Can someone please explain why, in the reloading manual the min case trim length is 2.035, and max case length 2.045. Yet three different factory loads have cases measuring 2.355, 2.390 and 2.420. Am I missing something here?
243 case length query
- Thread starter old keeper
- Start date
Heym SR20
Well-Known Member
Which reloading manual?
Have a look at the Saami and CIP specifications for the cartridge. Max case length is 2.045. You trim to a bit shorter than max case length as the last thing you want is the case mouth jaming into the bullet lead (a touch bigger than bullet diameter but narrower than case) as this will in effect produce a super tight crimp on the bullet raising pressures. You would notice this if babying the bolt. You probably wouldn’t if you ran it hard.
Different manufacturers will have slightly different case lengths, but these should all be in tolerance as specified by Saami or CIP. As for your measurements quoted being well over, were these from using your own callipers? I would suggest you have either not zeroed, are misreading the dial, callipers are at an angle or you are measuring once fired brass.
When a cartridge is fired and the walls are squeezed against the chamber walls, the brass will be forced somewhere. Since it can’t go backwards (bolt face), or minimally outwards (chamber walls) it can only go forwards hence cases get longer and thus the need to trim to length.
Trimming really needs to be done after resizing. This too can further squeeze the brass and further increase length.
Thanks for the reply, Heym.
The Hornady manual, 11th edition. states max case length as 2.045, as you say. My fire-formed cases measure around 2.390-2.440 before resizing. My query really is, why, when the max case length is stated as 2.045, are the factory cases anything up to 2.420?
I have several callipers, all give the same reading. The three new factory rounds I measured are Hornady, Sako and Remington.
I always trim after resizing.
The Hornady manual, 11th edition. states max case length as 2.045, as you say. My fire-formed cases measure around 2.390-2.440 before resizing. My query really is, why, when the max case length is stated as 2.045, are the factory cases anything up to 2.420?
I have several callipers, all give the same reading. The three new factory rounds I measured are Hornady, Sako and Remington.
I always trim after resizing.
Why don't you post a photo of a case and the calliper reading? Your numbers quote above suggest that you are trying to resize by 0.4 inches, and not the 0.002 inches that I would expect.
Regards
JCS
shakey jake
Well-Known Member
thats 10mm out of spech, something must be wrong
Thanks, JCS, now sorted! A senile moment, I think!
Happens us all. That re zero button can be a demon sometimes!!,
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