JimGnitecki
Member
- Joined
- Mar 28, 2010
- Messages
- 1,258
Lousy & Illogical statistics but GREAT 5-shot pistol groups. Go figure . . .
You are about to see some pretty lousy and sometimes seemingly illogical statistics for the ammunition I loaded and fired recently. But three 5-shot groups qualify as probably “great”, considering my mediocre talents as a shooter and my aging eyesight.
I am scratching my head trying to figure out why the groups are so good when the individual statistics on the ammo are either mediocre or actually lousy.
Some background:
I have been working to develop a 9mm 115g load for my SIG P210 pistol. I load on a Dillon XL750. I recently added Armanov bolted-in toolheads and free fooating die rings. I also replaced the Dillon bullet seating die with a 9mm Redding Competition Bullet Seating Die. These changes were to address an inconsistent Cartridge Overall Length (COAL) problem that I thought might be increasing group sizes.
The load under development is:
9mm Luger
Using new, and then pre-fired by me Hornady cases
115g Hornady HAP bullets (jacketed truncated cone with hollowpoint), which were designed as XTP bullets withOUT the expansion cuts, for use in Action Pistol competition shooting
Federal Gold Medal Small Pistol primers
8.0 grains of Vihtavouri 3N38 powder, which is a slow burning powder, again targeted at Action Pistol shooting competitiob, where the slow burn rate supports high velocities and has sufficient post-barrel residual pressure to operate a compensator to reduce recoil
The objectives of the load include high accuracy, muzzle velocity of around 1300 fps, manageable recoil, and lower peak pressures than you might expect due to the slow powder burn rate. All 3 objectives have apparently been met, but the load exhibits some statistics that leave me wondering why it works so well despite those statistics.
The Pistol:
The pistol is a brand new SIG P210A Target model, that before yesterday’s shooting session had only 240 rounds fired through it.
Here are the 3 best targets from a shooting session yesterday to test multiple different COALs. Remember, these are 5-shot groups, fired at a verified 25 yards, from a SIG P210A Target model pistol:
I think we cna all agree that while these are by no means “perfect” groups, most pistol shooters would be happy with them. And note that they were fired at the local outdoor range, in 0 to 4 degree C weather (32 to 40 degrees F), using a 6” x 6” x 6” carpeted cube as a rest, and I am 70 years of age, have had cataract laser surgery, and wear progressive bifocal eyeglasses. And yes, open sights.
The Analytical Excel Worksheet:
I had prepared an Excel worksheet that documents the 35 prepared cartridges, plus 5 cartridges that were used for sight adjustment beforehand. This Excel worksheet was filled in gradually, before, during, and after firing the rounds, as the information for the worksheet fields became available.
The worksheet image included here is very hard to read, because Excel does not support exporting as a jpg file. So I had to zoom OUT in the Excel view, snap a desktop image, and then import that image into the Apple Photos program. There, I trimmed it, optically enhanced it, and saved it as a jpg that can be printed on an 8.5 x 11” sheet of paper and that could be imported into this forum. If you unexpectedly find yourself mesmerized by the patterns, unexpected results, and apparent contradictions in it, and want to look at it more closely, you might find it best to print it out on paper where it iS legible.
Here’s the worksheet image:
Here is how to read the worksheet (if you actually want to do so) taking it one column at a time:
Target no: Each target sheet contains one 5-shot group, and is labeled as either 1 through 7, or as “Sighting 4”. Sighting 4 is the 4th group fired in the process of adjusting the sights to shoot a bit below the point of aim, which is the bottom point of the black triangle. I wanted to shoot below that point so that any shot holes would not obscure the aimpoint.
Round no.: This shows the sequence in which 5 x 7 = 35 rounds were actually made, measured, and then fired. They were fired as 5 shots into each of 7 targets. In addition, the 5 shot numbers for the “Sighting 4” target are shown as being the 16th through 20th shots fired at sighting targets. These shots do NOT have detailed measurements like the other 35 shots do because they were not part of the control group.
Crimp diameter: This is simply the measured crimp diameter of each round.
COAL to Tip of Bullet: This is the COAL for each round, measured simply as the distance from base of cartridge to tip of the Hornady HAP 115g hollow point bullet.
