POI differences

[Foxbat]

I was doing another round of sighting in my open guns and saw something that I have not noticed before.

While having the same basic geometry (dimensions, vertical C-More mounts, etc) different guns had different near-far POI shift behavior.

With one gun the difference in POI from 7 meters and 15 meters was pronounced and pretty much what you would expect from geometry - a 2" to 3" shift. With another the shift was less than an inch.

True enough, these guns have different barrel/comp configurations, but I can't see how that could be responsible for the effect.

Any ideas?

[CocoBolo]

The more Bizzare the theory, the more likely the simplest detail is ommitted.

First were both guns exactly zeroed at the same distance using the same ammo and the same method? Are the mounts for the C-more the same height about the bore line?

Each factor, the load, the zero distance, and the method can all have effects on the POI at a given distance.

I have 3 open guns with 6 barrels and an extra top end, so I've zeroed these guns a bunch of times. I don't tend to worry much with the distance since 2 have the Quinn and one has a Cheely. None of them vary more than 1" between near point blank and 50 yards (I use the top of the dot at 50 yards).

[Foxbat]

The more Bizzare the theory, the more likely the simplest detail is ommitted.

First were both guns exactly zeroed at the same distance using the same ammo and the same method? Are the mounts for the C-more the same height about the bore line?

Each factor, the load, the zero distance, and the method can all have effects on the POI at a given distance.

I have 3 open guns with 6 barrels and an extra top end, so I've zeroed these guns a bunch of times. I don't tend to worry much with the distance since 2 have the Quinn and one has a Cheely. None of them vary more than 1" between near point blank and 50 yards (I use the top of the dot at 50 yards).

Both guns were initially zeroed in at 15 meters, then the POI at 7 meters was checked. Both have same vertical mounts - not the same brand, but nearly identical geometry. The gun with 90-degree mount was not one of these.

Some additional info - the gun whose POI shifted significantly has no popple holes, the one with very small shift has two. The result was so surprising that I rechecked it a couple of times.

[CocoBolo]

The first obvious thing is we proably have a significant difference in velocity. Which will affect the trajectory.

[RH45]

But, I wouldn't think a slight difference in velocity would make much difference over 8 yards.

[Foxbat]

That's what I would think too.

Be it as it may, I have a gun that shoots true at both 7 and 15 meters, so who am I to complain? Used it last night in a local match, targets ranged from 5m to 15 meters, hit within 3" center circle without any problems by aiming to the center of the circle in both cases.

Go figure...

[RH45]

If I remember correctly, with my .38 Supercomp, open gun that still has a conventional mount, it is dead on at 16 yards, about 2" high at 25 yards, and still a little high at 50 yards.

If those pistols were mine, I'd shoot them at 50 yards, just to see if they are indeed sighted in the same. I'm thinking one has to be different if the scopes are the same height from the center of the bore.

In my 9mm, open gun, with the scope tipped sideways, it's within an inch from 5 yards to 50 yards.

[G-ManBart]

Just a very slight angle on the mount could cause some of this. Add in slightly different height from the boreline, different comp/barrel setups, a different velocity and it could all add up to make perfect sense from a ballistics standpoint. R,