The “least powerful” .45 in my acquaintance is the .455 Webley, also known by a host of other names I won’t bother to get into. The British service cartridge is rare over here and so I have only fired a small few as originally chambered. I do have a shaved-cylinder MarkVI built at Enfield. It is dimensionally the same as every other I have run into, in that it has undersized cylinder throats. It now chambers .45 Auto-Rim and .45ACP in “moon clips”. However, loads at .45 ACP pressure levels are not safe in the old Webleys. To be sure, these are robust guns, but they were only built up to the level of the comparatively low velocity/low pressure .455.
So there are two challenges, safety and accuracy. Choices include reaming chambers so that the throats match the bores and sizing bullets accordingly, shooting soft lead so that bullets “bump-up”, or not worrying about it and accepting mediocre accuracy.
As this is not a serious defense gun in my arsenal and only something fun and historical to shoot, I have no interest in the expense of reaming the throats of this revolver. I do not use very much really soft alloy in my pots so I also didn’t want to make up a new batch just for low volume shooting in the old beast. I chose the next best option, which is Hornaday’s 255 grain swaged round nose bullet for the .45 Colt.
There is surprisingly little load data for .45AR/ACP Webley loads to be found so I chose Titegroup to experiment with as it works well with light charges. I worked my way up and found two loads that worked well enough for my purposes. I found there was plenty of room in the chambers to seat bullets way out (COAL 1.293). This, I assumed would allow for best accuracy and somewhat lower pressures. Accuracy was initially underwhelming, especially at longer ranges. As powder charges increased, accuracy from 25 yards-in was acceptable. 4.5 grains of Titegroup delivers the same velocity as the original military loads (265 grain LRN/650 fps). It shot reasonably close to the sights and was relatively accurate. 4.8 grains, while it slightly exceeds military specs, showed improvement in accuracy. When I managed sight picture, trigger press, and follow-through successfully (not the world’s best trigger) accuracy was actually quite good.