Case trimming

[GaCop]

Is it really necessary to be anal about case length, ie, a difference of .004 to 006" if within minimum/maximum length? For years I've trimmed to the shortest case but have been wondering if it really pays off in the long run.

[Celtic Warrior]

For me yeah. I had some work up brass, Win, that stretched after being shot once. After reloading them, the second time, I couldn't get some of them to go into battery and the ones that did got stuck in the chamber after firing. Upon inspection the ones that fired had a ring at the very top of the neck, like a crimp (I don't crimp my 308 rounds, single feed). Normally I resize every three reloads with Lapua brass, I wasn't expecting the Win to stretch so quickly.

Additionally, when everything is the same you get better precision.

[Elkbane]

Gacop,
I've often wondered about that - I typically try to keep mine within 2 thousands, but don't know if it really matters.

Theoretically, the gripping friction overcome in bullet release, all other factors being equal (same neck tension, metalurgy, same inside surface treatment, etc), will be a function of the surface area of the contact interface between case neck and bullet shank. Surface area of a cylinder is circumference x height, so 2*pi*r*neck length. I just did the math on surface area of a 260 remington case with 2.035 case length versus 2.030 case length with a given 1.7755" to the top of shoulder; 5 thou difference in neck length. The difference in surface area is 1.93%.

Whether that matters is probably up to you and your application. I wouldn't be worrying about it on a .223 for an AR, but I might for a bolt gun for matches.....
Elkbane

[Eric in NC]

The answer I have found is "it depends". If I am shooting something that headspaces off the case mouth (30 carbine, 45 ACP) I see a lot of difference in accuracy from a uniform group of cases vs. a group that are all just "within spec". See a difference but less so in accurate rifles with quality barrels and precision chambers. Don't really see a difference at all in things like my M1s and FALs - as long as they are in spec and fit the case gauge they all seem to do the same.

Oddly enough, I don't seem to see a difference in revolver and lever gun rounds that require a crimp. You would think that case length would be most critical on those as it directly impacts the crimp but I honestly can't tell a difference in performance (maybe I just can't shoot revolvers worth a hoot?).

[Nor Cal Mikie]

What you need to know is the "exact" length of your chamber. That will tell you how long your brass can get before it "needs" to be trimmed. And the type of dies you use makes a difference on how much your brass grows.
Standard full length dies with the neck expander ball pulls the neck area longer every time you resize. If you shoulder bump and neck size, you can keep brass growth to a minimum.
I've got brass that has been resized 20+ times and still hasn't needed to be trimmed.
Example: 6BR/22BR that the max trim length is 1.560. "Actual" measured chamber length is 1.585. That leaves me "lots" of room before I have to start thinking about trimming brass. And my brass lasts longer. 8)

[82boy]

Is it really necessary to be anal about case length, ie, a difference of .004 to 006" if within minimum/maximum length? For years I've trimmed to the shortest case but have been wondering if it really pays off in the long run.

In the accuracy game, you better beilive it. I have seen groups tighten up after trimming brass. The main thing is that they are ALL the same length. I dont pay attention to published maximum and minimum length in loading manuals, with new brass I find the shortest piece and triim them all to that length, and keep trimming them to that length.

[GaCop]

Is it really necessary to be anal about case length, ie, a difference of .004 to 006" if within minimum/maximum length? For years I've trimmed to the shortest case but have been wondering if it really pays off in the long run.

In the accuracy game, you better beilive it. I have seen groups tighten up after trimming brass. The main thing is that they are ALL the same length. I dont pay attention to published maximum and minimum length in loading manuals, with new brass I find the shortest piece and triim them all to that length, and keep trimming them to that length.

Great Pat, that's what I was looking for. I'll continue to be anal about trim length.

[Joe O]

I want to know the exact chamber length,so I use a Sinclair chamber length gauge for each gun ($7).I then then trim after the first fireing.I don't use the shortest case,but a average of the ten shortest,and trim to that length.I want to be .005-.010 shorter than chamber length.The few shorter cases are trimmed and used for fowlers/sighters,and dummy rounds for measurements.

[Celtic Warrior]

In theory, repeat "in theory" all chambers are cut with consideration to the SAAMI spec. http://www.saami.org/specifications_...wnload/206.pdf so cartridges should be kept to the same spec. When you look at the specs, pls note, the overall length of a cartridge is held to + 0.000 and - 0.020 (usually). So when you trim, all cases should be in that - 0.020 range and the same length, preferably a few thou short of the max length.