I have a Challenger III, (the Buck Mark before the Buck Mark). It really doesn't like to cycle anything other than round nose bullets. The feed ramp will kick stepped nose bullets high. Other than that, it is the most accurate pistol I own. It points like an extension of my arm. Mine is not for sale.
The older Ruger Government came with a test target showing one hole from the 25 yards. Might be something to consider. I have one of them and found it more accurate and easier to shoot with regular ammo than my S&W 41 which I no longer have, FWIW. JM
As much as I like the Buckmark, one caveat.... Do not dry fire it unless you use dummy rounds. If you plan to dry fire a lot the Ruger is better for that.
As for the Ruger, I would not get a Mark III. They have a fugly loaded chamber indicator and the trigger pull is inferior compared to the Mk II and even Mk I.
The Ruger I like is the Mk II Government Model. I would look for a used one long before buying a Mk III. The only reason to get a Mk III is if you absolutely have to have the version that takes 1911 grip panels.
As mentioned above, yes, I do have a Buckmark. It's a 5.5" Field model. And as Buzzgun notes, yes, I did have it threaded and use it with a suppressor. It's been very reliable, and cycles everything from subsonics to hyper-sonics. My son also has a Buckmark Threaded Camper model. Identical to the standard Camper, except it came factory threaded. Both are very accurate, taking a back seat only to my S&W Model 41.
If you take your Buckmark apart for cleaning on a regular basis, it's not a bad idea to get spares of some of the small parts. I plan to make a small spares kit for my range box. Be aware that when you remove the RH grip panel that small parts will fall out.
In addition to Midwest Gun Works, Brownells and Midway also carry Buckmark parts. A lot of guys are customizing their Buckmarks by replacing some black parts with nickeled parts, like slide release, mag release and safety, etc.
In addition, a little known trick is to flip the existing spring over for a lighter trigger pull. This is called the Heggis Flip. You can google for it if you're interested.
One last thing... Buckmarks have THREE different frames. The standard frame as shown in the photos in the previous post. The UDX models have a slimmed down grip frame that is scalloped with shallow finger grooves. The URX models also have a narrow grip frame, but they have a wrap around rubber grip with finger grooves. Make sure which one you want after trying them, because the grips DO NOT interchange. I prefer the standard since most finger grooves do not fit me, and almost all aftermarket grips are for the standard frame.
I like my Buckmarks, but one thing I will add, is if you are out shooting and you decide to do some minor cleaning kind of be fragile with the extractor
One time I had my damn big fingers in there trying to get a piece of dirt out, and pulled the extractor a little hard and it all fell out, the amazing part was I caught all the pieces
The pi$$er part was when i was putting it back together the wind blew the spring off my shooting bench
We searched for an hour for it even with a magnet, but not to worry Brownells sells them for about $2 each plus $6 postage, so I got two of them so if it ever happens again I won't be about to find the spare