Trim length tolerance?

[Vegas]

Hey all,

For precision shooters, what is an acceptable range of tolerance for trim length? For example, I trim 223 to 1.75 and my tolerance seems to be in the .003 range or down to 1.747. Using WFT’s btw.

Interested to hear everyone’s thoughts.

Cheers.

[NWPilgrim]

Total neck tension and release of bullet from the neck include several factors. Case neck wall thickness, concentricity and consistent annealing will have more effect than .003" variance in case length, assuming you are not crimping.

I don't get that much variance using WFT so you might check whether the case holder that the shoulder butts up to is getting brass shavings in it. I periodically wipe it clean with a Qtip.

Since the WFT indexes off the shoulder, you want to make sure all the brass being prepped in that batch went through the exact same sizing die and setting.

It is also easy to get going a little to fast and remove the case before it is perfectly trimmed. I try to pause an extra second or two after I think it is done just to make sure the cutter is done.

Also, if you over chamfer or debur you might shorten the neck by a couple of thous.

[gunnerblue]

I have not observed any change in accuracy from variances that small in trim length only. Neck tension and uniform neck wall thickness are more important. I am not a benchrest shooter so my definition of precision stops at 1/2 MOA.

When I use a WFT I get .001” variance in OAL but strive to do each case as consistently as possible, to include speed of the drill which I’ve found to have a big affect.

[bigedp51]

You are full length resizing and will have brass spring back variations in shoulder location. The good news is the ejector and the firing pin push the case forward in the chamber until the case stops when the case shoulder contacts the chambers shoulder.

The WFT trims off the shoulder and the case shoulder will always be in the same position in the chamber and the case mouth will be in the same position every time also.

Meaning the only variations will be the head clearance or the air space between the rear of the case and the bolt face.

Below the variations in the measured OAL will be at the rear of the case and not at the case mouth.



Bottom line the distance from the case shoulder to the case mouth will be the same in the chamber.

[Vegas]

Thanks for the responses! That's given me a couple of things to think about.

[NWPilgrim]

Yeah and that all assumes extremely good chamber and barrel and shooting technique to be able to notice such fine variations in the larger factors, let alone a slight case length variation.

[Vegas]

I'm at that point where I get some inconsistency at times and I'm working to remove as much of that from the load as possible. That way, when the group or long range shot is off, I 100% know it's me rather than wondering if my load was a factor.

[markm]

I've not found trim length to be a critical factor. I almost never trim .308 brass anymore. .223 is done on the giraud. Our riflesmith is a fan of leaving necks a little longer for more neck contact with the bullet. But I honestly don't know there's a difference.

[rjacobs]

ive found the dillon trimmer setup has tolerance of about +-.002 or .003.... nothing I get worked up about and still seems to provide sub MOA accuracy.

[bb223]

+/- .002 on my WFT, no issues as I can't tell the difference between groups of "varied" length brass and brass that is all exactly 1.750"