Cast versus machined versus forged mainsprings: does it make any difference?

[Bob Roller]

I don't know if I clarified anything or not but 50+years of experience must count for something.The only thing really important to me was getting the right material and then  a technique to bring it to a successful conclusion and that helps in a big way to be worry free about breakage and that is because of the uniform quality of 1075.I still have enough to last longer than I will.I learned spring making from George Killen beginning at age 15 and he allowed me to watch him.His heat source was a big gasoline blow torch he modified with a tire valve so he could pressurize it with a tire pump.I was a willing student and wanted to know about making springs and anything else.Another one was Bill Large who taught me about machine tools and a myriad of other things.
This started in 1953 and that lasted until Bill passed away in 1985. Later I convinced one of Bill's daughters to sell Bill's shop to Jim McLemore so he could expand his shop.This has nothing to do with making springs but are part of my life experiences in a variety of venues.
Bob Roller

[Darkhorse]

After a few thousand cycles without issue, my main spring broke while bringing the lock to full cock in preparation toffee at one of the biggest bucks I've seen in my life.
The spring was cast, and although it functioned perfectly for years, the breakage revealed a tiny air bubble in the casting.  I now carry a spare spring in my bag, but that failure has stuck with me, and I will take one of Mr Kibler's machined springs or a forged spring over a cast spring any day if I have a choice . There is far less chance of a catastrophic failure IMO  [ I can still see that buck !  ]

I had called up two gobblers, got in front of them by wading and was hidden in the roots of a large, old oak. When they came out of the palmettos the first one was the biggest gobbler I have ever seen. He was in my sights when I cocked my rifle. And the mainspring broke......
First time that had happened and I was without a spare. No choice but to go home 65 miles away. Now I always carry a spare.

Before I retired I was a SME (subject matter expert) for the Air Force on several processes, one was the manufacture of hard critical airframe components, so I have some indepth knowledge on this subject. Based on nearly 40 years experience this is what I think....
If given the choice my mainspring would be machined from a forging. For me, that says it all.

[Chris Evrard]

I'm not a metallurgist, but here's what I gather:

- Cast springs are considered “fair-good.”
- Milled springs are “better.”
- Forged springs are “best.”

However, the difference between milled and forged springs is often negligible in many cases.

These theoretical discussions are fascinating. Would it be more effective to mill a spring flat and then bend it, or to mill it into shape directly?

If I’m understanding correctly, milling it flat and then bending it might align the grain structure but could also introduce some internal tension. This tension could be alleviated through reheating or tempering, allowing for grain recrystallization.

That said, if a lock functions properly, does it even matter? This topic keeps resurfacing—beating a dead horse at this point.

I think lock function and durability as a single unit is a better use for study. A tuned lock vs untuned makes the world of difference.

John, milling in a flat state and then adding the bend was one method I was working with. It was taking me too many heats to get to the end result.  There was a fellow who made locks back in the 70's who could get the whole thing done in two heats. I know it is possible so I may revisit this one day. Repetition breeds familiarity and I bet after a few hundred,  certainly several thousand, the process would become imminently more efficient.

CE

[Chris Evrard]

After a few thousand cycles without issue, my main spring broke while bringing the lock to full cock in preparation toffee at one of the biggest bucks I've seen in my life.
The spring was cast, and although it functioned perfectly for years, the breakage revealed a tiny air bubble in the casting.  I now carry a spare spring in my bag, but that failure has stuck with me, and I will take one of Mr Kibler's machined springs or a forged spring over a cast spring any day if I have a choice . There is far less chance of a catastrophic failure IMO  [ I can still see that buck !  ]

I had called up two gobblers, got in front of them by wading and was hidden in the roots of a large, old oak. When they came out of the palmettos the first one was the biggest gobbler I have ever seen. He was in my sights when I cocked my rifle. And the mainspring broke......
First time that had happened and I was without a spare. No choice but to go home 65 miles away. Now I always carry a spare.

Before I retired I was a SME (subject matter expert) for the Air Force on several processes, one was the manufacture of hard critical airframe components, so I have some indepth knowledge on this subject. Based on nearly 40 years experience this is what I think....
If given the choice my mainspring would be machined from a forging. For me, that says it all.

