I just received two ultra light 16" Bushmaster barrels... I love their barrels, alway headspace perfectly... but, when looking them over, I decided to stick a gas tube into the hole drilled for it, in the front sight base... it went in tight...pushed just a little more, and it was stuck?? What the hell? Couldn't pull it out for a while, lubed it up, wiggled it around for awhile and pulled it out, quite a bit of effort! On the end of the tube was a big glob of fine sand!! Cleaned it all off with solvent, high pressure air, and we're back in business...  port looks fine... didn't do the end of the gas tube any good... any one else seen this type of situation... should i toss the tube?? till...later...GT

Sounds like some left over casting sand. Was it black or light brown?  Casting sand is usually very fine black sand.

Another common sandy spot are the take down and pivot pin detent holes.  Needless to say, sand, spring, and detent don't all fit in there.

It can be cleaned out with a small drill bit.

Hi Guys! It was brown sand, (most likely core sand from casting) in fact, before I realized what it was, I thought it was some type of dried grease film, didn't even give it a second thought, (I will after this!) After cleaning, I looked with a light in the port on the sight base, couldn't see a mark or any scratches... the gas tube is another story... light scratches all around, looks pretty ugly with a loup... I don't think it will matter though... no loss of dimension, just pretty unsettling, you want every thing to go as planned, next thing you know your gas tube is stuck fast! Kinda like real life, huh?? Till...later...GT

Perhaps someone with more knowledge than I could shed some light on the manufacture of the FSB.  If Bushmaster uses forged FSB's why would casting sand be in the gas tube opening or anywhere for that matter?  To my mind it doesn't make sense to have casting sand residue on a forged FSB.  Or is Bushy using a cast FSB on the UltraLight barrel?

I've noticed residue, but in those cases the barrels and FSB's had been reparked after reprofiling.  The residue was in the gas tube opening, and in the A2 sight/detent area.  Cleaned up easily.  I've also noticed residue in the lower takedown and pivot detent holes during lower builds, but again, thought it was due to the lower finish process.


edited do to lack of coffee...

I assumed it was from sandblasting to clean up the surface prior to anodizing.

That makes sense to me, I'll bet thats it, They need to clean their parts a little better before they send them out! till...later...GT

Yes... I think we have a winner!  That would explain everything, and is a good reminder to check all the little nooks and spaces for 'whatever'...

I once found sand in the buffer retainer hole on a forged PWA lower.. now I know where it came from...