I am trying to find a proven load for a Chapuis double in 375. I want to use Barnes 300 gr TSX. I have H4381sc, H4350, and Reloader 15 powders on hand. Not looking for other bullets or speed. Just a good load for a double rifle that I can tweak for this gun. Thanks in advance.
Stay away from temperature sensitive RL15. Use modern temperature stable powder.
I have shot 300 gr TSX is three .375 H&H doubles. Double rifles are much like Tolstoy wrote about unhappy families, they are all different in their own way. My loads may but likely will not regulate in your 375 Chaupis. I did however have good results with a 300 TSX, H4350, RP 9 1/2m at 2550 FPS in a Merkel and a Blaser. H4350 and H4831SC are very temperature stable.
Have you clocked your Hornady loads with a chronograph or radar? If not, you do not have a baseline reference. Oh, do NOT believe the velocity that a manufacturer states their ammo archives. "The helicopter is on its way...". Without measuring velocity, one is just throwing mud against the wall hoping something will stick. I use velocity for same bullet weight as a starting reference. Every bullet will shoot differently but one needs to establish a baseline and make incremental adjustments to gather data.
If you do not have a good chronograph, one can buy used Lab Radar cheap now! Everyone wants the new Garmin Xero chronograph.
How well does your rifle regulate with that Hornady ammo? Is it good enough for you? Three inches at 50 yds is good for dangerous game but that will be probably 7 inches or more at 100 yds. I run Trijicon SRO reflex sights on my doubles and have killed out to 150 meters with my Heym 458. Not ideal but when opportunity knocks!
Working out loads for a double is fun but darn frustrating at the same time! Do it by changing one variable at a time! If you want 300 TSX, load four to six rounds with H4350 at published data 2400, 2450, again at 2500, and at 2550. Shoot them at 50 yds allowing barrels to cool between strings.
Record the data for each shot in a log book. Load data, velocity, impact elevation and windage, ie 2.25" high, 3" right.
Shoot each string on a clean target. Transcribe the data onto the target by each shot hole. Save your targets for reference
As your loads increased in velocity did the right and left point of impact come together or drift apart? When you find that sweet spot of load where the TSX produce your desired R-L groups at your desired range, your rifle which is regulated for Hornady ammo, will also "regulate" with your load.
Is is really that simple. You may find your desired result in one range session or 20 times to the range!
Don't forget to shoot your double from sticks or a standing bench, to provide the same opposition to recoil as you will provide when shooting in Africa ...
I hope this helps!
