Point of impact of 158gr vs. 130gr .38 cal.


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peacebutready
November 10, 2014, 02:42 PM
IIRC, the most standard bullet weight for the .38 is 158 grains. All other things being equal, lighter bullets hit the target a little lower than heavier. How much lower would say a 130 grain .38 cal bullet hit a target at 25 yards compared to the 158 grain one?

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J-Bar
November 10, 2014, 02:54 PM
In my slow cowboy action handloads, between 2 and 3 inches.

goon
November 10, 2014, 03:04 PM
It'll depend on the gun and the shooter. With the exact same gun and ammunition, most of the time I'll group 2" higher than my brother will because we grip the gun differently. Best way to find out is just go shoot a box, but I'd be surprised if it was more than 4" at 25 yards.

Haxby
November 10, 2014, 03:28 PM
I bought a box of 130 gr fmj once. It was really wimpy, and hit significantly lower than my 158 handloads. I don't remember exactly how much difference there was, but I remember it being a lot.

Sunray
November 10, 2014, 04:28 PM
How fast is your 130 going? There is no formula.

somerled
November 10, 2014, 04:40 PM
If the velocities were the same for both bullets (you said all things being equal), the bullet with the lowest ballistic coefficient will drop more. That would most likely be the heavier bullet. But most things aren't equal when one's shooting factory ammo at 25 yards without a Ransom rest.

tipoc
November 10, 2014, 05:15 PM
Actually, all else being equal, a heavier bullet will hit higher on the target and a lighter load lower on the target, irregardless of the velocity.

So the answer to the original question will be that you'll have to shoot and see how much lower depending on the gun and the actual load (bullet type, powder, etc.) The shooter will make a difference as well. I agree with the others not much more than 3-4" is usual with the bullet weights that were mentioned. But it can be larger if the differences between bullet weights and velocities are extreme.

tipoc

BCRider
November 11, 2014, 03:51 PM
Somerled, you're trying to apply long distance rifle like issues to a short distance handgun situation. At typical handgun distances the way the load makes the revolver recoil in the hand prior to the bullet leaving the muzzle counts for much more than bullet drop over the typical short distance due to BC's. Now if we start looking at anything much over 25 yards then I agree that we'd want to start considering the BC's. And by 50 yards out the BC's would be significant enough a factor to likely account for as much as the bullet weight and muzzle rise issue.


Back to the question....

Along with weight the power behind the bullet also matters. 158gn .357Mag rounds will also print lower due to velocity despite the heavier bullet. So if the load power is equal then you can expect the lighter bullet to print a fair distance lower. And from using 130gn mid power lead bullets as well as 158gn lead bullets from my Model 10 I'd say from memory that the difference is roughly 3 inches at around 20 yards. But again I didn't match the peak pressure or try anything fancy. Just brought the wrong ammo for a match one day and had to "make do" with the lighter bullets by aiming more at the top edge of the targets in a Speed Steel match.

tipoc
November 11, 2014, 06:53 PM
I agree that at common handgun distances the bc is not a factor.

Bullet weight is though.

Try this test: stand sideways in front of a mirror and point your revolver (it's easier to see with a wheelgun but is true for pistols as well) at a point on the wall opposite you about shoulder or chest height. Look in the mirror. Note that while the sights show you are pointing at the spot the muzzle points below it. If the muzzle was pointed straight at the aiming point the bullet once out the barrel would strike above the target. This is because the barrel begins to rise once recoil begins. Recoil begins before the bullet leaves the barrel. By the time the bullet does leave the muzzle the angle of the barrel has changed and the bullet will strike where it was aimed at (provided the shooter does their part).

Fixed gun sights account for this and calculate muzzle rise based on bullet weight. Adjustable sights do this as well but can be changed for different weight bullets. Most fixed site service guns are set for a 6 o'clock hold at 25 yards.

Take a 158 gr. bullet at 850 fps and say it's set to hit the center of a target at 25 yards. It's recoil and slow velocity will cause the muzzle to rise slowly and leave the barrel at a certain angle so that the bullet arcs to the target. If we increase the speed to 1200 fps with the same weight bullet, the bullet will leave the barrel faster, the rise will be faster, but the bullet will still leave the barrel at the same angle.

When you change the bullet weight, then the angle at which the bullet leaves the barrel changes. Lighter and faster bullets will leave at a lesser angle. This general fact allows gun companies to set fixed sights based on bullet weights and not velocities.

But guns are shot from human hands and how the shooter handles recoil from a particular gun and load effects how they shoot and where the bullet lands. As does the weight of a gun. So while it's generally true that heavier bullets will strike higher on a target, and that two bullets of the same weight but different velocities will hit a target at the same point it's not always true with any particular gun or shooter or load.

You have to shoot to see. There is no general formula that fits all.

tipoc

il.bill
November 11, 2014, 08:10 PM
tipoc -

Thanks for the extended explanation.

It is nice to have some background information to go along with an answer. Often I have to read or hear something multiple times from different sources before a principle begins to sink in.

Kleanbore
November 11, 2014, 08:33 PM
tipoc, that explanation, clear and to the point, is excellent. Thanks, on behalf of all of us.

rcmodel
November 11, 2014, 08:58 PM
This might help too?

204918

204919

rc

BCRider
November 12, 2014, 01:04 AM
Take a 158 gr. bullet at 850 fps and say it's set to hit the center of a target at 25 yards. It's recoil and slow velocity will cause the muzzle to rise slowly and leave the barrel at a certain angle so that the bullet arcs to the target. If we increase the speed to 1200 fps with the same weight bullet, the bullet will leave the barrel faster, the rise will be faster, but the bullet will still leave the barrel at the same angle.


This would imply that the rounds hit at the same point. Shooting a mix of .38Spl and .357Mag both with the same 158gn bullets this is not the case in reality. And I know this as I had a batch of both I reloaded with the same bullets.

The magnums still print on the target a good 3 inches low at around 15 to 17 yards. The speed rise does not match the muzzle rise rates so the faster bullets come out sooner and print lower as a result despite the same bullet weight and type.

goon
November 12, 2014, 01:09 AM
Yeah, it's been my experience that .357 Magnum and .38 Special with the same bullet weight don't hit to the same point of aim either. At around 20 yards, the .38 Specials shoot about 3" higher for me. Now if I switch to 148 grain wadcutters, I can get them to shoot to the same POA as the Magnums...

tipoc
November 12, 2014, 12:38 PM
It's my experience that what Goon and BC say is true. Theoretically, or "all else being equal", a 38 Spl. round and a .357 Mag round with the same weight bullets should have about the same point of impact. But in the real world they often don't...why? Because of felt recoil, how the gun moves (twists, bucks, squirms) in our hands. The kick of the one round is more powerful than the other and we react to that.

Gun manufacturers can't account for that when they set the height of fixed sights. They can't account for different velocities either or different types of powder or different type bullets. But they do have the formulas for muzzle rise based on bullet weights.

Gen. Julian Hatcher in "Hatcher's Notebooks" discusses this and Robert Rinker in his book "Understanding Firearm Ballistics" has a good deal about it as well. I have the 6th edition of that and that begins in the chapter on Handguns page 318. Rinker's book is inexpensive and you can get a used copy cheap.

tipoc

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