Trimming down brass that is below the COL

[Point_Taken]

So I have 6mm Creedmoor brass from Lapua and while I never initially checked the length on the brass, since firing it once it ranges from 1.905 to 1.908. The thing is, the trim down to length is 1.910. Should I trim them all down to 1.905 for consistency or what? I only check about 4-5 to be fair, not all 100 that I have. But I'm curious what your guys suggestion is in this instance?

 

[Blue68f100]

I do not trim unless they need it. Since these are under trim length, have they been sized? If sized let them be till they need it. It does not hurt if you really thinks they need trimming, your not going to notice 0.003".

 

[Point_Taken]

Yes they've been resized once since I fired them.

 

[ArchAngelCD]

Did you resize before you measured them this time? They grow from the sizing operation.

As said, don't trim until they are past the normal length range. 3/1000 can be a measuring error it's so small.

 

[jmorris]

Your numbers are under max so all you could add by using them is some unmeasurable amount of neck tension.

If you are not checking all of them, it doesn’t matter much anyway. You could be letting “bad” ones go by and only seeing good ones.

Whenever I don’t want to check each and every case, I size/deprime and trim on a progressive, every case goes through the same process, if it needs trimming, it gets cut, if it doesn’t, nothing happens.

 

[Highland Lofts]

Whenever I don’t want to check each and every case, I size/deprime and trim on a progressive, every case goes through the same process, if it needs trimming, it gets cut, if it doesn’t, nothing happens.[/QUOTE

This is what I do, that way you absolutly know there isn't anything over length.

 

[Charlie98]

Your numbers are under max so all you could add my using them is some unmeasurable amount of neck tension.

^^^ That. The only monkey in the wrench would be if you are crimping them, for some reason, then you might have issues.

 

[Slamfire]

See the space in front of the case neck, in this Sheridan cartridge gauge?



That is the clearance I have between the case neck and throat, and I want enough so that drive in, and unpredictable events, don't push the case neck into the throat and pinch the case. If the case neck is pinched, because the neck is sticking in the throat, that will create over pressure conditions.

I have trimmed a lot of cases well below OAL, I have shot a lot of 30-06 sized down to 270 Win. A neck sized down 30-06 is so short I don't need to trim after neck resizing. And I cannot tell much of a difference on paper, out to 300 yards, in my hunting rifles.

Now maybe some bench rest shooter, or F Class guy will see something on paper, but their equipment will hold inside anything I can do with a hand held weapon. So shooters saying it will affect neck tension and that will affect group size, need to put targets out there, with more than three shot or five shot groups, to prove this. Trim length is primarily a safety consideration, and I do it, or check, everything time the rifle brass is reloaded. I also trim new brass before loading, just to make sure.

 

[Steve in NC]

Slamfire has some very sound advice. I come from a benchrest background and have shot short range and long range BR for many years. When I fireform any of my long range widlcat cases they are ALWAYS well under COAL specs. Not a problem at all. The 338 Lapua Improved is the most dramatic in that the cases shorten up .030-.040 shorter than a standard 338 Lapua cases. I always trimmed before firing and left them alone.
I can confirm what Slamfire was saying about if you can "shoot the difference" between a case that measures say .003" shorter than the next case. I never could ever see that difference on paper. But if you could actually feel a difference in seating a bullet with my hand seating dies... oh yea. You will see vertical in a heartbeat. But COAL was never the culprit. Neck diameter or brass work hardening were the biggest issues that influenced neck tension.

To the OP that is only .002/.003 thousands under min spec. You can trim them to be all equal for a peice of mind and fire them without any issues. But if you don't trim them, you will not see that difference on your targets. Its all based on your comfort/confidence level.

NOTE: When firing excessive shortened cases..... use a good bronze bore brush while cleaning and keep after the front of you chamber/throat area. It is similar to firing a lot of 38 Spl in a 357 Mag chamber. You can and will get a carbon buildup there if you don't keep after it. Then if you ever do fire brass that is of full length you can run back into the issue slamfire mentioned about pinching the front of your brass. In my widlcats it never caused a safety issue with high pressure but it did cause chambering issues to where a properly sized/loaded round wouldn't fully chamber to where the bolt would not fully cam down. But this was with the 338 Lapua Improved that had cases .030/.040 short from the fire forming. I have never seen this from cases that were a couple thousands short personally.

Good luck be safe,
Steve

 

[Jack B.]

I make sure all my rifle brass is of equal length for the rifle I'm reloading for. Trim or not doesn't matter . To me what matters is that all of my reloads are the same.

 

[Rule3]

https://saami.org/wp-content/uploads/2018/04/6mm-Creedmoor.pdf

Your difference is .003 not a whole lot to worry about
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Specs
1.920 -.020 (48.77 –0.51)