Andy...nice choice, congratulations. You are the proud owner of a wildcat cartrdge that is easy to find brass to form and load for. As you well know it takes the same load data for 450 marlin and up to the strongest 45-70 data as well.
If your magazine well is long enough in a repeater bolt action,you can take advantage of bullets being loaded out longer too.
Starting with your question on the 350 Hornaday RN copper jacketed. I found this very accurate in my K98 mauser FN action. With peep sights a Williams Guide sight, 55 grains of IMR 3031, I believe winchester or cci LR primers worked equally well. From a rest at 100 yards easy to get 1.5 to 2 inch groups no problem. Some days a little better if I was up to it.
405 Remington RN copper jacketed also gave equally good results at 100 yards. For a laugh last winter Silverback and I would take turns shooting offhand and could routinely bang the 200 yard gong, of course this is once we worked out the proper holdover.
As far as forming brass if I was you I would choose to convert 458 full lenght of Remington-Peters brand. I have used 7mm Remington Magnum and 300 Winchester Magnum. However because the shoulder angle was so steep brass forming and bullet seating was more difficult and with handloads I am sure played havoc with accuracy.
I believe the greatest problem there was the extra brass in the walls of the case, that as you form from sub calibre to 45 is left behind without inside reaming of the case.
I went the more expensive route and purchased brass forming dies from RCBS.
That gives you the advantage of reaming tools for the inside of the case. And a fully flush uniform length and ability to nicely finish the end.
I feel if you use 458 Win Mag R-P brass, which I would use because you really need the added stiffness of the case for forming/cutting/filing the case mouth smooth.
In other calibres of Winchester brass I personnaly found Winchester brass cases sadly lacking in this department.
Which is fine for them but their priority is not the reloader.
Just use R-P brass, or Weatherby brass( good but$$$)
By the way Norma used to be the brass manufacturer for Weatherby I am unsure if that is true now.
Norma brass, I mean the Norma brass with their headstamp I found to be the first cases to end up with over large primer pockets.
This was a surprize to me but, the facts speak for themselves.
That load that you mentioned for deer I think will do it. But boy it will really rock your world.
If your action is strong, and I notice you did not mention action type. I assume it is a strong modern bolt action but this is my guess only.
Of course you can load it to maximum, and in some cases you could be experimenting with some load out of this world. Be warned though that you MUST have a well stocked rifle. You must have a recoil pad, I mean a GOOD one. And I fully recommend you get a Benilli Mercury Recoil Reducer also.
Any good Gunsmith in Canada can get you one and safely install it. Save your self some time and bother and get the GOOD recoil pad installed at the same time.
By the way have this rifle fully bedded as this will make the rifle stronger, really really really important with these HIGH kickers.
Or you will end up like me and break a really nice walnut stock and end up buying a Boyds laminate stock to replace it.
If you fell you MUST shoot your cannon before all this is done by a good gunsmith, at the very least keep you reloads loaded down to reasonable levels. AND wait and ensure all of the above was done before shooting those "hot as a rocket handloads."
Avoid IMR 4227 and IMR 4198 in hot copper jacketed loads, keep these powders for milder cast loads. They generate way too uncomfortable recoil once you get above 1800-1900 fps.
The best powders I can recommend are, IMR 3031: the old standby and THE 45-70 powder.
Reloader 7 from Alliant, again a very good powder, also easy to meter.
May be your choice for those Dinosaur killing loads.
Bullet choice, 350 Hornadays Perfect....closely followed by 405 Remingtons.
Some people decry this older bullet design and say the 350 beats it for performance
(penetration depth)which I would say is pretty much true. However that 405 Remy bullet has been used often by 45-70 shooters for up to Buffalo to kill.
Often one shot no problem. I imagine alot of thier success is from knowing what velocity to load this to.
Hornaday 300 grain HPs, easily available, not bad pricewise and should kill a deer like a "Hollywood Lightning Strike."
Yes I have shot 500 FMJs out of this rifle. I think loaded to about 1700 fps. Watching Silverback fire this rifle I am sure at full recoil the rifle raised to a 45 degree angle.
It sure rocked that 100 yard gong!
There is many many cast bullet shooters out there with more info than me...
All I can say about that is those Idaho Territory bullets 405 soft and no GC shot ok for plinking.....
Winning load 350 RN 55 grains IMR 3031, 405 SP 53 or 52 grains IMR 3031, these two loads, I did not even have to re/adjust the sights for at 100 yards!
Any H&H Magnum brand based case can be converted but for ease of forming get 458 Winchester Magnum of R-P brand as this is the closest too and best brass for your needs.
Once you approach 2000 fps in any normal bullet weight recoil becomes a limiting factor dependant upon the shooter's ability to withstand recoil, and desire to get better target groups.
Get in the habit of keeping your thumb out of the way when you fire,you WILL know what I mean if you do this with maximum loads!!!
Get used to calling it a cannon cause that what everyone else will refer to it at the range....
Hope this helps...and I know you will enjoy this versatile rifle cartridge.......