Base to .338 Gage: This is the supposedly more accurate way to measure cartridge length. Coal to Tip of Bullet is usually inaccurate with most jacketed bullets, as bullet manufacturers apparently are able to control bullet ogive dimensions and shank dimensions much better than they are able to control tip dimensions. I expected these to be much more consistant than the base ot tip of bullet dimensions, but was surprised . . . ! To measure this, I used a Hornady Bullet Comparator with my digital caliper. Hornady does not offer a 9mm (.355”) insert for the comparator, as the comparator was designed to measure rifle bullets, not pistol bullets. But that does not matter. To assess cartridge OAL consistency, the measurement can be taken from the cartrudge base to ANYWHERE on the ogive, as long as you always measure to the same point on the ogive (i.e. to the same ogive diameter). This is actually BETTER than trying to measure to the point where the bullet shank stops and the ogive starts, as there is obviously a transition zone there for any manufactured bullet, and therefore a potential for measuring error. So, I used the .338” diameter insert for measuring each cartridge. Ideally, each cartridge would have the exact same base to.338 gage measurement.
Why is this measurement “better’ than the Base to Tip measurement? Two reasons:
1.It should be more accurate, since ogive dimensions are betetr controlled by bullet manufacturers than tip dimensions are
2.We really don’t care where the tip ends up when the round is chambered, as long as the cartridge feeds through the magazine and can be chambered. But we are very concerned about the measurement from base to ogive, as it is the point at which the shank and ogive meet that first touches the rifling when the cartridge is fired. And we want to control that point, because it
COAL to Tip Std Dev for 5 prior: This is the standard deviation in COAL as measured by the “bullet tip” method in the 5 preceding rounds.
Base to .338 gage Std Dev for 5 prior: This column shows the standard deviation in Base-to-.338 gage, as measured by THAT method, in the 5 preceding rounds.
% Gage versus COAL Variance: This expresses, for each group of the 5 prior rounds (i.e. all the rounds included in that specific target no.) the magnitude of the length variance as expressed by the “.338 Gage” method versus the “COAL to Tip” method. Based on the bullet manufacturer assertion that ogive dimensions are much better controlled than tip dimensions, we epxect this ratio to be less than 100%. If it is more than 100%, it means that the standard deviation for the ogive based measurements was WORSE than for the TIP based measurments. That should not happen (But it did . . . )
You are about to see some pretty lousy and sometimes seemingly illogical statistics for the ammunition I loaded and fired recently. But three 5-shot groups qualify as probably “great”, considering my mediocre talents as a shooter and my aging eyesight.
I am scratching my head trying to figure out why the groups are so good when the individual statistics on the ammo are either mediocre or actually lousy.
Some background:
I have been working to develop a 9mm 115g load for my SIG P210 pistol. I load on a Dillon XL750. I recently added Armanov bolted-in toolheads and free fooating die rings. I also replaced the Dillon bullet seating die with a 9mm Redding Competition Bullet Seating Die. These changes were to address an inconsistent Cartridge Overall Length (COAL) problem that I thought might be increasing group sizes.
The load under development is:
9mm Luger
Using new, and then pre-fired by me Hornady cases
115g Hornady HAP bullets (jacketed truncated cone with hollowpoint), which were designed as XTP bullets withOUT the expansion cuts, for use in Action Pistol competition shooting
Federal Gold Medal Small Pistol primers
8.0 grains of Vihtavouri 3N38 powder, which is a slow burning powder, again targeted at Action Pistol shooting competitiob, where the slow burn rate supports high velocities and has sufficient post-barrel residual pressure to operate a compensator to reduce recoil
The objectives of the load include high accuracy, muzzle velocity of around 1300 fps, manageable recoil, and lower peak pressures than you might expect due to the slow powder burn rate. All 3 objectives have apparently been met, but the load exhibits some statistics that leave me wondering why it works so well despite those statistics.
The Pistol:
The pistol is a brand new SIG P210A Target model, that before yesterday’s shooting session had only 240 rounds fired through it.
Here are the 3 best targets from a shooting session yesterday to test multiple different COALs. Remember, these are 5-shot groups, fired at a verified 25 yards, from a SIG P210A Target model pistol:
I think we cna all agree that while these are by no means “perfect” groups, most pistol shooters would be happy with them. And note that they were fired at the local outdoor range, in 0 to 4 degree C weather (32 to 40 degrees F), using a 6” x 6” x 6” carpeted cube as a rest, and I am 70 years of age, have had cataract laser surgery, and wear progressive bifocal eyeglasses. And yes, open sights.
