Bushing an AR10 bolt by Carlsbad

[Bamban]

A friend had an AR308 built on a 20 inch Bartlein turned down from a HV blank. While the upper shot well, he was having a primer flow around the firing pin indentation. Getting one of the high dollar JP Enterprise high pressure bolt would have been an easy solution, but they don't have a lefty version
JP - Bolt Assemblies
https://jprifles.com/1.4.7_Bolt.php?menu_select=HPbolts

I contacted Carlsbad if he were willing to bush the bolt and turn down the FP. Good thing he took on the project as the bushing job took care of primer flow problem and occasional pierced primers.

Here is the field report from my buddy who shot the rifle at a mid range match.
"Shot the ar10 today. That fixed it. Primers look great!"

Thanks, Jerry.

 

[SG4247]

Looks really good!

 

[carlsbad]

My first response was to turn down the job but Nez made it clear it was important to him so I couldn't say no. AR bolts are difficult because they are hardened and they are hard to hold. The back side of the bolt has 4 different diameters and the larger ones aren't wide enough to hold. It takes a fixture to do it right. I also had to come up with a way to deal with the case hardening. The boltface can be machined with carbide but the inside surface will break your tools....

 

[whatsupdoc]

@carlsbad just wondering are the bushings pressed in or threaded?

 

[carlsbad]

I thread them in. I don't trust pressed in bushings not to move under repeated impact loads. Others may use them successfully but I've never had a problem with threads. --Jerry

 

[Bamban]

My first response was to turn down the job but Nez made it clear it was important to him so I couldn't say no. AR bolts are difficult because they are hardened and they are hard to hold. The back side of the bolt has 4 different diameters and the larger ones aren't wide enough to hold. It takes a fixture to do it right. I also had to come up with a way to deal with the case hardening. The boltface can be machined with carbide but the inside surface will break your tools....

I appreciate it that you took on the job. Questions were being raised about the barrel and chamber, I had to settle the issue by proving the issue is the bolt firing hole. And indeed it was.

 

[Bc'z]

I thread them in. I don't trust pressed in bushings not to move under repeated impact loads. Others may use them successfully but I've never had a problem with threads. --Jerry

Would you do more AR bolts in the future?

 

[carlsbad]

Sure. Just a few dollars more expensive as a tooling surcharge.

 

[Sandstorm]

Where were you when i was shooting a 308 Gas gun...I know right here..
Good to know if someone asks me Jerry.
sandstorm

 

[carlsbad]

Where were you when i was shooting a 308 Gas gun...I know right here..
Good to know if someone asks me Jerry.
sandstorm

Thanks Bamban for pushing me into developing it. --Jerry

 

[jonbearman]

Fantastic job. and you trued the face of the bolt. Did the guy shoot it yet and how did she shoot with the upgrade? (ar-10)

 

[Bamban]

Fantastic job. and you trued the face of the bolt. Did the guy shoot it yet and how did she shoot with the upgrade? (ar-10)

Yup, here is his initial report after the bolt work. This was more than couple of weeks ago when he shot it at mid range.

"Shot the ar10 today. That fixed it. Primers look great!"

The rifle always shot well, but prior to the Carlsbad bushing job, the shooter was seeing primer flow and occasional pierced primers. That all went away after the mod. Barrel is a Bartlein 10T, and he shoots 168 Berger Hybrids, Lapua Palma brass, 205MAR, velocity in the low 2700.

The upper will be a CMP/NRA legal service rifle, 20 inch tube, 0.750 gas block, and 4.5X scope.

 

[carlsbad]

Fantastic job. and you trued the face of the bolt. Did the guy shoot it yet and how did she shoot with the upgrade? (ar-10)

I don't do much to the face, mostly just take off the oxide layer. I don't want to change the headspace. So when I am close I take off .0002 to .0004 per pass until I get a very light cut on the face to make sure the primer isn't proud (sticking out). the key is setting the bolt up so the face is perfectly aligned with the cutting path of the lathe.

--Jerry