You mention cleaning BP occasionally and someone else asked do you clean both ends... Maybe I missed it, but do you also clean the barrel after every shot? (try every other shot, but shoot at different targets)... That way, the barrel is clean and partially cooled for each shot at one target and 2nd target is hot & dirty barrel (just like a 2nd shot while hunting - very instructive).
I also didn't see how much powder you are testing... I started with max loads of 150 grains of (I simply use Pyrodex pellets and powder), but quickly found that 120 grains shot best with 290 grain bullet and 110 grains was best with 250 grain bullet.
Wind also effects our slow ML bullets more than center fire... Is your vertical always on target, but off left/right? Ballistics predicts my 290 grain bullet (avg velocity measured at 1920 fps with 5 - 10 fps range should drift 2.12 inches in 10 mph cross wind... 160 grain 7 mm Rem Mag only drifts 0.58 inches - (but be advised, some velocities can be 200 fps slower and you would never know if not chronographed - why? who knows? chips in pellet? crushed pellets? Also check for creep on the plunger of your powder measure. I found that mine had started to unscrew and was measuring about 5 grains less than I thought.
1 MOA is tough because there are so many variables. You seem confident about the largest variable you can control; your shooting...
See if they will replace the gun. If not, keep searching for the best bullet/powder/primer combination... To do that, you can only change one variable at a time.
Try to get as close as you can to 1 MOA, because 1 MOA at the range always turns into 3- 4 MOA in the field, but still within 4 inch kill zone (if no wind)...
Good luck.
Thanks, great things to consider.
Starting with cleaning at the range. I usually start with a squeaky clean barrel and BP, then pop 2 primers. The first group is usually something I've previously tried, just to get the barrel dirty. On the advice of others I've stopped swabbing the barrel during a range trip since I'm using only BH209 powder. But after every group I turn the gun BP down and use a drill bit to clean out the area in front of the 209 primer pocket. Then I run a primer pick through the fire hole to ensure I didn't force any debris into it.
When I first started with 777 pellets (only powder in the local area at first) I swabbed between every shot with a lightly misted Windex/alcohol patch, and a dry patch. Went through most of a box of pellets before getting my hands on BH209. This seemed to keep the crud ring and loading pressure consistent.
For cooling I use my phone's stopwatch and don't start charging until 5 min have passed since the last shot (when it's in the 30s) or 8 min now that it's in the 50s and 60s. Also don't actually fire until 8-10 min have passed total (based on outside temp) but for each group the time between is consistent, unless interrupted by others wanting to check targets downrange.
For charges I was initially limited by pellets of 777 (50/100/150), but with BH209 I've used a variety from 60-82 gr by weight. Charges have been preweighed at home into loading tubes. I group my charges in batches of three in the charge box, so if there's any scale variation its minimal and the digital scale is calibrated when I start, and checked every few batches (scale is stored in a cold room, so it will vary slowly over time as it warms up; in-batch consistency should still be more than close enough).
Wind wise it has been breezy on sone outings, but most groups over the past few months have been shot at calm to under 5 mph, and I get as much vertical stringing as horizontal. Wind drift probably does have some effect, but shouldn't be keeping me near 3" groups most of the time.
I think i need to scale back my expectations of this gun. Will see what CVA has to say.