Greg Walley
Member
Yes - Yes - and YES!
I have fixed quite a few rifles that didn’t shoot by simply increasing the firing pin fall. Most of the rifles in question had fall around 0.210” or less total travel, and 22-23 pound springs.
About ten years ago or so, I experimented quite a bit with ignition. I used a 6mm PPC and a -0.100” short 22 PPC. I used surplus IMR-8208 in the 6mm and H-4198 in the 22, and Federal 205 (non-match) primers of the same lot number.
I did the testing with a Stolle Panda/Young rail-gun configured with an 8” long barrel block with a round cavity. Barrels were clamped into the block with two 4” Delrin sleeves. I used a variety of spring weights and adjusted the fall accordingly. The testing was done with a Jewell BR, a Kelbly, and a Shilen BR trigger.
I also tried three different styles of firing pins. I used a standard 41 gram firing pin, the same style of firing pin with flutes (don’t remember the weight), and a popular “speed firing pin” with a body made from lightweight metal. The fluted firing pin was interestingly enough, an original Remington. I don’t remember what model action it came from. Firing pin tip diameters were 0.067”. Firing pin protrusion with all three samples used was 0.050 to 0.055”.
Incidentally, the triggers and the firing pin assemblies were tested to ensure they had consistent lock time. This crucial parameter was measured with a fiber-optic/DAQ sensing system that I devised.
I wore out two good Krieger 6mm unlimited barrels and a Hart 22 unlimited barrel, and wasted countless amounts of really good bullets over a three year period. I say I wasted because I should have known better - and deviating from established standards would only create problems and be a disappointment in the long run.
In a nutshell, what I found was that fall below 0.230” with a 23 pound spring resulted in inconsistent precision. Under almost every circumstance, 0.250” to 0.280” of fall produced the smallest groups day to day. What made the testing so elusive was that it wasn’t as if short fall preformed poorly every day. Some days, the groups were just as small as they were with long fall. But after months of testing, it becamee quite obvious that short fall (<0.230”) didn’t perform as consistently from day to day. I remember the groups with short fall would often have low vertical or low diagonal shots.
One thing I found conclusive was spring weight below 20 pounds, or firing pin travel below 0.200”, and/or the lightened firing pins were worthless. Groups when using either-or would be random, and were often times never round in shape.
One way I quantitively gaged the firing pin inertia was by measuring the penetration of the firing pin into a live primer (no propellant or bullet). I used brass with tight headspace which would close with considerable resistance on a stripped bolt. I don’t have all of the detailed figures of measurements at hand, but I specifically remember that a 41 gram 0.067” firing pin using a 23 pound spring with 0.250” of fall penetrated a Federal 205 primer 0.018-0.020”. I got this idea for penetration measurement from George Sr. Kelbly and Mike Walker. Mike Walker said that ignition testing back in the day was done with specially made copper inserts used in a test fixture, and the amount of penetration should be around 0.020” for reliable ignition. Unfortunately I couldn’t get much detail from him at the time because he was quite difficult to communicate with due to his deafness. So, I surmised that my method would be a close approximation of the standardized testing.
The shortened fall and lighter firing pin spring weights all reduced the penetration to 0.012” to 0.015”. I also remember widely varying/inconstant amounts of penetration with the lightened firing pins.
My conclusion from the testing was that springs below 22 pounds and firing pin fall under 0.230” were undesirable. I also remember that a variety of springs would vary in tension depending on how much they were used. I tried springs that were 30 years old with heavy use, yet still had 23-24 pounds of tension, but sometimes new springs degraded below 20 pounds within a few months…or even only after weeks of use.
Another interesting side note concerned the tightening torque of the screws on the barrel block was very important, especially for long shot strings. If the torque on the (lubricated) screws fell below 60 in/lbs, the rail gun wouldn’t shoot good ten shot groups. It may have shot good three to five shot groups, but not ten shots. The groups would wonder around randomly and get larger if the torque on the block was too low. Also, after several years, I switched to an aluminum sleeve/collet because the Delrin seemed to cold-flow and would eventually move around regardless of the screw torque. I suspect this was worse under extreme temperature changes of the barrel. This is a whole ‘nuther topic in itself!
Such testing can be ephemeral when shooting out in the conditions. Obviously it would be more meaningful if I could have done this in a tunnel. It could have been that I had to go to extremes of firing pin travel and spring weights to see a subsequent and noticable change on the target.
Another definitive conclusion during my testing - the bullet had to be "somewhere" into the rifling to shoot well from day to day. Jumping the bullet gave almost as inconsistent results as short firing pin fall.
Other confounding variables I thought of years later which could drastically change the results (and maybe even invalidate my testing) are types of propellant and the amount of neck tension used. My circumstances required light to medium neck tension with the 22 SPPC and the 6mm PPC...the 22 especially so because H4198 seemed to prefer relatively light neck tension (about 20 lbs. seating pressure).
It may be that the current trend of using very heavy neck tension can allow for a lighter strike to perform consistently because it would allow the propellant to start the deflagration process before the bullet moves into the rifling. I suspect that the bullets were moving into the rifling under the initial shock of the primer detonation with the light neck tension that I used.
In conclusion, I wouldn’t recommend deviating too far from established ignition standards.
