how does case length effect performance? Is 2 or 3 1/100's going to cause problems? This would be less than suggested trim length.

IME it doesn't affect performance of the round but it can cause problems. If you are crimping and the brass varies in length, you can end up with inconsistent crimps and if you are loading a bottle neck case and it is too long, you may bump out the shoulder resulting in a round that may not chamber.
The greatest danger is with cases that are so long that the neck jams into the front of the chamber and cannot release the bullet on firing causing extreme over pressure.

If you are talking about tapered rifle brass it will not affect performance as long as all cases are trimmed to the same length. Straight walled pistol cases would be a different set of problems. Varying lengths of rifle cases will case erratic external ballistics; velocity will have excessive variation, and you will see a loss of consistent accuracy. How much loss of accuracy depends on how diverse the case lengths are.

Affect.
If you mean your cases are all trimmed to .020 or .030 less than the recommend trim length, it means nothing.

quote:

Is 2 or 3 1/100's going to cause problems

Unless you are crimping or shooting for the .001" group you will never see it.

I've gotten lazy in my old age. Many I shoot are wildcats. After my forming load I trim to the shortest length and normally don't trim again. They wear out or get lost first.

thank all of you for your reply. Its a Tac 20 I have the shorter brass for. I did not believe it would be a problem, unless I was crimping. But I feel better having run it past the group for comment.

The last few times I've gotten brass, it is all shorter than recommended trim
length....Norma, Lapua, as well as PRVI. What's up with that? Are the
litigation cops making these companies paranoid?

Tac 20 is a GREAT cartridge. I make all my own brass from .223. Have to
trim most of it. My Tac20 outshoots my .204R with less powder. Don't care
what Hornady says about the two in their handbook.....to do it over again,
I would not get the .204R!