Trim length, does it make a difference in accuracy???

[Bill Norris]

No, donuts form from sizing. FL sizing.
This is because brass only moves thick toward thin, and FL dies begin their sizing near webs.
This, rolling thickness upward from body to shoulder to neck to your trimmer to your trash can.
And every time that cycle happens your cases change in character.

That's the cool thing about the 40 degree AI chambers. Brass hardly moves towards the shoulders. I have some 260AI brass with 8 firings on them and F/L size bumping shoulders .002 each time with almost zero growth.

 

[Bronsin]

I trim my cases to maintain accuracy. It only makes a difference when I don't.

 

[South Pender]

I like K&M's idea of a pilot that extends through the pilot hole, but I think that there angle is a bit steep for the main chamfer. A while back Redding came out with this.
View attachment 1383629

I'm really late to this discussion, but your mentioning the Redding tool got my attention. Do you have experience with this tool, Boyd? It looks as though it should do a good job, and I imagine that you can set the length of the cut (similarly to the K&M chamfering tool) since the pilot would bear against the case web. And the pilot would probably keep the cutting head pretty square to the case, although it would be nicer if some different-diameter pilots were available to keep everythiing square regardless of caliber. Does the pin work in both small and large flashholes? Finally, Is the 15° angle of the Redding tool the best for easy and uniform seating?

 

[Janson]

To the OP, if your trimmer indexes off of the shoulder, IMO that is the best because the case is knocked forward during the firing process so that the shoulder of the case is in contact with the chamber shoulder and having consistent case length from the chamber shoulder is what counts functionally. All of that can be perfect, but sized cases can vary in their shoulder to head length and when they do, the OAL of perfectly trimmed cases (indexed off the shoulder) will vary by that amount. On the other hand if you use a trimmer that indexes off of the head, the case overall lengths can look really consistent but their functional length in the chamber will vary with the head to shoulder dimension. I have both kinds of trimmers, and if my sizing process is producing consistent shoulder to head dimensions then it does not matter which I use. If I was concerned about having too much variation in shoulder to head dimension, I would either have to sort and do separate die adjustments or anneal.

So all I have is the rcbs trimmer is it a good trimmer are a bad one

 

[David Milisock]

I don’t believe you can shoot the difference. I think it’s important that they aren’t too long and that they are square.

Bart

I would think that being of a uniform length per batch is important. Having a huge difference between the longest and shortest neck length seems like an error waiting to happen.