[LDBennett]

LurpyGeek said:

".... the brass begins moving backward in the chamber before pressures have subsided enough to be safe, leaving the shoulder, neck and base of the casing unsupported."

That's is exactly why the mass of the bolt and the force of the recoil spring (and the hammer spring too) are a balancing act against the pressures. The timing can be adjusted with those components to assure the bolt is closed long enough so that the remaining pressures will not bulge the case as the bolt opens. So if that timing is not possible (for whatever reason???) then the cartridge is not a good choice for a semi-auto blow back action. Remington apparently found that out as the 597 is a blow back operated semi-auto rifle.

I still stand by my initial premiss that the cartridge is a poor design because it has an unusually high peak pressure that occurs as a fast spike. While some claim to love these two cartridges my preference is still the good old 22LR. The ammo choices are huge with 22LR whereas with the 17HM2 (I know little about the 17HMR) you have CCI/Hornady, Remington, and Eley.

I have, as you indicated, had no trouble with my bolt 17HM2 but while ammo is available today it may not be tomorrow because the popularity of both of these 17 rimfire cartridge is hugely waning. That is the first sign that they will eventually quit making ammo. The cartridges, 17HM2 and 17HMR, were mistakes that we will have to pay for in the end.

This is my opinion and, of course, you can have yours.

LDBennett