Having shot and loaded cast for big bore lever guns for many years, I’d always wanted an accurate .45 caliber bolt gun to load 325 to 550 grain cast bullets in the 1300 to 2200 fps range with at least for me the most interesting being between 1600 to 1800 with the lightest to the heaviest. I didn’t want to have a custom chambered rifle made (458 American would have been a good one), and prefer Mauser controlled feed actions. I settled on a Winchester Super Express in 458 Winchester Magnum and got it late last year. I could have gotten one of the Zastava action 458’s, but I prefer the New Haven Winchesters with their modified pre 64 action and original trigger.
There is some, but not a wealth of information available on the net on loading cast in the 458 Winchester, and what info is available seldom gives all the specifics of the load, especially 100 yard accuracy. Also, enthusiasts keep chiming in on their Ruger No. 1 loads, which in most cases doesn’t translate to a bolt gun, in most cases because of OAL issues. I’d like to keep comments limited to loads for bolt action rifles only, keeping to OAL limitations, and with bullets crimped in their crimping grooves, i.e. with no exposed grease grooves. Perhaps then we can have in one place a decent reference to share our experience with the 458 Win Mag bolt gun.
What I’d like to do is provide information to help the 458 bolt gun shooter understand his rifle, and provide my experience with reloading cast in this caliber. Available 458’s come in two flavors. One are the magnum Mausers most from Zastava and imported over the years by many. The others are standard action length like my Winchester and most other manufacturers. The difference obviously is in the OAL available. Standard length actions have OAL of about 3.4 inches. Magnum Mausers have AOL limitation of about 3.7 inches.
What does this mean? Well, to the jacketed bullet shooter it means a bunch, and to the cast shooter not so much. Let’s look at a 458 Win Mag chamber drawing. Copyright laws won't let me post the image, but you can find and save it here.
Whoa! That chamber looks like a cast bullet shooters worst nightmare. A throat that’s over 1.1 inches long and tapered to boot. Hmmmm, a taper from .469 to groove diameter. One of the first things we learn is to size cast to be over groove diameter and fill the throat. Obviously, that isn’t going to happen. Next we learn to load cast to be a snug fit against the leade, or at least engrave a bore riding nose. Guess that isn’t going to happen either. Looking at the throat diameter it’s pretty clear we can’t cast them that fat. Even with a magnum Mauser action and 3.7 inch OAL it would take a cast bullet with a NOSE 1.2 inches long to get close to the origin of the rifling. With at least one caliber groove riding base, and a bore riding nose, the bullet would have to weight over 700 grains. With a standard action length AOL of 3.4 inches it’s impossible. As an aside, I said earlier that the longer OAL of 3.7 is an advantage to the jacketed shooter and it is, as 500 grain jacketed bullets are over 1.4 inches long and can be easily loaded to be close to the origin of the rifling and gain 0.3 inches of case volume available for powder or pressure reduction. For the cast bullet shooter who has to keep his grease grooves inside the case, it is of no benefit, as a 550 grain cast bullet has a nose of approximately 0.8 inches, giving an OAL of approximately 3.3 inches which fits in a standard length action. Basically, this means that even with the longest realistic bullets we can use, that the bullet will never (almost) touch the throat, and the closest it gets to the origin of the rifling is about 0.3 inches.
One other point. Notice that the twist on the 458 Winchester is 1 in 14. Who came up with that? A twist that fast is not necessary for jacketed bullets much heavier than usually used in the 458. Much more sensible for the bore would be around 1 in 20. A hard jacket on a groove riding bullet 1.4 inches long can take the stress, but it’s a lot to ask of a lead alloy bullet with from around 0.45 to 0.7 of groove riding base and front band, even with a nice bore riding nose. With most of the bullets available, they are completely unsupported leaving the case until they slam into the origin of the rifling.
Does this mean that a 458 Win Mag can’t shoot cast bullets accurately? No, it doesn’t. What it means is that you have to mitigate as best you can all the things that are going against you to give your bullet all the help you can.
These are my conclusions, and I’ll try to support them as best I can based on over 2000 rounds sent downrange to date. All of the bullets I’ve cast and shot are sized 0.460, are gas checked, and lubed with Alox/beeswax. Primers are WLR. All bullets are moderately crimped in the crimping groove with a Lee factory crimp die.
1. Use a harder bullet than you think is necessary for the velocity. The slam into the origin of the rifling and the fast twist requires this, especially the lighter the bullet. Having had 300-350 grain bullets keyhole at Brinell 12 until I got to a harder alloy confirmed this. The gas checked bullets also help with handling the twist. The slowest I’ve shot these has been 1600 fps and shot reliably to about 2100 with Brinell around 15. They should be more accurate with water dropped alloy of Brinell 18. I’ve not done it yet, but next on my list is to use water dropped and heat treated WW and redo the higher velocity testing.
2. Cast as fat as you can and still have room for the case to open up and release the bullet. Look at the chamber drawing. For me, sizing .460 gives me a couple thousands at the case mouth and is .002 over groove diameter. Using your fired brass, this centers things up in the chamber nicely. Don’t know if it is a major contributor to accuracy, but the .460 diameter also centers the bullet in the throat before it enters the origin of the rifling (remember the tapered throat).
