I've got a copy of Hornady reloading manual dated 1975 and it has load data for the 17-222. Loads were based on a Sako L461 wih a 19.75" bbl @ 1-10" twist. Case were Winchester with Rem 7.5 primers.
It only lists loads using a Hornady 25gn HP but you could extrapolate from there.
Powder -- Velocity
3400fps 3500fps 3600fps 3700fps 3800fps
4198 - 14.9gn 15.6gn 16.2gn 16.9gn (Max)
3031 - 16.2gn 16.9gn 17.6gn 18.3gn (Max)
4320 - 18.3gn 19.6gn 20.9gn 22.2gn (Max)
760 - 22.4gn 23.2gn 24.0gn 24.8gn 25.6gn (Max)
N204 - 22.7gn 23.4gn 24.2gn (Max)
I've recently picked up a custom Martini Cadet chambered in 17-222Rimmed and I'm about to start working out a load for it. I have a small stash of Remington 25gn Core-Lokts that I'd like to run in this rifle. I'll compare the above loads with what you've been running and come up with a load to start with. I won't be pushing the upper limit with the Martini but I'd think I should still be able to get 3600-3700fps without stressing the brass etc.
Nice - I'm looking forward to seeing it. A good friend has a very nice Martini in .222 rimmed. One day I would love to get a falling block action - Martini, Ruger No.1 or a Browning/Miroku 78
The falling blocks are a sweet action to base a fine custom rifle on.
Then again, even in basic factory form, such rifles are well worth the cost to have in your safe. I have a Ruger No1B in 25-06 that was a long, long term desire. Initially I got it to have the chamber lengthened to 257Weatherby Mag, but once I got the rifle and put a few rounds through it in it's factory chambering, it's staying as is!
I've shot a Browning B78 in 22-250 many years ago and loved it. You don't see them very often and when/if they do come up for sale, command bloody high prices. One day, one'll fall my way for the right price. Then all I need to look for is a Farquharson in an interesting chambering without having to sell a kidney and lung for!
So the load I have been using for the .17-222 is 21.2gn of BM1 with the 20gn zmax/vmax/Nosler Varmageddon. Accuracy is terrific and velocity is around 4,200 FPS.
I picked up a bottle of AR2219 for the .20-222 (I bought some loaded rounds from Missed, with one lot being AR2219 in Sako cases - the shoot very very well) and thought I might try it in the .17. A beautiful still day today so tried them right on dusk.
The powder increments I tried were informed by looking at BM1/2219/BM2 loads for the .17 Rem, and extrapolating based on the BM1 and BM2 loads I have already previously tried in the .17-222. The powder increment range I settled on was from 20.8gn up to 21.6gn with 25gn vmax in Lapua cases. Shot very well, but a bit warm with the bolt being sticky. I might try between 20.0 and 20.6gn next time, and also get the Chrony out to see what velocity they are making.