After resizing some 308 my lengths vary from 1.990 to 2.006+


I set my trimer to cut at 2.005.


Would it be unsafe or out of the ordinary to set my trimmer to cut to the shortest case: 1.990?

If I trim to the ideal trim length 2.005 and try to seat to the cannelure I'll more often miss the cannelure than seat in the cannelure. If I cut them all to the same length, I can guarantee a little more consistency; Is this true?

What's the shortest safe trim length for .308?

Everyone must be camping this weekend...

You should keep your brass in the range of 1.995" to 2.015".  Those are the SAAMI specs.

Most people would use 1.995" as the minimum "trim-to" length.

<edited by author>

The SAMMI spec drawing shows the case length for 308 Win to be "2.015 - .020". So by the book, 1.995 is the min trim length.

The choice to trim .005 shorter is up to you. The only concern would be that by trimming shorter, then seating to the cannelure, you've effectively reduced the case volume by .005. If your load is at max, you might have issues. If your load is gentle, you probably won't notice. If you aren't crimping, ignore the cannelure and focus on COAL.

When I trim blasting .223 my cutter cuts most cases but dosen't hit some. I don't sweat it that they're a few thousandths shorter, I seat all the bullets to the same length and don't see a difference on the target.

http://www.saami.org/specifications_and_information/index.cfm

I trim my resized .308 brass to 2.00" even. Always have since I started loading it around 1984.

Some people will trim them at SAAMI maximum, some will use the suggested 2.005". It doesn't really matter what number you use, just make sure you do it.

Agreed, you're fine.  A few thou short is totally irrelevant.

I can't see or imagine where my technique is off...

I'm using Dillon's trimmer on my Dillon 650.

The case is held by the sizing die. I set the trimmer to 2.005 but the case length variance is already there before trimming.

Suppose I choose to trim to 1.995 wouldn't that give me a more consistent trim simply because I chose a shorter size?

And if my trimmer is set to cut at 2.005 and a majority of my cases never get cut...
aren't I already seating and shooting shorter cases?

Unless you are neck only sizing your brass will eventually grow in length.

Unless you are roll crimping +\- .010" in case length is not going to make any noticeable difference in accuracy unless maybe if you are shooting a precision set up. You haven't mentioned what type of firearm you are loading for.

My personal opinion is:

If going .005" under (trimming to 1.990") is going to even out all of your casings to the same length I don't see anything wrong with that.

I'm a little surprised the spec is -.020" it's -.030" for some. The .308" is not a casing that suffers from having a short neck like the 300 Win Mag does so going .005" is not going to have much impact.

Set your caliber to .005" and look at the gap. Now imagine a ring of brass is .005" long. How much difference is that going to make?

This however is a one direction thing. Just for anyone new out there trimming is #1 a safety issue. You never want to cheat long. A long casing can allow the case mouth to engage the rifling which in turn prevents the case mouth from opening to release the bullet. If this happens a dangerous over pressure event will occur.

Motor

OP:

I suggest that you set your trimmer to 1.990" this time only just to even out your brass.

Then re-set it to the normal trim length of 2.005" and leave it there and let the brass grow to it.

Motor

I'm shooting an Armalite AR10 with a 20" Match Barrel.

I fully understand the need for trimming. I also really appreciate everybody's response and input.

I'm just trying to tighten and control my trim lengths. I'm certain that the variation in case lengths is first because my case size after firing is coming out short. and second my trim length is set too long.

I may indeed be making too big a deal out of it...

A few more firings and the short cases won't be short anymore.

I only have one 308, a precision rifle. I trim to min spec for 308 as I don't have a dedicated trimmer for it, I setup a contraption in a Bridgeport. I neck size 308 and it doesn't grow much so I don't need to trim often. I do like to keep all of the cases the same length, I just don't care what length it actually is.

For 556 every round gets trimmed on a 650 as part of the loading process so the trim length is set to the middle of the tolerance. When I process brass some get trimmed and some don't, but all are in tolerance. 

Forget about measuring OAL of fired casings. It's totally meaningless.

Cases get shorter when fired because they expand basically sucking in the length.

The OALs to compare are your trim length before firing and then the length after resizing.

This difference is a good indicator of how much brass you are losing per cycle to OAL growth.

Typically you should get at least 2 cycles before they "need" trimmed again. If you find that you are needing to trim every cycle because they are growing from trim length to over maximum you can expect poor casing life.

Motor

Actually, this batch will be on its 6th firing...

I just measured 21 pieces from a once virgin batch. Never fired but through my rifle. The average oal size of the 21 pieces came out to 1.994...

I'll clean them, resize them, then measure again. This should tell me how much they actually grow.

Okay. However, if the batch I'm measuring is all over the place (before firing and after trimming) how can I get an accurate understanding of how much they are growing?

It seems to me that the control batch has to be at least more uniform than what I have now, unless I try to track a single piece of brass...

In any case, I'll cut this batch to a more uniform length and track the average growth after resizing again...

I thought we covered that in the first part of this thread.

Trim them all to 1.990" if that what it takes to make them all the same.

You probablIy know this but: You should only be trimming brass that has already been sized.

Motor

We did. I was just reiterating.

I apologize.  I completely missed your intended meaning of your statement about the length setting.  I thought you were saying it was cutting variable lengths.  Apparently, you meant some were trimmed and others were not.