Why does a 125 gr bullet shoot lower than than a 158 gr bullet

[Counselor1977]

I recently purchased a S & W 360 .357 MAG. The manual states to use 158 gr. bullets. I am partial to the 125 gr. ftx hornady critical defense rounds. When I was at the range and shot 125 gr. xtp hornady, I noticed they were shooting a lot lower than when I used 158 gr. bullets.

I was just wondering why that is. Any help would be appreciated. Thanks.

 

[melensdad]

It doesn't. It shoots flatter. The heavier bullet has to be lobbed upwards so that when it reaches its target it hits to the point of aim. The lighter bullet also has to be lobbed upward relative to the line of sight, but travels faster so it doesn't have to be lobbed as high for a given set distance of travel.

All bullets drop when they leave the barrel. They drop toward earth at the same speed. The difference is the distance that a light bullet will travel in a given measure of time than a heavy bullet. Knowing the distance traveled allows you to sight in a gun at a give distance by adjusting the sights.

The sights on your gun are set for the heavy bullets.

 

[cosermann]

Yes, lighter bullets have a slightly flatter trajectory. However this does not account for the differences in point of impact observed at self-defense distances with handguns.

These differences are accounted for by internal ballistics. Very simply, recoil starts (and the barrel starts to rise) after the trigger is pulled. Lighter bullets accelerate more rapidly and exit the barrel sooner (i.e. have a shorter barrel transit time) in the recoil 'cycle' than heavier bullets. Thus, the barrel is pointing lower for lighter bullets, and higher for heavier bullets when they exit the barrel. This is oversimplified, but you get the idea. Even a lighter bullet, downloaded to the same velocity as a heavier bullet (and thus the same essential trajectory, or 'flatness') will shoot lower for this reason.

This accounts for lighter bullets shooting lower.

 

[Doug]

Yes, lighter bullets have a slightly flatter trajectory. However this does not account for the differences in point of impact observed at self-defense distances with handguns.

These differences are accounted for by internal ballistics. Very simply, recoil starts (and the barrel starts to rise) after the trigger is pulled. Lighter bullets accelerate more rapidly and exit the barrel sooner (i.e. have a shorter barrel transit time) in the recoil 'cycle' than heavier bullets. Thus, the barrel is pointing lower for lighter bullets, and higher for heavier bullets when they exit the barrel. This is oversimplified, but you get the idea. Even a lighter bullet, downloaded to the same velocity as a heavier bullet (and thus the same essential trajectory, or 'flatness') will shoot lower for this reason.

This accounts for lighter bullets shooting lower.

Correct. If you use put level on your sights and get them horizontal, you will see that your barrel is angled down. Longer barrels point down more because the bullet spends more time in the barrel while it is rotating up due to recoil.

Doug

 

[snapping turtle]

I believe that S&W says to use 158 grain for a reason. I do not think the 125 should be shot alot out of it. I think over a few thousand rounds it will mess it up.

Shoot what you want but might look into "The manual states to use 158 gr. bullets"

 

[jason867]

I have a taurus 85ul snub in .38sp with laser grips. Aluminum frame. Very light weight.

at about 10-12 yards, 158gr bullets hit about a foot higher than point of aim.
Meanwhile, lighter bullets, both +P self defense and standard pressure practice rounds (125gr-130gr-135gr) hit right about where I'm aiming.

This is aiming with both the laser and the fixed sights.

I figured it had something to do with my grip strength, the light weight gun, and the heavy bullet. Cause I have a heavier taurus steel snub that shoots 158s accurately.

 

[bod]

I figured it had something to do with my grip strength, the light weight gun, and the heavy bullet. Cause I have a heavier taurus steel snub that shoots 158s accurately.

jason867, do you notice any difference in recoil between your 2 guns? I have noticed, and anyone can correct me if I am wrong, but you are going to notice the recoil less with a heavier gun therefore your accuracy will also be affected as well.

 

[451_Detonics]

The 125 exits the barrel faster thus the recoil hasn't raised the muzzle as high as it does with the slower 158. If you shot a 125 and a 158 that were the same velocity they would group together more or less.

 

[UncleMike]

I believe that S&W says to use 158 grain for a reason. I do not think the 125 should be shot alot out of it. I think over a few thousand rounds it will mess it up.

Shoot what you want but might look into "The manual states to use 158 gr. bullets"

The reason for that is the issue of gas cutting into the top strap.
The higher velocity, light weight, slugs utilize a faster burning powder to achieve maximum velocity from a handgun barrel. The faster powder generates a hotter flame when ignited and as the bullet impacts the forcing cone the very hot flame erodes the underside of the top strap.
We used to see that a lot when we shot the old Super Vel brand ammo in K Frame S&W's back in the 70's.
We finally settled on the 145 gr W-W Sivlertips for duty use. They were faster than the 158 gr loads and did not cut the top straps.
(Just some more useless info. )
Mike

 

[Wabatuckian]

Hmmm. I thought only the K-frame was subject to forcing cone cracking. Topstrap erosion is pretty universal.

Try 145gn Silver Tips.

 

[451_Detonics]

S&W has solved the strap cutting on some of their alloy framed handguns by adding a steel insert like this one on my 325PD...

 

[Wabatuckian]

It will still eventually cut through. This was a problem on the K-frame magnums. I had a Combat Masterpiece I got rid of partially because of this. (I regret this now; it was a very nice piece. I was reading ay too much Marshall and Sanow at the time and was convinced that it had to be fast and light.)

Josh

 

[451_Detonics]

yep...and someday the sun will go super nova...just don't think either will happen in my lifetime.

 

[Counselor1977]

I had also heard that when one uses a lighter bullet, the source I was reading said lighter than 110gr. bullets, the powder doesn't completely burn before the bullet has left the casing and/or cylinder, causing the flames to scar/burn/stain the outter cylinder finish. I have noticed this a bit when using the 125 gr hornady xtps.

In this article, it stated that the scar/burn/stain can be removed with magnesum/rim cleaner.

 

[RetDep310]

Super Vels, I had almost forgot they even existed!! When I was going through firearms instructors school at ILEA, the staff always told us, heavy bullets hit high, light bullets shoot low! They never did give a reason behind that statement......