I assume you have not scoped that rifle. If not, 2" groups at 100yds is great! I had a scope on my sporterized M1917 by Remington, and it shot 1/2" 3 shot groups at 100yds. Very accurate rifle, to say the least. Shoots better groups than my Weatherby Vanguard .300 Win Mag, and it is a newer modern style rifle. I worked up a load using Hodgdon's H4350, Speer 165Gr BTSPs and CCI primers in Winchester brass, and the best charge weight I found for my rifle is 58.5Gr. I worked the load from minimum and watched for signs of pressure to be safe, and I recommend you do the same. I took mine to a gunsmith before shooting it, just to be sure as others have suggested. He said it was a little on the loose side. He said not to load it with real hot loads, so I stay away from max loads with it. I didn't need to go to max anyway before the rifle told me when to stop well short of max. The groups were excellent, even with me pulling the trigger.
I wish mine was not sporterized and in original condition as your is. Great rifle. It should give you years of happy shooting.
BTW, the Green book by C. L. Ferris is a good one if you like history in great detail. It has lots of facts in it. Not a pleasure book by any means, but worth the read at any rate! I do recommend it to any M1917 owner. It will tell you what to call your rifle too. It isn't an Enfield, although it is based on the Enfield design.
Good luck and have fun with your rifle. I sure know I am with mine!
Mike