Action Design

[GerryM]

Talking about lock time etc. anyone have a comparison to the Remington 788?
I believe it had one of the fastest years ago.

 

[Macropod]

I think a short lock time is not undesirable in any action. While it isn't a major requirement for benchrest or F class styles, the best and quickest locktime methods are often the best anyway. CG designed Belleville powerpacks get the job done with minimal vibration and upset and that has to be a plus. A heavy coil spring has an inherent vibration characteristic that the CG system manages to avoid. Putting on the flamesuit now! I know benchrest records have been made with a conventional coil spring firing pin but ultimately it must be an improvement if vibration and firing pin impact shock is minimized while maintaining a very consistent ignition.

The hard part is achieving a soft bolt lift to avoid rifle upset in the bags.

 

[Robert]

Alan Hall has an interesting take on the subject of ignition. He believes in a light, fast pin strike and that depth of indentation matters little.

+1 on this..
I would just quote Stuart Otteson:

From Stuart Otteson's book The Bolt Action’ (1976), p. 256:
"Both striker energy (1/2MV²) and impulse (MV) are functions of the mass and velocity of the firing pin, but with velocity more important in the energy term since it appears to the second power. If a firing pin is lightened, velocity will increase exactly enough to hold the energy term constant. Since impulse is only to the first power of velocity, however, it diminishes. Conversely, if the same impact energy is achieved with a heavier and slower-moving firing pin, a higher impulse effect results.

"It might intuitively seem that impulse improves the detonation effect of the firing-pin blow, and thus for a given impact energy, the slower and heavier type striker blow is more effective. It also apparently follows that the lack of momentum in a light fast firing pin fall requires an increased energy to compensate.

-"Both SAAMI and US Army studies on the subject show that exactly the opposite is true. At a given energy level, a light firing pin giving a snappy, low-impulse blow is more effective in detonating the primer than a heavier and slower pin’.

-‘A sharp, high-velocity impact transfers its energy to the primer faster and thus at a higher peak level. The low-velocity impact, with its greater impulse, not only transfers the energy over a longer time period, and so lower peak level, but it allows more cushioning in the energy-transfer process. This was graphically illustrated in extensive development work at Olin Corporation and described in US Patent 3,056,226 of Oct. 2, 1962 (Charles Hubbard and Robert Smith).

"The above explains a more subtle relationship between striker design and lock time. By only increasing mainspring power, and retaining a heavy firing pin, a low-velocity/high impulse ignition results. By decreasing weight, the percussion becomes a high-energy/low impulse type. This allows designing to a somewhat lower energy level, thus making possible a slight lock-time gain.

"Another practical advantage of a light, high-velocity mechanism, is that it allows ignition with a less violent striker blow. Since the jar of the striker blow precedes the bullet to the muzzle, this enhances a rifle's potential accuracy.

"Just how much impact is actually necessary for primer detonation depends also on a number of other variables. Certain standards are available, however, which consider normal manufacturing tolerances and a necessary margin for reliable ignition under varying conditions. Current US Army sensitivity requirements are 48 inch-ounces (0,34N/metre) for small-rifle primers and 64 inch-ounces (0,45 N/metre) for large-rifle primers.".

 

[Dusty Stevens]

Ive never considered army testing to be on the cutting edge of even marginal accuracy. They make sure the cartridge goes off reliably and makes sure the soldiers can deliver truckloads of firepower without fail at any moment. There is not a single innovation the military has contributed to competition level accuracy. Just the light firing pin thing has been and can be proven time and time again from anybody that has a rifle capable of shooting a 1/4" group. Do a search on here and see how many broken guns have been fixed by replacing the speedlock fix.

 

[JohnKielly]

But does Stuart Otteson's information have any reflection on what we are interested in - a consistent rate of ignition, the smallest possible velocity spread which isolation, would contribute it the greatest accuracy?

 

[dkhunt14]

But does Stuart Otteson's information have any reflection on what we are interested in - a consistent rate of ignition, the smallest possible velocity spread which isolation, would contribute it the greatest accuracy?

I feel velocity spread has nothing to do with accuracy. I have seen big velocity spreads shoot little groups and small velocity spresds shoot big groups. This is especially true at long range. This wasn't just one rifle or cartridge either.