Greg Walley
Abraxas LLC
I have fixed quite a few rifles that didn’t shoot by simply increasing the firing pin fall. Most of the rifles in question had fall around 0.210” or less total travel, and 22-23 pound springs.
About ten years ago or so, I experimented quite a bit with ignition. I used a 6mm PPC and a -0.100” short 22 PPC. I used surplus IMR-8208 in the 6mm and H-4198 in the 22, and Federal 205 (non-match) primers of the same lot number.
I did the testing with a Stolle Panda/Young rail-gun configured with an 8” long barrel block with a round cavity. Barrels were clamped into the block with two 4” Delrin sleeves. I used a variety of spring weights and adjusted the fall accordingly. The testing was done with a Jewell BR, a Kelbly, and a Shilen BR trigger.
I also tried three different styles of firing pins. I used a standard 41 gram firing pin, the same style of firing pin with flutes (don’t remember the weight), and a popular “speed firing pin” with a body made from lightweight metal. The fluted firing pin was interestingly enough, an original Remington. I don’t remember what model action it came from. Firing pin tip diameters were 0.067”. Firing pin protrusion with all three samples used was 0.050 to 0.055”.
Incidentally, the triggers and the firing pin assemblies were tested to ensure they had consistent lock time. This crucial parameter was measured with a fiber-optic/DAQ sensing system that I devised.
I wore out two good Krieger 6mm unlimited barrels and a Hart 22 unlimited barrel, and wasted countless amounts of really good bullets over a three year period. I say I wasted because I should have known better - and deviating from established standards would only create problems and be a disappointment in the long run.
In a nutshell, what I found was that fall below 0.230” with a 23 pound spring resulted in inconsistent precision. Under almost every circumstance, 0.250” to 0.280” of fall produced the smallest groups day to day. What made the testing so elusive was that it wasn’t as if short fall preformed poorly every day. Some days, the groups were just as small as they were with long fall. But after months of testing, it becamee quite obvious that short fall (<0.230”) didn’t perform as consistently from day to day. I remember the groups with short fall would often have low vertical or low diagonal shots.
One thing I found conclusive was spring weight below 20 pounds, or firing pin travel below 0.200”, and/or the lightened firing pins were worthless. Groups when using either-or would be random, and were often times never round in shape.
One way I quantitively gaged the firing pin inertia was by measuring the penetration of the firing pin into a live primer (no propellant or bullet). I used brass with tight headspace which would close with considerable resistance on a stripped bolt. I don’t have all of the detailed figures of measurements at hand, but I specifically remember that a 41 gram 0.067” firing pin using a 23 pound spring with 0.250” of fall penetrated a Federal 205 primer 0.018-0.020”. I got this idea for penetration measurement from George Sr. Kelbly and Mike Walker. Mike Walker said that ignition testing back in the day was done with specially made copper inserts used in a test fixture, and the amount of penetration should be around 0.020” for reliable ignition. Unfortunately I couldn’t get much detail from him at the time because he was quite difficult to communicate with due to his deafness. So, I surmised that my method would be a close approximation of the standardized testing.
The shortened fall and lighter firing pin spring weights all reduced the penetration to 0.012” to 0.015”. I also remember widely varying/inconstant amounts of penetration with the lightened firing pins.
My conclusion from the testing was that springs below 22 pounds and firing pin fall under 0.230” were undesirable. I also remember that a variety of springs would vary in tension depending on how much they were used. I tried springs that were 30 years old with heavy use, yet still had 23-24 pounds of tension, but sometimes new springs degraded below 20 pounds within a few months…or even only after weeks of use.
Another interesting side note concerned the tightening torque of the screws on the barrel block was very important, especially for long shot strings. If the torque on the (lubricated) screws fell below 60 in/lbs, the rail gun wouldn’t shoot good ten shot groups. It may have shot good three to five shot groups, but not ten shots. The groups would wonder around randomly and get larger if the torque on the block was too low. Also, after several years, I switched to an aluminum sleeve/collet because the Delrin seemed to cold-flow and would eventually move around regardless of the screw torque. I suspect this was worse under extreme temperature changes of the barrel. This is a whole ‘nuther topic in itself!
Such testing can be ephemeral when shooting out in the conditions. Obviously it would be more meaningful if I could have done this in a tunnel. It could have been that I had to go to extremes of firing pin travel and spring weights to see a subsequent and noticable change on the target.
Another definitive conclusion during my testing - the bullet had to be "somewhere" into the rifling to shoot well from day to day. Jumping the bullet gave almost as inconsistent results as short firing pin fall.
Other confounding variables I thought of years later which could drastically change the results (and maybe even invalidate my testing) are types of propellant and the amount of neck tension used. My circumstances required light to medium neck tension with the 22 SPPC and the 6mm PPC...the 22 especially so because H4198 seemed to prefer relatively light neck tension (about 20 lbs. seating pressure).
It may be that the current trend of using very heavy neck tension can allow for a lighter strike to perform consistently because it would allow the propellant to start the deflagration process before the bullet moves into the rifling. I suspect that the bullets were moving into the rifling under the initial shock of the primer detonation with the light neck tension that I used.
In conclusion, I wouldn’t recommend deviating too far from established ignition standards.
Greg Walley
Abraxas LLC
RG
