School me on neck trimming

[Texas10]

I am having trouble figuring this out, so if anyone has some ideas, experiences and input, please feel free to chime in.

I have noticed that there are basically two types of neck trimmers. Those that reference off the head of cartridge and those that reference off the shoulder.

Which is the better method and why?

[Rob01]

You talking about neck turning or just case trimming for the OAL length of the case?

[WinnieTheBoom]

You talking about neck turning or just case trimming for the OAL length of the case?

Assuming he's talking about neck turning as there's really only one way to trim case overall length.

[Rob01]

Assuming he's talking about neck turning as there's really only one way to trim case overall length.

Not really as there are the old standard units that you strap the case into to trim OAL and then the newer units like girauds and the kind that are chucked into drills that adjust length off the datum line of the shoulder. Both do the same job of trimming to the same OAL for the case but different ways.

[Texas10]

I'm asking about neck trimming, not neck turning. My worlds finest trimmer references off the shoulder and trims the necks to a uniform length, good for consistency. Others reference off the base or head, again good for consistency but unlike the WFT, trim to a cartridge OAL, not just a neck length. I'm trying to understand the difference between the two from a performance standpoint and all I read about is "here is how to do it", but not WHY do it a certain way.

Just curious, that's all and you guys are a wonderful resource of information. I appreciate all your kindness and help in schooling this newby.

[Rob01]

No difference in performance. Just using a different point to get a reference point to trim. You set the length by adjusting either. For a trimmer that references off the shoulder you need to have the brass sized to the same shoulder bump to keep them close to the same. Being off a couple thousandth won't damage accuracy.

[Texas10]

Thanks, Rob01.

So is neck trimming without first FL resizing a waste of time? I shoot a bolt gun and find little or no growth in case length, so I neck size only.

[Rob01]

Yeah I always size, whether just neck or FL/Neck, before trimming so you actually know the OAL of the brass before case trimming so you trim to the proper length.

[Iowa Fox]

I have both style. Trimmers that reference off the Datum and trimmers that reference off the case head. For accuracy loading I always use the Wilson referenced off the head.

[243LPR]

As long as you're between min and max length with the finished product does it really matter?

[FW Conch]

I like the Lee case trimmer better than any of them. Always trims to minimum case length from the base. Never found any reason not to do it this way. JMHO :-)

[Rob01]

As long as you're between min and max length with the finished product does it really matter?

Exactly. When measuring the OAL you still measure it from base of case to case mouth but when trimming you are just using two different points of where to trim from. Doesn't change the OAL in the end. And you can load very accurate ammo doing it either way. Depends if you want to spend a lot of time doing it with a small lathe or if you want to do it quicker with the powered units. If you plan on doing a lot of brass then get the powered units.

[2scars]

I would think that repeatability would be the driving factor, whichever keeps the case length the same over all your prepped cases would be the one I choose. I use the Lee also, because it's easy.

[Rob01]

Sure if you are doing 20 or 50 cases the older lathe styles are fine but try to do 500+ and you will be very happy with power. The power units will get you within .001" and that won't effect accuracy.

[yobuck]

How you go about trimming with regard to which tool or method is an individual call.
How to determine the actual proper case legnth is a different question. Most often the oal legnth
for standard cases is listed. For an exact case legnth for a particular gun a case legnth gauge
can be used. A 30 cal gauge for example can be used with any 30 cal cartridge in any 30 cal gun.
They can be purchased at places like Sinclairs and are very reasonable and easy to use.

[Texas10]

Sure if you are doing 20 or 50 cases the older lathe styles are fine but try to do 500+ and you will be very happy with power. The power units will get you within .001" and that won't effect accuracy.

Exactly, Rob. That's why I bought the WFT. I chuck it into my power drill and I'm done in a few minutes.

But again, I am confused by the shoulder (datum) vs Head measuring points. My WFT does not trim the case to a consistent length, it just standardizes the neck length. The OAL varies. This helps make my case neck tension more consistent. Good for accuracy.

Shoulder bumping on the other hand, and please correct me if I'm wrong, is to minimize case growth over repetitive loadings, a fit and function type of maintenance. But it not just as important that it standardizes case volume?

I'm thinking out loud here, so bear with me. FL sizing done first, helps insure that the case volume is consistent (assuming I've sorted by H20 volume first), and neck trimming helps to keep neck tension and case OAL more consistent, assuming i'm not shooting out of a chamber that requires neck turning?

Bottom line here is that since I don't seem to need to FL size (little case growth), trimming by referencing the shoulder is the best I can do?

[Rob01]

How much does it vary? Shouldn't be more than .001-.002" max. If you are not bumping the shoulder then the datum line should be the same from coming out of the same fired chamber and when you size it references off the same point. That small .002" difference in OAL will not effect accuracy.

FL sizing with a shoulder bump is to make sure the brass chambers without issue. You only bump back .001-002" so as not to over work the brass and lead to early case head failures.

[Texas10]

Thanks, Rob. Even after 10 reload cycles my brass chambers fine. I occasionally check OAL and re-trim necks as necessary but it is mostly to clean up the mouth to make seating the bullet easier. I'll measure some that have 10 cycles on them and report my findings.

The next item I want to explore is annealing. Still trying to shrink the groups.

[yobuck]

There will be case growth as to the legnth, wether you FL resize or not. Each time a case is fired growth takes place.
Some case designs with sharp shoulder angles grow at a slower rate than those with less shoulder angle.
Bumping the shoulder can also vary as to how often its necessary due to shoulder angle. Neck tension, meaning tension on the seated bullet
has no bearing at all on case legnth. 2 totaly seperate issues having no bearing on each other.
For guns used for hunting, the wisest thing for a person to do is to full legnth resize (every) time you load the case.
And a strong argument can be made that its always the wisest thing to do.

[FW Conch]

^ Why? And what is that argument ? ^

Thanks :-) Jim