A machined forging would be the nads. If I had a drop hammer this would become my goal
 I nearly bought one last year from a closed machine shop up in Philly.  The roof had caved in and getting that beast out was more than I wanted to fool with.  But someday....!

[alacran]

Is that not the way they did it on the old days, blacksmithing then white smithing?

[Jakob]

It was taking me too many heats to get to the end result.  There was a fellow who made locks back in the 70's who could get the whole thing done in two heats. I know it is possible so I may revisit this one day.

I was a smiths apprentice as my very first career and we had a saying that a good smith could forge a locomotive in one heat.

[Steeltrap]

I'm no lock expert. Nor do I have decades of lock or metalurgy experience. But I do have observations.

Several months back I was tuning a lock (New old stock Dixie flint) and during that process, I took my small group of flintlock firearms and measured the poundage required to pull the cock from rest, to full cock. Here's the poundage as measured by a Lyman Digital trigger pull gauge: Rifle L&R 9.1,  Rifle L&R 9.5, 50 Cal Pistol Chambers Queen Ann   7.15, 45 Cal Pistol-Dixie 10.1.

Now, all of these locks provide very good ignition and they all provide great flint life. A lock that would give me 4 or 5 shots before requiring a flint replacement would either be tuned or sent down the road.

It also seems to me that any lock with a pull greater than 15-lbs would give me pause as to why. If the answer is an almost imperceptible speed increase in lock time at the sacrifice of a new flint every 5 shots, I'd prefer adequate lock speed with longer flint life.

But, that's me.

[Jim Kibler]

I really don't know what the force is to cock our locks.  I don't measure it as I can feel what is a good weight and what isn't.  After all this hub-bub, just this morning I took about a dozen of our locks and checked each one for function.  They all felt really good.  Springs not too strong nor too weak.  I snapped each one a handful of times and no issues.  I snapped one at least 40 times and no issues with a flint.  This is how our locks generally work.  I see absolutely no reason to change a thing.  The spring weight is perfect in my view. 

I can honestly say, our locks are the gold standard of what is available today.  We're very proud of what we've accomplished with these. 

Here's an interesting thing about locks....  I recall years ago, Jim Chambers making a comment here about customer preferences.  In short he said the problem that one person might like weak springs and the next might like them really strong.  Each thinks they're absolutely right as well, so it goes to show you can't please everyone no matter what you do.  This was when he was working with his Ketland lock spring weight.

I'll also say that I believe flint breakage is sometimes due to the initial strike against the frizzen, but I think frizzen bounce back is more of an issue than we sometimes realize.  I'd like to dig into this more.

I'm also going to take 44 Henry up on his offer of building a test rig to cycle locks.  This should be interesting...

[Jim Kibler]

Also, does anyone have access or know of any way to get our hands on a very high speed camera.  No the level of a cell phone, but the serious ones.  I looked a while ago and saw they were very expensive; tens of thousands or even a hundred thousand.  I can't justify this, but do recognize one would be fantastic in evaluating a lock.  Not only for timing but also for examination of function in detail.  I recall seeing the Brown Bess show on PBS a while ago and they used something like this.  It was revealing for sure.

Thanks!

[HSmithTX]

Jim, you can rent high speed cameras.  https://www.renthighspeed.com/ I haven't used these guys but the site looks good.  The last time I rented cameras I had to rent the crew with them and it was a couple grand a day to troubleshoot some high speed automation glitches. Well worth it in my case but silly expensive for the subject of this thread IMO.

[Ky-Flinter]

Jim,

You might try contacting Larry Pletcher.  He is a member here and has done high speed videos and lock timing in the past.  https://www.blackpowdermag.com/category/videos/  Scroll down for videos.

Ron

[44-henry]

Professional high-speed cameras typically start around $3,000 and go up from there. That said, some of my students have mentioned hacks using Raspberry Pi setups and other systems that can replicate much of this functionality for just a few hundred dollars. Granted it sounds like they would all still be under 1000 frames per second which is low, but could still be useful for testing a lock. While perhaps not on par with professional systems in terms of high-end performance, I’ve learned that engineering students tend to get pretty creative when it comes to avoiding major expenses—probably so they have more money left over for beer.

