I sense a problem here, do you understand MZ harmonics? Do to them you need to start at about 80 grs. and run the powder ladder to the top, it really dont make any differance what you like when it comes to long range accuracy its what the gun will shoot accurate, for instance my new triumph,I had to put rubber warshers under the barrel to settel it down [Thanks to Sabot loader and a couple of others for help on that problem] Now I have it shooting 6 different bullets well so I have a choice. The one that stands out above the rest is the 50/40 200gr shock wave but it will only do it with one of all the powder loads I tried[110 of 777. Ever other gun I have had shot Pyrodex better this one likes 777 so thats what I give it even though I don't like 777, the other gun I have that will shoot it is my Rugar Black Powder which will also shoot Pyrodex P.
Suggest to try and lay out a plan and keep records.
Try and pick out at least 5 bullets and try different weights[my list is all 3 shock Waves the 250 and 300 Gold dot the 250 XTP and the 10mm 200gr XTP.
Take two powders, suggest Pyrodex both P and RS, and both grades of 777.
I now take several Primers my Omega shoots better with win- 777 and the Triumph wont shoot accurate with them it likes regular win 209. None of my inlines like the Rem made for MZ.
Also check you bedding and the way you reassmable your gun when you take it down ,the most commen mistake I know of is over tighting the screws that hold the stock and barrel together, I use 28 inch # on all mine.
If you can not get it together this way then you may have a problem in the way you mount your scope or have one thats no good I have run into several that change the POI every time you fired a shot. Not all scopes will stand up to the type of recoil that an inline MZ produces. Hope this helps Lee