Conclusion #1: I’m not going to sniper school

anytime soon.

If you’re not up on this, a while back I got one of the Paco Kelly Acu’rzr tools for modifying .22 rimfire ammo, for both accuracy(in some cases) and to make more effective hollowpoints. For accuracy testing I modified four brands/types of ammo:
Federal bulk-pack 36-grain hollowpoints
Eley Sport 40-grain subsonic
Centurion 40-grain HV
Federal Champion 40-grain HV
You’ll notice below that the Champion isn’t listed in the test results; somehow I walked out without those bags, so I’ll do them later.

The testing was done as follows:
Each target has three diamonds; top left for original ammo, right for sized .223", left bottom for sized .224”.
Fired several shots at a separate target with each rifle to both check zero and warm the barrel.
I had the modified ammo bagged and marked. Fired five original, five .223, five .224, then set that rifle aside and fired the same brand ammo sets with a Remington 512 bolt action.

Here’s the results. First, the Federal HP in the Martini:
Very little difference between factory and modified. You’ll notice one hole between the left diamonds; that was a .223-sized. Odd sound to that shot and it threw WAY left.

In the Remington:
Except for the flyer to the right, big advantage to the .224”. Un-modified, the Remington didn't really like this stuff


Eley Sport, Martini:
The .223 and .224 both gave slightly better groups, but within the margin of “Who’s doing the shooting” error, so can't really say any improvement.

In the Remington:
Shot way low with all three(subsonic, expected some drop but not this much). Factory gave more of a pattern than group, .223 not much better; I’d say the .224 did a bit better, except I have no idea where number 5 went. I'll note that for the .224 group I raised the elevation six clicks to keep it(mostly) on the paper.

Centurion, Martini
You’ll notice no ‘factory’ shots; somehow I walked out without that box(yes, I know I forgot TWO things after all this planning). So I’ll save these and, next time can get to the range I’ll shoot that. I have fired this ammo in the Martini before, and it shot well, but notice that big hole in the .223 target:
Damn. That I’m going to have to test again to make sure it wasn’t a one-time thing, but I don’t think it is. The .224” widened out quite a bit.

In the Remington:
Of the two groups, I think the .224” gave the best result, four nicely together and one outside; worth a re-test.

Conclusions
This is about what I'd expected; changing the bullet diameter by either uniforming it or making it larger would have to have some effect, in at least some ammo. For rifles I can say that if you've got access to one of these and can't find anything that shoots really well, it'd be worth trying the mod to see if it matches a brand up to the piece. Handguns, I'll have to try, but it'll need a proper rest to eliminate as much(of my) human error as possible.

Soon as I have enough jugs saved up I'm going to test the hollowpoint mods and see what they do; I do expect to see some interesting results from that.

One more thing: for this kind of testing the weight, trigger and wide forend of the Martini are wonderful. The only problem with the Remington is the forend is much more rounded, so not quite as stable on the rest; the lighter weight had more effect than I'd really expected, too.