I know that in a handgun, the combination of recoil and time in the barrel contributes to POI. Supposing I had a .44 mag hunting load with a 270gr bullet leaving the barrel at 1100fps. If I want to compute a target load that has approximately the same POI (short range - ignoring effect of B.C. that will occur at longer ranges), do I simply search for a lighter weight bullet/load combination that will equal that same 1100fps?
Question about managing POI
- Thread starter Doyle
- Start date
serf 'rett
New member
I don't think its that simple. I suspect dwell time will enter the equation. But what do I know....
Rett, that dwell time is the reason for slower loads to impact higher than faster loads - the barrel has more time to rise with recoil. That is why I'm thinking that a target load using a lighter bullet, but exiting at the same speed as the hunting load, gives me a better chance of sharing the same POI.
I do exactly that and it will keep you pretty close at common pistol ranges. While I'm sure it's not precision math down to the last decimal point, if you just duplicate velocity, you'll be pretty close out to 25 yards, and if your not using a scope and benchrest, you probably won't be able to tell the difference at 40 yards.
serf 'rett
New member
I'm in way over my pay grade on this one and should likely keep my flapping trap shut but...
...I wasn't thinking as much in terms of the velocity of the bullet (obviously 1100 fps exit velocity is 1100 fps exit velocity no matter if the bullet is skinny or fat) but I was wondering if the impulse difference would be enough to lessen recoil; thereby, changing POI due to more/less rise, even given the same exit speed?
When you postulated using a .44 mag, I assumed we weren't talking 5 yards, even though you also said "short range". The hunting part also indicated something a tad further. I wondered if you were trying to duplicate a hunting load feel for practice.
Anyhow, you got me thinking so I referred to the few notes I had made when I was able to borrow a chronograph for measuring 9mm pistol loads. Targets a 50 feet, shooting off sand bags on bench. One load using a Berry’s 124 grain hollow back round nose thick plated bullet over 5.2 grains of Power Pistol clocked an average of 1089 fps. The second load, with a MO Bullet Company 124 grain Smallball lead bullet over 4.2 grains of W231 powder, ran an average of 1090 fps.
I know its plated versus lead, but the same weight and velocity for both loads. Even though the velocities are equal, here is where to differences lie – the Power Pistol load has more perceived recoil and had a group centers of 0.431” and 0.809” vertical displacement from two different accuracy test, while the W231 load, with its softer feeling recoil, had a vertical displacement of 1.605” almost twice as much - same velocity, even the same weight bullet, but significant different POI.
Dang if I don’t love reloading…
...I wasn't thinking as much in terms of the velocity of the bullet (obviously 1100 fps exit velocity is 1100 fps exit velocity no matter if the bullet is skinny or fat
) but I was wondering if the impulse difference would be enough to lessen recoil; thereby, changing POI due to more/less rise, even given the same exit speed? When you postulated using a .44 mag, I assumed we weren't talking 5 yards, even though you also said "short range". The hunting part also indicated something a tad further. I wondered if you were trying to duplicate a hunting load feel for practice.
Anyhow, you got me thinking so I referred to the few notes I had made when I was able to borrow a chronograph for measuring 9mm pistol loads. Targets a 50 feet, shooting off sand bags on bench. One load using a Berry’s 124 grain hollow back round nose thick plated bullet over 5.2 grains of Power Pistol clocked an average of 1089 fps. The second load, with a MO Bullet Company 124 grain Smallball lead bullet over 4.2 grains of W231 powder, ran an average of 1090 fps.
I know its plated versus lead, but the same weight and velocity for both loads. Even though the velocities are equal, here is where to differences lie – the Power Pistol load has more perceived recoil and had a group centers of 0.431” and 0.809” vertical displacement from two different accuracy test, while the W231 load, with its softer feeling recoil, had a vertical displacement of 1.605” almost twice as much - same velocity, even the same weight bullet, but significant different POI.
Dang if I don’t love reloading…
serf 'rett
New member
I forgot one thing...
...Roll Tide.....
Its that time of year again!
...Roll Tide.....
Its that time of year again!
