POI Channge @100 Yards With a 'Similar' Load

[MMH]

On my 6.5CM I changed from shooting:
140 gr. berger @ 2690 fps (2250 ft-lbs) to 147 gr. ELD-M @2784 (2530 ft-lbs)

At 100 yards the 147 gr. load hits almost 1 moa higher than the 140 gr. load. Is the increased energy causing more recoil /muzzle flip resulting in the upward shift in POI? The 147 gr. load does have 12% more energy, but I am shooting a MPA rifle set up for PRS (heavy - w/ scope & bipod probably over 19 lbs.).

 

[Old Man with Gun]

Different loads have different POI, a dozen factors contribute. But just going to a different 140gr bullet will move POI.

 

[kilizyrag]

Yup, different flight characteristics.

 

[MMH]

OK, not disagreeing, but at 100 yards just because flight characteristics?

 

[Old Man with Gun]

Yep change bullet may have changed jump to lands, pressure pattern, bearing surface (friction), barrel harmonics, etc.

 

[Doom]

The primary change is most probably due to barrel harmonics causing the barrel release point of aim varing between the two but recoil is probably playing a minor roll. As for external ballistics the 100yd variation due to only the velocity/Ballistic coefficient difference is about +0.2" if you assume the barrel POA does not change. The internal ballistics variations can also be playing a part, especially those that effect the variation in the barrel POA relative to the bullet spin axis at muzzle release.

It only takes about a 0.008" variation in the POA of the barrel to cause a 1 MOA variation in POI at 100yd.

 

[diggler1833]

2-3 MOA isn't uncommon at all with a lot of the less expensive factory rifles, especially when changing bullet weights.

It is nice when everything still shoots to the same POA, but changes of a MOA are absolutely normal.