The do sell ramrods for that rifle. Get a good quality one and you will not regret it. As for how far can they stick over the end of the muzzle, well as long as they are not in the way of the muzzle to cause obstructing a projectile being fired there should not be a problem other then the fact they will get really fowled when you shoot.

I have a couple rifles that the end sticks over. Also I have one ramrod that has the T/C fold up T-handle attachment which sticks almost three inches past the end of the muzzle. I have shot the rifle. Personally I would get the ramrod unbreakable kind that fits the rifle you have and then get a range rod extra long. I use a 32" T/C rugged Rod for all the range work and cleaning of muzzleloaders. That extra length sure comes in handly. Then I just use the ramrod that the rifle has for hunting with. The next range rod I get though will have female ends on both ends so I can out the T-handle on the one end, then the bore guide and loading/cleaning jag on the other end....