How much variation in case length is tolerable for a person wanting to shoot half to three-quarter-inch groups?

If I lean a little too hard on my case trimmer I sometimes come out a little short. Or maybe there's some slight variation in how the brass is seated in the trimmer. But I usually trim, measure, and then trim again. Sometimes I come out .0002 shorter than I meant to. Occasionally I come out even shorter. I've been sorting cases by post-trim length but keeping cases together that vary by as much as .0003 (plus .0001 or minus .0002 from intended length). Is that much variation going to spread my groups?

I'm not a bench rest competitor, just a hunter wanting to shoot out to 300 - 350 yds.

thats kinda like asking about variations in powder, primer, etc. You cant tell, too many variables. I think you are fine with your slight variation. I usually dont trim if the cases are under max and I still shoot fine groups. Load em up and let em fly. Good luck!

First, I suspect that anyone who thinks they are measuring to a .0001" discrimination over a length of more than about half an inch is fooling themself. You'd have to have a temp controlled gauging site to pull that off, and use exactly the same spindle pressure each time you measured.

Second, I doubt that even a couple of thousandths makes any difference whatsoever. The length of the case neck does not affect the distance the bullet is placed from or into the rifling (with most seating die set-ups), and that is likely much more critical than case neck length.

I agree with the laddie who posted just above my post. Load 'em as uniformly as is reasonable, and shoot 'em as carefully as you can. Shooting experience makes for more accurate groups than anything else you can do. As a very general rule, the more shooting experience one gets, the better one will shoot.

That minute amount of variation in case length will have no effect. None of my equipment is even able to measure that. You'll be OK. Good shooting!

First of all I suspect you are missplacing your decimal points. For the type of shooting I do .010" difference doesn't seem to give me any problem as long as the case length isn't oversize to start with. Than some times there is a chambering problem. roger

Isn't squaring of the case mouth the more important factor? I would have thought that only a 'visible' difference in length would matter?

I used to trim my cases all the time. Then I started testing to see if it really made a difference. For my hunting rifles I could not see a difference in my group size that I could really measure. Most of my cases are necked up wildcats. The necks all start around .05-08 short anyway. I simply load and fire. Allowing them to grow just make sure they don't get to long.

Unless you have a very tight necked chamber, turned necks I really don't see a difference in lengths making a big difference. But heck I have been wrong before.

Thanks, guys. Seems pretty unanimous. That's one less thing to worry about. And I hate trimming cases to begin with. It's my least favorite step in the process.

The reason I thought it was important is because it's the friction between bullet and case neck that resists the forward movement of the bullet. Therefore, it seemed reasonable to me that, all other things being equal, a case neck at 2.020 would give less friction and therefore create less chamber pressure and perhaps give higher velocity than one measuring 2.025, which has a little more metal-to-metal contact. But the proof of the pudding is in the eating, and if you guys have been getting good groups without being really anal about case neck length, then that's the final word.

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The reason I thought it was important is because it's the friction between bullet and case neck that resists the forward movement of the bullet.

There probably is a difference in tension caused by a slightly longer neck. I simply believe other factors like, neck thickness, neck tension, hardness all play a larger part.

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Originally posted by audsley:
And I hate trimming cases to begin with. It's my least favorite step in the process.

Hey Audsley, One tool which "Lee" makes is called a Case Length Gauge/Trimmer. Very inexpensive and works better than the Lathe Style Case Trimmers.

I'm not a real fan of Trimming either, but I do it after every shot. Then Champfer, Deburr and Polish the Case Mouth with 0000SteelWool wrapped around an old 22cal Bore Brush. I just give it a couple of twists to remove any tiny Burrs.

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...if you guys have been getting good groups without being really anal about case neck length, then that's the final word.

Not arguing that some folks do a lot less Case Prep than I do and they are very happy with their results.

When I do Case Prep, it builds confidence in the Final Hunting Load that I've done everything I can to get the best possible consistancy. For me, it is worth it.

Best of luck to you.

I'm another Lee trimmer user. I chuck the cutter and caselength gage in my half inch drillmotor and hold the cases in the caseholder in my hand. It goes much faster than turning the case when you must stop the motor to changs cases.
Lyle

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How much variation in case length is tolerable for a person wanting to shoot half to three-quarter-inch groups?

Honestly I don't think even an 1/8" variance will make much difference in accuracy.......and I'd sure hope anyone can trim closer than that....

My trimming usually runs about .003-.005 total variance and that's using a Wilson trimmer.

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When I do Case Prep, it builds confidence ...

Very good point! Good reason to polish cases too. I like shooting the polished ones even though I know it makes not one iota of difference (and I seldom polish them - but when I do, I just have to make them count).

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... I don't think even an 1/8" variance will make much difference in accuracy ...

I once over-trimmed some 223 cases and got the impression that those did not group so well. Of course, an impression is neither proof nor evidence.