Wildcat 358-450 BM - questions/opinions

[jaymark6655]

So I recently moved to IN and they have some crazy caliber restriction.  1.8" max cartridge length and .357 min diameter.  There are a few calibers that one can get a bolt gun converted to, example 358 Hoosier or 358 IDC, but I can't see rechambering one of my existing rifles or buying one just to rechamber it.

Basically I would rather just get another AR15 upper.  There are a few legal AR rounds like the 450 BM, 458 SOCOM, 50 Beowulf and 358 Gremlin.  They all seem like "short range" rounds.  Then I had an idea, what about a 450 Bushmaster necked down to a 358, kind of like the 30 RAR?

My thoughts so far have been try to get it closer to the 1.8 case length rather than the 1.53 of the 30 RAR and use a 30 degree shoulder instead of the 25.  The 30 RAR can take a deer at 400 yards and I would like to push as close to that distance as I can and remain IN legal.  For the rifle - 450 bolt and carrier with a barrel for a 358 gremlin then reamed by a custom made reamer.

Any thoughts, opinions, knowledge, problems that you guys can spot?

[jaymark6655]

What is a good length for the neck since it will be used in an autoloader?
Say using a 200 gr SP, would a case length of 1.8 be too long for a COL of 2.26?
Does necking down a cartridge increase its case lenght or shorten it?
Has someone already done this and am I wasting my time?
Would it be possible to do this with already existing dies and reamers or is it worth the money to get something custom made?

[AWS]

Do just about as much research as you can.  Make some dummy rounds to see how they will fit in the platform you want to use.  I shoot a 22-204, 6mm-204 and a 25-204.  Just about anything can be done, but if someone has already done something close you will be money ahead to follow the leader.

[jaymark6655]

Thanks.  Been doing more research and it looks like 358/25 WSSM is similar.  Cartridge dimensions are really close to what I would end up with.  Only I could see is being able to get the case closer to 1.8 than the 1.62, but that might make it too long for the magazine.  Looks like it will throw a 180 gr sp at 2674 fps with enough energy to take deer out to about 400 yards.  At least with my proposed cartridge, the neck wouldn't be thinned out from increasing the diameter and I might be able to get the velocities needed for a 500 yard deer round.  If it failes I can always go the 358/25 WSSM route, it will be good enough until IN changes their backwards equipment laws.