Anyone bother to square the case rim?

[John W]

mdeland,

Thank you. Great information. I am understanding that BCPR accuracy is really a combination of a multitude of factors: some which are understood and have a great impact on accuracy, others which are understood and have a minor affect, and still more that may not be understood and have an unknown effect.

Guess I’ll try to control what factors I can, and just keep experimenting.

R,
John W.

[mdeland]

Well in my opinion it's the incremental accumulation of component factors that are proven to have some effect that when added together actually do improve accuracy. The experimentation is figuring out what matters and what just waist time and material.
For instance on this topic if your breech face is out of square with the bore then indexing cases is probably going to help. I suspect this may be one of the reasons fire-forming then indexing cases usually improves accuracy.
It wouldn't matter if the breech face is true but probably would if .010 out of plumb as it would tend to tilt the cartridge out of alignment.

[gunlaker]

Mike, I stooped using WW brass in my Shiloh's several years ago. Out of a bag of 50 new cases there were usually 3 or so that had enough rim thickness variation that I couldn't close the breech. On those cases you'd always find a portion of the rim ( never constant over the whole rim ) that was right at the outer edge of the SAMMI spec. I used those cases in lower quality rifles like my Marlin lever guns. I've never had that problem with any other brand of brass, although I do often see a fair bit of variation in Starline .45-90 brass.

Chris.

[Kurt]

Does this really matter with the head thickness variation if the front of the rim makes contact 360 degrees in the barrel rim recess?
Before Jamison made the correct brass for the .44-90 bn I used .44 Bell basic brass to make the cases and the Bell brass had a lot of rim thickness variances that I had to thin the rims in the lathe and when I started turning them down I wanted to turn the front and not the headstamp to hold the primer pocket depth and I found that the front was square when I moved the tool to make the cut and it did not have low spots clear to the base but the head on some the bit only hit a quarter of the head on some.
Kurt

[mdeland]

That's good information guys! I've never run into case head diameter variance that would not fit into a chamber rim seat as these are usually pretty generous on any reamer used.
I like W-W brass too because of the case capacity increase over most brands. Most of my brass is still R-P and after annealing it nibs out very well.
Also, I've never had to thin a case rim on either.
Interesting thread !

[Kurt]

I think the thickness variance comes from when the ran makes the head stamp.
I would worry about this more if I was in a bench rest match with a rimless case then I would with the rimmed case. Worry about the case neck more then rim thickness. Neck variance is more damaging them the head with rimed cases.

[mdeland]

The massive cross section diameter of our larger rimmed cases is what makes the thickness and breech face square so important as apposed to rimless cases which head space on the shoulder instead of the base as rimmed cases do.

[John W]

I think the thickness variance comes from when the ran makes the head stamp.
I would worry about this more if I was in a bench rest match with a rimless case then I would with the rimmed case. Worry about the case neck more then rim thickness. Neck variance is more damaging them the head with rimed cases.

Can you explain this to me?

My thought would have been that if the rim (the headstamp area) of a straight wall case was not square to the wall of the case, then upon firing the case would be pushed back against the block, and then the case would be off alignment in the chamber. Is this thought just theorectical and not really a factor?

It makes sense to me that what mdeland said about that's why maybe some align their cartridges to minimize the effect of this variance.

Thanks!
R,
John W.

[martinibelgian]

Luckily my No.2 Musket cases don't know about it - I use converted .470 NE brass, which has thin rims whereas 'normal' no.2 Musket has thick rims. Shoots like it should, no issues there, despite it not headspacing on the rim - at all. If you seat the bullet to firmly touch the rifling, and the Cartridge OAL is so tha tthe case will be cammed in when closing the breech, all's well, no matter what that rim does. It just serves to extract the fired case - which is its main purpose.

[Kurt]

I think the thickness variance comes from when the ran makes the head stamp.
I would worry about this more if I was in a bench rest match with a rimless case then I would with the rimmed case. Worry about the case neck more then rim thickness. Neck variance is more damaging them the head with rimed cases.

Can you explain this to me?

My thought would have been that if the rim (the headstamp area) of a straight wall case was not square to the wall of the case, then upon firing the case would be pushed back against the block, and then the case would be off alignment in the chamber. Is this thought just theorectical and not really a factor?

It makes sense to me that what mdeland said about that's why maybe some align their cartridges to minimize the effect of this variance.

Thanks!
R,
John W.

John sometimes we just get to scientific shooting these BPCR and get to over think things. I have shot 15 shots at the turkeys, 5 for sighters and 10 for record and all 15 hit with a mixed batch of stretched rem .45-90 and cut down bell cases that I took to empty and ended up using because what I had for my match loads didn't shoot for sour grapes.

[John W]

I think the thickness variance comes from when the ran makes the head stamp.
I would worry about this more if I was in a bench rest match with a rimless case then I would with the rimmed case. Worry about the case neck more then rim thickness. Neck variance is more damaging them the head with rimed cases.

Can you explain this to me?

My thought would have been that if the rim (the headstamp area) of a straight wall case was not square to the wall of the case, then upon firing the case would be pushed back against the block, and then the case would be off alignment in the chamber. Is this thought just theorectical and not really a factor?

It makes sense to me that what mdeland said about that's why maybe some align their cartridges to minimize the effect of this variance.

Thanks!
R,
John W.

John sometimes we just get to scientific shooting these BPCR and get to over think things. I have shot 15 shots at the turkeys, 5 for sighters and 10 for record and all 15 hit with a mixed batch of stretched rem .45-90 and cut down bell cases that I took to empty and ended up using because what I had for my match loads didn't shoot for sour grapes.

Thanks! Yes, probably just too much time on my hands and over thinking things. Best for me to just go out and shoot!

R,
John W.

[desert deuce]

No, but I do check the fired, unsized case mouth for square with chamber mouth.

[Woody]

As long as you are using a fire formed case, the "squareness" of the rim will not affect the concentricity of a round in the chamber. Fire forming fixed that, unless you full length resize. By the time the case is thrust against the face of the breech, the projectile is already headed downrange.

Woody

[MacRob46]

No.

[gus65]

Very informative. Thank guys for posting.