3. In every case where there is less than 100% loading density use a filler. There are members that are using shotgun granular fillers with great success. I do not. I’ve been using starch based packing peanuts from Office Depot (kudos to Bullshop) with very good results. To me they are easier to use without having to figure out how much and weigh for every load. The peanuts will put moderate compression on the powder keeping it where it should be. Velocity with and without has shown lower SD in velocity. Accuracy in all cases with is markedly greater with than without. Why? I can’t prove it, but I think that the filler acts as a sabot to help protect the bullet from gas cutting in that cavernous throat and helps center the bullet. Maybe so, maybe not, but it works.
4. Use a longer (yes heavier) bullet with a long bore riding nose. A 550 grain bullet is approximately 1.3 inches long. The bore riding nose of the bullet should then be entering the origin of the rifling while the base is still centered in the case. This is a good thing. Lyman used to make the 460560 which was about 550 grains and had a nice bore riding nose. However, it was designed to be loaded at 3.16 inch OAL. Mountain Molds made one to my design that weighs 550 grains, but has a 0.8 inch bore riding nose for an OAL of 3.3 inches. Remember that the .460 front band is centering the bullet in the throat.
The bullets used for testing are as follows:
You will recognize the first two as one of the group buys from NOE. They also cast the solid nose version of 350 and 425 grains. All of the loads tested used 45R Gator gas checks.
I started by working up light loads. From my 45-70 experience I felt that Unique and 2400 would be the way to go. I chose 2400 because it had worked well with the packing peanut filler and I was going to use them, and I had 8 pounds of 2400 on hand.
The rifle is a Winchester 70 Super Express with control feed with a 22 inch barrel. I did not rebed the action. Both lugs were correctly bedded and the forearm has full length contact. I changed the action screws to allen head to facilitate takedown and putting consistent torque in tightening the screws. The trigger was worked to 4 pounds with no creep. The scope is a Leupold Vari X III 1.5x5 set at 5 power. I should have put a higher power scope on it for accuracy testing. I do not have a baseline on this rifle with jacketed, so I really don’t know what it’s ultimately capable of shooting. All loads were tested at 100 yards shooting from sandbag rest and represent 5 shot groups. All loads were reshot on multiple days to confirm results. All loads were worked up using the range of charges from reputable reloading manuals, and the best results are shown. Velocities listed are from chronograph except where listed as estimated.
These loads can basically be found in Lyman’s Cast Bullet Handbook Third Edition.
1. 325 grain HP GC, 15 Brinell alloy, sized .460, 28 grains 2400 with whole packing peanut, WLR primer, 2.90 inch OAL, velocity 1620 fps. Groups: 0.8, 1.25, 1.07, 0.77
2. 395 grain HP GC, 15 Brinell alloy, sized .460, 28 grains 2400 with whole packing peanut, WLR primer, 2.90 inch OAL, velocity 1560 fps. Groups: 1.8, 2.0, 1.37. 1.67, 1.6
3. 540 grain FP GC, 15 Brinell alloy, sized .460, 28 grains 2400 with whole packing peanut, WLR primer, 3.3 inch OAL, velocity 1320 fps. Groups: 1.5, 1.4, 1.2, 1.3
I was very surprised at these results, not that 2400 was a good powder for light loads, as it is very accurate in a 45-70, but that it would perform this well in a 458 chambered rifle. The first two bullets were designed for use in the 45-70. I originally shot these made of 12 Brinell alloy which works fine at this velocity in 45-70 and other calibers but shot groups around 4 inches at these velocities. I plan on running this series again with water dropped alloy that is giving me a Brinell of about 18 or better. Don’t want to get into oven heat treating, but if harder continues to be better, may ultimately give it a try. Even if this was the best I could do with these bullets and velocities, these loads will do just fine for hunting anything in the US.
1. 325 grain HP GC, 15 Brinell alloy, sized .460, 66 grains IMR 3031 with one third packing peanut, WLR primer, 2.90 inch OAL, velocity 2200 fps. Groups: 2.2, 1.6, 2.3, 2.3, 1.5, 1.5
2. 395 grain HP GC, 15 Brinell alloy, sized .460, 66 grains IMR 3031 with one third packing peanut, WLR primer, 2.90 inch OAL, velocity 2120 fps. Groups: 2.3, 1.5, 2.0, 1.5, 1.9
3. 540 grain FP GC Haven’t shot these yet but have a series loaded using 5744 around 1600 fps, and IMR 3031 around 1900 fps. Also trying a load based on WW 760 velocity yet to be determined.
The first two loads will be repeated with water dropped alloy as I think it will result in an improvement. Again, both of the loads listed would make excellent hunting loads with a trajectory for about a 200 yard maximum point blank range.
I’ll eventually get into heavy load development but please post your results.
As I continue on this project, I’ll continue to post results maybe with pictures of groups, bullets, etc. for comment.
I’d appreciate it if the thread could stay on topic, i.e. cast bullets and loads for 458 Winchester Magnum Bolt Action Rifles with 100 yard 5 shot minimum group reporting. Please, if you want an in depth discussion of how 458 recoil causes brain tumors and other bodily damage, or how lower than recommended charges (severe low loading density) of slow burning powders are dangerous, or other off topic subjects, start another thread.
Maybe we can develop a meaningful reference for those wanting to make their 458 Win Mags fun shooting cast bullet guns.