So, say you've got .015" thick brass at the case mouth. That's .030" of headspace material.
I hear over and over that you should keep pressures low in cartridges like this, but I can't really see why. Assuming you keep them trimmed to the porper length, and since headspace shouldn't be "zero" anyway, what exactly is the problem?

some of the factory 45-70 ammo i buy there is a crimp BEHIND the bullet to prevent the bullet going back into the powder area and creating highter preasure under the recoil of +P+ ammo. so if you do a roll crimp i do not see any issue but i am not an expert. this would revolutionize wildcatting

if this were the case...

500 ultramag


500 and 550 lapua and the list would go on...

416-06 ect ect!!!

Actually, that's what brought this up. My uncle wants to make a 416"x57" for a 96 Mauser that headspaces on the mouth. I'm not exactly sure why, but wildcatting seems to be a singularly inexplicable pursuit sometimes.
And so it got me started thinking, "Why exactly not?"
I think I may have talked him into using a 9.3x64 case, but the question still remains.

o.k. now who wants to make the 2.3", 2.5", 2.7", and 2.85" case length headspacing off the casemouth 500 ultramag????

i also like the 416-06'

Ken Howell made a 444 Marlin in a Mauser that used 30-06 brass that headspaced on the mouth. He did a write up on it somewhere which I have never seen. What I understand is he had a reamer made with a square shoulder for the case to headspace against.

quote:

i also like the 416-06'

I took my wildcat 280 case. The shoulder is blown out to .458 and chamber a 416 barrel. Real close to a straight case. A little more performance than the 411 hawk. But not enough for me to keep the rifle.

Let me ask this question...what effect does chamfering have on the answer? In Boomstick's drawing above, I have .0312" of case mouth to work with. In half, that is .0156" basically around the mouth for thickness. If I chamfer, which I have to because my cutter will not cut a perfect flat, that makes that .0156" even smaller, even if it is right at the edge of the mouth.

Do you think that will be enough, or do you think there is too much possibility of the round being forced too far into the chamber and creating a crimp of sorts? With a pistol round, I'm not sure I care, but my bolt has much more camming force.

Just wondering your thoughts.

OK, my questions is why?

With most rifle cases you can headspace off the taper, or use a rimmed cartrige and headspace off that. While some pistol cartridges headspace off the mouth (becasue they are straight walled) I would think that the other to methods are far more reliable in a bottleneck rifle cartridge.

Headspacing off the mouth is option if no other way, but many of us in bigbores don't like to trim, like 12GA FH, I made chamber long enough
so at pressures used in my Savage, I might have
to trim at 100+ firings, The case I showed sectioned in other thread was fired 36 times and no trimming and still had .090 room to stretch in chamber.Ed

Sure you can headspace off the mouth on just about
any cartridge if the chamber is cut square at the
mouth. BUT, of the places you can headspace from
like the rim, belt, or shoulder, it is perhaps the
least desireable. You do it with 45 ACP because
you have no choice, not because you really want
to. Just remember that whatever you headspace off will take the full force of the firing pin.

Well, it looks like I'vegot him talked into the x64mm case, so it's a non issue now.
Thanks for the input, guys.