Trimming vs case length

[BigGame]

Thanks all for the responses. For those interested in more details, these are 6 Creedmoor ADG cases. I use a Redding bushing FL die and mandrel the necks. I bump shoulders about 0.001. I have measured the chamber and it is slightly longer than spec. While most of my rifles are for hunting, this is a target rifle shooting at 600 yards. I have 7 reloads on half of the cases and 12 on the other half. I no longer use wet cleaning with steel media, so no rim peening. I anneal each firing with an Annealeaze.

I do see some changes in length that is inconsistent across the lots. Some are short (below min) and none are at max.

It sounds like many are comfortable not trimming until necessary and having inconsistent lengths. It may be that those of you who trim each time also have a more consistent process than I do, so your case lengths are moving more consistently. What I’m gathering from this feedback is that my observations of variable length might to a window into my overall sizing regiment and I should likely focus some attention there.

I appreciate the feedback.

 

[RegionRat]

What I’m gathering from this feedback is that my observations of variable length might to a window into my overall sizing regiment and I should likely focus some attention there.

Here is a suggestion to help put your mind at ease if the idea of allowing them to drift till they hit a max bothers you.

Get a set of otherwise equal brass with a population of about 20 to 30 pieces that are very near max. Sort them to pull out all of the shortest ones and then split that batch in half. Trim the shortest ones to your limit for the range you would expect to have a significant difference and then trim the long group to make sure all of them have had at least a skim cut and the same chamfering.

This now forms your side by side test population with both the shortest and longest that have all been trimmed and chamfered identically with only their lengths being different. Pick a good day to test and see if you can spot the difference.

 

[Ackman]

My cases don’t seem to stretch. At least nowhere near a trimming length. Many of my cases are below the minimum length. I understand many will trim and chamfer cases regularly to maintain a consistent set. Seems prudent. But if I did that I’d whittle away the cases to nothing.

Do you trim when they’re not long? How short is too short? If weighing short cases vs consistent trim, where do you come out?

Case in mind is 6CM, but question is general.

Find out your chamber length with a gauge from Sinclair. They're cheap. Then, don't be trimming cases just to trim them because it's an "accuracy thing". If case length is within about .005" of chamber length, then trim. But don't go doing it just to do it.

 

[Coyotefurharvester]

I picked up about 1100 556/223 off the ground after a weekend off carbine classes. Tumble washed them. Universal decapped a couple hundred, and fl sized them about a thou short of the lower step on the Lyman small rifle ammo checker. Checking the length on a sample showed a little more than 0.020 length range, the mid being about 1.750. So I set my trimmer about 1.752-3. Seemed like about 1/3 had some trimming. Almost all had crimped/staked pockets and sealer, so after sizing and trimming I used my Lyman vld chamfering bit in the drill press to cut the pockets and chamber the case mouths, probably will set my trimmer slightly longer for the remainder. If the nephew goes on the next prairie dog shoot(be his first) he will have to load a couple hundred the night before we leave. The sizing/trim will make sure he can load and shoot without issues(having the kids load some produces careful/slower shooters).

 

[Ned Ludd]

Depending on the kind of trimmer used, it is just about as easy to set the trimmer to the specified length and attempt to trim every case as it is to actually measure them and determine whether they need trimming. If they don't need trimming, the trimmer simply won't take any metal off of the case mouth. If they do, it will. Whether or not a case actually has anything trimmed off, I would still suggest freshening the chamfer every time. There is no reason to trim cases to anything shorter than the desired length, but using the correct trimmer setting will take care of that. The cases either will be trimmed or they won't, then you can chamfer as normal. The key to this, of course, is to have a means to reproducibly set the cutting length of the trimmer when using it for different cases, which most of the trimmers I've seen do.

 

[ronemus]

The length of the neck in contact with the bullet is one of the factors that determines the bullet pull force, which in turn impacts the powder burn. If you're shooting MOA inside 300 yards, it probably won't be an issue. However, if you're shooting for extreme accuracy or at long range it pays to make everything as uniform as possible; it's one factor in a multitude, but it matters sometimes. You'll have to decide for yourself if it matters enough in your shooting to pursue it.

 

[PhilC]

Better yet, measure YOUR chamber, write that spec down and refer to it before you even consider/think about trimming. Chambers are usually cut about .020 longer that Max trim length. Don't fix it if it ain't broke!!

I do this for every rifle I own and only trim to match shortest case in the same batch (if I think necessary) OR when necks in that specific batch reach an individual rifle's determined maximum neck length.