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Old June 25, 2019, 12:45 AM   #1
Doc Holliday 1950
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ammo differences

Need some help on a question that I have no bloody idea about.

Why does different ammo of the same calibre & same grain shoot
higher or lower?

As always, all reponses are welcome.
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Old June 25, 2019, 12:57 AM   #2
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powder charge / velocity
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Old June 25, 2019, 07:37 AM   #3
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Add bullet shape and the relation between barrel and individual bullet design.
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Old June 25, 2019, 09:44 AM   #4
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Because recoil starts before the bullet leaves the barrel. Various factors will cause the bullet to leave the muzzle at different elapsed times. a longer time spent in the barrel will result in recoil pushing the muzzle higher. The shot will be high. A shorter time spent in the barrel will cause the bullet impact to be lower because the muzzle will be at a lower angle when the bullet exits.

Low recoil guns will not be too notable, the muzzle position will not vary much between heavy and light loads of .22 lr. When a person is switching between .44 magnum loads, the recoil impulse (and consequently the total amount of muzzle flip) will change, right? So will the length of time actually spent in the barrel, and hence the angle of the muzzle when the bullet escapes the barrel.

This is almost the whole answer. The other part of the answer is how well the gun is designed and the person's ability to resist muzzle flip.

There you have it. it is almost completely about recoil and the way it causes the pistol to move upwards above the actual initial line of the bore.
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Old June 25, 2019, 09:56 AM   #5
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I don't know how much a bullet s affected by a few tenths of a grain of powder or bullet weight, or by .001 smaller/larger bullet diameter, etc.
Perhaps the reloading guys can shed some light on that.

But I would think that manufacturing tolerances and process control would account for much it.
There is variation in everything that is manufactured.
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Old June 25, 2019, 12:14 PM   #6
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Quote:
Why does different ammo of the same calibre & same grain shoot
higher or lower?
If there is a significant difference in the velocity of the same size and weight bullet, there will be a difference in the point of impact.

If there is no significant difference in the velocity and you get a difference in the point of impact the reason becomes more ...elusive.

IF, for example, you have 158gr .38 special from maker A and B and both list the same muzzle velocity, but one shoots higher then the other from your gun, the cause is more difficult to determine, and may eventually boil down to "that's where your gun wants to put them". (and that's not sarcasm, even though it sounds like it)

It is always a number of factors acting together in just the right way to produce the results you get. Change one thing, just a little, and you may not see any difference. OR you might, it all depends on "how the stars line up".

Engineer types call it "stacking tolerances" or "Stacking variables" What it means is every single variable in the ammo gun and shooter combination act together in a certain way, and when that way is repeatable and consistent, we call it accuracy.

The most common reason for the same weight bullet to hit higher or lower than another brand of the same weight is a difference in speed, but WHY there is a difference in speed can differ. Powder amout / type is usually what is looked at, and is often the culprit, but its not the only possible reason.

Bullet fit to barrel bore, bullet construction (the actual alloys used) these are a couple of points not usually looked at but possibly the reason.

A "fatter" bullet (by a very small amount) creates a different amount of friction in the barrel than a "thinner" one. Also a harder bullet has a different amount of "drag" in the rifling than a softer one.

Things like this can cause velocity differences, even when fired using the most rigorously controlled identical powder charges. IT can get complicated.

Barrels vibrate kind of line tuning forks as the bullet moves through them. The muzzle moves up and down due to this (not visible to the naked eye) If the ammo from maker A times it so the bullet exits the muzzle when its on the "up" end of its swing, and ammo from maker B is just enough different in your barrel so the bullet exits on the "down" end of the muzzle whip, the bullets will go to slightly different places, even if the measured muzzle velocity is approximately the same.

Hope this helps!
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Old June 25, 2019, 12:34 PM   #7
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"...bullet shape..." Makes no difference. It's about velocity.
It's also why if you're not reloading, you must try a box of as many brands as you can. That includes brand name 'lines'. For example, Federal 124 grain 9mm HST and Hydra-Shok run at 30 FPS difference in velocity. Isn't much difference, but it's enough to have a different POI.
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Old June 25, 2019, 02:14 PM   #8
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Quote:
"...bullet shape..." Makes no difference. It's about velocity.
Yes/no....any benchrest shooter will quickly tell you "bullet shape" -AKA - ballistic coefficient - will have a dramatic effect on point of impact.

HOWEVER- since we're in a handgun section of the forum - B/C is mostly irrelevant.

