I bought a box of hard cast 300 grain bullets. I have a lot of IMR 4227 and SR 4759 powder. My questions concern fillers and velocity.
The Lyman section of my .45/70 One Load book listed loads for cast bullets with many of them requiring Dacron fillers. This book also had the 293 grain lead bullet for 4759 as not requiring a filler but said to use a filler with the 4227. The latest Lyman Manual does not mention fillers at all. Are they no longer being recommended?
Does anyone have any good loads for the Guide Gun using the hard cast 300 grain bullet and these powders? When does leading become a problem? My bullets have no gas checks.
I've got no experience with either powder in this caliber, but do use 2400 for most of my lower velocity loads. Make sure your bullets are sized .459 or greater. No fillers are used or recommended by Lyman currently. Doubt if there are many who use them anymore. I would stay with a velocity well under 1500fps. Try out 1200 to begin with. If no chrony, estimate based on the info given by Lyman. I do not have the info in front of me, but your typical plain based bullet can be sent fast, but he bottom will melt much past 1500fps and destroy your accuracy and increase leading. Leading will also be exacerbated if you have the wrong sizing. Most commercial lead bullets come out at .458. This is TOO small for a Marlin.
I do not like commercially made bevel based bullets. Some have better luck with them than I do, but once I got into casting, the accuracy improved 100 plus percent and leading also became a thing of the past.
In respose to using the two powders for the 300gr. Jacketed, I have no experience. I do use H4198 with good success, and am sure you could at least use the IMR 4227.
When I used IMR4227 (in a 444), the ES of the load was hugh. It was one of the worst loads I had ever tried. Thats not to say the same would be true of this small bullet in a 45-70.