I would.

Consistency of density from lot to lot of the same canister grade powders is a joke on a good day. At other times, they might as well not even be the same powder. Any time a component changes, especially when you have to buy a new lot of the same powder you're already using, REDUCE and work back up over a chronograph. Keep in mind that the short cuts that you can get away with in a bolt rifle are a really bad idea in a double.

The consistent best performer in one of my doubles is IMR 4350. With that rifle, all other components being the same except for an old lot of IMR 4350 vs a new lot (I ran out of the old lot and was having to redevelop with new), I have, on the same day, shooting over the same chrono, had to go from 51.5 grains of the old to 56.5 grains of the new to get the exact same velocity and regulation. Each time I have to work up for a new lot of powder in that rifle, a change of 2 to 3 grains, up or down, is NORMAL.

While I've found Reloder 15 to be more consistent between lots, I've always gotten a change when working back up for a new lot, sometimes several grains.

The usual conversion from the original Cordite charge to RL 15 is usually given as 119%. Despite what some have claimed, I have NOT found this to be a starting load, but a very rough guide to a max load. In 15+ years of using it almost exclusively in large bore doubles, I've never been able to reach 119%.

Earlier this year I worked up with RL 15 in a Holland .500/.465. It and the .470 are both 75 Cordite cartridges - thus both are 75 X 119% = 89.25 grains. I loaded four rounds each with 84, 85, 86, 87, and 88 grains with 480 grain Woodleighs. The 84 grain starting load was hotter than I thought it would be. 85 grains was a good, usuable load. 86 grains was spot on standard velocity as adjusted for barrel length (2100 fps; 2150 is standard in 28" barrels, and this rifle had 26"), with dead solid perfect regulation. 87 grains gave 2150 fps - too hot - and crossed at 50 yards. Since the 88s were clearly going to be too hot, I pulled the bullets and dumped the powder. With this particular lot of RL 15, a charge of 89.25 grains would have been a nasty overload.

I've just heard of another large bore nitro double blown to Hell. It isn't worth it. You don't need more than standard velocity as adjusted for your barrel length - it's worked for 100+ years. Work up over a chronograph with powders known to be suitable - and stop when you reach that velocity.