fireforming brass in a type 38

I read before you can use o-rings on the base of a case and wrap tape around it to fireform the case, I don't remember exactly what the process, can anyone explain it to me ?Thanks

Well it's been a whole 20 minutes and he hasn't responded yet, so I shall reveal the secret: it was a method devised and described by jmoore. I'm sure he'll be along in a while. Meanwhile, you could try searching through his contributions for "o-ring".

My question would be why fire form brass when it is readily available?

Privi makes it.

Oversized chamber, is the prvi correct size? I read lots of problems with brass of correcy size.

Fire forming then neck sizing or partial FL sizing without setting the shoulder back increases case life and reduces or eliminates case head separations. However I've never had any case head separation problems in T38 rifles at all. I'm still loading Norma brass I've had since the early 90's. And it gets FL sized each time.
Is PRVI brass the correct size in regards to how well it fits the chamber? No, and neither is WWII Japanese or 1950's Chinese military ammo.
Jap military, 1950's Chinese military, Norma, Grafs and PRVI case dimensions are all very close. The only area that differed more than a thousandth or two was the diameter at the shoulder. Jap and Chinese military are around .008'' larger than commercial.

If you can seat a bullet out long enough to seat hard into the rifling on the first firing it would make things good for later. Some of the bores are large enough that the .264 bullets we use can't be seated out long enough. After firing them with the bullet seated out, adjust your dies so that the shoulder isn't pushed back. The case is going to expand a lot. Some guys go with it, some, like me, form better fitting brass from .303 British or 30/40 Krag.

Andiarisaka , can you please share how you form better fitting brass out of .303 brass? I heard of this being done before, but can't find the info now. I once went through hell trying to resize .308Win brass using the 6.5x50 dies. I don't want to do that again.It would take more than what my Rockchucker press is capable of. Did you ream out the 6.5 resize die to a larger head diameter such as .458" ?

A good way to make 6.5 Japanese brass is to start with 35 Remington cases. Slowly size in the 6.5 dies and your ready to go. The neck is just a little bit short compared to factory brass but it works very well. The last batch I made was over five years ago and the brass is still good.

No Sunday interneting, hence the late reply. The o-ring trick is something I picked up from Edward Horton on the L-E forum. Parashooter uses monofilament, which might be better in this application due to the small rim and limited forward support on the breech.

Here's a link to a thread that probably goes into more detail than might be required, but hasn't been finished yet!:

6,5mm Japanese Arisaka Ammuntion Dimensional Revelations (Photo Heavy)

See Posts #21, #23 (for a photo of the breech) and be sure to link to this supplemental thread:

Japanese Ammuntion and Rifle Testing

Eventually, there will be more testing posted to these old threads, but there's too many projects going on at the same time!

So you just slide an o-ring down to the rim and chamber and fire? Would wrapping masking tape around the case also help to center the round? Would that be a good thing to do ?