9mm lower than 357

[wideglide]

I shot 24 rounds of 39 special through my Blackhawk then changed over to the 9mm cyl and my next 12 shots were low by an inch or so at 30 feet. 38's were Georgia Arms 800 fps and the 9mm was fmj Lawman 115gr. I was grouping the same and lateral shot placement was very good and similar on both cals just the 9mm was low. I changed the sight picture to Combat like on my P226 and hit the centers well. Both were accurate just needed the change in sight between the cylinders. I don't shoot much 9mm with the Blackhawk because I really like the 38 special round and the P226 is always close by. Anyone else have consistant differences between cylinders? Oh, and I really like the Blackhawk a lot!

 

[s4s4u]

What weight bullet in the 38's? Bullet weight has a significant effect on POI.

 

[whichwatch]

Maybe it's because you tried to shoot a .39 Special in a gun specifically designed for .38

 

[DeletedMember275]

What weight bullet in the 38's? Bullet weight has a significant effect on POI.

As does velocity.

 

[coach]

I get the same thing shooting .44 mag and .44 special from the same gun.
The .44 spec shooting higher.
The lower velocity of the special means it spends a little more time in the barrel and is affected more by the recoil.
My Blackhawk especially rolls up when fired.

 

[OldePhart]

You really can't expect the same POI with different loads in the same caliber, let alone different calibers. Case in point, I just came from a range session testing my new Glock 26. Last step of that process was to decide on the best carry load out of the three defensive loads I had on hand. The 124gr +P Gold Dot and 124gr +P Federal HST shot pretty much to point of aim where the 147gr +P Federal HST shot almost 2" low (all at 20'). So which am I going to carry? The 147gr for two reasons: it grouped significantly better than the 124gr bullets and I tend to pull shots a little high under stress anyway.

 

[cas6969]

Slower, heavier bullet in the .38
Lighter, faster bullet in the 9mm.
They did just what they should have.

 

[planetcat]

if they are not the same bullet weight at the same muzzle velocity, the poi will be different.

 

[OldePhart]

if they are not the same bullet weight at the same muzzle velocity, the poi will be different.

<beanie mode="propeller">

Technically...

1) Even if they are the same bullet weight at the same muzzle velocity the POI can be different if the acceleration and pressure profile differs. The longer the barrel the more likely it is that this scenario may come into play. With longer barrels, especially, even a machine rest may not eliminate this variance, due to "barrel whip".

2) Even though POI may be different it may not be perceived as different because depending on the range, inherent accuracy of the gun, and shooter ability the change in the POI may be considerably less than the group size, making it difficult to determine the "real" POI. This is very often the case with handguns and "tactical" rifles at short ranges...less true with very accurate rifles at longer distances.

</beanie>

Sorry...sometimes engineers just have this uncontrollable twitch... LOL

John

 

[s4s4u]

Even if they are the same bullet weight at the same muzzle velocity the POI can be different if the acceleration and pressure profile differs.

True. Details such as bearing length and seating depth can make a significant difference, as well as the style and degree of crimp.

 

[wideglide]

thanks for all the input. I'll try different weights on the bullets and see what happens. I was shooting 158 gr in the 38's and 115 in the 9mm and I was happy that the 9mm's grouped as well as the 38's. I need to get outside and get out to 25 yards too, we are warming into the 70's so the longer ranges will be a better test I'm sure. Again, thanks to the guys that gave a few tips, this board is more helpful than most.

 

[OldePhart]

The 158gr is a fairly heavy .38 load. You might be better trying the 135gr or 147gr subsonic 9mm loads. You might get closer to the same POI, though probably not identical. Also, the longer the range the more you can expect the POI to vary. Even just 25 yards at handgun velocities is enough for the difference in BC between a LSWC and a round nose bullet to possibly have a noticeable impact on elevation

 

[planetcat]

if they are not the same bullet weight at the same muzzle velocity, the poi will be different.

<beanie mode="propeller">

Technically...

1) Even if they are the same bullet weight at the same muzzle velocity the POI can be different if the acceleration and pressure profile differs. The longer the barrel the more likely it is that this scenario may come into play. With longer barrels, especially, even a machine rest may not eliminate this variance, due to "barrel whip".

2) Even though POI may be different it may not be perceived as different because depending on the range, inherent accuracy of the gun, and shooter ability the change in the POI may be considerably less than the group size, making it difficult to determine the "real" POI. This is very often the case with handguns and "tactical" rifles at short ranges...less true with very accurate rifles at longer distances.

</beanie>

Sorry...sometimes engineers just have this uncontrollable twitch... LOL

John

No worries. Engineer here too. Cal Poly Industrial Engineering class of 1990. So my response is..."Technically", I did not say that bullets of the same weight and muzzle velocity will have the same POI, I said "if they are not the same bullet weight at the same muzzle velocity, the poi will be different." Different statement. I do agree with your clarification however.

Cheers,

Mike.