Seating a bullet and trying to crimp at the same time is like trying to close the garage door as you are driving your car into the garage. The door is going to eventually hit the car. Park the car, then close the garage. Seat the bullet, then crimp it. Especially with lead bullets. You don't want lead shavings gumming stuff up (like dies and guns etc.)
As stated by the other posters, there is a good chance that your RCBS dies are indeed for a .452 bullet. You can see if your dies will load your ammo. (my RCBS dies load my .454 bullets just fine.) If you have a dial caliper, try to measure the thickness of your brass at the case mouth. Also measure your bullet at the base to confirm .454".
I would screw the seating stem down into your seat/crimp die and slowly seat your .454 bullet until the crimp groove just aligns with the case mouth. (Your seat/crimp die will not be screwed tight into your press and you are starting to adjust it.) You should have a bit of a bell in your case from the belling die so it could be hard to gauge the depth of the bullet. Don't seat it too deep. You will still be able to adjust it deeper in another couple of steps.
Once you get the bullet seated it is time to see what the die is going to do to your ammo. Screw the seating stem all the way up. We don't want it pushing on the bullet right now. Set your die about half way into your press and bring the press handle down all the way. You should feel your case go into the die, but should feel no other pressures. Now, with press handle all the way down, screw the die down until you feel resistance. This should be where the die is starting to taper down toward the crimp. As the die is tapering down, the bell in your brass should start to dimenish. Check your ammo to see if bell is still visible. If it is, screw die in about 1/8th to 1/4 turn and pull handle all the way down again. Keep adjusting die down 1/8th to 1/4 turn at a time until bell is gone and case mouth appears straight.
Check alignment of the bullet. You want the case mouth about even with top of crimp groove. You should be able to feel crimp groove with fingernail, but should not see the whole thing. The top .050" or so of your case is going to be rolled into that groove. If bullet is not deep enough, now is the time to screw seating stem back down until it touches the bullet. Screw it down 1/8th to 1/4th of a turn at a time until your bullet is seated as referenced above. Once bullet is properly seated, screw seating stem back up so out of the way.
With a .454 bullet in a 45LC case, you should see a bulge in your case where the base of the bullet sits. This is normal. Measure your ammo now. .454 + 2 times neck dimension is optimum. So if case is .006" thick, then .454 + .012 = .466" would be optimum. If ammo is larger than .466" (example from before) then it is time to start adjusting the seat/crimp die to crimp. Again, turn die down 1/8th to 1/4 turn at a time. You should feel the pressure increasing as you go. You can check ammo diameter periodically to see if die is slowly tapering case down. I adjust the die down 1/8th to 1/4 turn at a time until that case mouth just goes into the crimp groove. DONT go too far. You will bulge the base of your brass. You want a nice even roll that just goes all the way around the case mouth. Set your lock ring on your seat/crimp die. This is your final setting. (seating stem is all the way up, right?)
Measure your ammo again. Still .466" or more? You should be good to go. If you are less than .454 + 2x case mouth thickness, then dies could be swaging the bullet down. The lead in the bullet and the brass does have some elasticity in it. You could be just fine shooting these in your gun. If you need to, most die makers can polish out .002" if you send them in and request it.
I have a Ruger Vacquero and load a Lyman 245 grain .454 bullet in mine. I have RCBS dies and don't have a bit of a problem. I just got a 300 grain mold for my 45/70. I may try to size them down to .454 to see how they shoot in the LC. Lots of other projects going on.
I have 44 Mag and 357 dies also. They come with washers so you can set dies for 44 spec and 38s and use washers between die and press when loading 44 mag and 357. This washer works perfect to put between your set crimp die and the press. I always make a dummy round or use a previous reload to adjust my die the next time I load. I get the 45LC seat/crimp die and the washer and screw into the press. I grab the dummy round or reloaded round and put it in the press. The washer keeps the crimp away from the round. With press handle all the way down, all I have to do is screw the seating stem down until it touches the bullet and I am set for seating bullets. When time to crimp again, screw seating stem all the way up and remove washer. Die is already set to crimp from prior setting.
Hope this helps some.
Steve
