Do any of you folks square off the case heads during the prep of new brass? If you do how has it changed primer seating in your brass. What brass manufacturer is your preference, why?


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Rex

Squaring case heads used to be one of the gimmicks that some Benchrest shooters thought was beneficial. However, it soon fell out of favor because it didn't take a rocket scientist to realize that 60,000 psi of pressure was going to make case heads conform to whatever perpendicularity or lack of perpendicularity that the bolt face had in relation to the chamber.

IOW, if your fired cases had crooked case heads and you squared them in a mill, or whatever, they would go right back to being crooked on the first shot.

70 years ago new brass may have been bad enough to warrant some fixing, but today, it's doubtful if anyone can see any difference between squared heads and those right out of the box. Your time would be better spent in cutting a good, straight chamber. Or better yet, in practicing.

JMHO

Ray

Perpendicularity. Darn, I like that word.

I was having a run out problem with some 300 win mag loads in (new)Win brass and could not figure why. Long story short I discovered that the worst offenders were not very square so I dropped them in backwards on my Wilson trimmer (and what do ya know?) the problem evaporated! I had to remove a lot of brass from some of the cases. I tried my 308 Win Lapua brass and it was much better, some were out to the point where letters started disappearing. It is a hassle but it has helped keep the bullets in line and because my chambers are straight they do not go back to being off.

Interesting.

I'm having a hard time understanding how uneven case heads could result in bullet run-out in a straight chamber? Isn't run-out a function of the bullet, case neck, and case body?

Are you FL sizing your brass? That could be causing the problem. Check the run-out on fired brass before resizing and see if it's there then.

If you mean that a load in a new case shows run-out, I'm not surprised. A lot of the lesser quality brass is banana shaped. If you fire a full power load it will straighten out, assumimg your chamber is straight.

JMHO

Ray

I followed this issue for a while, and have lost track of where the BR boys are these days...

Cheechako's history more or less matches my recollection. Creighton Audette found that fired cases take on a curvature in the body related to uneven casewall thickness. He found that by identifying the "high side", and orienting it in the chamber, he could predictably alter the point of impact on the target. The non-square case base is a manifestation of the case curvature/uneven wall thickness.

I'd have to go back and see if Audette theorized the "why's" of this effect and if it had anything to do with the uneven thrust on the bolt face.

Later, Merrill Martin did similar experiments and found similar to Audette. He theorized that these "curved cases" cased a jet nozzle effect and started the bullets off in the wrong direction in the barrel. I have a vague recollection that he played with squaring off case heads to arrive at this conclusion, but you'd have to go search the back issues of Precision Shooting or call him directly to find out.

I was going to play and experiment with this a while back and had a big diameter cutter to square up the heads with a Wilson Case Trimmer, but discovered that Lapua Cases had excellent case wall thickness consistency, excellent runout and excellent headsquareness. I bought Lapua Cases and dropped the project.

If you plan on calling Merril take a lot of quarters. He's been deceased for a good many years.

quote:

Originally posted by eddieharren:
Perpendicularity. Darn, I like that word.

aka "right-angledness"