The vent liner is replaced every 100 shots--whenever the hole goes above a certain number .035. The vent liner is basically the little hole that your primer shoots thru to ignite the powder. With a regular breech plug,it is the hole, which is build into the breech plug. With smokeless because of the higher pressure, they wear a breechplug hole out very quickly, hence the work around is a vent liner. Cost from Savage is about $4. You can buy better breech plug liners, Randy Wakeman sells them that last a lot longer. Breech plugs for the Savage are about $28 bucks I think.

Yes, seating a projectile on a charge with Smokeless is a lot different than BP, because BP ignites so well. With smokeless unless it is compressed down, it doen't ignite well. Also the sabot must be tight, now how tight is the question. Well they say 30 lbs of force, that is why I make up my little "goldilocks example", because too loose (like a Parker BE) and the powder will not ignite and too tight (like the TMZ) and the bullet will not go down. Just right is real tight, but not push down with 1 hand tight.
Chap

Consider used then, here is a good company to deal with (Same folk that make the Williams open sights that are on so many guns, they have good fibre optic also for MLers):

http://www.williamsgunsight.com/gunsights/813usedblkpowderguns.htm

and here are the Omegas.That SS with scope looks sweet and in your price range, no FFL required.
They let you look them over for 3 days, and if you don't like them then return it. Oh, C/O means consignment, so they are selling it for a private owner.
Chap

I can not say I am not a smokeless fan because I reload and shoot all kinds of smokeless guns.
But I do believe that someday prehaps not to far in the future that the law makers will get their heads out of that spot where the sun dont shine and establish some sort of national referance of guide lines for the people who have to make laws like they have in some other areas so the state people have some sort of referance thats not pushed in one direction or another by some silly sort of fanitic or an other. If this comes about or any other sort of standarsization does its likely that one of the things that wont be considered any true form of muzzleloading will be smokeless. Not remember this is what I expect might happened not my opinion, if it were not for this I would build my own using a Remington 700 action for a base and a blank for a 50 X110 Dougles barrel with a shortened 44 mag case to hold a large rifle mag primer with a 200gr SW and the right powder I think you could get 2800 fps. Lee
PS If you are going to be a seasonal hunter Take a close look at these two guns if they are in your price range either one is a life timer if you keep on shooting. First is the Triumph Best points in my opinion very easy to clean and take care of properly, light enough that I would not want it any lighter, is very accurate and well built with lifetime service that means something. The KRB7 If you like some weight this might be the one I love the way they shoot but it felt just a bit heavy and a little of on the handling to me but they fit some people quite well they shoot just as well as the Triumph and the Omega and are not bad at all on the cleaning. they are also good conical shooters if you like conicals [I dont have any problem getting 2 inch groups with my Omega or my Triumph which I consider plenty good for conicals as they have a sharp trajectory anyhow but I have to us a wad and some cornmeal which you dont usually have to do with the Knights.
If your budget is a little tight take a look at the Z5 Omega at a lot of the Walmart stores, it is a high quality gun for a decent price ; it is a real shooter very accurate, much like the Triumph with out the break open action and the very neat breach plug which has no blowback and can be removed with fingers.
What ever you chose expect to spend a lot more time at the range than you would getting a cartridge gun ready to hunt with, and the real trick to getting a sabot gun to shoot right is in getting the right fit between the sabot with your bullet of choice in it and the barrel. Lee