Questions on hammer bobbing.....

[MrBorland]

Kevin -

Couple o' other thoughts -

If this is for PPC, I assume you don't need as rapid and as positive a trigger return as USPSA guys do. You can likely buy yourself a little bonus pull weight, then, by installing a rebound spring that's a bit lighter than you'd normally use.

Also, be sure to check to be sure there's no source of extra internal friction to rob the hammer/FP of oompf. The smoother & straighter the action is, the more oompf delivered. For example, I dropped the hammer into the empty frame and checked for free movement. I then installed the side plate and re-checked for that same free movement. Before re-assembling the gun, I did the same for all the other internal parts as well. Be sure the grips aren't touching the mainspring, and if you use rubber grips with a lateral screw, be sure the screw's not tightened so much the grips begin to pinch the mainspring. A digital trigger pull gauge was one of my most-used tools.

Tom

[Kevin Pledger]

Tom,

I do sometimes for fun, shoot IPSC, especiall my 686-2 which has a Douglas barrel and comp. When I seen the modifications which had been done it just got my interest.

This is an old picture of my PPC Gun, which had at the time a Aimpoint 9000 2x scope on it, now switched to a CompC3 8MOA. This revolver as a 5lb double action trigger now, so thought would try the Carmonizing method just to see the actual different in trigger feel.

The barrel is .750" shorter from the original, due to the fact I split the forcing cone apart, when using some 147ggn Winchester Silvertips for fun. Totally forgetting that my barrel is a Douglas barrel for lead only.

Cheers ....

Kevin

Edited December 6, 2011 by Kevin Pledger

[TheBrick]

Hello Hammer Bobbers

Help me try and understand the whole rational for bobbing hammers.

I am on old time revolver smith during the era of PPC shooting. I made quite a few guns, some for the top Governor's Twenty shooters in NY back in the 70's and 80's. I always gave the customer what they wanted be it, cut back the cylinder and set back the barrel, crane locks, cylinder timing for trigger staging and, of course, hammer bobbing to name a few. I have nothing against doing any of it save for some of the reasoning.

I am not a physicist but it is my understanding that a certain amount of kinetic energy is required by the hammer to set off that primer. That kinetic energy must be met and developed by the combination of mass (weight) and momentum (speed). That means that a lighter hammer must go faster to provide the same kinetic energy of a slower and heavier hammer. If a slow heavy hammer lights up a primer as reliably as a light and fast hammer then they must both be delivering the same energy to the primer. I am thinking this discredits the "jarring and jostling and gun upset" caused by the hammer fall. Regardless, USPSa shooting does not lend itself to the accuracy requirement of a PPC shooter trying to shoot out the X ring on a B-27 target at 50 yards.

Hammer speed for a shorter lock time I agree with but don't see the need. I can shoot .17 splits on close targets and really don't think a faster hammer will improve my ability. As Jerry Miculek says, I can never outshoot my revolver, the gun is always waiting on him.

One of my most successful action jobs is the "short stroke" where the hammer throw/trigger pull is just under 2/3 of standard issue. I was able to achieve the hallmark 6lb triggers and reliable ignition of Federal primers with target hammers, occassionally a regular hammer but NEVER with a bobbed hammer.

Is anyone using a short stroke and a bobbed hammer. If so, can you tell me how reliable ignition was accomplished.

Does anyone even make or use a "short stroke action anymore?

I am not bashing hammer bobbing, hell, I've done it. I am just not sure what the right reason is for doing it.

Peter

[Carmoney]

I am not a physicist but it is my understanding that a certain amount of kinetic energy is required by the hammer to set off that primer. That kinetic energy must be met and developed by the combination of mass (weight) and momentum (speed). That means that a lighter hammer must go faster to provide the same kinetic energy of a slower and heavier hammer. If a slow heavy hammer lights up a primer as reliably as a light and fast hammer then they must both be delivering the same energy to the primer.

