New project: Big bore No.1

Ardent

Ardent

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She'll be a .475 Morrison shortly, not a lot of meat left in that No.1S profile barrel though eh? I haven't decided how to load it, 500grs, but at what velocity. Idea is a mild mannered, small base straight wall dangerous game cartridge. It was dreamed up for a shotgun double rifle conversion to keep breech face pressure low, but still provide true dangerous game rifle performance without a giant case, by using modern powders. Have to decide whether to replicate .458 Win but at lower pressure, thanks to more case capacity and a larger bore, or step up towards .458 Lott and accept the recoil as necessary. I'll likely split the difference. Given this is a single shot, I'll explore the spectrum as no need to regulate barrels.

Based on the .45-2.6" Starline "Basic" case blown out straight, final case length 2.5" like the .458 Win.

Angus

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That looks really interesting and an ideal action to use for that cartridge.
Looking forward to more details and range reports, especially load particulars.
Thanks for sharing.
 
Ardent.......did you have it rebored or rebarreled?
I assume you're counting on the greater bullet base dia to make up for the decreased powder capacity. This case with a 2.5" length will have less capacity than the 458 WM and significantly less than the Lott. Have you long-throated it to help overcome these shortfalls? Curious how you will get 458 WM or Lott velocities with less pressure from a case with less capacity. Although you will have a slightly greater expansion ratio due to the .475 bullet do you think it is enough greater to make up for the less case capacity, by using a faster powder?
Not critisizing, my friend..........curiosity is all, as I have played extensively with this and longer cases but never in .475. Is there a reason you decided on the 2.6" case as opposed to the 2 7/8 or the 3 1/4 as either of these would decrease your needed pressure significantly?
 
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Actually the case has about 9% greater capacity than .458 Win Mag (H2O capacity) due to thinner brass, and a larger internal diameter at the same length. A .475 500gr bullet is 8% shorter than a 500gr .458 bullet as well, further boosting capacity, and yep you nailed it being a double and single shot rimmed cartridge I have a long throat in it and won't stuff those 500grs way into the case like the bolt action magazine limited .458 Win & Lott. In the end I'll have as much as 25% more case capacity than a .458 Win Mag I figure by rough math. Could likely even make more with seating out to the max.

Next benefit is it requires 6-7,000 psi less give or take to move a bullet of the same weight in .475 compared to .458 at the same velocity, due to the greater efficiency of pressure working on the larger bullet's base as you point out. I went with the 2.6" case to seize the maximum efficiency I could and burn the least powder possible, piggy backing on the recent very impressive performance gains of the .458 Win Mag with modern powders. Wanted a big bore with the lightest powder charge necessary to keep blast and recoil to a minimum that meets or exceeds .458 Win classic specs, which I consider the base of big bore performance.
 
Ardent said:
Actually the case has about 9% greater capacity than .458 Win Mag (H2O capacity) due to thinner brass, and a larger internal diameter at the same length. A .475 500gr bullet is 8% shorter than a 500gr .458 bullet as well, further boosting capacity, and yep you nailed it being a double and single shot rimmed cartridge I have a long throat in it and won't stuff those 500grs way into the case like the bolt action magazine limited .458 Win & Lott. In the end I'll have as much as 25% more case capacity than a .458 Win Mag I figure by rough math. Could likely even make more with seating out to the max.

Next benefit is it requires 6-7,000 psi less give or take to move a bullet of the same weight in .475 compared to .458 at the same velocity, due to the greater efficiency of pressure working on the larger bullet's base as you point out. I went with the 2.6" case to seize the maximum efficiency I could and burn the least powder possible, piggy backing on the recent very impressive performance gains of the .458 Win Mag with modern powders. Wanted a big bore with the lightest powder charge necessary to keep blast and recoil to a minimum that meets or exceeds .458 Win classic specs, which I consider the base of big bore performance.
Click to expand...


I'm going to trot downstairs and check that out right now, who'da thunk it?


Well that was a bust, all my 458 cases I made into 416 Taylor and all my 45-2.6" I've trimmed to 2.4" for my 45-90........for what it's worth though, those two have identical capacities. The 2.4" is HDS brass and the Taylor is W-W, so extapolating a bit I see your point, it would appear that the 2.5 case would hold at least as much as the 458 and conceivably maybe a little more. I think make of brass would have a lot to do with this as well, but certainly it would appear to have a very smilar capacity.........long throat and bumped to 475.........I'm a believer!!
 
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