I have used Fed. LP Mag. primers for blackpowder loads in .45 Long Colt, .45 Schofield and .44-40 when I could get them. The claim is that Magnum primers effect a quicker & cleaner combustion.
At CAS-distances I don't think it matters at all...so I have switched to regular Large Pistol primers.
I save my Magnum primers for dedicated Long Range Lever-action Pistol Caliber ammo.
BPCR-shooters use a newspaper wad or toilet tissue wad over the flash-hole to dampen the ignition sequence when firing bullets that are hand seated, and not crimped in the case. It keeps the bullet from being pushed out of the case by the initial shock of the primer detonating.
If you crimp your .45 Colt and .44 Magnum ammo, a paper wad over the flash-hole will have little purpose.