So Al, what’s the purpose of paying for a 3” bag + adapter if you don’t have a rifle with 2 3/4 - 3” fore end instead of buying a a front bag that fits for 90% of your firearms used off of said rest?
The adapter fits virtually every fore end and gives amazing stability to sporter style stocks. Why have a bag that's a compromise for everything you put in it? You have to buy a bag anyway so why not get a 3" and the adapter? Trying to do meaningful testing with a stock that fits in the bag like a saddle on a sow is like pushing a rope...lots of effort and with no repeatable results.
Dr. Mann used a wooden V block with sand bag IIRC. Ever tired that.
They used to start cars with cranks, too.
This 3" bag is what gets used with the adapter. The black bag and top is for 2.25" fore ends and will go about 1/4" each way and still work decently.
Good shootin'. -Al