Buck13
Member
My observation is that revolvers are more sensitive to bullet weight changing the point of impact than semi-auto pistols. I've tried to do some thought experiments on it, and I believe that the springs in an auto mean that the relative effects of variations in bolt thrust by the case head and travel time of the bullet down the bore are papered over by the action of the recoil and hammer springs. In other words, all loads transmit ROUGHLY similar net forces to the frame of the gun *during the time the bullet is in the bore,* since during that time the initial motion of the slide is against similar spring forces. Transit time in the bore will vary between different loads admittedly, but at least the spring forces during the crucial time should be pretty constant between loads. The force against the bolt face is higher with a hot load, but that difference appears as the greater *acceleration* of the slide, while the force on the frame (which determines how much the muzzle rises) is determined by the springs. There is *some* difference, of course, since the greater acceleration of the slide means that the slide moves more distance per millisecond and encounters somewhat higher spring forces by the time the bullet leaves, but this is still less than the force differential in a revolver.
The importance of this may be more clear if we go with a reductio ad absurdum example: If there was no recoil spring (and no hammer or hammer spring; say we were using some sort of electronic ignition of the primer/powder), the muzzle wouldn't rise AT ALL. In that extreme case, the slide would accelerate backward while transmitting no force to the frame other than rail friction until it hit the slide stop (or your face), by which time the bullet would be long gone.
In contrast, in a revolver, the net force on the gun is simply the chamber pressure times the bore area, minus the friction of the bullet in the bore. With a hot load this force is very high, but the acceleration of the bullet is very high too and the transit time goes down accordingly, so at a constant bullet weight, these effects tend to cancel out (approximately). With the hot load the gun starts to rotate up quicker, but the bullet exits quicker so the angle through which the gun rotates ends up about the same for all bullets of a given weight. But reduce the bullet weight (at a constant chamber pressure, or rather an identical peak chamber pressure) and the thrust of the case head stays the same, while the bullet acceleration goes up and transit time goes down, so the gun rotates less before the bullet leaves. Conversely for heavier bullets, transit time goes up and so the muzzle climbs higher before the bullet exits.
A significant fraction of recoil force is the "rocket exhaust" of the propellant gases leaving the bore, which is why muzzle brakes and compensators work well. This happens AFTER the bullet exits, so it doesn't affect how much gun rotation changes the launch angle of the bullet. Hot magnum loads with lots of muzzle jump might lead you to think that they'd make the bullet hit higher, but I don't believe this is the case. Or maybe I don't shoot handguns at ranges long enough to see these finer points when keeping bullet weight constant and increasing the powder charge... (In contrast, I do seem to remember making some very hot loads of .357 with Lil'Gun powder and seeing them hit much higher at 25 yards with my Rossi 92 rifle than a lighter load with the same bullet. My explanation for this would be that the long rifle barrel exposes the fact that in the distal part of the barrel, light loads have lost most of their pressure, so net bolt thrust is low and the gun is no longer being forced back and up, while the hot load is still pushing hard on both the gun and the bullet, but in a short handgun barrel the bullet force is more nearly constant along the whole length of the barrel.)
I realize this is all very non-quantitative, and I may be wrong. Maybe some engineer can pick apart this argument. That would be interesting. Tell me how wrong I am!
Of course, the range of bullet weights in autos tends to be less, too. I've only bought 9 mm from 115 to 147 grains, although lighter bullets are available in boutique ammo. I've handloaded .357 bullets from 75 grains to 215 grains, and .429 from 200 to 325 grains (and the first box of .43 Magnum ammo I bought after getting my Redhawk was Remington 185 grain JHP, because that's all I could find that day). In my Redhawk, the 300 or 325 grain bullets require the sight to be screwed all the way down to the frame to give a POI roughly on the POA.
