Wondering if anyone had used the Pachmayr flush-mount sling swivel system? Pros and cons?

Pachmayr Flush Mount Swivels

Have had them on a SA Ruger 77 for many years. They are unobtrusive and work as advertised. I like them.

Used them for over 20 years and have had no problems. Easy to use.

+3 ... Had them installed on the first custom rifle I had built about 15 years ago. Still have the rifle. Work as advertised. No issues.

Can I swap factory studs for these without much improvisation? Are the holes/threads the same?

Have to drill it out. They're a good bit larger diameter than standard. Have them on a b78 single shot and the millet version comes standard on steyr sbs's. Have three of those presently, I like them. Switch slings between those quickly and don't have to worry about them coming loose.

It is probably a good idea to have them installed by a gunsmith with the proper drilling fixture. The larger diameter hole required can be tricky to center and if not centered can cause a splinter to be pulled up by the threads. It's not impossible to do it if you are proficient with hand tools, just measure twice and drill once.

Agree. At a minimum, use a drill press and clamping fixture to keep the hole square to the work piece and prevent drift. Also, I believe there may be a special tool or insert for driving them into the stock. Unless you are going to do a number of stocks, this is one of those places where you are probably money ahead just to pay to have it done. JMO...