Underhammer Build - Status Report #3
 

Finished the final "to scale" plan today and double checked trigger, sear, and striker function. Everything will fit OK and looks like it will work.

First real fabrication begins tomorrow. I'll be cutting the breech block out of that 3/4" x 6" x 16" chunk of steel.

Here's the final drawing and parts list.

Looks quite interesting though, cant wait to see the finished product and results. Holding thumbs that it's accurate.

Don't know about that trigger. ;) Maybe you should put a notch at the rearward end of the cocking lever slot to act as a safety. A shroud that is only open at the bottom might be a good idea to cover that nipple area.

I don't know about it either UC. It functions perfectly as a cardboard cutout model. But of course, the model is not under spring pressure. Sear pin engagement and shape will be critical and something I will need to play with after it's built.

Yeah, I'm considering that and two other possible set-ups for a safety. Those adjustments will be easy to make after the build. The problem with a notch is the striker would have to rotate for the cocking rod to drop into the slot. That would require the sear pin engage a differently shaped cavity in the striker rather than a simple round hole. But it's probably doable.

Actually, I plan to have the rear of the forend extend all the way to the breech face with a hole in the bottom to install the cap. I'm hoping I will be able to put a cap on the nipple with my fingers, but may need to use a capper. I dislike cappers for some reason. Maybe I've never had a good one.

Looks like a modified inline,all the underhammers I ever seen or owned had the hammer underneath striking upward. Also it looks like the leverage on the trigger is wrong making for a very difficult trigger.

True, except the barrel is interchangable.

Yep. And until Knight marketed in-lines all of the muzzleloaders we saw had hammers. Playing with something different is fun.

We shall see. The trigger has a mechanical advantage as it's rear rises against the far end of the sear bar. I hope it's enough.

Semi

Because of the size of #11 caps and how easily they can be contaminated... I think the capper (good well built brass capper) ideal is the best most positive to handle them.

They make a very small brass capper, that holds 5-7 caps. That is what i use for hunting.

I think you have started yourself an awesome project. Hope it all comes together for you.

Semi I understand this is your design but maybe the trigger design can be altered a bit to give you some advantage. How about making the end of the sear bar a hook with a mating notch on the hammer/striker? Then, instead of the sear pin you have, you can drill and tap a hole just behind the trigger that would run up to against the rear of the sear bar. Turning this set screw in or out would enable you to adjust the sear engagement. Pressure from the trigger return spring would provide the necessary upward resistance on the sear.

DANG Bronko! You may be old, but you're not entirely useless.

That looks like the way to go. Thanks buddy.

Instead of just a simple hammer notch, make it follow the circumference of the hammer by a bit more than the amount of travel needed for a notched safety to operate. If that were cut true, it would work nicely.

I would also be sure the only place the trigger bar contacts the sear bar is near the aft end. I'm thinking too much contact along those parallel surfaces would make for somewhat erratic function, especially if any debris gets in there. The contact between those two parts could be limited to the facing of the adjustment screw if the screw was mounted inside the trigger bar itself. Access might be a bit of a problem but that could also be a blessing. You could do just a simple hole upward through the guard area to get to the screw.

A small set screw in from the side of the trigger bar to keep the adjustment screw from moving might be a good add. You will probably only adjust that trigger once but it could still be altered later if need be.

Thinking outloud. ;)

ps: you any good at case hardening? ;) And remember... wood burns.

Or you can just have the adjustment screw be a self-locking screw. These do not back out or move on their own.
I think with all these hints on design changes you should call the rifle the "Huntingnet Black Powder Special"

Right on UC. I planned to do that because it would facilitate using a safety notch at the rear of the cocking bar slot.

I tried that with a model. The geometry and mechanics didn't seem to work well and for some reason I don't quite understand required a longer trigger pull. The slide fit worked beautifully. I've considered putting a teflon coating between the two. But they should fit together tight and should slide well with a good polish.

Good suggestion UC. Keep them coming.

Bronko, it keeps eating at me that this design is asking an awful lot from one little spring. I'm all for K.I.S.S. but this might be too much?? Posted before seeing your comments, Semi. Thanks.

That's even better!

Not a bad idea Bronko. I don't usually put a name to a gun, except for "Miss Piggy", my very first build in the early `60s. But this one already seems to have a name associated with my long suffering wife.

I have some Kasenit around here someplace. I've used it before to good effect.

Semi - I'm looking at this design and started laughing to myself. Why? Because when I shoot off the bench, I have a habit of wrapping my 'free arm' around the rear bags. This puts my forearm directly in front of the trigger guard. I can just see myself firing this rifle and getting a flash burn on my forearm or wrist.
I'm not sure what the dimensions of the striker will be but I suggest making the cup of the striker deep enough to prevent such an incident.
I still have a scar on my right wrist from firing a RH flintlock with my free hand too close to the flash pan. Happened a very long time ago when I was young and not too bright. (And don't you dare say now I'm old and not too bright - cause I know that's what you're thinking.)

Leather arm guard from an archery shop? :s2:

OK guys, here's the updated diagram with changes so far. Any other suggestions?

209 primer :D

I was thinking that would be an easy change over just swapping out the nipple for a primer 'cup' and changing the striker to a firing pin. But then I thought more of it and you would have more blow back and no containment system. The #11 cap is much safer.

I've considered a small pistol primer. In fact, I plan to make an extra striker with a pin in the face and a modified niple/primer holder somewhere down the road just to try. The problem is - how do you remove the spent primer? A 209 might work though.

Forget that. Back up a little. ;)

Naw UC. "Somewhere down the road just to try." :wink: