Pellet pulling to right

scope not in perfect alignment to your bore. look up scope mounting and remount.

peace
kj

Do you have a bubble level on your bsa? You might be canting your gun without realizing it.

Sounds like scope cant to me too. Whether it is due to improper mounting, or self induced, remains to be seen. And if you do opt for a level, get one which mounts to the rail, and not the scope. Should be obvious why.

I would have jumped right to your scope being not level as well. 
Here's my scope mounting video. Maybe trying a different method will ensure your dead on true and level. Also, double check your anti-cant level to make sure it hasn't shifted (if you haven't already).

If you're sure the scope is good and level, then I think your barrel might actually be pointed to the right slightly. It's a rare occurrence but, it does happen from time to time. Take a look down the rifle from the back and see if it looks like it might be off a bit. You might also try holding a long straight edge against each side of the breech to see if you can measure any difference at the muzzle. 
If you find out your rifle's barrel is not pointed straight you'll need to pick up some scope mounts with windage adjustment. I really like the Sportsmatch ATP66 (for 30mm and dovetail). Other options might be to send it in for repair/replacement. Bend the barrel back yourself. Personally, that's not something I would do but, it is an option. 
Good luck!
Tom

But is the muzzle exactly vertical to the scope line of sight when "level"?


I'm wondering if your reticle could be adjusted to "max windage" which would also cause the pellet to traverse the line of sight at different distances even if the gun is "level"

Anywhoo.....I used to have this pellet shifting issue when shooting 10 yard targets with a 30 yard zero. Before doing the following I could count on a horizontal shift of about 3/8" to the left at 10 yards when the gun was zero'd at 30 yards.

I solved this problem by optically zeroing the scope and then bending my barrels till the poi was within about 1" of the aim point at 30 yards, then the fine adjustments were done with the turrets. The I go upstairs to my "man attic" and level the R9 or HW95 using a magnetic "torpedo level" on the barrel pivot block top like this............
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LOL, my high tech box with cut vees isn't real steady but with some "fiddling around" I'm able to perfectly level the barrel pivot block, rotate the optically centered scope reticle to line up perfectly with the hanging plumb line 18 yards away...........
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Then I tighten the scope mount cap screws alternately just about 1/4 turn each time till the screw torque is good, then recheck the alignment. If the reticle is still aligned with the plumb line while the bubble of the level is perfectly centered then the adjustment is good to go!

Use plumb bob line, set vertical on scope, take a straight line
and level and make a + ( electrical tape works good) set target
at 30 check vert and horizontal with plumb and level then repeat
at 50. If your problem persists try shimming between scope and rings.
If it goes away or at least is lessened you are canting. good luck. 

I believe kj's said it. Don't think this is a cant problem. Try to switch the mounts, or turn one of them half way around and see what happens.