Shot Grouping question

[Mellow]

I did a second day of target shooting yesterday evening with my Glock 19.
100 rounds Winchester White Box FMJ 9mm 115gr
10 rounds Winchester PDX1 BJHP 9mm 124gr +P (My defense ammo, this stuff is expensive)

15' away from a 8.5x11 target
With the FMJ ammo, my shot grouping was right around the center of the targets where I have been working to keep it.
I noticed that my grouping with the 124gr +P was way off, tight grouping, but about 4-8" to the bottom-left of center.

Can anyone tell me why the PDX1 preferred to go to the bottom-left compared to the FMJ? Has anyone else seen this effect?
Common sense tells me it was probably the +P/heavier grain/ and Glock barrel Riffling, but I would like to know more, and perhaps some physics of why it did that.

 

[GoDawgs]

Diagnostic Target - TheFiringLine Forums

I'd say it is trigger control with the +P. I tend to go in that direction when I focus too much on the shot. I used to think that the placement of shots was related to the gun/ammo, but for me I know it is 95% the shooter.

 

[Titanium_Frost]

I hate PDX1 ammo. It doesn't expand reliably. Put a pair of jeans against a water jug and catch the bullet with phone books. I have never had one expand like that.

I would say trigger control as well but I haven't shot a Glock before so that may be your problem Try out a good single action capable pistol and see if it improves.

 

[jblomenberg16]

You're anticipating the recoil and pulling the gun down and left as you pull the trigger.

I do that to with my G19 when I get lazy. I can shoot great groops all about 2" low and left of center.

 

[illmaniac123]

Go back to 115 grain. Having hydrashocks or gold dots still have grgeat expansion and power even though they are a lighter bullet

 

[esrice]

Can anyone tell me why the PDX1 preferred to go to the bottom-left compared to the FMJ?

Unless you shot from a bench rest, I'm gonna say that your problem is most likely mental. You think "big scary +P round" and start flinching and yanking that trigger down.

Try benching it and see if you get the same results.

 

[IndyGunner]

I hate PDX1 ammo. It doesn't expand reliably. Put a pair of jeans against a water jug and catch the bullet with phone books. I have never had one expand like that.

I would say trigger control as well but I haven't shot a Glock before so that may be your problem

Try hornady critical defense and speer gold dot

and...

Gogawgs is right...

Top right sounds like anticipating recoil for the regular rounds. Bottom left sounds like anticipating by overly squeezing.