With his engineering background, Randy Lee can explain it far better than me, but my layperson's understanding is that fast slaps are better than slow crushes when it comes to igniting centerfire primers. I do know that Randy tested it extensively when developing his aftermarket hammers. And I found the same thing with my own cut-down hammers. All other things being equal, a significantly lighter hammer will fall faster and ignite primers better. It's not a huge difference, but it's measurable and repeatable. All other things equal, I can take the action on a revolver noticeably lighter with a Carmonized or Randy hammer, but still keep it reliable, than I can with a stock hammer. Note we're not just talking about "bobbing" hammer spurs, we're talking about radically cutting them down to reduce the curb weight by about 50%.

Short throw actions do not seem to be in vogue these days. The few that I've seen have been fairly heavy. Which of course makes perfect sense--if you reduce the arc of hammer travel, it's going to need more spring tension to get it moving fast enough to pop the primer. And if you're still required to pull the trigger all the way through its full range of travel, what benefit really comes from the hammer arc being shorter--for an action shooting gun, anyway?

Edited December 6, 2011 by Carmoney

[Tom E]

I agree with Mike. I have hammers installed with varying degrees of "bobbed" from in variuos stages from none to a "factory replica" bob down to the 50% lighter version. As the hammer weight is reduced, the mainspring tension can be reduced. It seems the CF primers just require a certain amount of hammer/firing pin velocity regardless of hammer weight, at least on our S&W revolvers with a "std" action and normal hammer arc. Reduced lock time isn't the issue or goal and probably is very close to the same with a stock or lightened hammer if the mainspring is reduced to "just reliable" on both. What's amusing is a stock mainspring and strain screw with a 50% lighter hammer, it's surprising how fast the hammer falls. Rimfires are a different animal.

[MrBorland]

That means that a lighter hammer must go faster to provide the same kinetic energy of a slower and heavier hammer. If a slow heavy hammer lights up a primer as reliably as a light and fast hammer then they must both be delivering the same energy to the primer. I am thinking this discredits the "jarring and jostling and gun upset" caused by the hammer fall.

Momentum, which jars the muzzle, is proportional to mass and velocity. Kinetic energy, which is what lights off the primer, is proportional to mass and the square of the hammer speed. You can reduce the hammer mass so the KE increases, but momentum decreases.

Imagine a 70,000lb tractor trailer traveling at 5mph and a 3,500 lb sedan traveling 60mph. Which do you think would do more damage if it hit you? Intuitively, it seem the sedan would. Indeed, while the semi has 66% more momentum, the sedan has over 7 times the kinetic energy.

[TheBrick]

GrandBoule,

Sharpened up my pencil and did the math.

You finally explained this whole hammer bobbing reasoning to me. I guess I gave momentum very little credit but it is what makes the difference.

Momentum is mass times velocity.

Kinetic energy is actually momentum squared divided by 2 times the mass. At least according to my reference.

Regardless, your numbers in the truck/car example were correct and cleared up this whole mystery to me.

Thanks

Peter

[MrBorland]

Thanks, Pete -

Actually, I finally sharpened up my pencil, and did some work, too. And it's been a real eye opener, as it turns out I wasn't entirely right on the technical details. I used a simplified trigger, uncut, and cut to remove 25% of the mass (figure & analysis below), but the general gist is valid, I think.

The take home points are as follows:

1. Bobbing the hammer does reduce total mass, but more importantly, it lowers the Moment of Inertia (the effective weight) even more by bringing the Center of Gravity closer the the pivot point.

2. If you bob the hammer, but keep the mainspring "as is", the lighter hammer will accelerate faster. Lock time and momentum will decrease 20%, but interestingly enough, kinetic energy doesn't increase - remains unchanged, which is fine and dandy, since the stock KE is enough. The KE ends up staying the same, since the velocity doesn't go up enough to make up for the loss of rotational mass.

