Evaluating the new chamber.

[frwillia]

I recently set back an Adams and Benett barrel I bought from a club member for $40.00. The barrel was chambered in 6mmBR when I got it. I sawed the chamber off through the neck.

I did it for the practice, a chance to try out my new reamer holder, and because it couldn't be as bad as the factory barrel on my Model 10 Savage .243 sporter almost no matter what I did.

I used my new home-made reamer pusher discussed in an earlier thread,

and the two line method of aligning the bore with the lathe spindle. The reamer was hand restrained, the spincle set for 36 rpm, dark thread cutting oil as the lube.

The reamer fit the chamber perfectly when I was done, it had no perceptable movement from side to side when inserted in the completed chamber. The chamber was lightly polished for 5 or 6 seconds with 400, 600, 800, and 1000 grit oiled paper and is shiney smooth inside.

The bolt face was "just" in contact with the go gage with the receiver and barrel nut finger tight, when I started to torque the barrel nut. I held the receiver motionless and after torquing the barrel nut to 150 ft-lbs (threads lubed with assembly lube) the go-gage wasn't touching. The go-gage wouldn't fit with celophane tape on it.

I kept some spent brass from the factory .243 Win barrel to compare with the spent brass from the re-chambered A&B barrel. This is the comparison with both the spent brass and full length resized brass before firing in the new chamber.

The load was 44.0g of H4350, 70g Nosler BT, Winchester Large Rifle Primer, COL = 2.668" which places the bullet 0.020" off the lands. Since this is a hunting rifle, I don't want the bullets jammed into the rifling.

Comparing measurements of the fired brass same measurements on a FL sized case before firing:

The over all case length did not change when it was fired.
The base to shoulder measurement did not change when it was fired.
The shoulder diameter increased ~.0005".
The base diameter did not change.

Comparing fired brass from this chamber to the factory chamber:

The water grain capacity for this chamber's fired brass is 55.0g.
The water grain capacity for the factory chamber's fired brass was 55.33g.
Base to shoulder measurement of this chamber's fired brass is 1.625".
Base to shoulder measurement of the factory chamber's fired brass is 1.630".
Shoulder diameter of this chamber's fired brass is .4525".
Shoulder diameter of factory chamber's fired brass is .455".
Neck diameter of this chambers fired brass is 0.2745".
Neck diameter of the factory chamber's fired brass is 0.2755".

I have to conclude the chamber I made is considerably tighter than the factory chamber which was apparently made to the outside of the SAAMI specifications. It is much better polished. I think it should be a lot easier on brass. The rifle shoots better already (0.546" group compared with 2" groups) and there is no suggestion that I've tried the optimum load yet.

I head spaced it to clock the muzzle so that the muzzle run out was pointing up. The rifle zeros with the windage about centered in the scope travel which was one of the goals.

Fitch

 

[Butch Lambert]

Sounds like you did a good job. Did you run your indicator into the throat after chambering? I personally would not polish the chamber as you did. I wouldn't go over worn out 320.
Butch

 

[Richard]

A highly polished chamber

combined with moderate to high pressure loads will give you a "clicky" bolt upon extraction. Not every time, but I have had rifles in the shop that had that problem, a light pass with 320 took care of it. This was with 220-ppc stuff that the die-chamber relationship was good.

Richard Brensing

 

[JerrySharrett]

Fitch, see, the floating pusher works every time, but why in the 'ell did you have to "clock" the barrel??

 

[frwillia]

Fitch, see, the floating pusher works every time, but why in the 'ell did you have to "clock" the barrel??

Jerry, I confess to being very happy with the performance of the floating pusher. I like it even better since I figured out why it works so well. I like it when physics is on my side!

Regarding "clocking": I used the 2-line alignment system chambering through headstock. Muzzle was making an 0.011" orbit when the bore at the breech was aligned from the breech to a little past the new throat (as far as I looked) +/- .0001". All I did was set the chamber so the muzzle would point up. No biggie. Easily done. It will be even easier on the next one where I'll have a shoulder to work against. That part will be all done before the reamer makes it's first cut.

I've set the muzzle pointing up on both chambers I've done (two-in-a-row isn't much of a string compared to the rest of you folks, but it's better than one-in-a-row which is where I was before I did this one ). It could be a coincidence, but in both cases the rifle shoots with the scope windage almost centered. A feature IMO.

Butch,

I don't have an indicator that will reach to the throat, but I did stick the Grizzly rod back in to the throat and about a half inch beyond before I took the barrel out of the spider and it was still running true. My other check was to put the DTI on the chamber wall just inside the breech where it was still running dead true as well. That is the limit of my measuring capability, but those two measurements would seem to indicate that the chamber is true to the bore at the breech. The muzzle was still making the same 0.011" orbit.

Fitch