Most semi-auto .17 HMR's were .22 LR or .22 WMR rifles reconfigured to shoot the .17 HMR. Thus the bolt, etc. were not designed for the pressures of the cartridge.
Bill Alexander went the other way, and started with a rifle designed for a centerfire cartridge, and then built a completely new system for the .17.
I was privy to the design almost from day one, when I saw the earliest prototype drawings on the board on a visit to AA.
There were teething problems, of course, and it didn't like some of the .17 ammo, but I ran one of the prototypes for months, and the only real issue I had was polymer mag issues. Those have been addressed with a change in the composite used for the mags.
HOWEVER....The .17 is a descendent of the .22 LR and the .22 WMR, and the powders and primer used are noticeably dirty. That litte tiny bore can get fouled fairly easily, and it does. You can't run 1000 rounds a day and expect to function, it needs to be swabbed down and have a brush run through the bore occasionally.
I had LOTS of friends get a chance to shoot it and every single one of them would, inevitably, be giggling like a school girl by the 10th shot in the mag. It is honestly one of the most fun guns to shoot I've ever run.
The protoype I ran was sub MOA out to 100 yards with 17 grain ammo, and MOA with heavier stuff.
I've talked to several owners in the Pacific Northwest, and as soon as I ask about it, they start smiling. None of them are willing to consider selling or sending it back.
The only issue with current production is that there isn't enough of them. The backorder list is long!