Thought I might tough out a hot morning at the range to test some loads at higher temps. The ambient temps were 90-93 F in the shade.
The tests were on 458 Hornady factory DGX Super Performance and some new handloads.
Chrono; Oehler 35
Rifle; Browning Safari; 24" ; Leupold 1.5 X 5 VX3 in Talley QD's. I recently had 1 lb added to this gun (mercury and lead) with an additional scope and bases so I think I added close to 2 lbs and it is much more pleasant to shoot at a shade beneath 10 lbs.

1) Hornady DGX 500 gr Super Performance; Avg 2114 FPS; Std Dev was 2 and accuracy very good. I would say about 2125 at the muzzle. This is about 35 FPS faster than the last Hornady 458 heavy Mag I tried.

2) I hand loaded some 500 gr Hornady Interlock some time back with 2230 up to 74 gr with no pressure indictaions so I experimented with some 450 swifts. Hornady brass and Fed 215 primers and a light roll crimp.
450 swift ; 73 gr 2230 Avg 2252 FPS; No signs of high pressure and bolt opened easily
450 Swift ; 74 gr 2230 Avg 2281 FPS; No sign of high pressure and bolt opened easily.
Measurements were taken 12 feet from the muzzle. You might add 10 FPS to the measurements for accurate muzzle velocity.

I may standardize on this last load. a 450 gr bullet at about 2300 FPS with acceptable pressures should be a good buffalo load.

The next load really surprised me. I used Hornady brass (new) Fed 215 primer with a 500 gr Hornady DGS projectile ahead of 73 gr of AA 2230.
3 shots; 2214, 2214, 2217 FPS (WOW; probably 2225 FPS at the muzzle) I expected more like 2170 FPS. The bolt opened easily on all shots (Ambient lower 90's). I actually came home and decapped these hulls and re primed them to feel for friction inserting the primers and it felt about like new brass. Never the less, I am going to back down 1-2 gr with these DGS projectiles. I think 2200 FPS is plenty with this gun and a 500 gr bullet.
There were no shiny marks on the face of the cartridge or cratered primers.

I am more impressed with this cartridge all the time with the AA 2230 powder.BTW. the 500 gr DGS shot 1" below the 2300 FPS swift at 100 yards which is good enough for me.
The Hornady DGX Super performance is not bad factory fodder either at 2125 FPS with a 500 gr bullet!

I really like this Browning Safari Grade!

I suggest anyone beginning 3-4 gr (powder charge) below the loads I mentioned in loading. All guns are different

EZ

Thanks for the report on the .458 win. mag. loads. Always like to see someone out there shooting the 458. I just picked up an older Ruger no. 1 in .458 win. Have had a win. mod 70 for over 25 years and just got the ruger. So my interest has been energized again. Could not find any 2230 last time at the store so got some H335 and so far have been quite pleased. Lots of powders to be tried. Thanks again for the great report.
Kidd

Thanks EZ for the good report.

I finally was able to get a can of 2230. Haven't been able to give it a try to date, but hope to do so soon in my CZ as well as my Ruger No1 in .45-70 IMP. Should work well in my Marlin and H&R .45-70s with heavy bullets as well. I use H335 in all 4 with 500s and 465s, so 2230 might give (hopefully)a bit better response, though I'm in no way dissatisfied with H335.

But thanks again for that data. It looks very good for the .458WM.

Bob

www.bigbores.ca

I finally found a can of Accurate 2460 which supposedly produces a little higher velocity than 2230 with a bit less pressure. Just not sure it is worth spending the money to test some new loads when the 2230 appears to be working OK.
I did load 3 cartidges each last night with 72 gr and 71.5 gr of 2230 to push the 500 DGS and check groups and velocity on Saturday morning. This projectile shot about 50-60 PS faster than the 500 Hor interlocks with the same powder charge so I suspect it creates higher pressure to swage that steel case bullet down the throat.
We will see what the chrono shows in a few days.
Looking for 2150- 2180 FPS and I will be a happy camper.

Thought I would follow up on my original report with with the loads I mentioned in the last report
The temps this morning were identical to the last report ; 90 - 93 F in the shade.
458 Win Mag; 24" barrel : Browning safari grade;
Hornady Brass

1) 500 gr DGS; 71.5 gr Accurate 2230; Fed 215
Lo 2106; Hi 2134; Avg 2120
2) 500 gr DGS; 72 gr Accurate 2230; Fed 215
Lo 2136' Hi 2168; Avg 2147

I thought about trying a different projectile with the 73 gr load posted last week; This time a 500 gr Hornady Interlock. The results were the same as the DGS.

!) 500 gr Interlock;73 gr Accurate 2230; Fed 215
Lo 2211; Hi 2237; Avg 2225

You may note a significant gain in velocity between the 72 to 73 gr load. An average between 2147 and 2225 FPS. These velocities were measured 10' from the muzzle to add about 10 FPS to the listings.
The 73 gr load opened easily and showed no signs of high pressure on the brass. The 72 gr load should be a very safe load even in hi temp areas and still achieves the "magical" 2150 FPS. As always start below these charges as all rifles react differently.

I tested this 73 gr load on 12/9/2009 @ 60-65 F and used Rem brass inlieu of Hornady The average velocity was 2157 FPS. I am curious if the ambient temp being 30 F higher or the brass was more of an issue in this deviation in velocity: 75 FPS change.

I also checked the Hornady 458 Lott factory loads out of my CZ with a 23" barrel. These were 500 gr interbonds,

1) Lo 2262; Hi 2274; Avg 2267; Add 10 FPS for distance from the muzzle to the chrono. A real average of 2277 out of a 23" barrel confirms Hornady's posted data.
BTW; I cannot tell any difference in recoil between the Win Mag and the Lott. My Win Mag may be a bit lighter.

EZ