3. You can lower the relative mainspring tension the same as the relative moment of inertia before lock time increases. KE has decreased 37%, though, and it's unknown how much you can lose before reliability becomes an issue.

4. You can extend this analysis to ask how low you can lower mainspring tension to get any relative KE.

5. This analysis shows that it's not so much the mass of the bobbed hammer, as it is where the mass was removed to get it. It'd be interesting to play with different shapes to figure out what shape gives the best balance of lowered inertia & strength, or how to minimize KE loss while reducing spring tension. I'll have to play with this some more.

Cheers -

Tom

Edited December 7, 2011 by GrandBoule

[Bubber]

Thanks, Pete -

Actually, I finally sharpened up my pencil, and did some work, too. And it's been a real eye opener, as it turns out I wasn't entirely right on the technical details. I used a simplified trigger, uncut, and cut to remove 25% of the mass (figure & analysis below), but the general gist is valid, I think.

The take home points are as follows:

1. Bobbing the hammer does reduce total mass, but more importantly, it lowers the Moment of Inertia (the effective weight) even more by bringing the Center of Gravity closer the the pivot point.

2. If you bob the hammer, but keep the mainspring "as is", the lighter hammer will accelerate faster. Lock time and momentum will decrease 20%, but interestingly enough, kinetic energy doesn't increase - remains unchanged, which is fine and dandy, since the stock KE is enough. The KE ends up staying the same, since the velocity doesn't go up enough to make up for the loss of rotational mass.

3. You can lower the relative mainspring tension the same as the relative moment of inertia before lock time increases. KE has decreased 37%, though, and it's unknown how much you can lose before reliability becomes an issue.

4. You can extend this analysis to ask how low you can lower mainspring tension to get any relative KE.

5. This analysis shows that it's not so much the mass of the bobbed hammer, as it is where the mass was removed to get it. It'd be interesting to play with different shapes to figure out what shape gives the best balance of lowered inertia & strength, or how to minimize KE loss while reducing spring tension. I'll have to play with this some more.

Cheers -

Tom

Hey, Hey Pie are round cobbler are square!!! Too technical fer me. later rddd

[TheBrick]

GrandBoule

I think you are talking a bit over my head now.

I tried to follow the math but I don't know what formulas you used to arrive at your numbers.

I do find your statement confusing; if a lighter hammer does accelerate faster than a standard weight, how can lock time actually decrease by 20% ????? Momentum, YES, because of the reduced weight, but not lock time.

What you say about the shape of the hammer does make sense since weight above/below/front of/behind the pivot point and it's relative point to the pivot point can actually speed up/slow down or cause greater/lesser kinetic energy as well as momentum to the primer or so it seems to me.

In statement 3 it seems to me that you are saying that you can only reduce mainspring tension by the weight of the material removed from the hammer which will result in a 37% reduction of KE.

This is actually driving me crazy and if I had a physical measurable way of identifying both momentum and Kinetic energy; I would engage in an actual experiment instead of all this THEORY.

In the end, if the shooter BELIEVES there is an advantage, that it FEELS better, then psychologically he/she will be better off.

As to the actual physics of it all, I remain skeptically yours,

Peter

PS Thanks for the headache!

[Bosshoss]

Thanks, Pete -

Actually, I finally sharpened up my pencil, and did some work, too. And it's been a real eye opener, as it turns out I wasn't entirely right on the technical details. I used a simplified trigger, uncut, and cut to remove 25% of the mass (figure & analysis below), but the general gist is valid, I think.

The take home points are as follows:

1. Bobbing the hammer does reduce total mass, but more importantly, it lowers the Moment of Inertia (the effective weight) even more by bringing the Center of Gravity closer the the pivot point.

2. If you bob the hammer, but keep the mainspring "as is", the lighter hammer will accelerate faster. Lock time and momentum will decrease 20%, but interestingly enough, kinetic energy doesn't increase - remains unchanged, which is fine and dandy, since the stock KE is enough. The KE ends up staying the same, since the velocity doesn't go up enough to make up for the loss of rotational mass.

