FWIW:
With a little testing it's fairly easy to improve the performance of your 357 loads. The brass ,crimp, type of expander used all play a part in how the powder performs. After the brass is dialed in the bullet selection makes huge differences in performance. How far out they're seated into the cylinders, alloy, body length, crimp groove/depth of cannelure all play a role in accuracy and velocity.
Awhile back I decided to do a little testing looking for a sd/hd load for a l-comp 586.
I decided on this bullet and used 8/9bhn pc'd bullets sized to .358" testing both hp & fn versions of the bullet.
I like this bullet because the nose of the bullet reaches out the filling the leade's of the cylinders (bottom bullet is out in the leade).
Cylinder gap looses +/- 10fps for every 1/1000th". Using 38spl's in a 357 cylinder looses 10fps+. If the bullet has to travel/jump to seal the cylinders the load looses fps and more importantly. The short start pressures go do making slower powders burn less efficient.
I used that 2 1/2" bbl'd l-comp 357
2 4" bbl'd 357's (same revolver 2 different bbl's)
3 6" bbl;'d 357's (revolvers)
8" bbl'd 357 (revolver)
10" contender 357 bbl
I used full house loads of 2400 VS MP-300 VS H110
When the testing was done the 2 1/2" bbl performed the best with 2400 producing 1200fps+. The bbl was too short for the MP-300 & H110.
They all performed pretty much the same with the 4" bbl's (1300fps).
The MP-300 & H110 started outperforming the 2400 in the 6" bbl's with both doing 1450fps+ (1400fps with 2400)
The 8" bbl did 1500fps with MP-300 & H110 (1450fps with 2400)
The 10" bbl'd contender did 1600fps+ with MP-300 & H110 ( 1500fps+ with 2400)
I settled on the 14.7gr 2400/170gr bullet for that snubnosed l-comp'd 357 doing 1200fps. Really wasn't too concerned with accuracy, that load easily held 3" @ 50ft.
When you start seeing a lot of unburnt powder, low velocities or fliers in your groups when using slow powders in your 357 loads. It's a tell tail sign of weak brass/poor short start pressures and worst case inconsistent ignition from light springs in the revolvers.
Typical 6-shot groups @ 50ft using junk brass that looked like the puppy played with it for a week before reloading. The tell tail fliers