Case Trim Length References - Pros and Cons?

[Alexander-M]

When it comes to cartridge case trimming for case length, there are two distinct approaches, and as far as I can tell, both have worked well for the shooters who use them. I am about to change my trimming equipment and procedure, and wondered what are the pros and cons for these two methods.

One method uses the base of the case as the reference to establish the trim length, and the other method uses the shoulder as the reference. Regardless of the equipment used, each method must have its pros and cons. What is your opinion on the pros and cons for each method?

Thank you!

Nando

 

[artbosco]

If you think [every case], is and always will be, identical in length, from the base of the case to the shoulder junction, for a specific cartridge, then index off the shoulder. I don't believe that hypothesis, so I always index off the base of the case.

 

[Patch700]

Apart from the possible ability to speed up the process due to the type of tool used I don't see a real advantage with respect to trimming and using the shoulder as a reference point.. If you have your die set up correctly you can still wind up with variances in shoulder bump unless each piece of brass is of the same hardness and pre-sized dimension.

This would obviously translate into uniformity problems in the length department and although it may not be more than 0.002-0.003" it's still a number that could be held to a tighter tolerance if the base was used as the reference point.

I've had cases that didn't show any signs of being too particular to being uniform in case length.. until I shot those same cases at longer ranges.

 

[BCoates]

I have both types of trimmers. I use a Wilson trimmer for my precision bolt guns. The trim length tolerance is about +/-0.0005". I use WFT trimmers for my AR calibers (.223 and 6.8 SPC) which index off of the shoulder. They are much faster (3-4 seconds/case) but the trim length will vary based on shoulder bump, so +/- 0.0015". I think both methods are very acceptable for my uses. The WFT trimmers are great for high volume, and their trim length variance probably would not show up on paper for my skill level. The only reason I bought the Wilson trimmer is because I can add a cartridge for the cost of a case holder vs. $70 each for the WFT trimmers.

 

[bigedp51]

Nando-AS

I have the “World's Finest Trimmer” (WFT) for trimming .223/5.56 cases for my AR15 rifles for its speed and I use a standard trimmer for everything else. The WTF works great with rifles that throw perfectly good brass away when you pull the trigger. A standard trimmer that trims from the base works great for people with brass OCD that like to to inspect, fondle and drool on the brass after firing that you spent so much time prepping before loading.

An AR15 carbine isn't a bench rest rifle and the WFT works fine for that application and the case lengths only vary a few thousandths. If you want uniformity as you would get from trimming from the base of the case then stick with that method.

I use the following trimming guidelines, if your rifle throws your brass away and it bounces off the concrete shooting bench to the right and then hits the concrete on the ground and then bounces into the gravel its trimmed with the WFT.

If I can eject it slowly into my hand and feel its burning warmth, fondle it, inspect it and take pride in my work it gets trimmed from the base. If you hold your cases for a long time after firing them, and say "My Precious, My Precious " like Gollum in the lord of rings then a WFT isn't for you.

 

[jlow]

You are focusing on the wrong thing.

The thing to keep in mind is accuracy with headspace is much more important that accuracy with neck length. Headspace affects how your round sits in the chamber and how much it rattles around. It affects your case volume which can affect your MV and thus how consistently you sit in your sweet spot.

Conversely, neck length apart from potential safety issues (if it is really long), only affects how much of the neck grip your bullet, and although that is important for consistent neck tension, the slight difference is a small percentage of the neck that grips your bullet.

So focus on getting the proper headspace and once you get there, it really does not matter whether your neck trim index off the case head or the shoulder.

 

[Alexander-M]

Good explanations for your choices. I am inclined to continue using the base as reference.

Thank you for your responses.

Nando