The 1917 was of course intended to fire jacketed .45ACP bullets. The rifling is very shallow and short of custom sized bullets, accuracy of these guns tends to be far better using jacketed projectiles than "normal" cast. Worth noting that the rifling is so shallow the jacketed bullets do wear the barrel comparatively quickly.
The shallow rifling has nothing to do with the lack of accuracy with these 1917 revolvers and cast/lead bullets.
A standard 1911/45acp bbl with shallow rifling.
3 different cast bullets with the same 4.3gr of clays doing 850fps+ with a 16,00psi+ load.
5-shot groups @ 50ft with those 3 bullets pictured above in that shallow grooved 45acp bbl. All 3 loads have 5 bullets touching, less than 1" groups.
The issue with the 1917 revolvers is how the cut the chambers in the cylinders. A cut away of revolver cylinder, where the case ends you can see a "step" cut in the chamber. That "cut" is the leade of the chamber in the cylinder. One bullet is set out further into the leade increasing accuracy.
At the time they started making the 1917 bbls the tooling was setup for the 45lc/.455" bullets. You never want the leade/throats in a revolver cylinder smaller than the bbl diameter. They ended up cutting the chambers in the cylinders throats that tapered down to .455"
The jacketed ball ammo used had an open exposed lead base. The jacket extends past the lead base creating in effect, a hollow base bullet. The jacketed bullets base will expand filling the oversized throats and bbl's.
What I find interesting with that saami auto-rim spec sheet is that it's asking for a .451" bbl but still uses a .455" throat in the cylinders.
Anyway it's hard to put a .454"/.455" cast/lead bullet in a 45acp case without swaging the bullet down or even getting the round to fit in the chambers from bullet buldge/too fat.
