I just got a 375 H&H AI and am starting to gather info on working up loads for it. I will be using 300 Gr TSX's and would like to use RE-15 because I already use it in three other cartridges, (keep it simple). I figured I could possibly get a little more velocity than a slower powder as well. I heard the AI adds about 5% case capacity to the parent cartridge and to adjust the powder weight accordingly. When looking at other loads that people have posted for the 375 AI and then comparing to the loads for the same powder for the 375 I found that people are loading a lot higher than 5%.

Anyone use RE-15 with 300 gr bullets and have a suggestion for a starting and a max load?

Thanks

quote:

I heard the AI adds about 5% case capacity to the parent cartridge and to adjust the powder weight accordingly

A rule of thumb is around 4-5% for an AI. It really depends on the taper of the parent case. A 243 will have far less than 5% a 7x57 will have over 7%. I don't have the capacity of the 375AI but it has a larger taper. The capacity should be real close to the 375WBY (NOT THE 378) since the 375Wby is a blown out 375H&H case with the rounded Wby shoulders. Using the 375Wby I get around 8+% capacity increase.

Simplest way is to use 375WBY load data starting low and working up.

As to the loads posted for various AIs on this board or any other please take them with a grain of salt. The AI case hides pressure signs. People will normally load it until they get uncomfortable with the pressure signs they are seeing. Those are usually far higher than the max listed pressure for the parent.

Key example the 7x57 & 257Roberts all show large gains over posted parent velocities. The pressure for the parents are in the low 50,000s and reloaders are puxhing 65-70000+ with some of their loads. AI will show a small increase from capacity. Most increases I have found from my own work is pressure related.

For the 375Wby Loadtech shows 64-71.3grs of RL15 with a 300 gr. It also shows higher velocity from powders like RL19 and 4350.