Muzzle diameter and upper receiver fit

[Biggs]

I'm in the process of collecting parts to build my first AR upper receiver, in part because I haven't been able to find a complete AR I like that's in stock, so I figure if there is a gun ban at least I can upgrade/backup my current AR parts. I ordered a JP enterprises BCG, and a wilson combat m4 barrel because it's the same diameter as my current DPMS lo pro. This barrel has a diameter of .920 which in my understanding is wider than the typical AR barrel. Does that limit me in my choice of upper receivers? I don't know whether to backorder a Wilson Combat or Noveske upper, or if I shoud go ahead and order an in stock JP enterprises upper, but I'm concerned since JP doesn't make any barrels in .920 that it wouldn't fit. As I say, this is my first build.

 

[JWarren]

The barrel you are talking about is a bull barrel. It is .920 at the muzzle, and is .936 at the gas block.

This has NO bearing on the upper receiver that you can use. All AR barrels are the same diameter at the receiver.

Where you may run into fun is:

1. Finding a muzzle brake that doesn't "dip" in at the brake due to the .920 muzzle diameter

2. Finding .936 gas blocks in stock if you are getting a low-profile one (trust me-- I have one on back order.)

BTW...

Pencil Barrel: .625 at the muzzle
M4: .750 at the muzzle
Medium Contour: .875 at the muzzle
Bull or Heavy Barrel: .920 at the muzzle.

Understand this...

The barrel at the chamber is where the barrel connects to the receiver. All of them will be at the "bull" diameter at the chamber.

The contouring begins AFTER the chamber on profiled barrels. In the case of the Heavy or Bull Barrel, you have NO contouring-- basically a straight barrel.

Therefore, barrel diamter has no bearing on fitting into the receiver-- since they all are "bull" at the receiver.


Hope that helps.


-- John

 

[Biggs]

Thanks, John. I can picture it much better now.