505 Gibbs cast bullet loads with SR4759?

[SilverBow]

Hi folks,

I'm in the process of creating my first 505 Gibbs reloads, and I'm interested in finding some relatively light starting loads (say 500gr bullet at 1500fps). I've found some info on AA5744 loads on this site, but unfortunately, I have no local source for this powder:

http://castboolits.gunloads.com/showthread.php?71409-Official-505-Gibbs-Data-Base-and-Image-Thread&p=1005306&viewfull=1#post1005306

My fallback is to use IMR Trail Boss and follow Hodgdon's technical notes on how to determine safe starting loads based on case capacity. However, I also have a large quantity of SR4759 --- having no prior experience with light cast loads, especially in large cases, is there any chance that SR4759 could be appropriate/safe for use in 500gr 505 Gibbs load?

If so, has anyone used it, or know where I can find published loading data? None of my reloading books cover the 505 Gibbs. Is there any "rule of thumb" that can be used for determining a starting load like there exists for Trail Boss?

Any pointers are very much appreciated!

[Nobade]

I have found 4759 to be fairly similar to 5744, and use the same data for both to get started. 50gr. of 5744 will do about 1500 fps with a 500 in that rifle using a 22 inch barrel, and make 15,000 psi. This is very much on the low end of where that powder burns properly and will leave a lot of unburnt powder in the barrel. I would use the same load of 4759 and shoot over a chronograph to get the speed you want. Since that's only about a 40% fill you might try some pillow stuffing to hold to powder next to the primer and possibly get smaller velocity variations.

Another powder to try, which would give a better burn, is Blue Dot. 40gr. of that will also give 1500 fps and a much cleaner burn. You can't go as far on the top end with that powder but it will work better for these very light loads.