17 November 2010

How about a Double Set - trigger Underhammer?

Double set-triggers aren’t a common feature in underhammer lock designs, new or old. The fact is that underhammer locks were so simple, with direct engagement of the hammer and trigger, that a double set-trigger was not usually needed to achieve a crisp, light trigger pull.

With a conventional sidelock, the trigger is a separate unit that must make contact with the spur on the sear to release the lock’s tumbler thus allowing the hammer to fall. Because of the “looseness” and tolerance between the trigger and sear there was quite a variation in trigger pulls between guns even of the same design and from the same maker. Achieving a really light, crisp trigger release in the typical sidelock rifle with a single trigger required the skills of an advanced gunsmith. All that equates to added expense to the rifle. Which, of course, spawned the creation of the double set-trigger.

However, when the hammer and trigger are directly connected, as in most underhammer designs, it is much easier to achieve a nice release of the trigger without a double set mechanism.

All that said, I have to admit that double set-triggers still intrigue me and I am guilty, too, of designing them for underhammers that just don’t need them. It’s a dichotomy that plagues me because while the double set mechanism intrigues me with the possibilities of clever design, it also violates my sensibilities regarding an adherence to the KISS principle in underhammers. Unless, of course, maybe I was making another long-range or offhand schuetzen rifle! That would be really cool and the set-trigger would be a real advantage.

One of our readers, Jonathan Bumstead, who is also an underhammer designer, has shared with us his latest creation in which he, too, succumbed to the allure of the two-trigger system. While he hasn’t shown us how he did it, I am really curious because anyone who can make a set-trigger mechanism that will consistently work in such a small space is on to something and I, for one, would like to know more!

Check it out. Remember that clicking on the photos will enlarge them for a close-up view. Just click the Back arrow on your browser to return you to the text.

Hello Roger,

This is the Underhammer rifle that I've been working on. The frame is patterned after the Numrich “H&A” type that my buddy, Marlow Westerbeck, and I make at his shop. The 'lock' is machined as an insert and is fitted into the frame. This design gets me away from using those visible hammer and trigger screws. 

This system has an internal mainspring and uses double set triggers! It also has a hammer with a half-cock position and a fly on its tumbler. I designed the lock as a proof of concept to see if I could fit it within the space allowed by the machined opening in the cylindrical frame. From the front to the rear of the parts, the lock spans 3.5". It gets kind of crowded in there! Normally I lean towards mule ear locks, but have two people to thank for turning my world upside down - Marlow, of course, and Laurie Fenton from NSW Australia. Both of those guys started me looking at underhammers just a little bit differently.

The stock is a maple shotgun set from Tiger Hunt (www.gunstockwood.com). The barrel is .45 caliber and is 32” X 1” and rifled with a 1:56” round ball twist. The trigger guard began as a Hawken style, until I fab'd it into an English-looking piece. The buttplate was also purchased, but was modified to suit my idea. I fit the forearm with a horn cap at each end and made all the other parts, including the wooden bottom rib, in my shop.

The gold bands on the receiver were a shared idea between Marlow and me. It was one of those, "Hey what do you think about this? " asks one, "Well, that's simple enough to do. " says the other, and it went from there. Marlow is the welder, so the bands on the frame are his doing. Basically it amounts to using a lathe parting tool on the raw bar stock and laying in some shallow grooves. He brazed in the grooves with some brass rod and then trued the bar back in the lathe.

While we were brazing on the frame it was heated and the resulting heat-blue really made the brass bands POP. So it was decided that the frame would be heat-blued. The blue finish isn’t very wear-resistant and would benefit from some laquer sealer like that used on case hardened guns. The blue color in the photos is a bit different than what it looks like close up. I also attempted the same treatment on the pipes which produced a nice effect.

The mainspring in this action is flat because there is precious little space inside for a coil spring and strut. If the frame had been machined a bit differently, there might have been a way to use a coiled mainspring. However, on the MK. 2 version of this lock insert, I'll be doing things a bit differently. There still won't be a lot of room, but it should be a more mechanically sound unit. With a little bit of alteration this lock design could possibly be retrofit into other UH rifle designs. I'm working out the details of a flint version as well.

As for the actual lock design, I'm not keeping it a secret, it’s just that the first version is rather crude! Most of the UH locks I build could be considered variations of the Cook or Bacon-style locks. My original design was really worked out by the T.L.A.R. method i.e. That Looks About Right! 

I had a simple idea and sketch, but basically I built it by first making one piece then making the next and fitting them together and so forth in progression. The second version will be made using all the experience (translate that as, "mistakes made") that I gained building the first one.

Thanks for your interest.

All photos copyright by Jonathan Bumstead

Thank you, Jonathan, for sharing another successful build. I don't know about the rest of your readers, but I am really impressed with the creativity of the builders we've showcased, like Jonathan. It's a developing body of great work that, again, I am hoping will be an inspiration to more of you to build your own underhammer rifle. 

There is nothing quite like walking through the woods, or wherever your sanctuary may be, and hunting it with a rifle that you made with your own two hands. When you fill the larder with that rifle, it then holds a very special place in your heart and in your memory. Unless, of course, you're not a hopeless romantic, then it's just another gun.

I suppose that if you're stalking and shooting paper bullseyes the feeling might be similar. Although I have never developed such an affection for one of my target rifles. It just isn't the same as a rifle that you use to make meat. It's just different.

Oh well, it is what it is.



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About Me

Roger Renner

Hi. I've been a student, admirer, and designer/builder of underhammer guns for over 30 years. In that span I've built over 200 semi-custom underhammers exploring the possibilities from the ordinary to the exotic. In 1996 I founded Pacific Rifle Company to explore the market's interest in a high-quality underhammer rifle. Thankfully, that interest was, and still is, there. I sold PRC in 2006 but continue to craft high-end underhammers as I am truly afflicted with underhammeritis - which can be contagious!