Mainspring "preload" for percussion lock placement, or percussion hammer and nip

[HighUintas]

I don't like making so many posts because I don't want to pester people or monopolize the threads here, but I can't find this discussion anywhere. Neither here or anywhere on the web. So I have to ask.

When laying out a percussion lock on your build print, of course you want to place the lock plate so that it fits the stock design of what you're building. For percussion locks, that can end up being problematic because you want to align the hammer cup with the nipple correctly. That's ok, just heat and bend the hammer.

But, how much "preload" on the mainspring do you want when the hammer cup is resting on the nipple?

With the lock out of the gun and the hammer all the way down, the hammer will stop when the tumbler backside contacts the bridle. You do not want the hammer being stopped by the bridle when shooting as that would damage the bridle. You want the hammer stopped by the nipple and cap.

So, how far down below the top of the nipple do you want the hammer cup to rest if there's no nipple screwed in, or in other words, how much preload of the mainspring do you want or how far away from rest do you want the hammer when it is resting on the nipple?

Does it matter how much as long as you have the hammer hitting the nipple before the tumbler hits the bridle?

[Daryl]

Depending on the geometry of the lock, there is considerable pre-load on the hammer, which is why you need a mainspring vice to remove that spring.
The cap stops the hammer. There should be enough pre-load that the cap is still on the nipple after the gun has been fired.
A spring (or burnt out hole in the nipple) that allows the caps to be fragmented and blown free of the nipple, are dangerous, for your eyes or the person next to you on the firing line.
NEVER pull the trigger of a cocked lock that does not have a nipple in place. Also, never dry-fire the hammer onto a 'bare' nipple as that will peen the top surface of the nipple & could damage the bridle. As well, the mainspring might break out the lock inlet below the lock plate.

[Bob Roller]

The preloading of the mainspring must be enough to keep the hammer on the nipple during the ignition cycle'On a lock  with proper spring/link relation there should be noticeable resistance to the first effort to cock it and affer coming past the half cock,if the lock has a half cock should be very easy.A nipple with a hole that's too big can create a blow back problem as well.
Bob Roller

[whetrock]

So, if I can paraphrase, Bob, I think your point is that the hammer pressure on the nipple needs to be sufficient to hold the spent cap on the nipple and not allow blowback to knock the cap off the nipple. And the amount of pressure required for that will depend in part on the size of the hole in the nipple (and perhaps on the load, as well).

So, can you recommend an effective range, stated in pounds? This would be something measurable with a small spring scale. When you were building locks did you measure things like that with a gauge or scale, or just by how it felt under your thumb?

[Bob Roller]

I compared my preloading with a fine 4 screw Brazier lock on my Whitworth and copied the geometry of this lock and a nearly identical lock from a Rigby I borrowed from Lynton McKenzie in the mid 1990's.
Bob Roller

[HighUintas]

That is all good information and helpful. Thank you. However it might be speaking to the design and strength of the spring itself, rather than the hammer position in relation to the nipple when the hammer is at rest.

Here's a picture.

Davis Hawken lock and Griffith breech below. The top of the lock plate is roughly on the bore centerline. The hammer cup at rest is very low in relation to the nipple. If the lock and barrel were in a stock like this, the hammer would be preloaded quite a bit when sitting in the nipple.



Same setup here but I've pulled the hammer back to about where the cup would rest in the nipple. Lots of hammer preload. But the cup is shallow so I'd probably want to deepen it so it covers more of the nipple and cap.



Here's a different one. Griffith lock and breech. Bottom of blue tape is a hair lower than depth of the hammer cup. The hammer seems too tall and/or the cup is too deep. Setting the top of the lock plate line on the bore centerline causes the hammer cup to not hit the nipple at all.... I'd need to bend the hammer nose down. How much? Just enough to have it rest on the nipple rather than the bridle, or enough so that the hammer is preloaded similarly to the Davis lock hammer?



For the Griffith lock, I think I'd have to bend the hammer rather than moving the lock plate down... Doing the latter would put the lock much too low and would throw off the gun geometry

The Griffith lock spring is super strong by the way. Stronger than the Davis. Maybe because I asked him to leave some meat on it.

[Bob Roller]

Show those locks with the hammer all the way down.I think the tumbler can be reshaped on top to lower it.
Bob Roller

[HighUintas]

Show those locks with the hammer all the way down.I think the tumbler can be reshaped on top to lower it.
Bob Roller

The hammers are all the way down in those photos above.

