45-70 on shotgun action
Sir,
I built a 45-70 on a shotgun action as per the method laid out in Ellis Brown's excellent book, and in the process learned quite a bit of what actions I would use next time. I was fortunate in that I chose a good action for my first one. It came out excellent in every way, and I am very happy with it. I found that there is a hell of a lot more pressure generated when a rifle round fires as compared to a shotgun. I knew this intellectually, but not until I went through the process of building and proofing did I understand what that really meant. The action I used was an old, no name Spanish built 16 gauge hammer gun. It had the double bolt lock-up and the greener style crossbolt common on better European guns. These are items I consider necessary for such a conversion. My action also had side clips, which are cool and look great, but I doubt they add any stiffness to the action as intended. With the double underbolt lockup, and the greener crossbolt, I think almost any action would be sufficient. I would not use a dolls head third bolt, but some other third bolt styles would probably be OK, like the rotary style on the Fox's. But I would not make such a conversion unless there was a third lockup of some sort.
I would not use a 20 gauge frame at all. Too Small. I would probably not do it on a 16 next time, rather go with a 12 gauge action. All it takes is one failure to ruin your day. The firing pin holes really do need to be bushed. Both for safety and more importantly, because typically shotgun firing pins are larger in diameter and the higher pressure rifle primers extrude into the pin holes making the mechanism hard to open. Also this increases the chance of a ruptured primer. The pin on the gun I used was .125 in diameter. I am in the process of bushing it down to .080 now. After I am finished I will post some photos.
The thought that "just about any modern action will be strong enough" is a risky approach. The newer guns are often held together by adhesive, like some of the Beretta O/U the barrels are secured in the monoblock with Locktight. This works OK for shotguns, because there is not that much forward friction of the shot passing through the barrel trying to move the barrel forward. When you squeeze a 45 cal slug through a rifled barrel at 2000 FPS there is a lot of forward force. I am afraid the locktight method may fail under these conditions. Even if it passes proof, what is the fatugue life of these new cyanoacrilate adhesives? Will it fail after a hundred shots? A thousand? There is not enough steel in the monoblock to allow threading, so the whole shebang holds together on the strength of some glue. This worries me. I think a mechanical fastener is a better approach, such as the threaded and soldered assembly Brown shows in his book.
I have two other shotgun actions I am getting ready to start on. One is a Belgian Armaf 12 gauge side by side. The other is a Simpson 12 Guage side by side. They both have the double underbolt locking with greener type crossbolts. They also both feature side clips, although as I said, I do not think this is important. These are both fairly light guns, and I am sure the resulting rifles will be fine. There is not too much sense in going for absolute lightness in a double rifle in my opinion, as a heavier rifle points and steadies better in my opinion, as well as reduced recoil. My next rifle will be in 450 Nitro Express, so that has a lot to do with my thinking on this matter.
I looked at a number of other shotgun actions in my shop. One is about the sweetest pointing shotgun ever, a 12 Ga SxS Batavia side lock. But there are no underlocks at all on this gun, only a cross bolt. I just am not willing to risk all the work involved in this conversion on such a mechanism. I also have an old Remington SxS (1889 model I think) that could be used. It has a double underlock and a dolls head crossbolt. This action would probably be OK for a light cartridge, but it is too heavy an action. Who wants an 11 lb. double unless it is a dangerous game rifle?
So my recommendation based upon experience would be two fold: Get Ellis Browns book and follow his advice regarding action selection, and stick with European actions with the three lock mechanisms, or maybe an American action if it has a really strong lock up. And make sure to bush your firing pins.
There is an article in the double gun journal, volume 20, issue 3, page 59 that is worth reading. The author (Ken Owens) opinion is this conversion is something to stay away from. I disagree, but he makes some valid points all based upon his experience. Seeing photos of guns that blew up is always sobering too...
Another good article is in the latest issue of Machinists Workshop, which is the Nov-Dec 2009 Issue (I think) about converting a modern Berretta O/U into a rifle. This is made with the locktight glued system. It is an excellent article by a great machinist full of tricks and tips worth reading for anyone who is thinking of making a double rifle. I highly recommend this article along with anything else you can find on the subject. This is a big job and a lot depends on doing it right, so get all the advice you can from people who have actually done it.
Good Luck with you new double! Maybe we will meet up over a campfire in Darkest Africa someday!
