More 'mixed messages' from me.
Below is a 'spread sheet' copy and paste, sorry they don't transfer well.
The columns are:
Caliber
Bullet type
Bullet weight
Powder (O) indicates 2400 of the old formulation
Powder charge, Xs are not numbers
'S' = Standard CCI primers, 'M' = Magnum CCI primers
Average velocity at 10 feet, number of test rounds vary between loads. Rounded to nearest 1/10th
Weapon the tests were shot in
44 LSWC 240 2400 O XX.0 S 1079.3 S&W M29-2
44 LSWC 240 2400 O XX.0 M 1116.5 S&W M29-2
44 LSWC 240 2400 O XX.1 S 1088.8 S&W M29-2
44 LSWC 240 2400 O XX.1 M 1127.6 S&W M29-2
44 LSWC 240 2400 O XX.2 S 1148.8 S&W M29-2
44 LSWC 240 2400 O XX.2 M 1150.6 S&W M29-2
In my not as scientific as I would like test, I came up with the opinion that 'Magnum' primers will produce marginally higher velocities and little more. (I did enjoy the shooting.)
What I came away with as 'fact', further comparison was fruit less, the component combination was approaching max (sticky extraction) and the bullets used (Missouri Bullet) were hard enough and sized properly for my barrel, I am happy.
And for the 'mixed message', greater velocity WITH mag primers, I use STANDARD primers with (almost) all 2400 powder loads.
Remember, the destination is the goal, getting there is the fun.