3. You can lower the relative mainspring tension the same as the relative moment of inertia before lock time increases. KE has decreased 37%, though, and it's unknown how much you can lose before reliability becomes an issue.

4. You can extend this analysis to ask how low you can lower mainspring tension to get any relative KE.

5. This analysis shows that it's not so much the mass of the bobbed hammer, as it is where the mass was removed to get it. It'd be interesting to play with different shapes to figure out what shape gives the best balance of lowered inertia & strength, or how to minimize KE loss while reducing spring tension. I'll have to play with this some more.

Cheers -

Tom

OK I guess I should have paid more attention in math class

Interesting read though.

This should spark some discussion.

[Tom E]

I do find your statement confusing; if a lighter hammer does accelerate faster than a standard weight, how can lock time actually decrease by 20% ????? Momentum, YES, because of the reduced weight, but not lock time.

Lock time is the time from hammer release to the firing pin igniting the primer. The faster the hammer moves (accelerates) the shorter the lock time.

The hammer's kinetic energy cannot be greater than the mainspring's stored energy. Same spring rate and preload, same energy, hammer weight doesn't matter, energy is the same BUT a lighter hammer will accelerate faster giving a higher final velocity.

[MrBorland]

The hammer's kinetic energy cannot be greater than the mainspring's stored energy.

Yep - makes sense. You can't get any higher than a relative KE of 1.0, as that'd be exceeding the potential energy (PE) stored in the spring.

I do find your statement confusing; if a lighter hammer does accelerate faster than a standard weight, how can lock time actually decrease by 20% ?????

TomE beat me to it.

In statement 3 it seems to me that you are saying that you can only reduce mainspring tension by the weight of the material removed from the hammer which will result in a 37% reduction of KE.

I may have over-generalized. I dunno. I'm no physicist. If you lower the mainspring tension by the same percentage as the Moment of Inertia, you'll get the same lock time as a stock hammer/spring. But a corresponding 37% reduction in KE. Whether it's coincidence that these 2 elements are the same, I can't say yet. DId I mention I'm not a physicist? I'll have to look further into it. The general point is that, depending on how material was removed, you can lower spring tension (to some point), and still get the benefits of lower momentum (less hammer jar), shorter lock time, without sacrificing reliability.

This is actually driving me crazy and if I had a physical measurable way of identifying both momentum and Kinetic energy; I would engage in an actual experiment instead of all this THEORY.

I hear you. Been thinking of that myself. I'm not physicist (did I mention that yet? ), but I am a scientist. Nothing beats a good experiment. The best I came up with so far is

. It's my original coin-on-the-barrel drill with a S&W Model 65. Try as I might, I could never keep the on-edge coin on the barrel when the hammer hit the frame. It wasn't until

, with a radically-bobbed hammer, that the coin could withstand the hammer jar.

Tom

[Kevin Pledger]

Okay,

Some very interesting reading and a lot of information to digest.

But now totally convinced, so will commence some radical surgery(small steps) over the weekend if time permits on a spare hammer.

Cheers

[SteelShooten]

if I had a physical measurable way of identifying both momentum and Kinetic energy;

There is a way to demonstrate the amount of energy that the firing pin delivers when it strikes the primer. You need an object that the firing pin can eject from the barrel when it strikes.

Once upon a time a pencil was used to check function of Govt 45s. If the pencil launched from the gun, the pistol could be expected to fire live ammo. If the pencil didn't go very far the gun likely needed maintenance. A pencil isn't ideal for our purposes though since the eraser steals some of the impulse. The concept is similar though.

You can use a piece of aluminum rod Ø.312 x 3 in long to tell you how much energy is being imparted by the firing pin.

