Case Trimming?

[Ernest T]

I use the Lee case trimmer which uses the case base to set the length of the case. I like it because its easy and repeatable, but I've seen and read some things that say that's not the best way to trim a case. Any thoughts about measuring from the shoulder?

[bootsmcguire]

I have used that same Lee system for years with no issues, not saying it is the most productive way but it works. I would think measuring from the shoulder may be less accurate because one would be taking for granted that all other measurements from that junction on the shoulder to the base are equal from 1pc to the next. Maybe there is a tool or system for that, I don't know at this time. Trimming is chore that I am never excited to do and as such my higher volume shooters are mostly Ackley Improved chambers which practically eliminates trimming and with the added brass life I use them when practical. But that's another topic Lol.

[Blue Avenger]

Even if they can show it's better, I'm not going to add a new method into the program at this stage. They fit the Die, Crimper and chamber with my current trimming tooling. I'm not currently pursuing 1000yd moa.

[Dave Hoback]

I use the Little Crow trimmer & measure the old fashioned way; “How it was done back in 19-Aught-Eleventy-12!”

[Ernest T]

I've been working on the theory that no matter where you measure from, you trim the same end so what difference does it make? I've seen shooters who advocate indexing off of the shoulder, claiming the critical measurement is shoulder to end of case neck. I can't see how you can do that and get consistent overall length.

[Stumpkiller]

I've been using a Lyman Universal hand-crank trimmer since 1980 or so. Indexes on the head.

[Ernest T]

I started looking the Lyman Case Trim Express and realized it trims the case without reference to case length. That got me to wondering why, so I did a little web searching and now that I understand the difference, I'm wondering why again.

[Nor Cal Mikie]

Used a RCBS hand crank trimmer THEN a Power Trimmer on my 7.62 and 5.56 brass. After the initial trim. switched to Precision Bushing Bump Dies and don't need to trim anymore. Bump dies won't let the brass grow. 20 to 25 resizes on my BR brass and it still hasn't grown.

[PhilC]

I have been a trim from the base guy forever. Really like my Forster with the 3 in 1 heads, trim and chamfer inside & out in one operation.

[wbm]

Really like my Forster

Me too.

[Iowa Fox]

I think it all depends on what your end result goal is. Trimming for some is no more than making sure the neck doesn't get pinched so it can release the bullet with building pressure when it fired. For some it maximum precision on the target.

Myself and everyone I know trim base to Datum 98% of the time, I use a Wilson trimmer for that. If I'm prepping brass for ar blasting I'll use a trimmer set to trim off the shoulder for production speed only. The short range BR guys and the F class guys are trimming every time they load. They swear you can see the difference on the target.

[Blue Avenger]

I have been a trim from the base guy forever. Really like my Forster with the 3 in 1 heads, trim and chamfer inside & out in one operation.

Have a few of those set up and do not disturb for favorites.
Large jobs get the RCBS universal power trimmer with 3 way heads

[RCE1]

I have a bunch of different trimmers. I think if I had to choose just one, it would be the Wilson with a power adapter. I don't care for the trim systems that use a "universal" collet system to hold the case as I've found it difficult to get each case seated the same, resulting in variation. I'd prefer to hold .002 if possible, but will accept .005. It can be a bit of an art, getting everything the same each time.

[Ernest T]

So the consensus is measuring from the base is the way to go?



Does brass stretch more when new and less as you reload it multiple times?

[Stumpkiller]

It stretches most on the initial firing (in your chamber - which may stretch the case to move the shoulder without changing the overall length much) and stretches less thereafter. Especially if the headspace is tight. But that's the shoulder and not so much the neck/overall. After that initial it is a pretty steady creep. I have some cases/chamberings that don't seem to stretch at all. Depends on the brass, the pressure of the load, and a dozen other variables.

[Dave Hoback]

So the consensus is measuring from the base is the way to go?



Does brass stretch more when new and less as you reload it multiple times?

I say measure it how You achieve the highest consistency. But…, yeah!

Slightly more when new, but also there is a direct correlation to case stretch & pressure. So, more powder, heavier loads will see more stretch.

[charlie b]

Doesn't really matter which way you measure it. What you want to avoid is the case being too long such that the neck 'enters' the throat.

The 'easiest' way to measure that is from the base, but, the shoulder based trimmers will do the job just as well if adjusted correctly.

[Whynot]

After talking to a guy who was telling me that having exact same trim lengths was very important I went out and tested it (not extensive- but enough for my purpose). He said that you would get different bullet seating pressure and different velocities due to different grip on the bullet. Using a bullet seating gauge and then shooting over a chronograph with cases that were exactly the same vs those with some variations (still within min and max) I could never see a repeatable difference.

If you are putting a role crimp on then it is important to be the exact same- but not many people seem to be using a role crimp anymore.

[GrenGuy]

In 1,000 yard Bench Rest Competition:

1. EVERYTHING matters...until it doesn’t

2. Nothing matters...UNTIL IT DOES

[PhilC]

I'll add two things, one, I usually buy brass in same lot# to minimize variables, and two, I always measure actual chamber length with a Sinclair gauge and set trim length to the chamber which does not change for life of that barrel.

Caveat - I only do this for bolt action rifles all others I defer to SAAMI "trim to" specs.

[Balvar24]

I use the Lee case trimmer which uses the case base to set the length of the case. I like it because its easy and repeatable, but I've seen and read some things that say that's not the best way to trim a case. Any thoughts about measuring from the shoulder?

I chuck mine up in an electric screwdriver to make it a little quicker. Drill spins too fast for me.

[Ernest T]

Thanks for the replies.

I'm on the 4th reload of my Lapua 6.5 CM brass. I've trimmed the cases every time I've reloaded them, going on the theory that everything being consistent is better. Now, I'm not cutting much brass so that's why I asked about how much a case stretches when its new vs an older case. I'm definitely not running high pressure in my reloads.

How do you use a case trimmer that measures off the shoulder? My cases have varied very little after firing - in other words, all of them were within a couple thousandths of an inch of the same length. In theory, I could measure a few to figure out how much I want to trim, then set up the cutter to trim that much. I'll end up with cases that are in spec for overall length, but vary in length from each other by that same few thousandths of an inch. Is that a concern? The alternative is to measure each case and adjust the trimmer to cut it to a specific length. That seems super tedious.

[Stumpkiller]

If you are putting a role crimp on then it is important to be the exact same- but not many people seem to be using a role crimp anymore.

I do on straight-walled pistol cartridges and .303 British/7.62x54R. Which are, by coincedence, the only bullets that I use that have cannelures. The latter being a collet crimp - not a roll crimp.

[charlie b]

Everything is really based on the shoulder to base measurement. This is dictated by the headspace in the rifle. You set your resize die based on that headspace. Trimming the neck is only to keep it from hitting the end of the chamber. A little shorter is not the end of the world, but, too long and it will jam the neck in the throat and 'crimp' the bullet. Extreme cases cause big pressure spikes.

Since the headspace is based on base to shoulder measurement, then the simplest case length measurement is base to end of neck. As long as your cases are prepared the same, measuring/trimming based on the shoulder will get the same results as measuring/trimming based on the case base.

Bottom line. Set your trimmer of choice so the neck does not enter the throat. Do it the same for every cartridge case. Doesn't really matter how you accomplish that.

[ramon]

I use the lee trimmer for most of mine. Also have the forster trimmer for the ones that the case length gauge is not available.