Seeking advice on reloading.

Up till now I've only loaded black powder in my 450 and 500 BPE rifles, and for those, I've been full length resizing and then belling the mouths before seating paper patched and cast lead bullets.

But for this rifle's first range trip, since I wanted to try smokeless 4198, and I had some already resized and primed cases that snugly accepted a .452 bullet, and this rifles muzzles were tighter than my other 450s, I tried hand seating 452 bullets. These just took a few taps with a soft faced hammer to seat to the cannelure. So no crimp of any kind. And accuracy was good.

My 450 3.25" dies are from CH4D. The full length sizer takes the case mouths down to where a .452" bullet is tight entering. Now my cases fired in this rifle readily accept a .458" bullet -- even looser than the resized cases with .452" I take this to mean the bores are tapered, which would be appropriate for an 1887 rifle. Sound right? (Yes, casts would confirm)

So now the question...and maybe it is two questions...

First, given that the chambers are 0.458/459, is there any reason to not try .458" jacketed bullets? I can do a chamber cast when I get home, but I'm taking this with me on a long road trip west starting Tuesday, and I need to load ammo for that trip and pack, so a bit time crunched.

Second, assuming the kapok filler supports the bullet adequately in previously fired cases while seating, I am thinking I am done with the full length resizing step (as long as I can de-prime these somehow without using the resizing die.) I'd just use the resizer to taper crimp if neck tension is too loose, which it appears to be with 458 bullets and fired cases from this rifle.

I'm thinking to try 300gr 458 bullets with same 4198 charge and filler, given that 452s JHPs were relatively slow and not crossing, and rifle handled .458 LRN/patched well.

Below are the chronograph results from yesterday's shooting:
1) .452 jacketed HPs from Hornady. 300gr, over 44gr IMR4198 and about 3gr kapok fiber. Hand seated/no crimp. Avg velocity 4 shots: 1664fps. Std dev 14.4fps. Great accuracy at 50yds (on bullseye, small group) Not crossing.

2) .452 lead flat points. 300gr. Same powder and filler. Hand seated, no crimp. Avg velocity 5 shots: 1800fps, std dev 37fps, poor accuracy (4-5" group at 50yds). Not crossing, ~2" high.

3) .452, paper patched LRN to .458. 300gr. 110gr 2Fg. Crimped. 1701fps avg velocity. Std dev 6.6fps. Better than #2, but still 3-4" at 50yds. Not crossing.