I've got a M4 14.5" upper that I'm trying to fit my bayonet on, but it seems to tight.

It's got the Phantom flash hider on it, and I'm thinking that might be the problem. I've been thinking that I could just dremel the inside of the bayonet hole where it slips over the hider. Has anybody else tried this? Can anybody see any problem from doing this?

It's a USM8A1 bayonet if that helps.

Suggestions?

Bayonets designed to fit the "Bird Cage" flash suppressor on M16. Diameter around .863" then you have the length between bayonet lug and flash suppressor mounting point for the bayonet. Sure other's can give better info as I've never seen the "Phantom" as to how it is built. An adjustable reamer would make for a better job on enlarging the bayonet hole part, machine shop's have. But like I said, you have the length dimensions to check.

Guys, I think I'm just an idiot, sorry for wasting your time. I looked a little closer, and it seems that it's not the flash hider.

I think it may be that the bayo lug may be to blame.

It fits just fine on my 20" A2 just fine.

From what it looks like, the fit between the bayonet and the lug is really tight. So maybe it's just the fit. BTW, the upper is brand new.

So, should I buff the inside of the bayonet where it locks so it will go on easier? I've had to do this with AK bayonets before, but wonder if I should just try out another bayonet.

Thanks for the help by the way.

Well I guess my only other question would be, can I mess with the bayonet lug without hurting the finsih. Like I said, the bayonet fits just fine on my FN 20" upper, so I guess it would have to be the lug.

But at the same time, if I have to go throught the trouble of either grinding the bayonet lug or getting a new front site post, wouldn't it still be easier to buff on the bayonet?