just not catch the next round at all but would eject the previous casing. I had an adjustable gas block as well turned all the way open and it acted like this. I will also note that I was running a standard spring and a light weight buffer and carrier in that gun so I really felt that it should have ran but just didn't. My feeling and others was that it would have ran fine with a can on it or with 220g subs but I can't say for sure.