I've shot under 2" the odd time with my Hi Power - when I don't flinch or fly - and in excellent light so I can actually see the sights. This is the same pistol that I really had to have my act together to keep all the shots on target when I first got it; it shotgunned the target, and it took me the longest time and a lot of skullsweat to figure-out what I was doing wrong.
The first thing is, I had to fit the bullet to the bore. It slugs-out to 0.357" so I wanted a 0.358" bullet to feed it; but that bullet-width plus the thickness of the cartridge walls, made the round too fat to chamber. The only bullet I could cast was the Lee 125gr RF; the others weren't quite 0.358" out of the mould. In the end, I had to stop using Winchester brass because it's the best 9mm brass out there - the walls were too thick - and getting a mag-full that didn't have at least one FTF jammed in the chamber was a rare and wonderful thing.
I tried one bullet I'd rejected before; the Lyman 147gr BB 2RF. I love this bullet - the 4-cavity iron mould is delightful to use, and I frequently have perfect bullets from the first pour, but neither of our 9mm's liked that bullet. I started using it again because it mikes-out at ~0.3575", and just that little bit of difference was enough to make it easier to load with fewer FTF's. But very inaccurate; shotgunned the target. Then I realized something (I have no brain - my skull is solid bone, and it takes a long time for realizations to sink-in
- I was getting 2 or 3 keyholes per 10 rounds with that bullet.
Well, why is it keyholing? - because clearly, the pistol is not spinning it fast enough to stabilize in flight, so it topples. Short of ordering a new barrel with a faster twist (and good luck getting it across the border), the only way I could spin it faster was to push it down the barrel faster. So I added a pinch more powder - literally, 0.1 grain - and the pistol immediately started showing-off; that was my 2" (from 20 yds, in bright sunlight) group.
If you are buying your ammo, there's not a lot you can do to improve its performance; I would suggest you try and get it into bright sunlight where your vision is the best it can be, and concentrate on your sight picture. The sights on my 'classic' Hi Power are about as bad as sights can be, with rounded sides front and back (lots of glare off them), adjuster screws that love to back themselves off randomly and a short sight picture because the pistol isn't very big. If you are handloading, try moving your bullets faster (WITHOUT exceeding safe powder loads, natch) or slower (especially if you're getting lead fouling), and experiment with your C.O.A.L. 9mm is a finicky round to reload; attention to detail might yield big results.
Best of luck!