The end must be cut square so it rests cleanly on the breech for the experiments

The quick and dirty method:

Use strong rubber bands or tape to fasten a yardstick to your revolver barrel so that it projects past the muzzle and is aligned with the barrel.

Hold the revolver so the barrel is vertical (as close as you can manage) and the yardstick is an effective height scale.

Draw and hold the trigger back far enough to allow you to advance the cylinder and line up the proximate chamber with the barrel.

Keep holding the trigger and drop the aluminum slug down the bore so it rests on the breech and then pull the trigger the rest of the way to release the hammer.

The slug should jump out of the barrel and you'll be able to read its highest point on the yardstick. This height represents the energy delivered by the firing pin.

Try it again with the other hammer in the gun and compare the test results. More height = more firing pin energy.

[Shadowrider]

Thanks, Pete -

Actually, I finally sharpened up my pencil, and did some work, too. And it's been a real eye opener, as it turns out I wasn't entirely right on the technical details. I used a simplified trigger, uncut, and cut to remove 25% of the mass (figure & analysis below), but the general gist is valid, I think.

The take home points are as follows:

1. Bobbing the hammer does reduce total mass, but more importantly, it lowers the Moment of Inertia (the effective weight) even more by bringing the Center of Gravity closer the the pivot point.

2. If you bob the hammer, but keep the mainspring "as is", the lighter hammer will accelerate faster. Lock time and momentum will decrease 20%, but interestingly enough, kinetic energy doesn't increase - remains unchanged, which is fine and dandy, since the stock KE is enough. The KE ends up staying the same, since the velocity doesn't go up enough to make up for the loss of rotational mass.

3. You can lower the relative mainspring tension the same as the relative moment of inertia before lock time increases. KE has decreased 37%, though, and it's unknown how much you can lose before reliability becomes an issue.

4. You can extend this analysis to ask how low you can lower mainspring tension to get any relative KE.

5. This analysis shows that it's not so much the mass of the bobbed hammer, as it is where the mass was removed to get it. It'd be interesting to play with different shapes to figure out what shape gives the best balance of lowered inertia & strength, or how to minimize KE loss while reducing spring tension. I'll have to play with this some more.

Cheers -

Tom

...snipped the most awesome physics lesson

Not to muddy the waters, but would mainspring geometry have any effect? The usual bend in the spring for tuning like a Wilson or Miculek vs. the straighter stock type?

Edited December 8, 2011 by Shadowrider

[MrBorland]

The hammer's kinetic energy cannot be greater than the mainspring's stored energy. Same spring rate and preload, same energy, hammer weight doesn't matter, energy is the same BUT a lighter hammer will accelerate faster giving a higher final velocity.

Been thinking about this more. Very insightful. In fact, the Kinetic Energy will always be the energy delivered by the spring, no matter the mass of the hammer. Seems obvious now. Until now, I've always preached the lighter hammer picks up KE, but it's not so. Bobbing in and of itself neither increases nor decreases KE. Disregard my tractor trailer analogy, Peter.

But here's the rub: I've also always believed it's KE that lights off primers. And my experience tells me a lighter hammer will provide more reliable ignition as the pull weight goes down. So if it's not KE that lights off primers, what is it? Very likely, it's Power. Power is energy per unit time. In my example, the bobbed hammer reduced lock time by 20% and gained 26% in velocity, leading to a 26% in power. The lighter hammer is literally more powerful. Gonna have to take that to pencil & paper a bit more.

would mainspring geometry have any effect? The usual bend in the spring for tuning like a Wilson or Miculek vs. the straighter stock type?

Experience tells many of us it does. I have my guesses as to why it works, but as saw here, there's nothing like a little basic physics & paper & pencil to shoot holes in guesses . I'd like to look into the physics of leaf spring a bit more. Just curious.

Cheers -

Tom

[TheBrick]

Tom E and GrandBoule,

I am about to surrender but I have one last thing to throw into the works.

