I will not encourage you to shoot lead through your FB. That being said. I have shot tons of home rolled lead loads throught the FB. I have had excellent groups out to 100yds, and even in our long range shooting here on the ranch, we have shot some stuff (playing) out to 3/400 yds as well with the factory barrel. The after market barrel is wise because it does have a more fully supported chamber area, and is better for using lead bullets and gives you more loads per piece of brass.
Plated and jacketed bullets have all done real well for me out of the FB, the jacketed you can take to faster Vels, than you can the plated.... (understand some of this depends on caliber and what your doing). I say this becuse ina 45acp for example, there is NO NEED to bump up the speed, and plated 45's at 830/850fps have been for me 'very accurate.' Now n my 10mm, I use jacketed or lead, so I can get max vel out of them.
As for acurracy. You will gain a tad with the AB over the FB, but in my excperience, It is not much to write home about. There is a small advantage, yes. But just not that awful much IMO.
If you choose to shoot lead in the FB, i will give you some sound wisdom. Clean that barrel out every 40/50 rounds, and use a bullet with a BHN (hardness) of at least 18/21. 20/21 being the best I've seen for keeping the FB the cleanest, BUT I still srongly suggest you clean every 30/40/50 max shots. Pressure can build very fast, and nasty things can happen. DO NOT let that scare you off using the FB with lead. Just keep watching and keep it real clean and very often. Some guys say.."Man I shot tons through the FB with no cleaning in between.." Great. They will learn one day when the gun blows up !
FB is fine, and has been for me out to 100 yds for deer with a hardcast bullet or a heavy XTP. For "play time in the canyons," when we get frisky and want to "shoot the rock by the log by the stump thing" at long ranges. If you can see it. You can hit it if you know how.....
AB is better for the brass life, and safety issues...
Use jacketed for full power, and plated for plinkers in FB. Even in the AB, do not
load up hot with a plated bullet
. Many do, but there again, one day they may have some big trouble if the jacket trys to shed, besides they (plated) are not that accurate in a full house load anyway, and do not crimp them to much or they mash the bullet, and it is some what deformed to a small degree before it even leaves the barrel.