In the reloading world we throw around a lot of dimensions such as overall case length. As an example a manual will say to trim a 6.5 remington case to 2.025" but it does not specify any tolerances, such as +/- .002 etc.. In the machine/manufacturing world there are few machines that can hold a dimension dead on. And with our hand operated reloading tools I would say it is impossible to hold a consistant dimension.

Sooooooooo, in your opinion, what do you consider an acceptable tolerance when trimming cases?

I feel as long as you are within a few thou throughout a batch, you'll be fine.

Reloader

I take the easy way out. Lee case trimmers and no measuring. I stay happily ignorant!

IAH I try to keep everything +/- 0.002". I think that is somewhat easily accomplished with what we use, not taking into consideration variances in components of course.

That is in the caliper measurements of course, lengths and whatnot. Runouts, diameters, and other mic work is another story.

Just don't get caught up in the "mic" mentality! I worked for an engineering firm once (and for not very long) that had the "mic" mentality. "Measure with mics, mark it with chalk, cut it with a torch"

The normally accepted tolerance for case length is + 0", - .010".

Most - all? - factory chambers are actually cut long so it isn't much to worry about but, unless you measure your chamber correctly, making it match the spec. is good.

Most loaders worry far to much about case and cartridge OAL lengths. As long as a cartridge OAL works in the magazine and chamber throat without jamming into the rifleing and the case neck is just a bit short of the chamber neck, everything is ok.

Precision trimming of case lengths, within 10 to 15 thou., does nothing for final accuracty.

quote:

but it does not specify any tolerances, such as +/- .002 etc..

Well in my 30+ years of reloading I've gotten very lazy. The majority of my cases are fire formed. When formed they are around .05" short. I then simply let them grow until they reach max length and trim back .05". In my testing in a MOA hunting rifle I have never been able to tell the difference between cases .05" diff vs cases the exact length. Heck I even rrim my new factory cases by .05". Then trim after 4 or 5 loading.

When I was shooting BR many of the shooters would simply prep and trim all their brass .02-.03" short of Max and simply let them grow until they were at max and then retrim.

Ref Trim To Length, actualy there is a tolerance level of +/- .009.
SAMMI spec's a Max for case length (IE not to exceed x.xxx), and the spec minimum length is normaly .020 shorter than the Max. The "Trim To Length" is normaly 1/2 way between min & max.