I have a 4" fixed-sight GP100. Pretty much all 158 grain ammo hits fairly close to the POA at up to 25 yards (I shoot it mostly at 50') although I'm sure there are some finer points of just *how* close to POA which I've forgotten. Keith's 358429 170 grain LSWC are close enough as well. It seems pretty clear that Ruger designed the sights of that gun to work with 158 grain ammo. The POI is definitely low with 125s, sufficiently that it would be hard to hit empty beverage cans at more than maybe 10 yards without learning to hold the front sight a little high, IIRC. That might be an interesting skill to cultivate, but not a habit I'd want to get into.
The importance of this may be more clear if we go with a reductio ad absurdum example: If there was no recoil spring (and no hammer or hammer spring; say we were using some sort of electronic ignition of the primer/powder), the muzzle wouldn't rise AT ALL. In that extreme case, the slide would accelerate backward while transmitting no force to the frame other than rail friction until it hit the slide stop (or your face), by which time the bullet would be long gone.
In contrast, in a revolver, the net force on the gun is simply the chamber pressure times the bore area, minus the friction of the bullet in the bore. With a hot load this force is very high, but the acceleration of the bullet is very high too and the transit time goes down accordingly, so at a constant bullet weight, these effects tend to cancel out (approximately). With the hot load the gun starts to rotate up quicker, but the bullet exits quicker so the angle through which the gun rotates ends up about the same for all bullets of a given weight. But reduce the bullet weight (at a constant chamber pressure, or rather an identical peak chamber pressure) and the thrust of the case head stays the same, while the bullet acceleration goes up and transit time goes down, so the gun rotates less before the bullet leaves. Conversely for heavier bullets, transit time goes up and so the muzzle climbs higher before the bullet exits.
A significant fraction of recoil force is the "rocket exhaust" of the propellant gases leaving the bore, which is why muzzle brakes and compensators work well. This happens AFTER the bullet exits, so it doesn't affect how much gun rotation changes the launch angle of the bullet. Hot magnum loads with lots of muzzle jump might lead you to think that they'd make the bullet hit higher, but I don't believe this is the case. Or maybe I don't shoot handguns at ranges long enough to see these finer points when keeping bullet weight constant and increasing the powder charge... (In contrast, I do seem to remember making some very hot loads of .357 with Lil'Gun powder and seeing them hit much higher at 25 yards with my Rossi 92 rifle than a lighter load with the same bullet. My explanation for this would be that the long rifle barrel exposes the fact that in the distal part of the barrel, light loads have lost most of their pressure, so net bolt thrust is low and the gun is no longer being forced back and up, while the hot load is still pushing hard on both the gun and the bullet, but in a short handgun barrel the bullet force is more nearly constant along the whole length of the barrel.)
I realize this is all very non-quantitative, and I may be wrong. Maybe some engineer can pick apart this argument. That would be interesting. Tell me how wrong I am!
Of course, the range of bullet weights in autos tends to be less, too. I've only bought 9 mm from 115 to 147 grains, although lighter bullets are available in boutique ammo. I've handloaded .357 bullets from 75 grains to 215 grains, and .429 from 200 to 325 grains (and the first box of .43 Magnum ammo I bought after getting my Redhawk was Remington 185 grain JHP, because that's all I could find that day). In my Redhawk, the 300 or 325 grain bullets require the sight to be screwed all the way down to the frame to give a POI roughly on the POA.
I have a 4" fixed-sight GP100. Pretty much all 158 grain ammo hits fairly close to the POA at up to 25 yards (I shoot it mostly at 50') although I'm sure there are some finer points of just *how* close to POA which I've forgotten. Keith's 358429 170 grain LSWC are close enough as well. It seems pretty clear that Ruger designed the sights of that gun to work with 158 grain ammo. The POI is definitely low with 125s, sufficiently that it would be hard to hit empty beverage cans at more than maybe 10 yards without learning to hold the front sight a little high, IIRC. That might be an interesting skill to cultivate, but not a habit I'd want to get into.
Last edited:
)