Gunsmithing New barrel chamber issue

fnbrowning

Sergeant
Full Member
Minuteman
Feb 16, 2007
263
31
St. Louis Missouri
I recently rebarreled my AR-15 upper. The barrel was made from a Douglas premium air gaged 1:7 blank, with a .223 wylde chamber. A new bolt was headspaced to the chamber. All work done by a reputable shop, but I decline to name them as I'm not looking to complain.

I have shot the rifle with a variety of ammunition, starting with Radway Green, to Federal 69gr, Black Hills red box 69gr, and my reloads. I’ve run about 150 rounds down the bore in two sessions.

One thing that does concern me is the throat. After shooting several of my reloads, I ejected a chambered round. I quickly saw the projectile was set back noticeably. I stopped shooting that box immediately, but it caused me to examine things closer. I had not put a lot of neck tension on those reloads, but they were seated no longer than commercial premium length. I never had a setback issue with my Colt HBAR upper, so I wanted to find if other rounds were getting set back.

I commenced to examine the Federal, Black Hills, Ultramax and Radway green ammunition after it had been chambered. On each round I was surprised to find the ogive marked, with one easily seen spiral traveling from the end of the ogive onto the body of the projectile. This spiral on the bullet jacket can be felt with a fingernail. In my opinion, all the bullets are riding on something when fully chambered.

Of greater concern is my reloads. They are made with LC brass, full length resized with a Redding die, and topped with a SMK 69gr to an OVL of 2.2490. They fall into a Wilson cartridge gauge perfectly, they chamber and eject in a Sig Sauer M400, and can be chambered by hand in a Colt HBAR upper, but are jammed when chambered in this current chamber so hard the bolt has to be drifted back to eject them! SS109/M855 bullets with an OVL length of 2.485 are hard to eject.

As I understand it, a Wylde chamber is a mid-spec between a 223 Rem and a milspec ... and most people report that they can load SMK’s to a magazine length loading, though I’d not go that far myself. Just to check my work, I talked this afternoon with an experienced benchrest shooter from my club who shoots a precision AR-15 rifle, and he measures his SMK reloads at 2.250.

I would like to know what you think is happening here.
 
Re: New barrel chamber issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">Sounds like you have a short throat on your chamber.

If it shoots good, don't fix it. It'll wear out soon enough and you can just start pushing your COAL as it wears.
C. </div></div>

Chad;

I forgot to mention my barrel was Nitride/FNC/Melonite treated after it was chambered. I don't think it's going to wear any time soon!

Why would a machinist put a short throat on a AR barrel? If the machinist did not specify the throat was to be cut short, would that then be a chambering error?
 
Re: New barrel chamber issue

Is it possible that you are having a feed issue? The mark on the bullet that you just described makes me think that it is riding on the feedramp's edge on the barrel's extension either from extraction or feeding. Do the setback rnds show a mark all the way around the bullet from the lands? I know, two different issues.
 
Re: New barrel chamber issue

Is it possible there is a feedramp mismatch? Receiver with M4 feedramp cuts and the barrel extension with standard feed ramp.

Or

Maybe your smith used a .223Rem spec reamer instead of 5.56mm.
 
Re: New barrel chamber issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hdbiker1</div><div class="ubbcode-body">Is it possible that you are having a feed issue? The mark on the bullet that you just described makes me think that it is riding on the feedramp's edge on the barrel's extension either from extraction or feeding. Do the setback rnds show a mark all the way around the bullet from the lands? I know, two different issues. </div></div>

Good thought, but when I started my investigation, I stopped using the magazine and placed the cartridges into the chamber by hand. I get the ogive marked when the bolt runs home at normal speed.
 
Re: New barrel chamber issue

A true Wylde chamber will allow a 80gr SMK to be seated much longer than mag length and still not touch the lands. Any 68/69 grain bullet should be able to be seated to mag length(2.260) and not be close to the lands. You had it coated after chambering, could the coating be too thick? Sounds more like you have a very short throat chamber. Think I would be calling the guy who chambered it. He may have just used the wrong reamer and tell you to send it back.