Recoil force is equal and opposite to the bullet propelling force. That force multiplied by the time it takes from the start of bullet movement to the moment it clears the muzzle is the impulse. The muzzle elevation will be dependent on that. This is why, in general bullet weight has more effect on POI than powder charge does. Yes, a higher charge puts a short range bullet higher, but it's not as much higher as you expect. That's because th the force times the barrel time isn't as much different as velocity alone. That is, the faster bullet takes more force to accelerate, but it also spends less time in the barrel, which mitigates the influence of the extra force. The result is roughly proportional to the square root of the difference in velocity for a same-weight bullet, where the same force on a different weight bullet causes a difference closer to directly proportional to the weight of the bullet.
All this, of course, assumes a relatively short range; certainly not over 50 yards. That's because, given the arcing trajectory of a pistol bullet, drop starts to factor into the equation as well as muzzle elevation from recoil.
All this, of course, assumes a relatively short range; certainly not over 50 yards. That's because, given the arcing trajectory of a pistol bullet, drop starts to factor into the equation as well as muzzle elevation from recoil.
Nick, it has been a LOOOONG time since I've done heavy math (and even then I wasn't great at it) but I think what you are saying is that to match POI of an 1100fps 270gr bullet, a lighter bullet will have to actually be loaded to a higher velocity which would give it more recoil energy to drive the barrel up.
Doyle,
You got it. And I doubt that getting to enough higher velocity is practical, with exceptions for certain specific ranges where the trajectories cross one another on the drop from apogee. In other words, the heavy bullet will trace a larger arc, so there will be some distance at which it drops to the lighter bullet's POI. That can be calculated with an exterior ballistics program if you have the BC's and velocities.
You got it. And I doubt that getting to enough higher velocity is practical, with exceptions for certain specific ranges where the trajectories cross one another on the drop from apogee. In other words, the heavy bullet will trace a larger arc, so there will be some distance at which it drops to the lighter bullet's POI. That can be calculated with an exterior ballistics program if you have the BC's and velocities.
serf 'rett
New member
Thanks Unclenick! I knew it wasn't as simple as matching exit velocity.
In a few years I might actually understand what you wrote...
Point of Impact - most everyone likes folks to admire their targets with all the holes grouped on the "X". I was that way too until about 24 years ago when I watched a guy shooting hand guns at blank paper set 25 to 50 yards out. After seeing him several different days, I had to ask him "Just what are you aiming at?" I got a great lesson in sight picture and trigger control being the key to good groups -and good groups was THE primary goal. And he had good groups.
I'd leave the sights alone if I had a favorite hunting load. For range fodder I wouldn't worry if I'm 1.6" low on target.
Auburn is a long way off. We have to get past MS State before we see Auburn.
In a few years I might actually understand what you wrote...
Point of Impact - most everyone likes folks to admire their targets with all the holes grouped on the "X". I was that way too until about 24 years ago when I watched a guy shooting hand guns at blank paper set 25 to 50 yards out. After seeing him several different days, I had to ask him "Just what are you aiming at?" I got a great lesson in sight picture and trigger control being the key to good groups -and good groups was THE primary goal. And he had good groups.
I'd leave the sights alone if I had a favorite hunting load. For range fodder I wouldn't worry if I'm 1.6" low on target.
Auburn is a long way off. We have to get past MS State before we see Auburn.
Rett, check out this month's Sports Illustrated. Fear the dog.
http://www.si.com/more-sports/photos/2015/01/06/si-covers-2015/3
http://www.si.com/more-sports/photos/2015/01/06/si-covers-2015/3
Good thing I didn't know this was impossible two weeks ago. 300 gr Hornady JHP over 56 gr of Varget flies at 1650 fps. (.45-70).
300 gr Missouri lead over 54.5 gr of Varget flies at 1580 fps.
At 100 yards they are two groups about an inch apart. The lead is high. I do not understand why. I ran 3 powders and three bullets at 9 loads to find this. Six glorious hours, undisturbed at the range. I can now shoot lead instead of JHP for practice, likely saving me dozens of dollars a year.
I also determined that hot hi-tec coated loads group like buck shot. It very much likes the lead range. I'm guessing it slides over the rifling.
300 gr Missouri lead over 54.5 gr of Varget flies at 1580 fps.
At 100 yards they are two groups about an inch apart. The lead is high. I do not understand why. I ran 3 powders and three bullets at 9 loads to find this. Six glorious hours, undisturbed at the range. I can now shoot lead instead of JHP for practice, likely saving me dozens of dollars a year.
I also determined that hot hi-tec coated loads group like buck shot. It very much likes the lead range. I'm guessing it slides over the rifling.
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