Hardened Arms 300BLK Upper

[BLKOUTAR]

1st post here - Recently ordered a cheap M&P 15 Sport II ($500) and I'll be swapping with a $250 Hardened Arms 16" 300BLK upper (using the M&P charging handle & bcg) for chasing whitetail.

First impression - the upper looks great and fits tight with the M&P lower. It's a shameless budget build so it's sporting a budget friendly Bushnell rds & cheap Leapers UTG iron back up sights, rail inserts, generic flashlight for hiking in/out of the woods and a spare vertical grip from my crossbow.

I'll take it to the range 4 days from now and post some updates after that

https://drive.google.com/file/d/1L4nXEK ... p=drivesdk

[AndrewRose]

Welcome to the forum, there is a wealth of 300 blackout knowledge here. I just finished my 300 pistol build and the fellas here are helping me get it tuned and ready for hunting season.

[BLKOUTAR]

Thanks AndrewRose, it's a solid pool of info for sure.

The day with the Hardened Arms upper performed as expected. Solid construction and great accuracy. The 15" rails on the handguard was surprisingly functional compared to shorter rails (able to mount front iron sight very far forward for a better sight picture, able to get a good angle with the gopro for hunting footage, etc.)

I did have one pretty persistent issue though, and I haven't yet done enough testing to really ID the root cause. I started with a 10 round 3rd gen 5.56 pmag that i'll be using to hunt with no issues. But as soon an I switched to my 30 round 2nd gen 5.56 pmag, I had very frequent extraction/feed issues.

Has anyone noticed issues with 5.56 gen 2 pmags? I want to think the mags are not the issue and it was just coincidental timing, bcs it looked like the the spent round wasn't getting fully extracted and the round on deck couldn't feed as a result. Doesn't that sound like possibly gas issues? (the upper has a pistol length system).

But as soon as I went back to the 10 round mag, no issues whatsoever for the rest of the day. I then tested both the mags with the M&P 5.56 upper and .223 rounds and had no feed issues.

[FOB]

What bullet weight/profile, cartridge OAL. Factory loads? Handloads?

BCG too wet or too dry?

Action might be sluggish and needs a little break-in time.

Just some thoughts.

I use 30 rd Gen 3s and have never had a problem.

Edit:Poor extraction, your chamber may need a little polishing, had to do that on the carbine upper I assembled.

[BLKOUTAR]

What bullet weight/profile, cartridge OAL. Factory loads? Handloads?

BCG too wet or too dry?

Action might be sluggish and needs a little break-in time.

Just some thoughts.

I use 30 rd Gen 3s and have never had a problem.

Edit:Poor extraction, your chamber may need a little polishing, had to do that on the carbine upper I assembled.

Yeah those are good thoughts, just looked up some polishing ideas and it seems like a good step to try with a new upper. https://youtu.be/nn9VVhSCt4I

The 300 ammo was 110gr frangibles, brass cases. What threw me off was just the fact that it happened several times in a row with one mag and ceased when I went back to the 10rd.

I'd hate to blame the upper for a mag issue, but I realize the mags have a lot less variables to go wrong than an upper would, so I think polishing up some edges (basically giving the effect of a more 'broken in' upper is a good next step.

'preciate it!