Home Forums Reloading Big Game Rifles Case trimmers

Do you experienced hand loaders consider a trimmer that trims to over all length or one that references off the shoulder to be a better way to trim?

this write up is from a bulletin from accurate shooter.com I never heard of it but now that I have I always wondered why I never got a squared case mouth. Don't know how much of difference it makes, though. Not having a squared or concentric shoulder would throw it off too. I would say a good quality die is needed.


Indexing off the Shoulder (Datum Line)
The second method I mentioned, trimming off the shoulder or the datum line of the case, has its pros as well. I have found this to be the quickest of the methods and very accurate as well. After the case has been sized through the die the dimensions (particularly the headspace) of the cases are usually very uniform and exact, this allows the case to be trimmed by indexing off the shoulder. This method can be done very quickly, by hand, or by powering either the case, or the trimmer. You also don’t have to worry about the case heads being out of square with the body using this method. Generally the trimming time is cut in half, and this leads to greater focus on the job, without becoming careless.

Bullet travel/release is directly controlled by the length of the neck. By indexing off of the case head, it follows that you will have varying case neck lengths (in theory). By indexing off of the shoulder, assuming your dies are producing the same shoulder dimensions, it follows that you would be able to control neck length more precisely. (in theory) I know I am getting into minutiae here. It seems as if this would mitigate cases being slightly different in length as the case would be pushed forward by the firing pin, making the bullet travel/time to be identical between each cartridge from the case neck. If a case is trimmed to length by case to mouth measurement, then there would be variation in bullet travel/time between cartridges due to different neck lengths.

Again, I know it is minutiae. Just curious what others thought and if my logic is off.

Bullet travel/release is directly controlled by the length of the neck

Negative.

A good quality rifle and platform and Neck tension along with other variables is. But neck tension is a big part.

I think I may have stated that in an unclear way. What I mean is if a neck is .250" long. The Bullet has to travel .250", being constrained by neck tension, etc. If a neck is .270" long, it must travel further, to escape the neck while being under the same tension.

If you say so

I am not trying to argue, just have a discussion. How does having varying size neck lengths in your reloads not affect bullet/ignition behavior and therefore accuracy.

I am asking because I am trying to determine the best trimming method, if it even matters. The Giraud and Lyman automated trimmers trim based on the shoulder. The Henderson, Lee case gauge, Wilson, and other manual trimmers I have seen trim based on the over all case length. I don't want to waste my money and I want to improve the cases I produce. I have used a Lee case length set up with an adapter made to use the Lyman prep station. It is easy and fast to use, but I notice that even though my cases are the same length, head space may be different and measured neck length may be different.

If you think about it, consistency is key. So if you're always using the same method and using the same measurements to create the next case, you're going to be miles ahead of somebody who is not doing that. Now I guess you could argue that some measurements (case/shoulder) are more accurate than others whether it's shoulder or overall, but at the end of the day I think you'd be real hard pressing just average shooting to find the difference between the two methods so long as either set of test cartridges stayed within predictable production method.

I didn't include this in my earlier reply but, from my understanding, neck length directly reflects neck tension by creating more bullet to case contact. Maybe I am not using the correct terminology, but that is what I was trying to express in my earlier comment.

Very good.

If the OP has a BR quality rifle, some of what he’s trying to do ties in. I would be pretty hard pressed to try and resolve a 1 thou variation of neck length caused tension increase in a average factory rifle.