Cutting 45-90 to fit in 45-70 chamber- how much clearance?

[Radarsonwheels]

I am shooting a pedersoli 1874 that has room for a 2.129" oal case. My starline cases are not even 2.1". I bought some 45-90 that should show up in my mailbox any day.

I have read that the exact maximum might be too long and could stretch and curl during firing, cutting patches and increasing pressure. So obviously the 0.035 extra space I have with *-* 45-70 brass is too much, but how much is just right?

I understand there is a shortening of straight (tapered) wall rifle brass that isn't resized, just fireformed and reloaded. My plan is to anneal, trim, fireform (light smokeless load?), and final trim/chamfer before trying my paper patch BP load. Any advice on efficiently and accurately getting this right?

Thanks!

Radar

[BrentD]

Radar, this post reminded me that I had not responded to your PM. Sorry about that. You have two messages now.

[Radarsonwheels]

No need to apologize I would never expect folks to be obligated to spend their time giving free advice! Your PMs are much appreciated.

[JDNC]

I know this post is old but what was the advice?

[country gent]

Make a good chamber cast of the rifles chamber. This will give an accurate dimension to work from. Would start out the first case at 2.125 see how it fits, blacken with sharpie to see any rub marks. Fire form it quick and see how much it shortens. Then trim to 2.124 with the shortening accounted for. I would trim to -.0010 under chamber cast dimension if needed after fire forming them. You need some clearance for the mouth to release the bullet cleanly or pressures rise a lot. Cant give actual dimensions since I dont have rifle to work with

[JDNC]

I have a Pedersoli RB 45/70 which doesn’t have a freebore but has a gradual leade angle/throat. So far using a .442 diameter patched to .451” it gas cuts and gives blow back except when using a .125” lube cookie. Also the brass stretches pretty bad using poly wads.

Some of the best groups so far have been with new WW brass FL sized. I can’t tell any difference in ref to the gas cutting or blow back using FL sized or fire formed but a lube cookie stops both. I’m now going to try FL sizing just for giggles as the case mouth is closer to the bullet diameter and easier to taper crimp.

BTW the chamber end is around .480” and the fire formed brass measurements I get are about the same so I don’t know what’s causing the blow back.

[EDG]

http://castboolits.gunloads.com/showthread.php?397532-45-70-case-stretching-problem

[Gobeyond]

I used 45-90 brass to form 43mauser and shortened a little. You have a very complicated problem to work with. Get a case trimmer and shorten about 2/100,s and go from there. Too exacting can be a lot of fuss and frustrating. Are you a perfectionist or something?