So i wanted to make a 300blk pistol with a 9" or 9.5" barrel and wanted to get a handguard that sits as flush to the muzzle device as possible, was thinking a MI 9" handguard on a 9.5" barrel but wasnt sure if that would be enough room on the threads to get a rugged surge on without hitting the handguard.

Would i have to step it up to a 10" barrel for that to work or does anyone know if it would be fine?

Would the 9.5" barrel you're considering happen to be a BA version?  Even if not, I'd expect most of them to have roughly the same length of threaded section to shoulder.  On my 9.5" BA barrel 300BO, the barrel nut to muzzle shoulder...where the can should stop at the end of the threads...is 8.75".  So, it appears that a 9" handguard that is truly 9" would probably hinder the can...unless the can has a very small diameter and the MI handguard has a big opening.  I'm not familiar with that handguard.

Now, you mentioned "muzzle device".  If you're installing some type of QD on the muzzle threads that has some decent extension that would place the can further out, well, who knows.  I've always been a can-directly-on-muzzle-threads guy.

Generally speaking, I think most barrels are threaded .60" to .62", which would put the rearmost portion of the mount under the handguard. The question you need answered, is how far back, or forward, of the rear of the muzzle device does the surge engage?

Example:

10" barrel, 9.4" of unthreaded barrel, .6" of threaded barrel. True 9" rail.
If the Surge engages flush with the rear of the mount, you'd have .5" between the handguard and the rear of the can, assuming .1" thick shim behind muzzle device to time it. (in lieu of crush washer).

General rule is a barrel 1" longer than the handguard allows the shoulder of the threads to sit right at the end of the handguard/rail.

I have an 8" BA 300blk modern barrel and a 7" (or 7.125"/7-1/8th" actual) MI G3 M-lok rail.  It leaves me approximately ~1/8th" between the end of the handguard and the shoulder of the barrel where the threads begin.

Allows me to have my Specwar 762 sit flush with minimal barrel exposed.

I got a BA 9.5" barrel,  first ordered the 9"  thin profile MI rail and it didn't work with a can. The 9" SP series works like a charm though, If you don't mind the outer diameter size.

thanks, exactly what i needed to hear.


guess ill go with the 10" barrel and 9" handguard.