If this was absolutely true one would think the PPC Shooters would weigh charges on a precision scale. Matt

 

[Dusty Stevens]

I feel velocity spread has nothing to do with accuracy. I have seen big velocity spreads shoot little groups and small velocity spresds shoot big groups. This is especially true at long range. This wasn't just one rifle or cartridge either.

If this was absolutely true one would think the PPC Shooters would weigh charges on a precision scale. Matt

Like matt said chasing velocity aint the ticket. Reading the wind is way by far the most important thing. Invest in windflags and learn what they tell you

 

[jbhotrod]

I feel velocity spread has nothing to do with accuracy. I have seen big velocity spreads shoot little groups and small velocity spresds shoot big groups. This is especially true at long range. This wasn't just one rifle or cartridge either.

If this was absolutely true one would think the PPC Shooters would weigh charges on a precision scale. Matt

Any chance you could give a brief summary of your load development process sir?

 

[BoydAllen]

A couple of thing on the firing pin spring thing: I have no doubt that people have fixed problem rifles by replacing firing pin springs, but there is a variable here that should be mentioned, firing pin tip diameter. Back when Jerry stiller was testing the first Viper prototypes they did extensive testing of spring weights looking at consistency of pressure rise curves using an Oehler 43 http://www.dexadine.com/wizard.html
Those actions all have a small firing pin tip. I believe that the nominal measurement is .062. Anyway, mine came with a cocked weight of 19# and I have tried heavier springs and lighter pins in various combinations without any apparent ignition problems. I believe that this is because of the small firing pin tip. The testing that Stiller did included springs that were a lot lighter than 19# and they never saw any pressure rise consistency issues even at the lightest weights. Concentrating the energy or momentum in a smaller area seems to have the benefit of allowing lighter everything, pins and springs. Of course there is always the question of whether there are other issues that effect the performance of a smaller pin tip. I will leave that to those who have more experience with both.
As far as the vibration of coil springs goes, I believe that the action that Bart mentioned has dual opposite wound springs that the designer thanked David Tubb for his assistance with. David offers springs of that design for a few actions including the SA Remington, which fit Pandas, and my Viper. That setup decreases bolt lift effort a the top of the lift slightly without decreasing spring weight and also decreases bolt vibration. I learned about this spring setup from a Facebook post by Speedy, and investigated further on Tubb's site before ordering one for myself and a couple for a friend who shoots Pandas. We both like them. Of course neither of us are in Bart's league, but I think that we are both capable of seeing a change for the worse if there had been one, and we did not.

 

[Alex Wheeler]

This is a quote I found from Jerry Stiller. His experience mirrors what I have seen to a T. Right down to his pin fall numbers. He was not just making this stuff up.

"In general, you want to have about .240 minimum fall on the pin without a primer in it. (hard stop inside bolt) It is hard to make up for travel with spring force or additional weight. Additional weight tends to slow the pin, but helps if there is any drag. Our experience with the standard Rem type of pin is that .220 or less is not very desirable. It is hard to add enough spring or mass to fix that. Small rifle primers from Federal are a little forgiving, but that is kind of our spec. As a note of interest, we bought a bunch of old 308 machine gun ammo to test our actions with. It had HARD primers in them. A factory Rem or Savage wouldnt even reliable fire them. Our Viper with a 20 lb spring and .250 fall wouldnt either. I put a 25 lb spring in it and no go. I made a longer hanger and put .300 fall instead with both springs and it fired like a big dog. That extra .050 made the most difference. If you look at the energy equations, it made sense too. I wouldnt fix a problem you dont have, but extra travel is most effective. Only problem is that a lot of br guys dont like the "Cock on close" feel they get on the bolt when it picks up the trigger at the last moment. I never let that bother me. I prefer it to have enough fall and dont even notice the timing thing anymore so I usually put our hangers on the longer pull setting."

