From reading this forum, if you have the barrels crossing on the bullet POI, then your loads are too fast.
My lower barrel shoots 1.5" above point of aim at 100yds. The upper barrel is 1.5" low of point of aim. About 1" difference left/right.

Is there a "rule of thumb" on how much a velocity change of "X" will change the POI? I.E, 100fps will make an approximate change of "X", so I need to slow down the load a certain amount?

Or is it all dependent on gun/shooter/load and each gun is different? Still learning about these things

Thanks

RR, that really isn't too bad for a DR regulation at 100 yards, especially to start. Have you tried different loads and/or bullet weights? I don't know if you're using factory rounds or handloads, but if it's a handload, back off 1 grain and see what happens. That might do it.

Handloads, as factory loads are unavailable/not produced.

420gr cast @2013fps with groups from each individual barrel very good. Lower barrel about 1.5" and upper barrel will go under 1"

Light bullets group very well individually, but seperation is about 8" vertically. It shoots the heavier slugs best.

Rockrat,
Could you tell me what rifle you are shooting? IS it the 9.3X74R Chapuis?

Rockrat -

I have found that with my sxs double rifle the rule of thumb holds true and if your barrels are crossing then back off a grain at a time till they get close then go to .5 etc. N.E.450#2 helped me fine tune my sxs rifle. in the end I changed the loads by 10ths.

Heres the kicker, when I changed components for my O/U double I was surprised to find that the starting load shot about 6" apart at 50 yards. in this case I found that reducing the load brought the barrels together. I know this is against conventional wisdom but thats the way it shook out for me.

It sounds like your double is an O/U. you might want to load up a tray of test loads marking the pawder charge with a sharpie on the side of the case. Go up a couple of grs. and down a couple to see wich way you need to go.

Its a Beretta O/U. Don't have a SxS (yet). Shot some today, lowered velocity to 1700fps and spread is now just below 2" vertically, and horizontal dispersion is now less than 1/2".

Think I will leave it where it is.

On another note,took the Tikka 512 9.3x74R out today also. It liked the Hornady 286gr slug over 68.0 WW760 +WLRM, in Norma brass. 2272fps (28 degrees out, at the range)

Seems to me you are defeating the purpose of the cartridge by reducing loads that far below factory specs.

Me, I'd try a different powder.

It's more about barrel time than about muzzle velocity, although the two are related.

Since this is an O/U, your problem is crossing. Try a slower powder for roughly the same MV. Or a heavier bullet.

But as someone else said, your group is adequate for hunting.