Tight chamber at base and finish reaming query

[corbinace]

Greetings,

I have a Arisaka 38. The chamber has been reamed to 257 Roberts (or nearly so). When I got the rifle it had a stuck case with the head torn off at the extractor.

I cast the chamber and all of the measurements , including case mouth depth, seemed to be fine with the exception of the base.

The chamber base only measures 0.4685-0.469. The brass from the tightest of my resizing dies is 0.4705-0.471. This dimension disallows bolt closure.

Now the questions; Is this chamber maybe only rough reamed? Could the chamber reamer have been dull and not cut the base adequately? Is there a DIY remedy without a new reamer?

Please hold the rocks now.
I had thought of lapping compound on a sized (or possibly unsized) case that was fitted with a mandrel for hand drill motor.

This was after throwing out the thought of a 5/8" Dormer frame reamer:oops:.

My concern with the compound method, is the radial scratches left in the chamber causing cases to be sticky. Or, could they be polished out well enough to avoid that?

Open to all knowledge on this subject, as it is a new frontier for me.

Thanks, Tim.

[Artful]

Did they rebarrel it or is it still 6.5mm?
You may have a 6.5x57...
http://home.comcast.net/~bcpryor/temp/6-5cartridges.jpg

A 257 Roberts and 6.5X57 are close, but NOT identical.

[corbinace]

It is still the original barrel in the original furniture.

You may very well be onto something.

The chamber cast is a bit hard to read because of the Arisaka type of feed ramp. I am having a bit of a time getting the exact head location down to the thousandth.

I get off of my three week old cast;
1.715 base to shoulder. No a match to either, so must be incorrect.
0.350 top of shoulder to mouth.
2.241 case length.
0.434 shoulder dia.
0.469 base dia.

I will see if I can get a protractor and discern the difference between 16 and 20 degrees. Not holding my breath. Maybe I can find some other case and compare.

Thanks for the insight and picture that is so close together. I had about worn by book out with page turning.

Tim.

[Mk42gunner]

Many of the 6.5 Japs were reamed to use the 6.5mmx.257 Roberts because of bass availability in the postwar years. My bet is this one was done with a homemade reamer to fit the brass on hand.

Best option will be to rent a chamber reamer to fix it right.

6mm Remington brass also works in the one I have. I don't have any loads to share, I am at the fire forming stage before working on sights.

Robert

[corbinace]

I get off of my three week old cast;
1.715 base to shoulder Not a match to either, so must be incorrect.
0.350 top of shoulder to mouth.
2.241 case length.
0.434 shoulder dia.
0.469 base dia.
21.8and 23 degrees were the two measurements I got trying to measure the shoulder angle. (Thank you Mr Earl, drafting teacher 38 years ago)

My crude measurements look to be closest the the 257Bob.

But... I may be able to use the 6.5x57 dies to get my cases down to the smaller dimension and maybe make it work.

Thanks for the insight and picture that is so close together. I had about worn by book out with page turning.

Tim.

[corbinace]

Sorry Robert, I was typing while you were posting. The home made reamer may indeed be the culprit.

I have some 100 gr bullets that I was going to try. Both the 257 Bob and the 6.5x55 Swede have data for the 100 grainer, sharing the same powders and I thought that might prove to be a close starting point. Not to be construed as advise just a point of reference. I may end up using TrailBoss to start.

Tim.

[Jedman]

Sounds like your sizing die is oversize.

[corbinace]

Sounds like your sizing die is oversize.

That is a possibility. My RCBS old dies size to 0.471-0.472" and my newer Lyman dies size about a thousandth smaller at 0.4705-0.471. These are 257 Roberts dies. This is using 6.5X55 Swedish brass.

This makes me think...I am going to try some 7x57 brass. Maybe the web of the 6.5x55 case is too tough to swage down and the smaller base 7x57 brass will get smaller. Hmmm.

[corbinace]

HA...That worked. I had a couple Remington 7x57 brass on the bench and they sized up and fell into place. Measuring 0.464 after sizing. Maybe the Swede brass has a taller web that resists sizing at the base.

Now all I have to do is get rid of this 6.5x55 Swede brass and get some 257 Roberts or 7x57 brass and I will be in business.

Anyone need Swede brass[smilie=b:.

Thanks for all the help guys, Tim.

[Grendl]

If you are serious about the swede brass; I would be interested.
Thanks
rick

[corbinace]

If you are serious about the swede brass; I would be interested.
Thanks
rick
Hey Rick,
I do not have a need for it anymore as it will not work for me. I just bought it on Oct 23 from the Swappin' & Sellin' forum. I cannot find the link for some reason. I paid $60 for it, is that in your budget? If so, I can priority mail it tomorrow.
There are the following headstamps:
2 PMC
15 GRAF
19 Sellier & Bellot
38 NNY
129 RP
202 total

All appear and were represented as once fired.

[leadman]

The 6.5X55 Swedish is listed as having a base of .477" versus .470" for 30-06 based cartridges. That extra was causing your problem as you found out.

[corbinace]

You are correct Leadman. This is my first foray into the world of case re-purposing and I am learning, if only slowly. I wanted to use the Swede case for the neck dimensions so the thickness would be right and thought that the rest could be squished down. I was wrong there for sure.

Tim.

[Ballistics in Scotland]

That chamber isn't unlike what someone, doubtless a member of the intellectual classes, might have got by excessively deep use of a 6.5x57 reamer. What I am pretty well sure of, though, is that nobody wrenched off the head of a good case. The extractor would have pulled through the rim first, or perhaps broken. Maybe he just used his brass too long, but an excessively deep chamber could have been decisive.

It sounds like brass for the German Mausers has solved the problem. But for others in this situation lapping should be fine. I would amputate the case shoulder so as not to change the headspace, and I would at least finish with something finer than automotive valve grinding paste. The fine silicon carbide grits in oil, used by the lapidary for polishing gemstones should be good. I should think you can find them on eBay, my standard source for technological oddities. The things to search for are "gemological" and "gemstone polishing". I hve seen finishing with jeweler's rouge recommended, but you don't have to go that fine, and would probably find it makes no discernible difference.

[corbinace]

You are correct about the case ripping. I mis-worded the case failure. It extractor did indeed, pull the rim off, just as you surmised, not the head.

That is the exact type of lapping process I had intended. Fortunately, I have dabbled in the Lapidary world a bit and have all of the polishing compounds on hand. I still think the chamber is on the tight side of the spec, but it is of no concern now, as I have been able to get the firearm up and running.

It actually surprised me with it's accuracy. At 25 yards (the only bay open) I got one group of four that was able to be covered with a 20mm paster. I say "group of four" because the fifth was about an inch out and called. The other groups were closer to 1.5". Not too shabby for the first trial run and those atrocious sights and trigger.

Thank you one and all for the education, Tim.