I think you'll run into trouble (not big trouble because your using cast) at .005. For breech seating, I use .010 short. The cases will grow in length especially shooting fixed and I think .005 isn't enough to last and may even hit the end of the chamber at that length when fired.

I alway make my cases .020 short of the chamber for fixed and I don't think you'll have any trouble, accuracy wise at .030 short.

Since your already resizing the 45/70's, you might start at .010 short and see how long it takes to hit the end of the chamber but, watch it closely.

Frank

Quote:


the cases that I received from Starlight measured 1.990 new. They even state in their catalog that cases may be to short after fireing and if you want correctly sized cases you need to start with 45-70  cases. A real  "what the heck" statement if I ever read one!
They measured about 1.980 once fired.
My rifles chamber measures 2.015  to .018, near as I can measure off of the chamber cast.
45-70 cases formed down to 40-65 measure 2.041 to 2.048.
I trimmed all cases to 2.025 prior to  fire forming,figuring they will shrink about 0.010 in fire forming and leaving me only a couple of thousandths to trim off. 
I also annealed the cases after running them through the full length forming die, before trimming to 2.025.
Since my new cases will only be used in this one rifle, and they will be indexed, I do not plan on ever running them through a  full length sizing  die again.  At most I will run them into a neck sizer, but only to achieve whatever neck tension the rifle prefers. 

I have a lot of fun work to do this winter!
Thank you for your responce. 

My personal thoughts are you might get more consistency, and better accuracy with some slower powders. Bullseye is not the best choice for large rifle cases, and wont give you optimum accuracy. Might have better accuracy (regardless of case length) with 2400, 4759, or Unique.

Interesting. My Starline 40-65 brass measured 2.085 when I got it and, shooting black, neck sizing only, and annealing every couple of firings and after reloading I don't know how many times (a lot), it still measures 2.085.

I would trim to.010 long and just shoot with your load of 3031 with cast, you will get a better fire form. Then neck size and trim to chamber length. That way whatever the brass shrinks when firing the neck sizing will bring back to spec. That's what I do with my 2 40/65's.

Like oneatatime, I've found Starline cases for my 40-65 (which I shoot 3000+ rounds thru each season) to be quite stable in length, although short at around 2.085". On the other hand, I have to trim the Winchester cases at least once from new as they are long when sized down from 45-70. However, they hold considerably more powder and the 65gr of 2F I use for rams and longer distances works great in the Win case and must be too highly compressed to fit well in a Starline.

While your 300gr bullet is likely quite pleasant to shoot on a recoil basis, it is also likely one of the problems in ho-hum accuracy. Suggest you try something longer, like the Saeco 640 or 400gr BACo Money bullet. I've had good luck annealing after every 5th firing , which is once at the start of the season and again mid-season.