If I had to choose between the two, I would use the 20 ga with the more open choke, or try to borrow a slug gun from a friend who has one.

dig4gold, You wouldn't happen to own a muzzleloader would you? That would solve your problem. If you don't, then I would suggest the 20 gauge as well. My little sister has hunted with a 20 gauge 870 with a slug barrel on it for quite a few years. And the deer we have around here are pretty large bodied and she has dropped them out to 140 yards or so. The past couple of years she has caught the muzzleloader bug so her 870 has been collecting dust. But since she has a slug barrel on it, she has been using saboted slugs. You will be using full bore diameter slugs in that smooth bore 20 so you will have a bit more grain weight to work with. Brenneke slugs should shoot well in it out to around 75 yards with that mod choke.

your better off with rifled slugs than sabots, sabots are designed for rifled barrels or smooth bores with rifled chokes, they will not damage your gun.
RR

Thanks all!! Gonna try and find a variety of rifled slugs and see which my gun likes.

I would retire the 1897 except maybe for light loads of shot and use a more open bore for slugs as has already been said.
I am not a shotgun expert but I do read a lot. In the book "Shooter's Guide to Shotguns" by Gun Digest and written by Terry Wieland shotgun choke is discussed. On page 87 it says "Because bore diameter can vary considerably, simply measuring the diameter at the muzzle will not tell you what choke you have. For example, the nominal diamer for 12-gauge is .729-inch, but it can run as low as .720 or as high as 740. It's all relative. For this reason, the old wives' tale about fitting a dime into the muzzle of a gun to check choke tells yor, as Jack O'Connor wryly put it, only two things: 'You have a dime, and you have a gun.' I would put more trust on what the marking on the barrel by the maker said then the dime test.