Gunsmithing Answered - Setting up headspace on a Remington 40X 22LR

[Dstoenner]

I found out recently that my original 40X barrel has some asymmetrical projections on the lands right in the ramp up to a full land. I would have thought those would have been worn down years ago but.. So I went on the look out for somebody selling a take off. I managed to land one. Looks like it came off of a 40X, not 40XB because its barrel date is 5/61.

I have cleaned up my new to me barrel and managed to pull my original barrel Seems Remington had to REALLY put the screws to my original barrel to get it to time. The shoulder is visibly barreled out. Based on having both barrels in hand and looking at them I think I have figured out what Remington designed for production. All barrels were made identical in the threaded area. They then selected a bolt, took a bunch of measurements and then milled out the back of the barrel recessed to set the headspace. My guess is that they did this last operation once the barrel was installed through the back of the action. Just a guess on my part.

I have a set of go/nogo gauges for 22LR. Before I started to remove the barrel, I tested the GO gauge on my 40X. It would not close all the way but most of the way. Closes just fine in a real 22 cases. Just a tight headspace. What I have figured out that I sort of won the lottery because the new to me barrel I just got is actually even tighter.

So that leads me to the questions at hand.

For my original barrel and bolt and action with recoil lug I can measure from the shoulder of the barrel to the rear surface, then I can measure how far down they back milled the surface to set the headspace.

Question 1, is my assumption that this measurement represents the target of what I want the new to me barrel to be when I am finally done? This then sets the premise for the following.

Here are my measurements.

Original barrel:

Distance from shoulder to rear of barrel = 1.680
Distance from rear of barrel to the face of the breech = .021

Therefore the distance from the shoulder to face of the breech that establishes the headspace with this bolt is 1.680 - .021 = 1.659

New to me barrel:

Distance from shoulder to rear of barrel = 1.670
Distance from rear of barrel to the face of the breech = .003

Therefore the distance from the shoulder to face of the breech that establishes the headspace with this bolt is 1.670 - .003 = 1.667.

My conclusion is that in order to be able to use both barrels interchangeably with my original bolt is to mill that face .008 deeper on the new to me barrel. Correct?

Secondary question, does it have to be recessed like the original or can I just machine the whole back surface flat .011 deeper? I am thinking that this "recess" is by product that this area was out of reach of the reamer since it is close to the measurement of the bolt body.

Hope all of this is clear

Thanks in advance for any and all advice.

David

 

[Dstoenner]

I found the answer in a field service manual on the 40x. It specifically says you mill the breech end of the barrel to set headspace. Don’t touch the bolt

David