6.5 Jap Type T-38 PROBLEM - Page 2
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Old 02-10-2010, 11:04 AM   #11
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Default To eliminate any confusion

I should have posted that "checking" the headspacing would not be expensive. As posted above, correcting the problem may be more than you are wanting to spend. But as you posted, "in for a penny, in for a pound". I'm very interested to follow this one out and see what you find.

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Old 02-10-2010, 12:22 PM   #12
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TheOldMan:

The ammo is new Hornady 6.5 Jap. As noted in my first post the brass is headstamped nny 6.5 x 51R, but the brass measures almost exactly per the dimensions shown in the Hornaday reloading manual. The 6.5 Jap is actually a semi-rimmed round.

I have pulled the bullets and dumped the powder from 10 rounds so far to test primer firing and firing pin impressions after I cleaned the inside of the bolt.

The amount of powder recovered seems to be about 23-24 grains per cartridge. Of course I do not know what kind of powder this would be. I had planned on reloading with IMR-3031 (because I already have that powder) and would have used +/- 30 grains.

I have read up a bit on headspace and what happens in the chamber during the firing of a rimless round, and I was on the track of thinking that the Hornady rounds were loaded so lightly so as not to re-seat the primers in the firing process.

Last night I did an experiment. I installed an unfired case in the chamber with a bit of soft waxy material (actually a bit of SPG BP bullet lube) stuck on the case head over the primer. I then removed the extractor from the bolt and ran the bolt fully home in the chamber. I then extracted the bolt and case and measured the thickness of the (now compressed and flattened) SPG wad. I did this twice and ended up with readings of .032" -.042". I repeated the exercise with a case that had actually been fired and not re-sized. This SPG wad measured about .024" thick.

So this tells me what? That the headspace with new brass is excessive at .032" - .042" That the once fired brass has been somewhat fire-formed to have stretched the case a bit to reduce the headspace by approximately .013"?

I was hoping to see if the once fired brass would have fire formed to lengthen the case shoulder dimension to eliminate the headspace. If it did, then I was going to pursue just neck sizing the once fired brass. But I did not see that much of a difference in the headspace between the unfired and once fired cases. Maybe, if the factory rounds were loaded to very low pressure levels, then a higher pressure load would more fully fire-form the brass to fit the chamber?

Now at this point I am WAY beyond my level of competency on this subject, so I'll be calling a local gunsmith today and talking about what he may be able to do.

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Old 02-10-2010, 01:17 PM   #13
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Very clever way of checking the headspacing. According to what you've found out so far, it sure looks like you've found your problem. I'd never heard that primers would buldge and retract as was mentioned in a prior posting. The more I thought about it though, it kind of makes sense that it could happen.

Learned something new today... Thank you sir.

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Old 02-10-2010, 06:15 PM   #14
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I agree with The Old Man that you've probably found the problem, that is if semi-rimmed headspace is measured the same as rimless, which I expect it is. Good luck with the old rifle there and keep us up to date on what's going on.

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Old 02-11-2010, 03:22 AM   #15
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As Ron said- smith removes barrel, cuts shoulder of barrel on lathe, adds thread, so that when replaced, screws in further. DO check inside the brass- also check chamber for roughness/pitting, etc. Those rifles got used hard, put up wet, tough climate, corrosive primers, etc. Something is keeping it from reseating primers.

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Old 02-11-2010, 11:52 AM   #16
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Thanks C3 and ronl (somehow I missed reading the last part of Ron's prior post). Now I understand what the gunsmith will have to do, I'll be checking this out next week!

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Old 02-27-2010, 01:11 AM   #17
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Have a 'smith check the chamber. At some point in its life this rifle may have been re-chambered for 6.5/.257 Roberts. That was a popular conversion many years ago.

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