Quote:
The most common reason for the same weight bullet to hit higher or lower than another brand of the same weight is a difference in speed, but WHY there is a difference in speed can differ.
<--right there is the bottom line. Velocity is the usual reason, but, the "why" is what drives certain shooters (Bulleye - Benchrest) to go to extremes.
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Old June 25, 2019, 03:46 PM   #9
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Quote:
If there is no significant difference in the velocity and you get a difference in the point of impact the reason becomes more ...elusive.
I beg to differ. Okay, I differ just because I'm different.

Muzzle rise is a factor of two things, mostly. Recoil and the angle of the recoil impulse vs the "tipping point" for lack of a better term.

Recoil should be measured by Ft/Lbs of momentum rather than Kinetic energy. It's the only way to examine how much force is actually transferred from the light high speed object to the larger, low speed object. A 90 grain bullet (ordinarily a .380 bullet) could probably be cranked up to fired at the same velocity of a 158 grain .38 special or even a .357 or much higher and still not generate the proper momentum to create the same amount of muzzle the heavier bullet. Now will the heavier bullet leave the muzzle at a different time and mess up the equation? No, it's going to leave the muzzle at exactly 900 fps, as will the 90 grain bullet.

So we have two factors that with other things equal can affect muzzle rise and hence vertical shifts in POI.

And then we add in the elusives.

BTW, bullet shape doesn't matter a bit if the velocity and weight are not altered. The thing will exit the barrel at the very point as an equal bullet of another shape, and when that bullet is a fraction of an inch past the muzzle, that bullet is on its merry way and will not change it's predestined POI.

I'm discussing these as being a matter of pistols fifty to 100 feet. Not hundreds of yards

Momentum creates recoil and the recoil acting on the fulcrum causes muzzle rise.
This determine the bullet's position when it leaves the barrel. You should be able to take a contender and using different barrels of equal weight and length fire bullets of identical momentum and have these barrels all shoot to the same POI relative to the axis of the bore when fired.

Of course as you said, there are the "elusive" and small factors that can still influence the POI at longer ranges. (I refer to them as the 'PITA factors' or 'that stuff that I forgot to think of')
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Old June 25, 2019, 05:18 PM   #10
Doc Holliday 1950
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Your responses has given me a much better understanding on my post. Yes it all helps.
The revolver that I'm posting about is the new
Colt King Cobra 3" which is my new carry. I'm on a quest
now to find the ammo in 38 special P+ and 357 in magnum
that will go exactly where I want it to go.
Thanks everyone.
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Old June 25, 2019, 06:06 PM   #11
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44 Amp hit close to something not covered. The bearing surface of the bullet can play a part- thinking along the lines of drag factor if anyones done accident investigations. Bullets of equal hardness/softness and weight but having different bearing surfaces can effect how much force is required to squirt them out of the noisey ends.
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Old June 25, 2019, 06:22 PM   #12
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Quote:
Originally Posted by Jleonard
I don't know how much a bullet s affected by a few tenths of a grain of powder or bullet weight, or by .001 smaller/larger bullet diameter, etc.
Perhaps the reloading guys can shed some light on that.
Never mind reloading. Just look at commercial ammunition.

The Sportsmans Guide Company doesn't have the best prices on ammunition, but they're often competitive. They sell a lot of ammo. More to the point, their listings include the muzzle velocity and muzzle energy for all the ammunition they sell. Since the OP asked why point of impact varies from one ammo to another within the same caliber and bullet weight, I would invite him to peruse the offerings from a number of ammo makers and see the difference that exists from one make to another, even within the same caliber and bullet weight.

https://www.sportsmansguide.com/prod...121&c=95&s=959
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Old June 25, 2019, 08:49 PM   #13
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A friend and I were testing his STI 9mm in a Ransom Rest. We were testing 115 g. 124 g. and 147 g. bullets both factory and reloads. The distance was 20 yards because of range layout..
All the ammo had the same POI give or take and inch. I think much of the shift of poi is due to the recoil in a persons hand and is not much if the gun is held solidly.
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Old June 25, 2019, 09:10 PM   #14
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Quote:
Bullets of equal hardness/softness and weight but having different bearing surfaces can effect how much force is required to squirt them out of the noisey ends.
Yes, of course size matters.
just another one of the numerous factors that can affect velocity, and thereby the time the bullet spends in the barrel.

Bullets of different hardness and equal bearing surface size can have different amounts of friction in the bore and therefore different velocities using the same powder charge.

Exactly the same effect happens with bullets of the same hardness but unequal bearing surface sizes.

Take a look in the handloading books and you can find a few loads with the same weight bullet one jacketed and one cast with the same powder charge, fired from the same length barrels. (yes, there are some) and see what the difference in velocities is reported as. Those few loads will be a case where you have both extreme different hardness (cast vs jacketed) and different bearing surface sizes.
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