Two loads with POI shift at very short range

[RickT]

Went to the range with some old 124gr loads for my HK P2000 EDC and some of my very soft 135gr loads for my competition (SC) 9mm 1911.  Range was 7 to 10 yards.  Worked the HK a bit in preparation for an Enhanced CCW class (Idaho); just moved two months ago and hadn't touched a gun in 4 months.  Switched to the 9mm and found I was grouping about 1" high.  Hadn't brought that much of the usual 1911 ammo so tried the near-factory HK load and the groups were centered on the target.  I repeated this "experiment three times and the POI of the 135gr load was consistently high.

 

This is certainly not the ballistics; I expect what I'm seeing is the difference between a light/faster and heavier/slower bullet POI, but an inch at that short range seems extreme.  The gun is on the heavy side, but at 73 y/o I don't have a gorilla grip.  I've seen discussions noting differences between 147gr and 115/124, but I'm wondering if the degree of POI shift makes sense?  FWIW the recoil of the HK round (124gr FP) is slightly greater, but still very slight.

[Hi-Power Jack]

I've had POI change vertically AND horizontally from lighter/heavier bullets.

 

And, an inch at 10 yard is only 2.5" at 25 yards - I don't find that too hard to believe.     

[zzt]

Bullet weight.  Nothing to get excited about.

[RickT]

I did believe it to be a "real thing".  The magnitude of the effect surprised me.  Note to self, always sight in a new load.  I switched to the slightly heavier bullet because I preferred the feel, but didn't both to shoot any paper.

[BallisticianX]

Normal for different bullet weights (as they relate to different velocities) to shoot at different POI. Velocity equates to a distance traveled in a period of time, so a slower load usually a heavier bullet, but that depends on the load moreover) takes X milliseconds longer to exit the barrel allowing for a smidge more muzzle rise to occur before exiting.