Trailboss in Extra-Large Cartridge

I did one quick look through Lymans Cast book

375 Weatherby

powders listed did not include trail boss

Trail boss is a high pressure powder --- bulky but high pressure

Maybe the case is too big in 375 Weatherby

trail boss does good in smaller / less volume cases
 
I have read that you fill the cast to the base of where the bullet will be, weight that and that is your absolute max.

You should start at about 75% of that amount and start playing around there.

I made up some Unique loads with 270gr cast in a .375h&h last week. I didn't chrony them but 15, 16, 17 and 18gr all work fine. 15 was nice and light and I'm guessing 18 is somewhere in the 1500-1600 range. H&H and Weatherby aren't that different.
 
one thing to remember is that Trail boss is very "position sensitive " where case volume is much bigger than the charge volume. Very erratic combustion/ballistics with powder anywhere but seated close to the primer.
 
pr connection's link is broken, but the formula for trail boss is here: https://www.hodgdon.com/wp-content/uploads/2016/11/trail-boss-reduced-loads-r_p.pdf

As noted in the powder description section, Trail Boss was designed primarily for reduced loads using lead bullets in pistol cartridges. However, Trail Boss offers superb versatility in rifle cartridges producing reduced loads using lead or jacketed bullets. These reduced loads make firing such cartridges as the 300 Winchester Magnum or even the 458 Winchester Magnum pure fun! Listed below we show a few examples of such loads throughout the Reloading Data Center, but the fun doesn't stop there. If you don't see Trail Boss data for your favorite cartridge we have a formula for developing loads for all cartridges and it's simple to follow. This formula may be used in both rifle and pistol applications:

1)Find where the base of the bullet to be loaded is located in the case and make a mark on the outside of the case at this location. Then fill the case to that mark with Trail Boss, pour into the scale pan and weigh. This is your maximum load. Pressures will be below the maximum allowed for this cartridge and perfectly safe to use!
2)Take 70% of this powder charge weight (multiply the maximum load from step 1 by .7), and that is your starting load.
3)Start with this beginning load and work up to your maximum charge, all the while searching for the most accurate reduced load. Once found, the fun begins!
 
Several years ago an author, by the name of Sherman Bell, did an experiment in the Double Gun Journal.

He pressure tested some old large bore rifles. The big bore African elephant hunting (and poaching?) rifles. He put a strain guage on these guns and then ran a bunch of tests with different powders and bullets in the guns.

TrailBoss was good to go in any combination so long as the loads weren't compressed. If he compressed the powder, pressures would skyrocket.

I don't know what bullet you plan to use, but I don't think that TrailBoss would be a bad choice. It's bulky and expensive but you'll have a silly grin on your face after your first range session. I wouldn't try going to slow, just in case you stick a bullet in the bore...
 
I have some loads of TrailBoss in my 458 Lott with 325 FTX bullet on top. Much more pleasant range load or deer load for that matter. Just follow the loadin directions on their website and you should be in business
 
just having some fun said:
Trail boss is a high pressure powder --- bulky but high pressure
Click to expand...


wrong. It generates very low chamber pressure.

28grs, a 100% load density (fill to base of bullet) in a 375 Wby with 270gr Hornady would yield approx 1625 fps @ only 34,000PSI chamber pressure

70% of that would be 19.6grs, 1343 fps @ 22,000 PSI
 
Follow the Hodgdon formula and you will be fine. I am in the process of testing loads with Puff-Lon ballistic filler... will do a post once I get the results in my .458 and 450/400 NE 3"... early reports are that you can load FB Cast to GC Cast velocities.
 
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