Are there any negative aspects to using a Hornady factory crimp die on .458 Lott handloads (Barnes TSX-FB 500 gr., and Swift A-Frame 500 gr.)?  Both of these bullets seated in new Hornady brass with SIGNIFICANT neck tension.  Even using compressed loads pushing 105% of case capacity (Win 748 powder and also some loads using RL-15), the bullets have not tried to unseat at all.  So, do I crimp for ultra reliability in the field, in case I have to chamber and unchamber rounds multiple times?  And, will I see any increase in chamber pressure after crimping vs. not crimped chamber psi?  - C. Smock

Thought you crimped b/c of the recoil of that monster.

logic says try it both ways and see which is more accurate, which one shows any overpressure signs etc. if it were me and these were for danderous game shooting, i would crimp due to the recoil and compressed load considerations. do not want the bullet moving at all until i light the fuse. jmtcw

Crimp, and make sure that you don’t keep loading fresh rounds on top of rounds in the magazine.

I've pondering doing this myself but always revert to a question that haunts the crimping process- how do you provide a uniform crimp to every round every time. It's just trading the problem from setback worries to over or under crimping worries. Personally I would take the chance and measure rounds for set back or get rid of them if they have gone under too much recoil.

Bullet setback is from the rounds in the magazine subject to repeated recoil and this causing the bullets to slam into the magazine box's front wall, pushing them further into the case.

Setback, in this case, is not from repeated chambering and unchambering.  The vast majority of rifle cartridges headspace off of the shoulder or a belt, so the bullet, unless in contact with the lands, isn't gonna be pushed back.

Topping off and not firing the rounds in the bottom of the mag is the basic underlying problem.  That said, I read, but can't find it right now, that some setback occurs in some cartridges regardless of how much you crimp them. IIRC, the 416 Rigby was one that was particularly prone to setback, regardless of amount of crimp.