Lightweight 9mm barrels: What diameter?

[MemphisMechanic]

My new CMMG Guard upper has a rather hefty .750” barrel that’s 16” long. A machinist buddy is about to cut it down for a pinned & welded comp.

 

While he has it, we want to look at turning it down to a smaller OD.

 

For those of you who have an MBX barrel or any similar lightweight unit, what do a pair calipers show that your barrel OD is?

 

Edited May 4, 2018 by MemphisMechanic

[MikieM]

I don't know what my barrel starts at because I didn't want to remove the handguard, but the diameter just before were the thread protector screws on is .625 inches.

The barrel is a Kaw Valley 16 inch, and I think it's called a pencil profile. With a thread protector it's a smidge over 19 ounces.

[Timido]

My Faxon/  Kaw Valley is .625 at the smallest   There is a good diagram or the steps of the barrel  https://www.joeboboutfitters.com/Kaw-Valley-Precision-16-9MM-4150-QPQ-AR-15-Barrel-p/kvp-9mm-bbl-16.htm

[Aircooled6racer]

Hello: I think it depends on the weight of your handguard. As I have stated before I think you can make the too light. My lightweight upper weights 2lbs 1oz with no bolt or charging handle. I think it is about as light as I would want to go. My other lightweight upper weights a little more and I shoot it just as quick. I would turn it down to 0.700" diameter and try it. 5/8" diameter is kinda a standard measurement but I have also seen 0.560". If your barrel has a sight boss turn that down first and check it. It is easy to remove weight but harder to add weight to a turned down barrel. Thanks, Eric

[MemphisMechanic]

@Aircooled6racer funny you should mention that: I’m going to be mounting that ultralight (and ultra-spendy!) Brigand Arms carbon fiber hand guard on this gun. UPS says they’ll deliver it tomorrow:

 

https://www.rainierarms.com/brigand-arms-ar15-carbon-fiber-handguard-edge/

 

4.6 ounces... with barrel nut.  

 

I’m making no move to reduce weight in the upper (has forward assist and a door) or lower (QC10 ain’t light) but going to play with seeing how much weight I can possibly shed out in front.

 

I may hate it, but that’s the beauty of AR’s. Someone will buy it, and I can play with something different.

 

I think I’ll go with .625 like the KAW valley barrel measures. Thanks everyone!

Edited May 5, 2018 by MemphisMechanic