This is a very confuseing topic about 45 colt yes or no . Heres some info i have learned from handleing alot of diffrent antique handguns just trying to shine some light on the subject.
There are a few antique guns that can chamber cycle and shoot 45 LC altered and unaltered Theses are guns that were never original chambered in 45 LC.
a 455 chamber is not deep or long enough to do that however but a 455/476 cal chamberd gun can chamber a full sized 45 colt. if it can cycle the round is another mater.
The only guns ive seen this in is the webley WG armys 455/476 and some cycle and chamber 45 colt unaltered but because the guns were never made in 45 LC if that cartridge just happens to cycle in your gun your Ok as far as antique status goes same with the webley no 4 pryse.
But if your gun is altered to alow a 45 colt to fit by the cylinder being shaved or other forms of altering then its not OK as a antique.
Most WGs wont cycle the 45 colt (rims to thick) but some do alot of guys shoot 45 schofield in theses guns not 45 Colt as trying to explain what i just typed to a CO or Police Officer they would just look at you and say ya right lolooking at a fired 45 colt case in the chamber cant say id blame them its very confuseing

But thats the way the rules on theses guns are, only a very few exist that will chamber and shoot a 45 colt without being altered to do so ive never seen a webley No 4 that would cycle a 45 colt unless it was altered to do so only WGs.
Ive seen a few 455/476 WG armys that let the 45 colt cycle that were not altered but like i said alot will not cycle the 45 LC
And remember a 450 and a 455 chamber is to short even for a 45 schofield only the original 476 chambers will chamber a 45 colt.
If that round cycles or not is another mater can be affected by wear and looseness.
Not saying i know everything but ive handled a few WGs and other guns so just going off my expreience.
Another gun that has a longer cylinder is the COLT DA 1878 in 476 cal. a 476 cal chamber is long enough for 45 colt to chamber, the question is is there enough head space to alow the rim of the thicker rimed 45 colt to cycle past the recoil sheild.
Alot wont let this happen some will.
I think its best to use 45 schofield in guns that cycle 45 colt its just easyer to explain and 45 sch is not on the stupid list.
Just a side note if you have a gun that is 455/476 and it cycles 45 colt and you dont want it to anymore you can add some material to the front face of the cylinder bushing, pushing the cylinder back a few tho can stop the 45 case from cycleing all the way around. Yes it opens up the barrel cylinder gap abit but alot of antique handguns had bigger cylinder to barrel gaps than guns today anyway.,,,