Anyone bother to square the case rim?

[John W]

Hello All,

I am still learning the about reloading for the BPCR, and am reading as much as I can on these forums and outside books.

I haven't seen much about whether it is worth it to square the case rim to the body of a straight walled case.

Just theoretically, I was wondering if a non-square case rim would make a straight walled case press/lean more towards one side of the chamber, and thus throw off accuracy?

R,
John W.

[Lumpy Grits]

If you can close the breech on the case. The rim is fine.
Gary

[Kodiak]

I full size all new cases. Then try each in the chamber and close the action. Most new brass these days will let the action close as though the chamber is empty. When I find one that is different than the others, I slowly turn the case in the chamber until it turns loosly. If it tends to hang-up, even a little, I toss it in a box with others that do the same. Lately, all new Starline cases work very well.

YMMV,

Jim

[John W]

I full size all new cases. Then try each in the chamber and close the action. Most new brass these days will let the action close as though the chamber is empty. When I find one that is different than the others, I slowly turn the case in the chamber until it turns loosly. If it tends to hang-up, even a little, I toss it in a box with others that do the same. Lately, all new Starline cases work very well.

YMMV,

Jim

Ahh... so you are using the actual rifle chamber as a "gauge" to see if the rim is square? Then, if not, you discard the case?

R,
John W.

[Kodiak]

"Then if not, you discard the case?"

No, I save those that aren't to my liking. Then I will load and fire them, separate for the "good" ones. Then resize them and check those in the chamber again. Most times they will straighten them selves out, but sometimes not. All of my cases in that lot are fired in the same rifle, as I keep same caliber cases apart for others fired in other rifles of the same caliber. Each rifle has its own lot of cases.

Make sense?

Jim

[Lumpy Grits]

I have never had to discard a case for rim fitment issues.
I use R-P brass in my .45-70 and Starline in the .45-90.
G.

[martinibelgian]

Is this like indexing primers? Looks like something to do when you're bored, and cannot find anything else to do. Like a solution looking for a problem... I'd suggest spending that time on the basics of rifle shooting - hold, trigger and sight management. Likely to give you much better results downrange.

[mdeland]

One of the main problems I run into all the time on all manor of action type is the breech face not being square (perpendicular) to the bore. This is especially prevalent with Rolling block actions but have also seen it in High and Low Walls and Ballard actions.
What can happen is the case head gets bent our of square by back thrust and unless indexed the same each time it gets tight in seating when out of index. If this occurs it can lead folks to think there case rims to thick or uneven. There is usually some variance in case rim thickness as well as diameter when checked four equal-distant points around the rim but in factory rounds seldom varies more then .002 in thickness .
This is the reason I always cut a chamber at go plus .002 which is still half again tighter than most factory head space is set.
For this reason there is some logic to indexing cases.
A case in point, Pun intended: Low wall breech face I squared last year

[John W]

"Then if not, you discard the case?"

No, I save those that aren't to my liking. Then I will load and fire them, separate for the "good" ones. Then resize them and check those in the chamber again. Most times they will straighten them selves out, but sometimes not. All of my cases in that lot are fired in the same rifle, as I keep same caliber cases apart for others fired in other rifles of the same caliber. Each rifle has its own lot of cases.

Make sense?

Jim

Thank you.

R,
John W.

[mdeland]

As can be seen in the photo the lower side of the case was a good bit out out of plumb with the bore from the factory. I think this particular breech face was out .010-.012 from bore plumb.

[John W]

One of the main problems I run into all the time on all manor of action type is the breech face not being square (perpendicular) to the bore. This is especially prevalent with Rolling block actions but have also seen it in High and Low Walls and Ballard actions.
What can happen is the case head gets bent our of square by back thrust and unless indexed the same each time it gets tight in seating when out of index. If this occurs it can lead folks to think there case rims to thick or uneven. There is usually some variance in case rim thickness as well as diameter when checked four equal-distant points around the rim but in factory rounds seldom varies more then .002 in thickness .
This is the reason I always cut a chamber at go plus .002 which is still half again tighter than most factory head space is set.
For this reason there is some logic to indexing cases.
A case in point, Pun intended: Low wall breech face I squared last year

Ahh... this makes great sense. Thank you.

R,
John W.

[mdeland]

Lumpy, your Shiloh's are the reason you have no case issues. They are built like a rifle ought to be!
Breech face plumb can be checked easy enough with a feeler gauge and new factory case. Make sure the chamber rim seat is clean before doing this check.
Put the case in the chamber, close the action and start with a .0015 feeler gauge pushed in from 12:00 o'clock feeling for any tightness as you move it across the case head from 12-6 o'clock and then 9-3 o'clock. Keep moving up a gauge size until you feel resistance at some point on the case head. The case head face will not be prefect but the gauge will give you some indication as to breech face plumb. A fore instance is if you can get a .010 gauge in the top and it sticks at the bottom or sides of the case head. Yes they can be out side to side as well as top to bottom.
The only way I know of to actually measure it is to build a action hole spud and lap the face until it is plumb and square, as in the photo.

[Lumpy Grits]

Thank you for the info.
You have taught me much, over the years.
G.

[John W]

mdeland,

Do you ever run into cases where the rim is not square, or made not square by a reloading die? And can that affect accuracy?

R,
John W.

[mdeland]

I've not seen any factory new case heads out of bore square and that is because of how they are die drawn but as stated I've measured a lot of rim thickness and diameter variation in new cases. Generally in cross mic-ing and rim thickness checks at four equal-distant points around the case head, the variance will generally be in the .002-.003 range. This variance along with case body wall thickness differences are what make case weights vary.
The die drawing method is pretty accurate but does leave some case body wall unevenness. I find this almost universally when stretching cases with the lathe nibbing method I use. This is the reason for case neck turning in precision shooting.
NIbbed cases are more co-axially aligned but there are so many other factors that effect accuracy that nibbed or turned cases is hard to definitively prove advantage, especially in our game.
I remember making a Rolling block some years ago for a friend in 38-55. I had standard go/no-go gauges on hand but for this match rifle I called the friend and ask what brand of brass he was going to use so as to fit the chamber head space to the brass he was going to use. He said Winchester/Western so I chose three of the largest head size cases of that brand I had on hand ,miced the rim and set the head space at my standard go +.002. I test fired the rifle when finished and all was fine. I sent the gun off and about a week after he received it I got a call and he said about a third of the cases he had on hand would not chamber and could I loan him the match reamer so he could scrape cut the chamber just a skoach longer. I sent him the reamer with instructions on how to use it and I guess it turned out well.
Thinking on it now I bet his case heads were bent out of square a bit and did not really have over thick or uneven rims. It was just that the tight breeching revealed the problem.