If you both agree that kinetic energy comes from the energy in the spring and hammer weight is not a factor; consider the formula for kinetic energy: KE=Psquared/2M

P is momentum which is speed times mass.

M is mass

How could mass which is a factor in both momentum and KE formulas NOT be important.

I think the Truck/car analogy was on the money.

As I said previously, if it feels good or it makes you think you have an advantage, then do it.

Just not too sure there is really a perceptual difference to the average shooter when shooting fast as in USPSA or that the muzzle jump when the hammer falls (unbobbed) disturbs the sights enough to cause a C instead of an A. My opinion.

A High Master PPC shooter on the 50 yard stage, maybe but not in USPSA.

I misread the part about greater acceleration reducing lock time. Got it now.

Thanks,

Peter

[JFlowers]

So..... with Carmoney out of the business as he builds his legal business, where do hammers go to die these days?

[Tom E]

I've also always believed it's KE that lights off primers. And my experience tells me a lighter hammer will provide more reliable ignition as the pull weight goes down. So if it's not KE that lights off primers, what is it?

Maybe it's simpler. Maybe it's just a matter of the primer being sensitive to the velocity of the firng pin impact. The firing pin has to dent the primer to crush the media between the cup and anvil. It has to do it with enough velocity to ignite the mixture.

Reducing hammer weight makes it easier to accelerate so "less" mainspring (allowing us a lighter DA pull) is required to get enough velocity. This does get modified by primer cup hardness and seating depth, both of which can bleed velocity of the primer cup impacting the anvil.

Then there's the leaf spring and the link between the spring and hammer. There appears to be an issue with link geometry wasting (inefficiently transferring) hammer energy. Mechanical "bottoming" of the link against the hammer aside, we bend a stock mainspring to maintain "good" link geometry with less spring preload. Stock mainsprings get bent. Wolff appears to just put more arch in their reduced power spring. Same result and reason, good link geometry with the spring installed with less preload.

[lugnut]

Hmmm, It's been too long since my engineering degree but here's my take on this. It's like splitting hairs IMO. I have one bobbed hammer on one of my 686s and the rest are not bobbed. The 686 without the bobbing has a lighter pull than the bobbed gun- each are

set for reliable ignition.

I think the most important reason to bob is to get a high grip without the spur hitting your hand. When I get a high grip sometimes the spur will hit the fat between my thumb and index finger... not much so it doesn't bother me. Matter of fact when it just touches I know my grip is just the way I want it.

This all being said, I'm not looking for that extra 1/2 lb in the trigger... 6-6.5 lbs is quite fine for me. At the local level I've seen people dick around with their guns so much they are unreliable. In action shooting reliable ignition is paramount- especially for revo.

Then again... the best revo guy in the world bobs his hammers huh?

[snertley]

So..... with Carmoney out of the business as he builds his legal business, where do hammers go to die these days?

In the dark back corners of many dusty, beer can filled workshops at the hands of nervoius dremalist.

[JFlowers]

Snertly, while I can write code like a banshee, I am well aware of my mechanical ineptitude and have had all dremels on my property removed and hidden. My backup 625 has been polished with a Wolffe spring kit, but still remains fully hammered with a heavier trigger than my Carmoney main gun.

[snertley]

Snertly, while I can write code like a banshee, I am well aware of my mechanical ineptitude and have had all dremels on my property removed and hidden. My backup 625 has been polished with a Wolffe spring kit, but still remains fully hammered with a heavier trigger than my Carmoney main gun.

lmao I could not write a single string of code if my life depended on it. But I can operate a dremel pretty well. I have only done one hammer but have done a bunch of cylinder chamfers free handed with the dremel. That tool is one of the best gifts my wife has ever got me.

[MrBorland]

So..... with Carmoney out of the business as he builds his legal business, where do hammers go to die these days?

Well, the bench grinder, of course. The dremel took too long. (see my 625 on post #19).

Out of town at the moment with tenuous internet connection...More later...

Tom