Mattl, I built a 45/70 double rifle from a 12 ga.sidelock double, about 20 yeatrs ago and did it without any instructions on what to use how to do it ect. The double I used was a high quality Spanish made gun that I was able to buy for a fraction of it's value at the time. It has 2 locking lugs below the barrels and a third fastener at the top end of the breech. The reason I chose this gun to make the rifle on was , # 1 A tight lock up on the barrels to the frame , bushed firing pins removable from the breech,Ejectors, Sidelocks, PRICE PAID, and it;s just great looking.
First of all unless you have a lathe , mill, LOTS of time and patience dont even think of doing this.
It is quite a project to do in a home workshop or anything less than full machine shop equipment to complete. I will give you the basic idea on how I did mine. First I cut the barrels off at about 2 3/4 " from the breech end to come up with a monoblock. Using a Bridgeport mill I bored the two chambers Parallel to each other until they cleaned up. Then I turned two barrel blanks to the length, and taper that I wanted, then turned the breech ends until I was very close to them fitting the monoblock. Then came the patience part, I fit each of the barrels to the monoblock a little at a time using bluing and valve lapping compound until both barrells fit the monoblock the way I wanted and were both the same length and flush at the breech. Then I reamed both of the barrels to basicly zero headspace. I was able to get new undrilled firing pin bushings, drill them for a .070 diameter firing pin, turn new firing pins from drill rod stock heat treat them and fit them so I was happy with the fitting and function of the hammer strike firing pin protrutions. Then to modify the ejectors was a matter of turning pieces of the cut off barrels to silver solder onto the 12 ga. shotgun ejectors to reduce the head diameter to that of the 45/70 case and cut the rim cut.
Then I made a rib, muzzle end piece , sight rib front and rear sights, and a alighnment jig to hold it all together and I silver solderered the barrels to the mono block and soldered the barrel rib muzzle piece , sight rib and everything else with Brownells high force 44 solder. Anyway it ended up shooting probably better than I expected, with the fixed rear sight the right barrel shoots dead on at 50 to 75 yards with every bullet I have shot from it from 300 gr. jacketed to 500 gr. cast and the left barrel shoots 3 inches low but on center if I shoot groups with both barrels ,using 350 gr. Hornadys I get a combined group size of about 4 1/2 at 75 yards. Just using the right barrel I can shoot 1 1/4 " groups at 75 yards. I was going to rechecker the stocks add a English type recoil pad and return it to like new but after the 4 to 5 months I spent on building it I was mentally done with it. I do hunt with it, 2 trips to Canada for Moose and bear and never got a shot !! The only thing I have killed with it was a little 70 lb. Bambi yearling whitetail. I have shot it alot at targets ect. and it is fun to shoot , and I am glad I built it , but at my age and patience now just give me a H & R handi rifle, I have built 5 in wildcats of my own design plus a couple others in 44 Special.
And to my way of thinking they are the best platform to play with.
If you think you got what it takes to build one, ( A double rifle from a shotgun ) go for it.
Jedman