Here they are from the backside.

Davis Hawken - I don't want to move the hammer down any further but you can see the spring hook and link are at the very bottom of the plate.



Griffith Hawken - there's about 1/16" or maybe a touch more before the spring hook and link at at the bottom of the plate. I could take some off the backside of the tumbler to allow the hammer to lower a little more.



upload pics

[Bob Roller]

That link is nearly vertical and that mechanism is designed for production and to meet a price.In 1963 I bought a Whitworth semi military match rifle with a lock unlike any I had ever seen made by Brazier in England.It was my incentive to do a better job.The locks pictured are good representatives of most caplocks seen on old American guns and it is what it is and changing the preload on the mainspring will make it worse.This opinion comes from decades of experience.
Bob Roller

[HighUintas]

That link is nearly vertical and that mechanism is designed for production and to meet a price.In 1963 I bought a Whitworth semi military match rifle with a lock unlike any I had ever seen made by Brazier in England.It was my incentive to do a better job.The locks pictured are good representatives of most caplocks seen on old American guns and it is what it is and changing the preload on the mainspring will make it worse.This opinion comes from decades of experience.
Bob Roller

That is interesting, Bob. So you're saying that it is preferable to have the link more at an angle (red line in picture) rather than more vertical when the hammer is all the way down?

And you're also saying it would be better to either bend the hammer or swap out the hammer instead of taking some metal off the back of the tumbler so that the hammer will lower a little farther due to the current link angle?

What mechanical advantage does having the link at an angle give?




where to upload images

[Adrie luke]

Wouldn't it be easier to fill the nipple hole for the cock
by welding or something? Here's an example of a cock that sits high.
Perhaps leaving the rest

[Bob Roller]

I started a detailed answer to the question about the angled link and am speaking from over 60 years of shop and lock making.I copied the best British locks to the best of my ability.When the tumbler and link are done and the mainspring forged and filed including the stabilizing pin on the upper leaf of the spring and the the tumbler is paced in the plate and the sear is set in place on the screw it turn on and the link is pushed back with the mainspring to the position it will be in as a finished lock and the hole for the pin is established and drilled.The tumbler is rotated so the link is straight down and then the spring is heated to an orange color and spread open with a tool made for the job to the point that the lower limb is about 1/2" below the extended link and then the spring is hardened,polished and tempered,allowed to cool and then connected to the link and tested.When the lock is assembled the link is in proper position and the lock is tested.Close fitting and decades of experience proves what I copied from the British lock makers was spot on.As I said,the locks pictured are like the old
ones seen on most American muzzle loaders and quality was not important. Look at pictures of my locks on THIS forum.Type in "Pictures of Bob Roller locks on this forum.
Bob Roller

[HighUintas]

Wouldn't it be easier to fill the nipple hole for the cock
by welding or something? Here's an example of a cock that sits high.
Perhaps leaving the rest

I could but it would be nearly completely filled and not look very good

[HighUintas]

I started a detailed answer to the question about the angled link and am speaking from over 60 years of shop and lock making.I copied the best British locks to the best of my ability.When the tumbler and link are done and the mainspring forged and filed including the stabilizing pin on the upper leaf of the spring and the the tumbler is paced in the plate and the sear is set in place on the screw it turn on and the link is pushed back with the mainspring to the position it will be in as a finished lock and the hole for the pin is established and drilled.The tumbler is rotated so the link is straight down and then the spring is heated to an orange color and spread open with a tool made for the job to the point that the lower limb is about 1/2" below the extended link and then the spring is hardened,polished and tempered,allowed to cool and then connected to the link and tested.When the lock is assembled the link is in proper position and the lock is tested.Close fitting and decades of experience proves what I copied from the British lock makers was spot on.As I said,the locks pictured are like the old
ones seen on most American muzzle loaders and quality was not important. Look at pictures of my locks on THIS forum.Type in "Pictures of Bob Roller locks on this forum.
Bob Roller

Bob, thanks for explaining that. I hope you didn't take my question the wrong way. I didn't mean to imply you were wrong. I only ask out of curiosity and to learn.

[Daryl]

Andrie, , those fences are totally superfluous on those locks. Fences are to protect the shooter from cap fragments. Those would not. The hammer's cup must be below the rear edge of the fence, for it to work as designed.
Check a well made Hawken ot English Sporting Rifle's hammer fence relationship.