[Steeltrap]

Here's a video I took of a Manton lock that was giving me fits as to why my frizzen was not opening fully. Well, you can see the frizzen was opening fully....and because of a weak frizzen spring it was snapping back to the flint.

BTW....taken with an iPhone 16 Pro with the video set in slow motion.

Not a high speed by any means and for a very detailed lock testing of hundreds if not thousands of cycles this may not "cut it".....but if nothing else it could provide some data.

FWIW

[FlinterNick]

I really don't know what the force is to cock our locks.  I don't measure it as I can feel what is a good weight and what isn't.  After all this hub-bub, just this morning I took about a dozen of our locks and checked each one for function.  They all felt really good.  Springs not too strong nor too weak.  I snapped each one a handful of times and no issues.  I snapped one at least 40 times and no issues with a flint.  This is how our locks generally work.  I see absolutely no reason to change a thing.  The spring weight is perfect in my view. 

I can honestly say, our locks are the gold standard of what is available today.  We're very proud of what we've accomplished with these. 

Here's an interesting thing about locks....  I recall years ago, Jim Chambers making a comment here about customer preferences.  In short he said the problem that one person might like weak springs and the next might like them really strong.  Each thinks they're absolutely right as well, so it goes to show you can't please everyone no matter what you do.  This was when he was working with his Ketland lock spring weight.

I'll also say that I believe flint breakage is sometimes due to the initial strike against the frizzen, but I think frizzen bounce back is more of an issue than we sometimes realize.  I'd like to dig into this more.

I'm also going to take 44 Henry up on his offer of building a test rig to cycle locks.  This should be interesting...

I use a spring tester / force gauge. The go pro cameras work in all speeds.

[Jim Kibler]

Jim,

You might try contacting Larry Pletcher.  He is a member here and has done high speed videos and lock timing in the past.  https://www.blackpowdermag.com/category/videos/  Scroll down for videos.

Ron

Thanks.  I've worked with Larry in the past and he graciously did some timing tests on our Ketland lock.  He uses a very old set-up that basically trips the sear, starts a timer at this point and then uses a photo cell that trips at a certain intensity of light from the priming powder.  The time between these events is what he measures and reports as the lock time.  Anyways, I was just considering with improved cameras today, you might be just able to measure lock time from the camera recording in some way.  It would also be neat to very carefully watch the flint and frizzen interaction along with potential bounce-back etc.

Jim

[Jim Kibler]

I really don't know what the force is to cock our locks.  I don't measure it as I can feel what is a good weight and what isn't.  After all this hub-bub, just this morning I took about a dozen of our locks and checked each one for function.  They all felt really good.  Springs not too strong nor too weak.  I snapped each one a handful of times and no issues.  I snapped one at least 40 times and no issues with a flint.  This is how our locks generally work.  I see absolutely no reason to change a thing.  The spring weight is perfect in my view. 

I can honestly say, our locks are the gold standard of what is available today.  We're very proud of what we've accomplished with these. 

Here's an interesting thing about locks....  I recall years ago, Jim Chambers making a comment here about customer preferences.  In short he said the problem that one person might like weak springs and the next might like them really strong.  Each thinks they're absolutely right as well, so it goes to show you can't please everyone no matter what you do.  This was when he was working with his Ketland lock spring weight.

I'll also say that I believe flint breakage is sometimes due to the initial strike against the frizzen, but I think frizzen bounce back is more of an issue than we sometimes realize.  I'd like to dig into this more.

I'm also going to take 44 Henry up on his offer of building a test rig to cycle locks.  This should be interesting...

I use a spring tester / force gauge. The go pro cameras work in all speeds.

The cameras I'm referring to are extremely high speed cameras.  We've used go pro, cell phones etc.  They don't slow things down enough for our purposes.  I'm with you on the force guages.

Follow the link that HsmithTX posted above to see what I'm talking about.

[Jim Kibler]

Professional high-speed cameras typically start around $3,000 and go up from there. That said, some of my students have mentioned hacks using Raspberry Pi setups and other systems that can replicate much of this functionality for just a few hundred dollars. Granted it sounds like they would all still be under 1000 frames per second which is low, but could still be useful for testing a lock. While perhaps not on par with professional systems in terms of high-end performance, I’ve learned that engineering students tend to get pretty creative when it comes to avoiding major expenses—probably so they have more money left over for beer.

