So I recently got a new rifle and took it to the range last week. Went to clean it today and found what I can only think to describe as sand in the trigger well, upper, face of the buffer, all over the bolt carrier, on the barrel extension.   Have no idea what it is and wonder if it's the ammo or am I missing something else. I've never seen this before. Being brand new from the manufacturer I didn't clean it but lubed the rifle before firing. Anyone have any idea what this is and if it's something I should be concerned with?

Specs
Noveske factory 10.2" SBR in 300blk
AAC 762SDN-6 suppressor
Gemtech 187gr subsonic 300 blk ammo

Remove the buffer.
Is the bumper disintegrated?

Its gunpowder. Either dirty ammo leaving unburned powder when fired or you lost the projectile from a cartridge with powder spilling out into the guts of your rifle. What ammo? Remington UMC by chance

Cleaning your weapon immediately after the range day...not just to clean stuff, but also a preventive maintenance step.










edit: Yes, I saw its 300 ammo. Just had to express dislike for the Remington ammo doing the same thing in a 20" rifle a while back.

Unburned gun powder.  The can is going to put more pressure back into the upper since the suppressor is basically containing a lot of the gas coming out of the barrel.  This can cause some of the unburned powder to blow back down the barrel vs. continuing out the muzzle.

I had the exact same thing on some of the 300BLK loads I was trying with some alternative powders.  Some were super slow and didn't completely burn resulting in that nasty yellow mess in my lower.

Unburned gun powder