Couple of items - - -
It usually takes a little more powder to get the same velocity from an FMJ bullet, as compared to the same weight of LRN.
Seating and taper crimping should be done in two different operations, with whatever bullet. You CAN get away with doing at the same time using jacketed bullets, as the jacket usually keeps the case mouth from digging in and rolling the lead up ahead of it, and interferring with headspacing. A taper crimp is the only proper way. A roll crimp serves no useful purpose with autopistol cartridges, and is usually harmful. The "rimless" case headspaces on the case mouth, and any degree of roll moves the point of contact. The minimum taper crimp to accomplish stbility merely constricts the case around the bullet and holds it in place.
The only time a roll crimp is of any use on .45 ACP is when the loads are to be fired in a revolver using "moon clips." This doesn't even work well with the single action revolvers fitted with the ACP cylinder, because they do not utilize the clips.
Most cast lead bullets are sized .452", and many FMJ are .451 or .4515. If your expander plug is set to load lead bullets, it may overexpand when using jacketed, and the tightness will not be sufficient. If this is the case, consider two possible cures - - -
a. Adjust the expander so that there is barely enough flare at the mouth to start the bullet. If case tension is still insufficient, you'll probably need to - - -
b. Either turn down the diameter of the expander plug a tiny amount. This may yield a good result.
c. Use another brand of case. Some are of thinner stock than others, and, no matter how well the outside is sized, the interior measurement is simply too great to hold jacketed bullets. Cases headstamped REM-UMC, and plated cases from W-W are notorious for this problem. Speer, Federal, and Star Line cases have thicker walls, hold the jacketed bullets well, and seem to last forever. Same comments apply to old US military brass--It's a hassle to remove the primer crimp, but once fixed, they are very durable.
I once bought several thousand cases from the estate of an old target shooter. Most were unplated REM-UMC, and would not hold FMJ or JHP bullets reliably. My home cast and commercially cast 230 LRN worked fine in these cases, though.
Best,
Johnny
