Re: Model 1898 Gallery Practice Rifles. The first batch produced (maybe 100?) were chambered for .22 Extra Long and have .226" groove diameters. They are hopelessly inaccurate as target rifles and are not much more than curios. If you are going to buy a GPR, either shoot it or slug the barrel before you hand over the money. The later production rifles are rifled and chambered correctly and shoot accurately. You cannot tell from looking at the rifle serial number. The actions were made and numbered and then put into a bin. Assemblers simply picked up the nearest action and went to work.
As an aside, I tried one of the early ones with CCI stingers and it shot OK, as far as Stingers go. Could one be made to handle the .22 WRF or Magnum? Removing & replacing the auxiliary extractor is a lot of work.
Re: Hoffer-Thompson. As I understand the production history, Hoffer (sp?) was the guy who decided to chamber the first GPRs for .22 Extra Long and drew up the specs for the .226 groove diameter. His next bright idea was the Hoffer-Thompson. They too are just curios and totally inoperable without the shell holders. I suppose replacement shell holders could be made easily enough. It would only take money.
If you dig into the Hoffer-Thompson, and especially before you spend a bunch on one, read the comments of Townsend Whelen (The American Rifle, 1918) and Phil Sharpe (The Rifle in America, 1937). Sharpe was known to say rude things and he was at his rudest when he wrote about the H-T.
But if it was not for Hoffer and the Army politicians, we would not have Winder Muskets.