Case Stretch

[Steveu]

All,

I have received my mould from Steve Brooks for my 40-65 and it shoots great, I will right up a post about it later. Right now I have been experiencing .005"-.007" of stretch per firing. I initially loaded some new cases that were formed from starline brass. I have been fireforming this lot of brass with my GG bullets and I get ZERO stretch. I loaded up 8 rounds for a quick test and noticed that all the cases grew .005-.007". I did some research and talked to Kenny Wassaburger and I trimmed the test cases back .002" in case the mouth was grabbing the bullet. More testing showed no improvement. But, on another forum there was a guy having the same issue I have. He used some rosin powder on the cases to see if that would help. I tried it and I found only a few cases stretched to .001". This led me to believe that my chamber is too slick after I had lapped it with some 400 grit and a fired case to alleviate the sticking case issue I had before the PP bullets. So I got some 320 wet/dry and a dowel and by hand I scuffed up the chamber by hand (I don't have a lathe). I loaded 2 cases that were trimmed to my chamber length, that were fired 3 times without annealing, 70 grains of Swiss 1.5fg and my 400 grain DDPP that light finger pressure will seat the bullet in the fired case. The necks were clean and I chamfered them before loading.

Any ideas on what to do?

Cheers,
Steve

[Don McDowell]

Check your case mouth thickness it’s not an unusual thing for Starline brass to be on the thick side and when necked to a smaller caliber experience case stretch or separation.
I have a 32-40 Ballard that if 38-55 Starline is sized down will be a mess of catastrophe. Weird part is if shooting smokeless it’s not the problem it is with black. So inside neck turning cures that

[beltfed]

We presume you have necked down 45-70 Starline brass???
Indeed, you may have thick neck walls.

I would always OUTSIDE neck turn. It will result in more consistant circumferential
thickness uniformity since you are turning against the pilot.
Inside neck reaming the neck is unsupported unless it is done by one of the old
systems where you ream thru an aligned hole inside a support die.

Also, FWIW, I have stuck with sizing down R-P or WW 45-70 brass for
my 40-65 that has fairly snug chamber neck. No Problem with stretching
and no need to trim them repeatedly.
PS, The bullets you sent fit my case necks well with the paper you patched them with. I hope to try them this weekend -tomorrow looks good for weather. Hope I can slip away for a while.
What paper did you use?
Arnie

[Kurt]

Check the rim thickness on your new brass to make sure they did not make a change. A change in head space can be a problem.

Also my .40-70 cases tend to stretch more back when I used the oil/water wiping solution with freshly annealed brass caused stretching and the problem ended when I quit using it.

A unsized case to close to to the chamber end transition and if full length sizing it gets longer and when the bullet bumps up tightening past the transition the longer brass will stretch.

Best tool for inside neck trimming

[Steveu]

Don, I checked the starline 45-70 brass after I formed it and it measured.010, it I did not check it all the way around. I will check it again and see. I prefer to inside ream also. My fired neck id is .412”, bullets patch to.4105”.

Arnie, those are patched with SC55W which shrinks .0005” when patched wet. I do have some WW brass I can use to see if it works. I’ll be shooting a gong match tomorrow to test them out. It is a short range due to the high winds forecast.

What I can’t figure out is why no issues with the GG bullets.

[Steveu]

Kurt, I will check the rims. I did check the headspace with a feeler gauge with a case in and the block closed. I could get a .004” in but not a .005”.

I do like that reamer you have!

[Kurt]

Steve,

To get a good head space measurement. Use a good solid rod that will fit inside the case all the way to the bottom.
Chamber that empty case close the breach and push the case to the reach block with the rod. This would be best if the rod was just an inch above the muzzle and take a depth gauge and measure the distance. Now open the breach with the rifle in a cleaning rack and push the case and rod all the way in. take a measurement and zero the depth gauge. Close the breach and push on the rod till the case rests on the block face and take the measurement again.
I did this when I formed the basic .44 brass that had rim thickness way over what would fit the rim recess and turned it down for a proper fit.

[Steveu]

All, I did get to try some WW 45-70 that I formed into 40-65. The neck walls measured .009" thick. I loaded them up with 74 grains of Swiss 1.5fg to maintain the same compression as the SL brass and wet patched with SC55W. The WW was about 30 grains lighter, hence the extra room for powder. The velocity was within 10 fps of the SL brass and I did not get any case stretch at all! After I cleaned the brass I measured the ID of the necks of the WW and SL. The SL would accept a .412 pin gauge but not a .413". The WW would accept the .413" pin gauge. So, I think I need to get a .413" reamer to take care of the problem with the SL brass, because I do not want to neck turn the brass. I have had better luck with reaming. I looked at Forester's website and they will custom grind a reamer for $50. I would buy some Rem or WW brass, but it is not available that I can find. Comments are welcome!

P.S. Kurt, I have not checked the using your method yet, that's next on the to do list.

[Steveu]

Kurt, I measured the headspace per your instructions with a caliper, ( I don't own a depth gauge yet) and came up with a measurement of .001". Rims run .064-.065".

[Kurt]

That's just about too close
That's what mine run also. When I get some fouling in the rim recess the head stamp gets a shiny rub.