 

[Brians356]

A couple of thing on the firing pin spring thing: I have no doubt that people have fixed problem rifles by replacing firing pin springs, but there is a variable here that should be mentioned, firing pin tip diameter. Back when Jerry stiller was testing the first Viper prototypes they did extensive testing of spring weights looking at consistency of pressure rise curves using an Oehler 43 http://www.dexadine.com/wizard.html
Those actions all have a small firing pin tip. I believe that the nominal measurement is .062. Anyway, mine came with a cocked weight of 19# and I have tried heavier springs and lighter pins in various combinations without any apparent ignition problems. I believe that this is because of the small firing pin tip. The testing that Stiller did included springs that were a lot lighter than 19# and they never saw any pressure rise consistency issues even at the lightest weights. Concentrating the energy or momentum in a smaller area seems to have the benefit of allowing lighter everything, pins and springs. Of course there is always the question of whether there are other issues that effect the performance of a smaller pin tip. I will leave that to those who have more experience with both.
As far as the vibration of coil springs goes, I believe that the action that Bart mentioned has dual opposite wound springs that the designer thanked David Tubb for his assistance with. David offers springs of that design for a few actions including the SA Remington, which fit Pandas, and my Viper. That setup decreases bolt lift effort a the top of the lift slightly without decreasing spring weight and also decreases bolt vibration. I learned about this spring setup from a Facebook post by Speedy, and investigated further on Tubb's site before ordering one for myself and a couple for a friend who shoots Pandas. We both like them. Of course neither of us are in Bart's league, but I think that we are both capable of seeing a change for the worse if there had been one, and we did not.

I wonder if any of the tricks used to smooth out and reduce vibration in quality high-powered spring-air rifles could apply to firing pin springs? I recall Robert Beeman made much of "super tuning" Weihrauch and other fine springers, but he was something of a smooth carnival huckster so I don't know if there was much substance behind it. There was polishing and special spring grease involved as I recall.
-

 

[BoydAllen]

This is a quote I found from Jerry Stiller. His experience mirrors what I have seen to a T. Right down to his pin fall numbers. He was not just making this stuff up.

"In general, you want to have about .240 minimum fall on the pin without a primer in it. (hard stop inside bolt) It is hard to make up for travel with spring force or additional weight. Additional weight tends to slow the pin, but helps if there is any drag. Our experience with the standard Rem type of pin is that .220 or less is not very desirable. It is hard to add enough spring or mass to fix that. Small rifle primers from Federal are a little forgiving, but that is kind of our spec. As a note of interest, we bought a bunch of old 308 machine gun ammo to test our actions with. It had HARD primers in them. A factory Rem or Savage wouldnt even reliable fire them. Our Viper with a 20 lb spring and .250 fall wouldnt either. I put a 25 lb spring in it and no go. I made a longer hanger and put .300 fall instead with both springs and it fired like a big dog. That extra .050 made the most difference. If you look at the energy equations, it made sense too. I wouldnt fix a problem you dont have, but extra travel is most effective. Only problem is that a lot of br guys dont like the "Cock on close" feel they get on the bolt when it picks up the trigger at the last moment. I never let that bother me. I prefer it to have enough fall and dont even notice the timing thing anymore so I usually put our hangers on the longer pull setting."

Jerry is the last person that I would ever think would make anything up. Having said that and not discounting anything that either of you have said, I think that there are other factors at work. My PPC brass has a 30 degree shoulder and the shoulders are bumped a thousandth from a tight case, no more. Also I always have my bullets seated somewhere in the rifling. Compare this to his .308 factory loaded test ammo, which was undoubtedly several thousands shorter than the chamber at the shoulder with a "softer" shoulder angle. I have accidentally combined (discovered sometime later) a 19# spring with a fluted aluminum shafted Tannel firing pin and never knew the difference, on the target or for reliability. Well let me say that the on the target was not match and I could have thought that I was dealing with a slight tuning issue, but I did not have issues like paper between shots when the wind was not an issue, after a little tuning. This was mostly with federal primers, with a .220 fall and Jerry's nominal .062 tip diameter. Long ago I had colored up the entire pin and spring and shot it that way for a bit and when I took it apart it showed not sign of drag. I had taken Jerry's advice some time before and reversed the hanger picking up a tiny amount of cock on close that disappears when running the bolt fast. Bottom line, it seems to work very well for what I use it for. One of these days I will probably take my tools to the range and do some pin and spring swapping and see if I can make it act up.

 

[Alex Wheeler]

Extra hs actually increases pin fall, hs would have to be quite excessive for the pin to stop in the bolt rather than on the primer. Primers usually indent .030"ish. Assuming .055" protrusion, hs would have to be about .020" to have negative effects on ignition.
What I like about what he was trying to convey is that its very hard to make up for fall with more spring and weight. Jerry is not the only action designer with that opinion.
Load some cci 450s and bring the chrony when you do your testing or better yet shoot groups at long range.

