Trimmed Cases too short

Rocketmandb said:

The .007" variance is larger than it should be. Of note is that the trimmer indexes off the shoulder of the case, so if your shoulder bump is inconsistent, the case length will be inconsistent. Have you checked your shoulder measurements?

Also, trimming short is not the end of the world. The cases will grow back as they're sized over subsequent firings. The worst side effect is that shorter cases leave more of the chamber exposed to the gasses of combustion, meaning there is more area to build up carbon, and thus carbon rings. Keep an eye on this.

Additionally, if you mix and match brass that hasn't been trimmed as short, you will get slightly different effective neck tension. This difference is directly related to the difference in bearing surface against the bullet. If you're roughly 15 thousandths off from one case to the next, depending on how much of the neck the bushing in your dies sizes, you're probably 5-10% different in effective neck tension. That will yield a slight difference in SDs, but shouldn't affect much else.

Click to expand...

straightshooter1 said:

Then this suggests to me that something is loose or flexes in the trimmer . . . .???

One of the things I had to learn with my Giraud trimmer, which likewise indexes off the shoulder, is to have consistent pressure into the cutting head. When I first got it I was getting variances of ~.004, which was coming from variances in just how hard I pressed the case into the trimmer. After some a few hundred trims, I've now got a pretty good feel for it and get very consistent trim lengths that go with my consistent shoulder bumps.

Click to expand...

MMH said:

Talked w/ Little Crow & they said that a bad cutter will cause this. They also said that all you have to do to get a burr on the cutter is to run it backwards. Not sure I understand this, but will get some new cutters & try again...

Click to expand...