adjusting point of impact w/ powder charge


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thomis
January 16, 2013, 09:53 AM
Using a handgun with fixed sights (in this particular case, a S&W SD40VE), I know I can adjust windage by tapping the dovetailed rear sight back and forth. But not elevation.

Assuming I use the same bullet weight and powder , would increasing the powder charge raise or lower the point of impact, assuming the same sight picture and the same shooting distance?

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bds
January 16, 2013, 10:30 AM
If the pistol is new, I would wait until the pistol was sufficiently broken-in before adjusting sights.

With new guns, many shooters complain about needing to adjust sights. I usually tell them to shoot several hundred rounds first for the gun to break-in and parts surfaces to settle in. A friend's new 1911 POI did not correspond to POA at first, but after 200-300 rounds, POI matched POA and sights did not need to be adjusted. This was with several different lighter target loads and full power factory loads.

I usually conduct a full powder workup in 0.1 gr increments to map the accuracy trends from start to max charges. Once I identify the most accurate shot groups, I then make any adjustments to the sights. Usually, the most accurate shot groups trend with high range+ load data and sights don't need to be adjusted.

Most factory fixed sights work relatively well for POA/POI with full power loads.

918v
January 16, 2013, 11:11 AM
Primers affect poi more than powder.

MrBorland
January 16, 2013, 11:24 AM
Assuming I use the same bullet weight and powder , would increasing the powder charge raise or lower the point of impact, assuming the same sight picture and the same shooting distance?

I'm interested in others' take on the question, but my take is that the answer is that the POI won't change. Increasing bullet mass raises the POI, but increasing bullet speed doesn't. A fixed-sighted .357mag revolver, for instance, will shoot 158gr .38spls to the same point of impact as 158gr .357mags.

Because of the longer time of flight, it may be a bit different story with rifles shooting longer distances, but I don't believe muzzle velocity alone changes POI when we're talking handgun distances.

GooseGestapo
January 16, 2013, 11:31 AM
With a semi-auto, you'll not likely see much difference in elevation with different powder charges, assuming they are functioning the action.

With a revolver, (fixed breach), you can increase bullet weight/decrease velocity to increase the barrel lift prior to bullet exiting the muzzle, giving an increase in elevation, or, going to a lighter/faster bullet to lower the impact..

However, with a semi-auto, the bullet exits the barrel before the slide starts to move (casued intentionally by delay in unlocking of barrel through design), such that increases in velocity and bullet weight make little difference. (as contrasted to "NO" difference).

Such is why most semi-autos, aside from those intended for competition aren't equiped with adjustable sights.....

I've had to either lightly file down the front or rear sights to correct an elevation problem with fixed sighted semi-autos..... The latest one, a Springfield XD "Compact" in 9mm.

It shot high at 25yds. I lowered the rear sight and brought it to zero.... But I'm told that you can now get different highth front and rear sights from Springfield to correct this issue.

I too would suggest that you shoot the gun a bit before messing with the sights.

Also, how you grip the gun makes a substantial difference in how it will shoot.
I see some of the most atrocious grip/stances at a public range I frequent. Often a shooter will ask me why they can't "hit". I show them the correct grip/stance and they start hitting, till of course they revert to the way "they want" to shoot... Then they start to miss again and can't understand why.......

Remember; shooting a handgun it's: 1. Grip; 2. Sight alignment; 3. Trigger-squeeze
You can be "dipping" the front of the gun as you fire, causing the gun to shoot low....
focus on the front sight, and once you start the trigger squeze, follow though with it till firing.... If you try to "trigger off" the shot, you will "pull" the shot every time....

918v
January 16, 2013, 11:39 AM
However, with a semi-auto, the bullet exits the barrel before the slide starts to move (casued intentionally by delay in unlocking of barrel through design), such that increases in velocity and bullet weight make little difference. (as contrasted to "NO" difference).

False.

The slide and the barrel will move to the rear between 1/32" and 1/16" before the bullet exits the barrel, depending on the pistol.

MrBorland
January 16, 2013, 12:06 PM
With a revolver, (fixed breach), you can increase bullet weight/decrease velocity to increase the barrel lift prior to bullet exiting the muzzle, giving an increase in elevation, or, going to a lighter/faster bullet to lower the impact..

As bullet velocity decreases, yes, the bullet spends more time in the barrel, so the muzzle spends more time rising...but, the velocity of the muzzle rise is slower. In the end, the 2 effects cancel out...the .38spl muzzle rises slower, but longer, than the .357mag, but the distance the muzzles have risen while the bullet's in the barrel is the same, all else being equal. IOW, velocity alone has no effect.

James2
January 16, 2013, 12:18 PM
Fixed sights are pretty much that. Yes, some can be done with filing a sight off a bit. I have done that with the front sight, but have never tried to file a rear sight.

The ol timers used to say "Take a fine bead." There is a lot to be said for that technique. One just needs to adjust the sight pattern to compensate for where the gun shoots. It doesn't take long to find where that is. Its a matter of getting to know your gun.

I don't know about you, but when I shoot at a target, I like to see the group in the center of the bullseye. Anything else is a miss. I am an old hunter and misses don't bring home any meat.

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