So I bought a 458, with a 20 inch barrel today....

[Letzhunt]

I wacked 3 1/2" off of my 458 WM+ (3.6" mag box) Winchester Safari. I was getting 2410 fps when it was 24". I am hoping to get around 2300-2350 now out of it at 20 1/2". I am shooting 450 North Fork SS and flat and cup nose solids. I use both TAC powder and A2230. Even if I only get 2275 FPS it will certainly do the job needed at the ranges I will be shooting it. My only fear are the Swarovski scope and walnut stock handling the recoil long term. You should be able to find as great load for that rifle. I think you likely limited on COAL with the magazines it uses. But NEW factory ammo is good. Try Buffalo bore with there 400 Barnes or the 450 Barnes.

 

[Andrew62]

I had the barrels of both my .375H&H and 416 Rigby cut down to 20". At buffalo/elephant ranges, which is what I use these guns for, I cannot see a meaningful reduction in velocity to matter.

 

[hoytcanon]

I have half a dozen big bores with barrels from 18" - 20"... no issues, plenty of power but much handier than a 24" rifle.

 

[Hyde Hunter]

Buffalo Bore has 400 TSX loads at 2650 fps

 

[AZDAVE]

I picked up a 458 takedown with a 20 in barrel last month. Following this thread. Need to find some brass and dies.

 

[illini]

Buffalo Bore has 400 TSX loads at 2650 fps

I ordered a sample pack from Superior Ammunition, 450 northfork, 450 barnes, 45 A frames
I also ordered a box of factory 450 ttsx. Depending on velocity and accuracy the BB 400s maybe something i try.

 

[generalzip]

Find a safe handload that uses the fastest-burning powder, which is normally the powder load with the least amount of grain weight. Then you will suffer the least amount of performance drop from your short barreled rifle.

I’m not sure where this myth originated but it’s just that. A myth. The powder that produces the highest velocity in a 24” barrel will also be the powder that produces the highest velocity in a 20” barrel given the same bullet weight.

That said large bores are much less sensitive to barrel length than smaller bores because the gas has much more volume to expand in a larger bore and the pressure drops faster. 20” is long enough in a 458 win mag. You could probably even drop to 18” with very little velocity loss.

Most suppressors are only rated to 20” like the sico hybrid with this cartridge but you won’t be using one anyway. That should make for a very handy rife.

 

[illini]

Well I was hopping to have an update by now. But it's "in transit" and arriving late according to usps. It left the facility on the 21st and the package has not had another bar code update since, so I'm not sure what's going on. Lost in the dreaded usps system I guess.

 

[illini]

It finally arrived. Long story.
More importantly it looks better in person. It's a full custom. Trigger worked, bedded stock and barrel
Cock on open
Changed from cock on bolt close. Heavy barrel. 9 lbs 10 oz
I might need to add some weight to the butt stock. I'll update velocity reports in a few days.

 

[illini]

450 grain buffalo bore tsx. Box said 2200
My rifle shot it 2160 consistent

 

[illini]

Its Gonna need a scope. I'm am not accurate in the least with the peep.

 

[Rifleman97]

In my experience most chamberings lose very little velocity from shorter barrels, typically 15-25 fps per inch cut from the 17 to 24 inch range. Magnums (by that I mean overbore, NOT just large case capacity. 458 win mag is the opposite of overbore) lose a lot more, in the range of 30-50 fps per inch from 20 down to 16 inches, and when longer than 20 lose/gain more like 20-30 fps per inch.

Being 2” short on a non overbore magnum you’ll probably be within margin of error for box posted velocities, on the low side of the margin but still. I wouldn’t be afraid to hunt with a 16” barrel 458 win mag if the muzzle blast wasn’t so atrocious with such a short barrel lol.