.300 blackout question

w321shark · Mar 7, 2014

Built my first .300 blackout ar today. Shoots great no issues. My only question is the carbon build up in the rifle seemed nuts even after maybe only 35 rounds. I haven't shot any ar's in a long time and I'm wondering if this is normal with a direct impingement system or could my head spacing be off a little. It has a 16" Wilson combat barrel and a ptac full auto bolt and carrier group. Like I said it shot fine just wondering maybe the neck didn't expand nice and uniform and some gas might be blowing back a little? Idk.

Paco · Mar 7, 2014

Where is the carbon building up?
What length gas system on the wilson?
Is it suppressed?
Do you have to scrape it off?

w321shark · Mar 7, 2014

Just pulled the bolt carrier and charging handle out and wiped the inside out with a paper towel not thinking anything was wrong so I can't say exactly. It's a carbine length gas system. Not suppressed and no scrapping, it came right off with a dry paper towel. Got all of it out with maybe one full size sheet of paper towel if that can give you any gauge of how much carbon build up there was. Cases seem fine no noticeable splits.

Clicker · Mar 8, 2014

I tend to believe that with subsonic ammo the pressure is so low that the case never expands to fully seal the chamber hence more grime and crud in the upper. Since I reload it seems that 1680 is dirtier than some of the other powders I've tried so that may be a factor. IMR4227 is my "go to" powder for subs at the moment.

Mike_Diako · Mar 8, 2014

Direct impingement systems are inherently "dirtier" than others but if it's excessive I would try a different powder and see if that helps. I don't reload for .300blk so I can't make a suggestion. Good luck

w321shark · Mar 8, 2014

This was the first few test shots so I was just shooting factory 150 grain reloads so not sure on the powder. I reloaded a hundred with 110 grain vmax and some h110 so we'll see if it's any better.

bigfutz · Mar 11, 2014

Clicker said:
I tend to believe that with subsonic ammo the pressure is so low that the case never expands to fully seal the chamber hence more grime and crud in the upper. Since I reload it seems that 1680 is dirtier than some of the other powders I've tried so that may be a factor. IMR4227 is my "go to" powder for subs at the moment.

I'm no expert, so take it easy on me... Isn't there something about using a neck sizing die (instead of full) if you are reloading for the same gun, so the case body is basically fire-formed to your chamber? Maybe the next batch will snug in there better.

Clicker · Mar 11, 2014

Sizing only the neck would work for bolt guns but in the case of semi auto AR's most people full length size their cases to avoid possible chambering problems.

melloyello · Apr 9, 2014

w321shark said:
This was the first few test shots so I was just shooting factory 150 grain reloads so not sure on the powder. I reloaded a hundred with 110 grain vmax and some h110 so we'll see if it's any better.

Are you using supersonic rounds? Typically I see subsonic 300 Blackout using 200+ grain bullets.
Same powder load with lighter bullets are supersonic but still have the pressure needed to fire form the case to the chamber sealing off the gas/carbon.