Love, and a Stupid Ballistics Question

C

Chris W

New member
Well, the Sherriff finally finished checking me out (and my three notarized character witnesses--it's quite a process here in North Carolina), so I could go pick up the 686plus (7 shot, 4") that's been beckoning to me. From there, straight to the range, and can I just say: wow. What a lovely, finely crafted tool this thing is. So that's love, and I'm in it.

Now, ballistics. I clearly have no idea of how trajectories work, because I can make no sense of this; When shooting plain old .38 specials (FMJ 158gr. Fiochi) from a rest, I was right on POA at 25 yards. So then I switched to a light .357 load, 110gr. Winchester JHP in the white box. First, I'm relieved it doesn't hurt--I had never shot a .357, and was a bit worried, but dude: it's really fun, at least with a three pound gun. However, the bullets are hitting 3 or 4 inches LOWER than POA at the same targets and distance. Switch to 125 gr. JHPs (local factory reloads), same thing. I really don't think it's me; really. So why would a heavier, slower .38 slug end up HIGHER than a faster, lighter .357 slug? I bet I'm missing something moronically simple, but I just know you'll break it to me gently. ;-)

FauxQ
 
Ah, one of the GREAT confusions about shooting lighter vs. heavier bullets out of a handgun...

Simply put, the rounds with the lighter bullets are doing two things...

1. Causing less recoil while the bullet is still in the barrel, meaning less muzzle rise and a lower point of impact.

2. Shedding velocity faster than heavier bullets. I don't know how much of a change this would cause between bullets of different weights, though.

The big player here, though, is 1.
 
Well, that makes perfect sense--though it does boggle the mind to think of all the factors that come into play in that tiny cluster of microseconds it takes to make the 4 inch journey down the barrel! I'm not thinking they will have lost all that much more velocity in a mere 25 yards than the heavier bullets, but the recoil factor explains it to my satisfaction, at least. Now why couldn't the guy running the range explain it? Hmmm....

Thanks, Mike!
 
That phenomenon is even more pronounce when limp-wristing a revolver. You can change the POI a foot at 25 yards.
 
Yep. Mike's #1 really puzzled me the first time I encountered it. It didn't make much sense to me, but when you understand what's happening with the internal ballistics (a whole different study) then it does.
 
Not exactly. It isn't a function of the amount of recoil but the time the bullet remains in the barrel during recoil. Lighter, faster bullets may actually have more recoil, depending on the velocity. For example, 125 gr. JHP .357 have much more recoil than standard pressure 158 gr. lead .38's. But lighter, hence faster bullets leave the barrel sooner than heavier, slower bullets. Thus, they impact lower on the target than slower, heavier bullets that stay in the barrel longer and exit after it has elevated more.

Don't believe it? Leave a little oil in your barrel and shoot 4 or 5 bullets of the same velocity and weight. The first shots will invariably impact lower as the lubrication reduces barrel friction and enables them to escape faster. As the lube burns off and the barrel fouls, the impact point will come up. Same recoil, different time in the barrel.

While that's usually true with rifles as well, the harmonics of a much longer and flexible (comparatively speaking) barrel have their own effect.

God bless.
 
I think that's what Mike said. The faster bullets will have less recoil while the bullet is in the barrel. Meaning, to me, that the recoil action (barrel rising) will be less for the lighter bullets while it can have any influence on the bullet's trajectory. That doesn't necessarily preclude more or higher recoil that may take place after the bullet has left the barrel. If I am interpreting his point incorrectly, I have absolutely no doubt he will correct me. ;)
 
The phenomenon is called "barrel time". It is easy to understand when you realize that the gun begins to recoil when the bullet begins to move. Take a ruler and lay it across the sights. You will see that the ruler is not parallel with the barrel. But with the ammunition for which the gun is sighted, the barrel will be passing the aiming point on its way up when the bullet exits.

An amusing story about this was that when one of the local departments was issued the .38 +P+ ammo (nearly .357 velocity), they found that it shot much lower on the silhouette targets than the old 158 gr. .38 Special. Their instructor told them that the ammo was supposed to do that so as to castrate the bad guy and make him less likely to commit crimes in the future! How's that for expertise?

Jim
 
Huge is more righter.
Quickest out of the barrel usually hits lower.
Muzzle rise and recoil are related but not directly equatable.

Big ol slow target bullet takes so long to get out of the tube that muzzle has risen appreciably. Yet very mild recoil and low energy.

Hot little smoker out of the tube before muzzle rises much even tho recoil and energy may be much higher.

Now you crank that big heavy bullet up to the same velocity and the heavy one will hit high. Much more flip than with the same velocity lighter bullet. Energy wins.

Sam
 
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