My 300 Blackout will not cycle subsonic

[Osage48]

I would really like to try AA1680, but not sure where to find it. I saw on other sites where Lil'gun often has trouble in 16" carbines cycling. I think this is probably my issue. If anyone knows where to find some, please let me know. thanks

 

[gmar]

I found some AA 1680 at Wannamaker earlier this year but I have not tried it yet. You might try H4198 which works for me when H110 wouldn't.

 

[Osage48]

I tried some IMR4227 and it worked just a little better. So I took all the weights out of my buffer and cut about 3" out the spring (it was a lighter spring already) and used motor mica lube and it cycles most of the time but still does not lock the slide back on the last round. I said it had a mid length but the gas tube is about 8" in length.

One thing I noticed is that I am having to use about 10% less powder than published to get below the sound barrier. It is the same with different powders.

I guess I will need to open the gas port. Can't think of anything else to do.

 

[Grumulkin]

My problem wasn't as bad as yours. I couldn't get IMR 4227 to work well but 1680 works fine. Another thing to try is to go with a heavier bullet so you get more pressure with less velocity; like the 220 grainers I use.