Have the guys on cast bullet forum been any help on your quest for data on the 370 gr CPB?
Why did you choose this weight bullet over a 420 or 440 gr?
kinda not utilizing the potential of a caliber like that in a way.
And I see that you haven't posted on Specialty Pistols yet.

Afternoon MePlat, as always it's a pleasure to get one of your encouraging & uplifting posts. I can't tell you how much it means to me to kinda have you as an "unofficial" mentor.
Sorry I haven't got around to posting on SP yet. I'll try & get right on it.
It wasn't one of my 1st priorities because I had posted both here & at SP looking for data on the 450 when I was still in the pre-purchase stage, & no one had much. Cast bullets was another venue to try. Obviously if you saw my post there you know I have received exactly one response so far.
As to the 370s, they seem like a good compromise of trajectory & power to start playing with. I also intend to try 400(or 405)s when I get the 370s worked out. The 370 seems like a good 200yd bullet for moose & black bear & I think that at close to 2000 fps @ the muzzle it will be fine for brown bear at reasonable ranges. If I can get a load that will do that worked out I'll probably start looking for a 400 gr load that does 18-1900 fps.
Have any load suggestions for me?
Thanks as always...

Vance,
If you ever decide to experiment with some jacketed bullets in the .450, the 350 grain Hornady RN is a good bullet at a great price. I think it would do well on black bear and moose.

VANCE: I was looking on CPB site and didn't see any 370 gr bullets for the 458 cal only for 452 cal.
Do you even have the bullets yet?
I think you are being optimistic on velocity somewhat. Let me tell you why.
1. most data that there is like Speer and Hodgdons are from 24 inch pressure barrels not production rifles.
If in fact you have a 450 barrel 15 inchs long in the rifled portion you can figure at least a 7.5 percent reduction in velocity from a 22 inch barreled rifle. From a pressure barrel 24 inches in length you will loose roughly 50 to 100 fps from pressure barrel velocities to a production barrel the same length. Then going to a 22 inch barrel will loose you maybe 30 to 40 fps more.
Now if you will look at Hodgdons data the 450 is no better than the 45/70 AT SIMILAR PRESSURES. Their data show a 400 gr Speer at 2023 fps from a 24 inch pressure barrel. Deduct 50 to 100 fps and you get 1973 to 1923 fps from a 24 inch production barrel. Deduct 30 to 40 for a 22 inch barrel and you get 1933 at best. Deduct 7.5 percent at least for a fully rifled 15 inch barrel at you get 1788. that is roughly what you would get.
As a control Buffalo Bore 45/70 magnum loads run on the hills of the 450 Marlin pressure wise and my 45/70 barrel will get 1780 with a 430 gr cast BB load over my chrony.
Even if you do get 370 gr bullets you won't gain another 220 fps. wirh anything near a SAAMI load.
I would set a goal of at most 1900 fps with a 370 1800 to 1830 with a 400 and be satisfied.
I know you won't believe me but those are reasonable expectations.

I think MePlat's figures are right on the money.

Thanks MePlat

you may well be right on your velocities. I'm currently getting 1713 fps with 58.5gr of Varget @ 19*, & it looks like max is around 61.0 for a 350 jacket bullet. I'll keep bumping the Varget up until I run out of room or start getting pressure signs (or hit published max). My 58.5 gr load is lightly compressed so I may run out of room 1st. The cast bullets from my 15" barrel are running the same speed they show for 350 Jacketed in an 18.5 inch ported Marlin barrel & theyshow 61.0 getting 1827 there. That's why I want to try H-322 also. In the same barrel they show 1842 with a 405 gr jacketed with 322 & 1960 with a 415 gr cast & Reloader 7 (which is another on my "to try" list).

As far as bullet weight, I didn't have the box in front of me when I posted. They are not 370s, but 365s. If you read my post again, you'll find they are not "CPB" bullets, but "PCB" bullets. Performance Cast, rather than Cast Performance. They are in Oregon & apperently have no website. That's the reason you couldn't find a like weight listed on the CPB website.

If I only get the velocities you mention I can live with that. I'll keep you posted as I go.

Thanks for your input, & trust me, just because I may not enjoy many of your posts doesn't mean I automatically discount your input or opinion.

Thanks for the input Tom.
We were postting at the same time & I missed your responce.

TCscout, I may give those a try if I decide to shoot something other than cast.