Reloading to adjust POI of fixed sight pistols

[ChuckS1]

Lately I've been playing around with 3 fixed sight pistols. I have a 4" .38 M&P, a M1917 and a USFA Pre-War in .45 Colt with a 5 1/2" barrel. In testing different loads, all with LRN loads, I've noticed that at some point, usually on the higher end of my velocities, my point of impact begins to move to the right. I noticed that with my M1917 when I was developing loads to adjust elevation, but today it became very apparent with the USFA revolver. I used a Lyman 452400 230 grain LRN, sized at .452, with loads starting with 7.0 grains of Unique and stepping up in .2 grain increments to 8.0 grains. Using an NRA B-8 target at 25 yards, I saw my groups go from 9:00 in the 9 ring (7.0 grains) to 7:00 in the 9 ring (7.2 grains) to 10:00 in the 10 ring (7.4 grains) to 8:00 in the 10 ring (7.6 grains) until the 7.8 and 8.0 grain loads generally centered on and inside the 10 ring. All the 5 round groups were less than 2".

Now I know that a lower velocity will generally cause a higher POI, all things being equal, due to barrel dwell time, but was wondering if any one else has seen the windage change as powder charges changed.

I did see this to some extent with my 1917 using 452190 250 grain bullets, but not this obvious and I chalked that up to shooter error.

Opinions? Am I imagining this or did I subconsciously adjust my sight picture? BTW, I was shooting off sandbags sitting at a bench this morning, about 32 degrees and a slight wind.

 

[OKFC05]

Personally, I've had good luck moving the POI with bullet change of weight, but not so much changing powder weight.

Such changes with powder weight seem to be small and unpredictable.

 

[jibjab]

"wondering if any one else has seen the windage change as powder charges changed."

I think this is caused by the barrels rifling as the bullet passes, imparting torque on the gun.

 

[Vulcan Bob]

Boy,I cant really give you an answer on this one as each gun seems to be a law unto itself. If it's printing a bit right, with a two hand grip try applying a bit of pressure to the left side of the frame with your offhand thumb (opposit if left handed) this will help to pivot the gun slightly left under recoil. Sometimes this works and sometimes not, as usuall results may vary!

 

[Ron H.]

Lately I've been playing around with 3 fixed sight pistols. I have a 4" .38 M&P, a M1917 and a USFA Pre-War in .45 Colt with a 5 1/2" barrel. In testing different loads, all with LRN loads, I've noticed that at some point, usually on the higher end of my velocities, my point of impact begins to move to the right. I noticed that with my M1917 when I was developing loads to adjust elevation, but today it became very apparent with the USFA revolver. I used a Lyman 452400 230 grain LRN, sized at .452, with loads starting with 7.0 grains of Unique and stepping up in .2 grain increments to 8.0 grains. Using an NRA B-8 target at 25 yards, I saw my groups go from 9:00 in the 9 ring (7.0 grains) to 7:00 in the 9 ring (7.2 grains) to 10:00 in the 10 ring (7.4 grains) to 8:00 in the 10 ring (7.6 grains) until the 7.8 and 8.0 grain loads generally centered on and inside the 10 ring. All the 5 round groups were less than 2".

Now I know that a lower velocity will generally cause a higher POI, all things being equal, due to barrel dwell time, but was wondering if any one else has seen the windage change as powder charges changed.

I did see this to some extent with my 1917 using 452190 250 grain bullets, but not this obvious and I chalked that up to shooter error.

Opinions? Am I imagining this or did I subconsciously adjust my sight picture? BTW, I was shooting off sandbags sitting at a bench this morning, about 32 degrees and a slight wind.

Sir, I've seen similar windage changes when working up loads in .45 Colt and .44 mag. At first the change was slight, but with both cartridges there was a point where the change became very pronounced.

I wonder if maybe it happens in the trans-sonic zone, as the load goes from sub- to super-sonic. The loads I was working with should have been in about that vicinity, but I didn't chronograph them. Or maybe it's just increased recoil changing the way the gun moves in the hand. This seems more likely, but it's hard to know for sure.

Anyway, I don't know why it happens, but it definitely does happen.

Hope this helps, and Semper Fi.

Ron H.

 

[Missionary]

Good morning & Merry Christmas
Internal balistics are well documented... books have been written about the effects of bullet passage through the barrel.
Generally duplicate the origonal factory load for that time period the firearm was manufactured and the sights wil be close.
Grip will also add or negate the effects of bullet passage to the target.
When all the factors are figured in that is what makes accurate hand gun shooting what it is...

 

[epj]

I once had a Marlin lever gun in .44 Mag. I loaded for it with both 240 gr. and 180 gr. bullets. I found that at about 50 yards, the 180 gr. bullet would shift a good 4" or more to the left. Changing back to the 240 gr brought the POI right back on target. Finally gave up the 180 grainers as a bad idea in that perticular gun, though they were probably a lot flatter shooting than the 240.

 

[Skip Sackett]

Finally gave up the 180 grainers as a bad idea in that perticular gun, though they were probably a lot flatter shooting than the 240.

I can tell you this, groundhogs don't like 180gr XTP's flying at them from a Marlin 1894! Never knew what hit it, but there it laid.