[Daryl]

Those locks look just like the poorly designed locks on a Pedersoli Kodiak rifle. I had one and was able to correct this defect by reducing the height of the nipples, so the hammer cup would curl over the front edge of the fence.
With these locks, this was possible  (on this particular rifle) without the mainspring beaking out the bottom of the lock mortise.

[Adrie luke]

The photo is of a Belgian hunting rifle.

This is a beautiful Forem, and we're learning more and more.

Thanks

[Bob Roller]

I started a detailed answer to the question about the angled link and am speaking from over 60 years of shop and lock making.I copied the best British locks to the best of my ability.When the tumbler and link are done and the mainspring forged and filed including the stabilizing pin on the upper leaf of the spring and the the tumbler is paced in the plate and the sear is set in place on the screw it turn on and the link is pushed back with the mainspring to the position it will be in as a finished lock and the hole for the pin is established and drilled.The tumbler is rotated so the link is straight down and then the spring is heated to an orange color and spread open with a tool made for the job to the point that the lower limb is about 1/2" below the extended link and then the spring is hardened,polished and tempered,allowed to cool and then connected to the link and tested.When the lock is assembled the link is in proper position and the lock is tested.Close fitting and decades of experience proves what I copied from the British lock makers was spot on.As I said,the locks pictured are like the old
ones seen on most American muzzle loaders and quality was not important. Look at pictures of my locks on THIS forum.Type in "Pictures of Bob Roller locks on this forum.
Bob Roller

Bob, thanks for explaining that. I hope you didn't take my question the wrong way. I didn't mean to imply you were wrong. I only ask out of curiosity and to learn.

No problem and I was not in any way offended by your post.Having access to fine old English locks gave me an advantage and to me making locks and triggers was just another job in the machine shop.The detailing of these locks is mostly bench and files and I liked to do it until a lower back problem came along and now my shop time is very limited.Getting back to learning,when we quit learning we are dead from the neck up.That came from my maternal grandfather,C.M.Taylor 1872-1972.
Bob Roller

[alacran]

I like the Griffith breech plug and the Davis lock combo. This thread got me wondering about my own Hawken. At one time I had three in different calibers.
As you can see in the photos the link is not near vertical. I built this rifle fifteen years ago and really don't remember if I gave a hoot about what the link angle was. You can see by the photos that I placed the lock on the breech plug as near as possible where it sits on the rifle.
I was more concerned with making the cut out for the plug on the lock. I made a hard carboard cutout to align everything.
You will have to bend the hammer, which to me is the most difficult part of the whole enterprise. By the same token you can rectify issues of alignment
when you heat bend it.
Hope this helps.

[HighUintas]

I like the Griffith breech plug and the Davis lock combo. This thread got me wondering about my own Hawken. At one time I had three in different calibers.
As you can see in the photos the link is not near vertical. I built this rifle fifteen years ago and really don't remember if I gave a hoot about what the link angle was. You can see by the photos that I placed the lock on the breech plug as near as possible where it sits on the rifle.
I was more concerned with making the cut out for the plug on the lock. I made a hard carboard cutout to align everything.
You will have to bend the hammer, which to me is the most difficult part of the whole enterprise. By the same token you can rectify issues of alignment
when you heat bend it.
Hope this helps.

It is a good looking combo. I am still in between on which lock I want to use. The Griffith lock is HUGE compared to the Davis so it's hard to picture how it will look when finished.

If I do use the Davis, I will have to modify the front of plate so that the front corner of the plate bolster curves down rather than a sharp corner.

How about a picture of the entire rifle?

[alacran]

Took me a while to find these. Actually I built this rifle 18 years ago. Not the best pictures. There is also all three I had at the time,
from top to bottom, .54, .50, .45.





minuscule lettre

[HighUintas]

Took me a while to find these. Actually I built this rifle 18 years ago. Not the best pictures. There is also all three I had at the time,
from top to bottom, .54, .50, .45.





minuscule lettre

I love the wood on that 54. Great job on those.

Since you have had 3 of those Griffith breeches ..  did any of them come to you loose fitting at all?  For the two I've handled I think the sides of the hook might potentially be a tad undersized due to the mold

[alacran]

When I built all of those, Track of the Wolf carried Griffith Plugs. They all fit together pretty well. I have bought one from the Hawken Shop and it also fit together well.
Track used to tout the fact that the Griffith plugs didn't need fitting.

[Bob Roller]

Fine job of inletting in these guns.Preloading a spring can be translated as tension.PREloading is another word for it
Bob Roller