Gunsmithing 300 BLK Question

[ChiefBDT]

I'm having problems with a new upper I purchased. I've tried everything from 110gr. to 220gr. ammo. The lighter projectiles will eject the empty cases but won't strip the next round from the magazine. The 220s will not even eject.

I've tried putting red lock tight on the gas block, on advise from a local gunsmith, .... no luck or improvement.

I've tried this upper on 4 different lowers, no positive results.

I measured the gas port in the barrel and it comes in at .95

I've cleaned and leveled everything, again no luck.

I decided I'd come to the experts for some advise.

Any help would be much appreciated.
Thanks,
ChiefBDT

 

[gszeto99]

Re: 300 BLK Question

I am no expert with this but it sounds like you have a short cycle problem. Is the upper made specifically for the 300blk round. I ask this because for the 300whisper round which is very similar to the 300blk round the gas block can not be placed too far forward on the barrel or the upper will now cycle correctly, mostly short cycling. I am sure others more knowledgeable than I will chime in. I hope you get this problem resolved.

Gene

 

[MitchInOR]

Re: 300 BLK Question

Powder?
Charge weight?
Gas block position?
Barrel length?
Suppressor?

 

[jbmillard]

Re: 300 BLK Question

Are you running it suppressed with the subsonic rounds? If not, you probably don't have enough pressure to cycle. That's what mine does -- without a suppressor, it short cycles -- you need the back pressure.

 

[mattbohac]

Re: 300 BLK Question

what barrel and what length gas system?

 

[Beef_Supreme]

Re: 300 BLK Question

Gas port seems awfully small. When developing my first one, I started at .085 and didn't get positive cycling until I got to .107/9 and my understanding is that AAC is running them even bigger now.
If you red loctited the gasblock on though...... you may have the fight of your life getting it off to open the gasport.

 

[tiNdvenTFHwMdqKW]

Re: 300 BLK Question

If you are running unsuppressed then I also vote for opening up the gas port. You may want to put an adjustable gas block on if you plan to switch between suppressed and unsuppressed.

 

[AKA-Spook]

Re: 300 BLK Question

ports too f'n small. drill it to .118.

 

[7.62_Reaper]

Re: 300 BLK Question

i agree you'll have to make the gas port larger or run a supressor to get the pressure you need.....mine was having the same problems so i put a can on the end of it.....problem solved

 

[TOPDRAGSTER257]

Re: 300 BLK Question

What brand of upper is this ?

 

[ohnomrbillk]

Re: 300 BLK Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: AKA-Spook</div><div class="ubbcode-body">ports too f'n small. drill it to .118. </div></div>

Spook, as usual, is 100 percent correct. Pistol port location and .118 is the magic combo