Help loading for a 416/375 Ultra Mag

[Hunterj50]

I recently had a wildcat made up by necking up a 375 RUM to 416 cal. This is almost identical to a 416 Dakota. I am interested in casting lead bullets for this and am considering a 400 gr. of some configuration from Mountain Molds.

After this conversion was in the works I noticed reading in the Hornady #6 Manual a caution not to use reduced loads in the 375 RUM as hang fires could result from the use of slow burning powders. Since I would be using lower charges of faster burning powders looking for 1500-1800 fps does anyone think this would also be a problem? Is the problem with the large case or the slow powders?

If anyone has any recommendations for load for this cartridge I would appreciate it.

Thanks
Jim

[Bass Ackward]

After this conversion was in the works I noticed reading in the Hornady #6 Manual a caution not to use reduced loads in the 375 RUM as hang fires could result from the use of slow burning powders. Since I would be using lower charges of faster burning powders looking for 1500-1800 fps does anyone think this would also be a problem? Is the problem with the large case or the slow powders? Thanks Jim


Jim,

Welcome to the board. Not much help on the load data although we have guys with that background.

But hangfires can leade to SSE which is a phenom that occurs when low volumes of slower powders are lit in virtually any case design. Low is defined in terms of load density. Obviously, the longer the case design, the more prone is CAN be. There are many ways around this. Hotter primers, drilled out flash holes, fillers, and my personal favorite, more slow powder. :grin:

Yep. Don't be afraid to go way slow on the powder chart and fill that case.

[BruceB]

Howdy,Jim.

I'm loading two cartridges which actually bracket your wildcat's case capacity. One is the .416 Rigby, which is a bit larger, and the other is the .404 Jeffery, for which I make brass by reforming .375 Ultra Mag cases, and which is thus a tad smaller-capacity than your wildcat. The .404 is the parent case for the Ultra Mag series of cartridges.

I've used powders as slow as IMR4831 in both cartridges, and as fast as Unique.

Reduced-velocity loads are NOT a problem in either cartridge, but I am using appropriate charges, powders, and fillers as necessary. REDUCED loads of slow powder can indeed give hangfires and Secondary Explosion Effect as Scrounger mentioned...."reduced" in this application meaning (to me) less than maybe 85% of a normal maximum load for the particular powder. "Slow" powder in these large bores I consider to be the 4350-and-slower types, 4831, etc etc.

For cast bullets, a powder normally considered TOO slow for the bullet weight, case, and bore size can work very well if it can be properly ignited, with compressed charges doing fine, consistent work. I don't go this route very often. IMR 4831 makes excellent FULL-power loads with cast bullets in these calibers, driving my RCBS 365s over 2600 fps in the .416 Rigby (with ZERO "leading").

The other route, and the one I use the most, is smaller charges of faster powder AND A DACRON TUFT FOR FILLING THE EMPTY SPACE. I'm taking my Ruger #1 (the .416 Rigby) hunting in Alberta in two weeks' time, and the load uses that RCBS 365-grain bullet, cast with a pure-lead soft point and harder WW-metal shank, loaded to 2100 fps with 55.0 XMP 5744 and dacron fill. This load is grouping very well at 100 yards, under an inch for five rounds last time out. The extreme velocity spread was only FIVE fps over five rounds, last time I checked.

The 4198s, also with dacron fill, give fine performance in both the .404 and .416, but I haven't really finished my work with it.

Loading cast bullets is an art form which does NOT always follow the same regime as laid out in loading manuals for jacketed bullets. Hang around here for a while, and keep asking questions, and we'll see where it takes you.

Before you order a custom mould, drop me a line with your address and I'll send you some of these RCBS boolits to test....I like the design a great deal, and recommend it highly. I also hope to find that it's a good hunting bullet, with the softpoint added. Also, I have quite a few .416 Barnes X-bullets here if you're interested, several boxes at least, and I'll make ya a good price on them...??

[Hunterj50]

Thanks much for the help here guys. Bruce I would like to try a couple of your RCBS bullets and I am interested in the X-Bullets depending on the price. I will PM you with my address.

While new to this forum I have some experience casting for 8 or 9 calibers. I just have never used a cartridge as large as this one. The biggest I have so far is a 45-70 and a 405 Win. I have Mountain Molds for both of them and they work great.

I have never however used dacron fill and could use some pointers on this procedure. Actually I could use complete instructions from A to Z. Like what is it, where can I get it, how much to use ect???

Thanks again for your help.