Had a bit of time today.

Looking through Modern Reloading at the pressure estimates for 55gr spitzer loads I saw something for IMR 4831
The start and max loads were the same figure, at 39.5 grains.
The pressure was one of the lowest of all the loads at about 46,000 psi, and velocity was listed at something over 3300fps

Seemed interesting, figured I'd give it a try.
Impacts appeared to be touching on the 200 yard steel plate, one small black dot on the white painted square.

This ends up being a full case of powder to the base of the bullet, and I have a couple of cans of this powder on the shelf. We'll see how it goes.

Something about the rifle.
These TC break open rifles can have different headspace between whatever barrels you have. Production rifles - but there's a way to adjust headspace by unscrewing the breech face and shimming behind the block. Of course a handloader can get there with an adjustment of the dies too.

I have fourteen loads through one piece of brass, which I started out by expanding the neck with a .243 expander button then putting it through the adjusted FL die.
I'm set up for about .001"+ headspace and I'm trimming about .001" after each subsequent pass through the loading process.

If I don't go this route I end up with excessive case stretch on the first loading. With this Hornady brass (which I'm not loving) the first shot on brass without the false shoulder on the neck gets me about .010" case stretch.
Subsequent loads with this low pressure load are about .001" growth, but I'll be starting the rest of this brass off with the false shoulder for maximum case life.