300 blk subsonic question

[GrantB]

I'm trying to run 165 grain bullets subsonic and having a velocity problem. I'm getting 100 + fps changes in velocity 850 to 950. I'm running a 10.5" barrel with 10.5 grains of 1680. running unsuppressed for now and have no problem with cycling after I opened the adjustable gas block 2 turns.
The only reason I'm trying 165's is because I have a bunch on hand, if they won't work i'll just get some 200+ grain. Has anybody had this problem before?

 

[jwb47]

a little more powder may help but I think your spinning your wheels with a gas gun unless you shut your gas block off and shoot them like a bolt action. try you some 208 grain amax start at 11 grains of 1680 and work down to 1050 fps.

 

[rjacobs]

running a light crimp from something like a Lee FCD seems to calm down the spreads that 300BLK sees, but large spreads do seem to be common with it. Usually not the case, but I have seen some GREAT groups out of the 300BLK from guys that showed crazy ES's.

 

[GrantB]

So in general i would be better off running heavy bullets instead of mid weight for subs. I've been through the process of trying to force a round peg in a square hole before and it never works out. I'll get some heavy bullets and give it a try. Any tricks to loading the heavy bullets in the 300 that make them perform better.

 

[rjacobs]

Ive settled on the 208g AMAX, but the 220g SMK and 220g Nosler CC are also great bullets. I just have better availability of the 208g AMAX locally so I choose to run them. The 220g Nosler CC's are pretty easy to find as well.

As for powder, A1680 and H4198 are probably the two best. 4198 is a bit cleaner than A1680.

The issue I see with loading smaller charges with shorter(lighter) bullets is that you arent filling up the case with much powder and thus get un-even burns. Thats one thing that shooting the heavy, long bullets gives you. It fills up the case itself quite a bit plus you need a bit more powder to send it down range thus getting closer to the optimum case capacity for an even burn.

 

[MarkCO]

Been happy with LilGun and 240SMKs, but the 220 is a better choice. My 240s only run 100% in Teflon coated aluminum mags. My ES for 14 different charge weights was between 4 and 30 with most in the teens and low 20s. I do not add any crimp at all.