I am not a fan of the Adapter. In the 577/450 chamber they can stick. That chamber was designed for a foil cartridge and only has standards of dimension in the head of the chamber for the steel head of the cartridge. The front half of the chamber is not standard. The shoulder is a ogee-two opposing arc, the radius of which is not standard and not precisely located.

When fired the shoulder of the adapter which is flat-straight is forced into the Ogee and sticks. The first time it sticks in a chamber should be the last time it is fired in the chamber.

I have removed several of these, the last which required removal of the barrel. Of course the gun owner had followed the advice of a Shade tree Gunsmith and filled the adapter with lead to try to get the adapter out. I had to put the barrel in the lathe and drill the lead out to get the adapter out.

I have an adapter. 45 ACP in 45/70 I haven't seen it in years. It was tedious to shoot. You have to load twice. Load the cartridge in the adapter, load the adapter in the rifle, fire, unload adapter from the chamber, unload the adapter-sometimes with a stick, repeat. To slow, to boring. It did not shoot well. .452/.454 bullet down .460 groove. Martini, 45 Colt in 577/450. .452/.454 bullet down a .468 or larger throat for about 6 inches to meet a .464 groove.

Analogy's I have used over the years to compare subcaliber adapters-Kissing your sister or showering in a rain coat.