Thread seems to have gotten a little rough around the edges. I hesitate to stick a toe in, but will anyway.
Weshoots,
Would you mind posting what primers you run with your loads?
I see Lyman and Hornady manuals put Power Pistol loads up to 5.7 grains with 120-125 grain bullets, so they're within your envelope. But there is a dearth of data on Ramshot Silhouette. The only comparison I can make is in QuickLOAD with the bullet seating adjusted to make the Power Pistol load velocities match the Lyman and Hornady data. In that circumstance the powder models show an equal charge weight of Silhouette running 30% higher peak pressure than Power Pistol. So, with 5.6 grains of Power Pistol running about 30,000 psi, 5.6 grains of Silhouette, without changing anything else, gives almost 39,000 psi by the computer model. But it also predicts 6% more velocity from silhouette than the equal weight of Power Pistol produces, and if you don't get that difference in real world testing, then something has likely changed since the powder model was made. That computer model isn't as good with straight wall and short pistol cases as it is with bottleneck rifle cartridges in the first place.
Since I haven't had any direct experience with Silhouette, I can't really say how it compares to my Power Pistol loads. I'm just throwing the data into the pot to see if you can verify or contradict seeing an average velocity difference for equal charge weights of the two with 125 grain bullets.
Engineermike,
I think you'll find that if you are roll crimping you'll see case length difference can result in performance difference with some powders, especially the slower ones. The taper crimp makes a slight step in a lead bullet that helps prevent setback, but the taper angle is steep enough that it doesn't impose a similarly hard resistance to the bullet getting out. The force would be the sine of the taper angle times what it takes to pull the brass open perpendicular to the case axis. That lets people get away with more case length variation than a roll crimp does as long as the distance from the bottom of the inside of the casehead to the base of the seated bullet stays constant and thus defines a constant volume for the powder to start burning in. COL is the indirect indicator of bullet base position with respect to the casehead.
One reason 9 mm brass is all over the map on length has to do with the pressure the 9mm operates at. As a rule of thumb, 30,000 psi peak pressure in loads is a rough dividing line between brass that stretches and brass that shrinks from one loading cycle to the next. It's not exact, since pressure curve shape and brass thickness and hardness affect the exact number at which brass friction with the chamber gets high enough to stick it to the chamber wall and whether that happens before or after the pressure peak. As a result, some 9 mm stretches, some shrinks, and some just stays about the same. I've noticed the same thing with some .357 Magnum loads running in that pressure range. Makes for an interesting brass collection over time.
Another factor with small cases and slow powders is the primer sometimes unseats the bullet before the powder gas does it, thus increasing the powder space before powder burn dominate pressure. This lowers the peak pressure same as having a larger case would. This is a problem the .22 Hornet is famous for, too. Small powder space relative to the amount of primer gas is culprit. The result is erratic pressure profile and with it, erratic muzzle velocity when the problem is ocurring.
The cure in the Hornet is to use the mildest primers you can find and a powder that's not too slow for it. The 9 mm may benefit from the same treatment. Trying different primers to see if velocity consistency improves is the only test I know to make. Perhaps Tula/Wolf primers would help. They seem to have helped the consistency of .32 loads I've tried them in.
Though geared toward rifle loading, Denton Bramwell's Varmint Hunter article, The Perverse Nature of Standard Deviation describes why significance of some elements of load inconsistency can get lost in the noise while others are easy to detect. There's a copy here.
Weshoots,
Would you mind posting what primers you run with your loads?
I see Lyman and Hornady manuals put Power Pistol loads up to 5.7 grains with 120-125 grain bullets, so they're within your envelope. But there is a dearth of data on Ramshot Silhouette. The only comparison I can make is in QuickLOAD with the bullet seating adjusted to make the Power Pistol load velocities match the Lyman and Hornady data. In that circumstance the powder models show an equal charge weight of Silhouette running 30% higher peak pressure than Power Pistol. So, with 5.6 grains of Power Pistol running about 30,000 psi, 5.6 grains of Silhouette, without changing anything else, gives almost 39,000 psi by the computer model. But it also predicts 6% more velocity from silhouette than the equal weight of Power Pistol produces, and if you don't get that difference in real world testing, then something has likely changed since the powder model was made. That computer model isn't as good with straight wall and short pistol cases as it is with bottleneck rifle cartridges in the first place.
Since I haven't had any direct experience with Silhouette, I can't really say how it compares to my Power Pistol loads. I'm just throwing the data into the pot to see if you can verify or contradict seeing an average velocity difference for equal charge weights of the two with 125 grain bullets.
Engineermike,
I think you'll find that if you are roll crimping you'll see case length difference can result in performance difference with some powders, especially the slower ones. The taper crimp makes a slight step in a lead bullet that helps prevent setback, but the taper angle is steep enough that it doesn't impose a similarly hard resistance to the bullet getting out. The force would be the sine of the taper angle times what it takes to pull the brass open perpendicular to the case axis. That lets people get away with more case length variation than a roll crimp does as long as the distance from the bottom of the inside of the casehead to the base of the seated bullet stays constant and thus defines a constant volume for the powder to start burning in. COL is the indirect indicator of bullet base position with respect to the casehead.
One reason 9 mm brass is all over the map on length has to do with the pressure the 9mm operates at. As a rule of thumb, 30,000 psi peak pressure in loads is a rough dividing line between brass that stretches and brass that shrinks from one loading cycle to the next. It's not exact, since pressure curve shape and brass thickness and hardness affect the exact number at which brass friction with the chamber gets high enough to stick it to the chamber wall and whether that happens before or after the pressure peak. As a result, some 9 mm stretches, some shrinks, and some just stays about the same. I've noticed the same thing with some .357 Magnum loads running in that pressure range. Makes for an interesting brass collection over time.
Another factor with small cases and slow powders is the primer sometimes unseats the bullet before the powder gas does it, thus increasing the powder space before powder burn dominate pressure. This lowers the peak pressure same as having a larger case would. This is a problem the .22 Hornet is famous for, too. Small powder space relative to the amount of primer gas is culprit. The result is erratic pressure profile and with it, erratic muzzle velocity when the problem is ocurring.
The cure in the Hornet is to use the mildest primers you can find and a powder that's not too slow for it. The 9 mm may benefit from the same treatment. Trying different primers to see if velocity consistency improves is the only test I know to make. Perhaps Tula/Wolf primers would help. They seem to have helped the consistency of .32 loads I've tried them in.
Though geared toward rifle loading, Denton Bramwell's Varmint Hunter article, The Perverse Nature of Standard Deviation describes why significance of some elements of load inconsistency can get lost in the noise while others are easy to detect. There's a copy here.
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