Do you shoot these original barrel?? Do you have a way of magnafluxing or some other form of non destructive proofing them??
I shot the first one, starting with about 40 grains and moved up to about 80. No more than that. The walls on that one were about 1/4 thick and in excellent shape. I cut off 1" from the breech and had it rethreaded for a modern plug and put in by a professional gunsmith here in town. (I still got the rolled eyes look when I told him what I was going to do with it.) No garauntee it will hold he said because it was an old barrel. I told him it was worth a try. That barrel is on the rifle posted in the thread about "pictures of first rifles" The one I referred to as Frankenstein.
The s Beck barrel has only been fired once. the walls on that one are almost 5/16 thick, as it is about a 36-38 cal .375 is "TIGHT". It was fired from a rimless tire with a powder charge measured from a .44 mag casing. No problems. 1st things 1st about old barrels, if it looks as rough as sewer pipe, Don't Do it! If it is just dirty and has minor surface rust and few pits, then, It will probably work out. Have a new breech plug installed and drum or flash hole. Don't over load it and as a rule about 1grain per caliber is a good load. To load a proper charge, use the old method of pouring the powder over the ball in the palm of your hand. That is what the barrel was originally intended to shoot! Not much more than that!