Great information once again!  Thanks so much.

[T*O*F]

Thanks.  I've worked with Larry in the past and he graciously did some timing tests on our Ketland lock.  He uses a very old set-up that basically trips the sear, starts a timer at this point and then uses a photo cell that trips at a certain intensity of light from the priming powder.  The time between these events is what he measures and reports as the lock time.  Anyways, I was just considering with improved cameras today, you might be just able to measure lock time from the camera recording in some way.  It would also be neat to very carefully watch the flint and frizzen interaction along with potential bounce-back etc.

Jim

Larry had access to a high speed camera for a while and made a series of videos that showed flint and frizzen interaction.  I used to help him once in a while and he burned me a CD showing the locks he was doing at the time.  I've probably still got it laying around somewhere.  If I recall, most of the locks had frizzen bounce back.

[Steeltrap]

The frizzen bounce back (FWIW) I discovered by accident. I could stare at that lock every time and the bounce back occurred so quickly, the human eye cannot see it. (Well...I think I'm human....just don't ask the Mrs).

So, at one point I was holding the rifle with my left had where my left thumb nail was (unbeknownst to me) in the direct line of when the frizzen snapped open. So, when I pulled the trigger the frizzen "WHACKED" my thumbnail!!  And I still couldn't see it happen!!  I did this a few more times (with thumbnail protected) and that's how I found the problem.

In addition, the bounce back usually won't occur if you're holding the lock in your hand (as opposed to the lock being in the stock). Your hand (well...my hand) would absorb enough of the energy that the frizzen would stay open. This gave me the "false" thinking that there was something in the stock that was impinging the lock movement....and me thinking not enough force was hitting the frizzen.

Very scientific method. It's called "whack your nail and withdraw in pain."  That's the scientific term....honest....google it.   

[Darkhorse]

I only use Chambers large siler LH locks because I'm lefthanded and I'm very familiar with these locks. When I tune a lock a priority is to get any jar out of the rifle when shot. I've tracked this to a heavy frizzen spring. Lots of testing has shown there is a fine line between no jar and bounceback.
I measure with a trigger gauge hooked to the top of the frizzen. My goal is to get as close to 4 pounds as possible. Testing has shown this weight removes all jar and creates no bounceback. I use a dremel to reduce the spring. I measure the spring thickness to control where I'm at. Starting with a coarse drum I transition to a fine drum. The last thing I do is polish any tool marks from the spring to help prevent a crack from starting.
I never reduce a main spring. Doing so will reduce the spring strength and slow the lock. Though I have polished the surface of a few.
I never weigh a main spring either. Like Jim I can tell if the spring is of a weight that works for me just by cocking it a few times.
I feel that too many shooters want to blame the mainspring for a variety of problems when in fact something else is the culprit.

[Bob Roller]

It was taking me too many heats to get to the end result.  There was a fellow who made locks back in the 70's who could get the whole thing done in two heats. I know it is possible so I may revisit this one day.

I was a smiths apprentice as my very first career and we had a saying that a good smith could forge a locomotive in one heat.

Was that a B&O yard engine or a Union Pacific "Big Boy" ? I have bent/forged lock mainsprings in 2 heats and used an acetylene torch,
1075 is a forgiving material for any lock springs and I have them all over the world and my methods rank with the stone axe.
Bob Roller

[Bob Gerard]

I have an L&R Durrs Egg flintlock that’s about 46 years old. It went through two broken cast main springs.
They refitted the lock to accommodate their new Durrs Egg forged (or machined?) mainspring.
I think the new one will last longer, though in 46 more years I don’t think I will be pulling too many triggers to know. 🤣

[mountainman]

I'm not a lock maker, but what does that mean when they say " a machined spring taking a set" ? or other versions of a mainspring taking a set. A set of what? Lock parts?

[Steeltrap]

"Taking a set" refers to when a spring is compressed, and doesn't return to its original "wanted" or "full spring" position. Thus it will be weakened permanently from the original intended power.

[bluenoser]

Weakened permanently until it is heated, restored to original dimension and re heat treated to a more appropriate temper.