 

[BoydAllen]

Having a lot of cartridge "headspace" interferes with the transfer of energy to the primer. Years ago, a friend had a scratch built .22-250 AI and took it to the range to make cases from two different brands of factory ammo. One brand fired every time and the other did not. We came to the conclusion that differences in the two brands "headspace" and perhaps primer hardness were the reason. I have observed that new brass is often well under SAAMI minimum chamber headspace. Neither had issues in a regular chamber that offered the stronger backing that having a chamber shoulder angle that matched the cartridge provided. When the firing pin hits a loose fitting cartridge some of its energy goes to moving the cartridge forward in the chamber.

Of course if you are merely calculating pin energy or momentum none of this comes into play.

Anyone who runs the numbers can easily see how important pin fall is to energy or momentum, because of the effect that it has on speed. I was just pointing out that while action builders have to cover all sorts of applications that for individual situations the requirements may be different.

If one looks at the groups and aggs. that have been shot with BAT actions and compare those actions pin falls to what have been called superior specifications there is a disconnect. I think that the reason is the common use of relatively soft cupped primers in 6PPCs, and that the case has a substantial shoulder angle and that shoulder bump is typically minimal, and closely monitored. Of course this is only conjecture, but the pin fall specifications are real as are the groups.

 

[Dusty Stevens]

There is headspace and then there is headspace.
Fguffey

 

[Alex Wheeler]

Having a lot of cartridge "headspace" interferes with the transfer of energy to the primer. Years ago, a friend had a scratch built .22-250 AI and took it to the range to make cases from two different brands of factory ammo. One brand fired every time and the other did not. We came to the conclusion that differences in the two brands "headspace" and perhaps primer hardness were the reason. I have observed that new brass is often well under SAAMI minimum chamber headspace. Neither had issues in a regular chamber that offered the stronger backing that having a chamber shoulder angle that matched the cartridge provided. When the firing pin hits a loose fitting cartridge some of its energy goes to moving the cartridge forward in the chamber.

Of course if you are merely calculating pin energy or momentum none of this comes into play.

Anyone who runs the numbers can easily see how important pin fall is to energy or momentum, because of the effect that it has on speed. I was just pointing out that while action builders have to cover all sorts of applications that for individual situations the requirements may be different.

If one looks at the groups and aggs. that have been shot with BAT actions and compare those actions pin falls to what have been called superior specifications there is a disconnect. I think that the reason is the common use of relatively soft cupped primers in 6PPCs, and that the case has a substantial shoulder angle and that shoulder bump is typically minimal, and closely monitored. Of course this is only conjecture, but the pin fall specifications are real as are the groups.

Ejector pushes the case forward. Aggs in short range where soft primers and es means little are different than aggs in lr where primers are harder and things get critical. My comments apply to lr only

 

[old leghumper]

Falling block actions? Let the debate begin.

 

[Dusty Stevens]

Falling block actions? Let the debate begin.

Never seen one make it to a match much less be ready to compete in one

 

[dkhunt14]

Never seen one make it to a match much less be ready to compete in one

In 2012 a Hall falling block won the Nationals heavy gun and a few others. I believe he also did good in 2013. Matt

 

[BoydAllen]

Ejector pushes the case forward. Aggs in short range where soft primers and es means little are different than aggs in lr where primers are harder and things get critical. My comments apply to lr only

Your last sentence was my point. Not all actions have ejectors, and not all that do have spring plunger. I have always said that for short range you cannot pick a load with a chronograph, having said that the last time that I ran a PPC over one I was surprised as to how good it was in that respect. I don't remember the numbers but I do remember that the bullets seated with very similar feel. When I load at the range, I group by seating feel and shoot like with like. If I were ordering a new BAT for long range, I would undoubtedly order a "long pin" (Did I get that right?) and I do not think that that option would have happened without all of the testing that you and Tom have done being published and discussed. Speaking of long range, some time ago I put a friend who builds his own rifle and for others onto the 6BRA which I had learned about from you. He continues to be amazed by what it can do, having built and shot any number of bigger case long range rifles. He and friends shoot out to 1,200 yards regularly. Thanks to your sharing, he has your identical reamer from JGS, the company that you use.