The big problem is....it costs as much to make a good inline ML only barrel as it does to make a SML barrel. So why not get the SAAMI spec barrel for nearly the same price. Just look at the GM catalog and compare the prices. McGowan barrels start at under $300 and a Beragara replacement barrel for T/Cs are not much cheaper and are mass produced. The McGowans are custom built to order for $25 more roughly not including any Smith work that might be needed.

When you get into this market the prices can sky rocket and only a break action becomes an affordable modern style platform. Ive been there and done that with a orginal Contender when barrels were reasonably priced. The Handi Rifle is one of the cheapest ways to get into a strong multi barrel gun through SMI using a $360 Douglas barrel. You can convert a NEF 45/70 for about $150 dollars as another example and the guns are under $500 for a nice one like Busta's NEF 45cal SS Super Slu.

It boils down to...if you wanna play...you gunna pay. Regardless if its a inline ML or SML build. Only the Hawkens type "drop ins" come closer to being cheaper and only when you can get them on sale. GMs custom shop barrels are far from cheap.