In my years of building customs guns the lever is the hardest thing to modify and get right. They always seem to be hanging down dangling after thoughts and are unappealing to the eye. Add a rounded edge piece of 2" x 4" as forestock and you have the classic example of an ugly gun.
Frank deHaas showed an H.L. Grisel open loop lever on a Martini his book Mr. Single Shot's Gunsmithing idea book. I though that was cool and it was the first lever mod I ever did. It was also the worst I ever did. I was building field guns for walking around shooting varmints. The little lever sticking out there hooked on every thing, clothing, brush fences-kept popping open. I once talked with Chick Donnelley about this and he was a bit reserved at me criticizing Pete Grisel. Next time I talked to Chick he said he had spoke to Grisel, he had mentioned my comments, and Grisel agreed with me. Humm.
I did a full loop lever one time at a customers request. When the customer came to pick the gun up he wouldn't take it. It look odd and was awkward to operate.
It cost him extra for a different lever. For a loop lever to work on a Martini it almost has to be fit to the shooters hand.
Schuetzen style lever have lots of swirls and hooks, but they are practical for the sport. Combined with ornate stocks they look good.
The fancy Peabody's that had a pistol grip has a short loop around the end of the pistol grip and I think the end of the lever snapped into a catch. I can not remember the last time I held one of those, so can not be be sure.
The 1215 style is very pleasing and the grip angle is very good. That wide tip at the end of the lever provides a wide point for leverage. That wide flat is needed on field guns as the the finger will get sore from opening a small tiny lever end.
The best cure I used for a long time for addressing the lever issue was a round ball. This worked quite well. I would save the cut off bolt handles from Mauser when I welded new handles on. I would cut the ball off and tap it, then screw the ball on.
The picture above is, top a modified Cadet with a ball end. The ball is a bit to big, but works.
Below it is an a period Isaac Hollis sporting Martini with pistol grip and barrel tip lever end.
Sporting Martini's with this type lever tend to be open gripped like this Naughton and Holloway sporter. They have that awkward angle open grip feel that is the bane of the Martini. The 1215 angle is more closed and feels more natural.
I recently acquired a Rawbone sporting Martini that has a horn lever insert.
This insert changes the hand angle to a more natural angle. It feels good. It doesn't look very good, but build a stock to this angle and bend the lever accordingly , this would be a nice lookinf gun
Notice the barrels on these lever ends. They are wider the the lever slight ly, They are barrel shaped-wider in the middle than the ends. If you examine them closely they appear to be lever ends rolled in a barrel. The front face of the lever extend around the outside as if the end was rolled upon the inside of the lever.
Looking back on the one loop lever I did and using what learned from my past experience, if I did a loop lever today, here is what I would do.
First I would make the pistol grip closed-tight and countersunk like the 1215. not open like the sporters. More like the angle made with the lever insert. I would fit the lever loop to the hand. It would be longer inside than the hand, but not a big Hollywood loop. A smaller loop. The front of the loop should not bind the hand in any way. Aesthetically if possible the loop should not be taller than the trigger guard, and only minimally if it must.
If I still had the hands and tools, I think this would be a fun challenge to try to do right