Not sure where to start. I have 5 M69s - three 4 1/4" and two 2 3/4". One 4 1/4" was function checked, sighted in and put in the safe in case S&W discontinues this model.
I have shot over 11,000 rnds thru the four guns and have been able to find lead bullet loads that shot well in all of them (not necessarily the same load).
You may have complicated the search somewhat by opening the throats on your _but, maybe not.
Three cast bullets that have worked in most of my gun (all have .4295 or .4285 throats) are:
1. 265gr Lyman Thompson SWCGC (429244) -- the ones I have are not real hard and are sized .428
2. 260gr LBT Montana Bullet Works (
44 Mag, LBT, 260gr, WFN-GC - Montana Bullet Works )
the ones I use are sized .432 and are BHN 22 -- loaded over 23.0gr of H110, they have been accurate in almost all .44 mags I've tried them in.
3. Lee 310gr FNGCDC, seated and crimped in the top crimp grove over 20.0gr of H110/W296, I haven't found a 44 Mag that won't shoot these well. The ones I have are .429 and aren't real hard.
Some of my guns will shoot the generic 240gr SWC BB over 6.0 to 7.0 gr of WW231/HP38 -- these are, for the most part hard cast, and run from .429 to .431. These bullets don't typically perform well with magnum loads.
One of my favorite loads is the above mentioned Lyman Thompson 265gr SWC GC, seated deep and crimped over the front drive band propelled by 17.5 gr of 2400.
My second 2.75" M69 with the 265/17.5 2400 -- rested on my range bag at 25 yards.
The load works in most .44 Mags, but not all.
Point being, some guns require a bit of effort to find a load they like -- there really isn't a magic combination that is guaranteed to work in all guns.
Again, as mentioned above, you may just have a lemon.
Sent it back to S&W and see if they can make it right. Test it when it comes back. If it still isn't up to your expectations, take Kasscop's recco, sell it and move on.
For those that are on the fence, the M69 in both barrel lengths have been great performers for me and are my favorite .44 platform.
Good luck!
Paul