NEVER TRIM more than 4x.....

[jlow]

My friend saw this in the Lyman reloading manual and is worried. Anybody would like to comment? I know what I think but.....

 

[riflewoman]

Depends a bit on how much you trim...but yes, by the fifth trimming the case is beginning to thin at the case body to head junction.

 

[lawrence97]

It also depends on how generous your chamber is. I know my custom chamber does not allow for much growth after the 2nd or 3rd firing and my reamer print matches what I can physically measure.
I suppose a loose chamber or saami spec might have more generous dimensions to allow for growth. The other issue is that reloading manuals have “recommended” trim lengths which most of the time are way too short compared to what the chamber actually measures and could allow for a generous carbon ring to form just forward of the neck.

 

[jlow]

Depends a bit on how much you trim...but yes, by the fifth trimming the case is beginning to thin at the case body to head junction.

Thin enough to cause case head separation??

 

[riflewoman]

Like it was alluded to, depends on how you size and your chamber. My limit for my M1A is 5 th trimming which is by the 5 th or 6th firing. Of course these rules are meant for “normal” people who trim when it gets to max length, not those that trim to uniform the brass.

 

[jlow]

It also depends on how generous your chamber is. I know my custom chamber does not allow for much growth after the 2nd or 3rd firing and my reamer print matches what I can physically measure.
I suppose a loose chamber or saami spec might have more generous dimensions to allow for growth. The other issue is that reloading manuals have “recommended” trim lengths which most of the time are way too short compared to what the chamber actually measures and could allow for a generous carbon ring to form just forward of the neck.

What you say is true but the concern is not carbon ring (I agree with that), but this idea that the case will be "severely weaken".... a separate issue.

 

[jlow]

Like it was alluded to, depends on how you size and your chamber. My limit for my M1A is 5 th trimming which is by the 5 th or 6th firing. Of course these rules are meant for “normal” people who trim when it gets to max length, not those that trim to uniform the brass.

Is it not true that an M1A brass also has a much shorter life? The point is this is a general statement directed at all calibers and not specific to an M1A?

 

[riflewoman]

Somewhat. But they generally required trimming every shot or so. So at the 5th trimming the brass has flowed .050 inches. That length comes from the head to body area.

 

[jlow]

That 50 thousand seem a lot! I certainly do not see anywhere that much for a bolt gun.

 

[lawrence97]

I guess it isn’t so much the amount of times you trim but the amount of material you trim off each time!

 

[jlow]

Agreed!

 

[Jennb]

I shoot a custom chambered .308 and trim minimal brass every firing. I have brass with 13 firings on it and we have cut one open to brass thickness. The primer pockets will be loose before the brass gets thin.

 

[jlow]

That’s consistent with my own experience.

 

[Dusty Stevens]

If you dont want to discard your cases after 5 trimmings then dont. Lyman is covering all bases from an h&r handi rifle to a garand. If youre on this site then youre probably past the general public disclaimers so proceed at your own risk. If you have to ask why they say this or dont understand what happens to cases that are on their 4th or 5th trimming then you need to follow the instructions in loading manuals on how to reload

 

[NorCalMikie]

The "need to trim" depends a lot on the type of dies you use. Shoulder bump will keep your brass from growing. Throw in a full length resize once in a while or a body size and your brass will last much longer than usual.
Got BR brass with 20 to 25 + resizes and still no need to trim.

Is it not true that M1A brass also has a much shorter life?

Hot brass being RIPPED out of the chamber is a good cause of shorter brass life, among other things. If you're not seeing it, you're not paying attention.

 

[Uncle Ed]

I would look at the Lyman manual to see how the die is adjusted prier the posted statement. But if you look below at the bottom image no case stretching and thinning happened until the 7th shot on the Nosler case. And the Norma case went 18 firings before any case stretch. Meaning chambers and dies vary in size along with the quality of the brass.

 

[JimSC]

I don't see how trimming or not trimming will affect the thickness of the brass in the junction area. It's not like the brass will migrate back from the neck to the shoulder/body if not trimmed. At least I have never had a case stop growing and become shorter as it is fired. Anyone ever had brass move from the neck to the body if they don't trim?

 

[jimmymac]

Trimming or not trimming isn't the issue. It's a brass thinning issue and the trim number is nothing more than a simple measuring stick (number of times trimmed) to give you a heads up that it might be time to consider new brass. A lot of variables. Not one size fits all.

 

[Uncle Ed]

If you want a accurate way to measure case thinning then buy a RCBS case mastering gauge.

It tells you in thousandths of an inch the amount of case stretching and thinning.

The factory loaded Winchester .303 British case below stretched and thinned .009 on its first firing.

Case stretching happens due to the amount of head clearance, and your head clearance corresponds to your amount of shoulder bump.

The amount you trim is governed by your chambers diameter the dies diameter and how much the case is squeezed when full length resized.

 

[Bart B.]

Case brass at the pressure ring work hardens before any other area.

Regarding fired cases from 7.62 NATO semiautomatic service rifles used in competition, nobody consistently shooting the top scores reloaded fired brass from them. Case heads were too much out of square. Shots strung between 7 and 1 o'clock on target; right angles to bolt lugs in battery. Their bolt faces were never squared up.

I gave away thousands of once fired M118 match cases to civilian shooters; their tax dollars paid for them.