The Analytical Excel Worksheet:
I had prepared an Excel worksheet that documents the 35 prepared cartridges, plus 5 cartridges that were used for sight adjustment beforehand. This Excel worksheet was filled in gradually, before, during, and after firing the rounds, as the information for the worksheet fields became available.
The worksheet image included here is very hard to read, because Excel does not support exporting as a jpg file. So I had to zoom OUT in the Excel view, snap a desktop image, and then import that image into the Apple Photos program. There, I trimmed it, optically enhanced it, and saved it as a jpg that can be printed on an 8.5 x 11” sheet of paper and that could be imported into this forum. If you unexpectedly find yourself mesmerized by the patterns, unexpected results, and apparent contradictions in it, and want to look at it more closely, you might find it best to print it out on paper where it iS legible.
Here’s the worksheet image:
Here is how to read the worksheet (if you actually want to do so) taking it one column at a time:
Target no: Each target sheet contains one 5-shot group, and is labeled as either 1 through 7, or as “Sighting 4”. Sighting 4 is the 4th group fired in the process of adjusting the sights to shoot a bit below the point of aim, which is the bottom point of the black triangle. I wanted to shoot below that point so that any shot holes would not obscure the aimpoint.
Round no.: This shows the sequence in which 5 x 7 = 35 rounds were actually made, measured, and then fired. They were fired as 5 shots into each of 7 targets. In addition, the 5 shot numbers for the “Sighting 4” target are shown as being the 16th through 20th shots fired at sighting targets. These shots do NOT have detailed measurements like the other 35 shots do because they were not part of the control group.
Crimp diameter: This is simply the measured crimp diameter of each round.
COAL to Tip of Bullet: This is the COAL for each round, measured simply as the distance from base of cartridge to tip of the Hornady HAP 115g hollow point bullet.
Base to .338 Gage: This is the supposedly more accurate way to measure cartridge length. Coal to Tip of Bullet is usually inaccurate with most jacketed bullets, as bullet manufacturers apparently are able to control bullet ogive dimensions and shank dimensions much better than they are able to control tip dimensions. I expected these to be much more consistant than the base ot tip of bullet dimensions, but was surprised . . . ! To measure this, I used a Hornady Bullet Comparator with my digital caliper. Hornady does not offer a 9mm (.355”) insert for the comparator, as the comparator was designed to measure rifle bullets, not pistol bullets. But that does not matter. To assess cartridge OAL consistency, the measurement can be taken from the cartrudge base to ANYWHERE on the ogive, as long as you always measure to the same point on the ogive (i.e. to the same ogive diameter). This is actually BETTER than trying to measure to the point where the bullet shank stops and the ogive starts, as there is obviously a transition zone there for any manufactured bullet, and therefore a potential for measuring error. So, I used the .338” diameter insert for measuring each cartridge. Ideally, each cartridge would have the exact same base to.338 gage measurement.
Why is this measurement “better’ than the Base to Tip measurement? Two reasons:
1.It should be more accurate, since ogive dimensions are betetr controlled by bullet manufacturers than tip dimensions are
2.We really don’t care where the tip ends up when the round is chambered, as long as the cartridge feeds through the magazine and can be chambered. But we are very concerned about the measurement from base to ogive, as it is the point at which the shank and ogive meet that first touches the rifling when the cartridge is fired. And we want to control that point, because it
- sets the amount of “jump” that the bullet has to make before it hits the rifling and pressure increases as a result, and
- affects the size of the “combustion chamber” in which the powder is ignited. The deeper the bullet is into the case, the higher the peak pressure generated upon ignition.
COAL to Tip Std Dev for 5 prior: This is the standard deviation in COAL as measured by the “bullet tip” method in the 5 preceding rounds.
Base to .338 gage Std Dev for 5 prior: This column shows the standard deviation in Base-to-.338 gage, as measured by THAT method, in the 5 preceding rounds.
% Gage versus COAL Variance: This expresses, for each group of the 5 prior rounds (i.e. all the rounds included in that specific target no.) the magnitude of the length variance as expressed by the “.338 Gage” method versus the “COAL to Tip” method. Based on the bullet manufacturer assertion that ogive dimensions are much better controlled than tip dimensions, we epxect this ratio to be less than 100%. If it is more than 100%, it means that the standard deviation for the ogive based measurements was WORSE than for the TIP based measurments. That should not happen (But it did . . . )
