New Hornady brass

[BigBluePup]

So I've got a run of 100 new Hornady brass that I'm getting ready to put some loads in and I'm curious.
I'm getting 1.514-1.517 CL on them.
How much are these things going to grow once fired?
If it's anything like my .300RUM the case length is almost always under spec first load then they grow past it once fired and I trim to length and very rarely get one that trims again.

What are you guys trimming to before, or just fire forming out of the box and trim back to out of the box length again to be consistent?

[Bwild97]

About .003 - .007" sometimes they shrink .002 - .001.

With new brass I only chamfer the inside diameter with a VLD chamfer tool. I trim my brass at odd numbers of firing 3rd, 6th, 9th and so on. I trim to 1.517.

I have yet to trim any of my Lapua brass, which started at 1.515 and most measure 1.513 - 1.517.

[12-99]

I've had several loadings on Hornady brass, some hot, some not. Haven't had to trim yet. Just chamfer and deburr.

[LRRPF52]

How much you need to trim can often depend on your chamber dimensions and their relationship to the bolt lock-up. Your loads can also have an effect on how much the brass grows.

A lot of bench rest chambers are so tight, there is no growth in the cases. A neighbor of mine has a 6mm PPC like that, which he just de-primes and loads on the spot.

Conversely, with gas guns, your dwell time and how soon the action begins to unlock can have a big influence on case stretching, which I have seen the worst of on bwaites' 28" Grendel.