The earlier CVA Kentucky's (with 2-piece stock) were known to be accurate shooters (for an inexpensive rifle), however I wouldn't reccomend much more of a "powder charge" then the 70 grs. of FFFG thet yore now use'n. In fact have you try'ed a bit "lower" charge (55-60-65 grs.) to see if it will group better??
For some odd reason, sometimes a courser powder will often shoot better in a particular small-bore, so if you have (or can borrow) some FFG, you might try it also.
Are yore "patchs" look'n good after be'n shot,.. are they intact without any holes burnt in'em?? They should look good 'nuff to use agin, and agin!! You will usually find them about 10-15 yards down-range from yore muzzle.
You might also try thicker patchs, or, 445 roundballs,.. maybe "both" if it loads real easy. I have a .58 cal. thet likes "denum patchs", so if you have an old pair'a jeans to cut up, thet is also a possibility.
Vaseline is petroleum based, and I suggest "NOT" use'n it,.... instead use ONLY "natural" grease such as "unsalted" Crisco. My favorite "lube" at the shoot'n-range is jest plain ol' "spit",... and for hunt'n I use a "bear-oil and bee's wax" lube thet I make.
Traditional muzzleloaders are "simple creatures", and when you find the powder-charge and patch/ball combination it likes,.... it should do you proud on the shoot'n range!!
Good luck, and keep us posted on yore "progress"!!