How does M1s measure their barrel? If it's the 11/2" that goes in the upper that's 6" forward from the receiver, with a front sight, that wouldn't leave room for a ff tube. On my 2 9mm the mini ff tube butts right up to the front sight

I'm fairly certain the measure from the breechface. 16" has the external length very similar the 14".223.

Every barrel maker pretty much measures their barrels the same way.  Depending on the caliber, you can end up with a different OAL of the assembled upper - a 16" .22LR barrel sits further into an upper than a 16" .223 barrel does, so the OAL of a complete upper can vary.

Here's a 7.5" M1S barrel inside a carbine length YHM tube.  Without the Spikes fake can/shroud, the barrel doesn't really make it out the end of the handguard.  With the fake can, it sticks out liek an 1/8th of an inch.


If you want a 7.5" barrel with a front sight post, you eill probably want to go with a YHM 4" mini tube.

The 4.1 YHM mini is what I have on my 9mms and they butt right up to the front sight. If I lose 1 1/2 inch in the receiver which is what the dedicated 22 barrels do I don't see how a mini tube would fit? Am I missing something?? I have been known to step on snakes