A real head scratcher

I've always been skeptical about there being bad batches of pellets (undamaged pellets that all of a sudden don't shoot well). I have a AT44 22 cal long that is regulated to shoot JSB 18 gr pellets and have always shot them very well. Recently I ordered 4 tins of 500 count pellets because i was getting low. Started on the new tin and noticed i couldn't get a consistent group even at 30 yards. So I checked the usual suspects, LDC and cleaned the barrel. Still no good. And I mean 2-3 inch groups at 30 yards. So I pulled out the chrony to make sure the regulator was functioning. shot 2 magazines and got 896 +/- 4 fps. My gun also shoot the AA 16 gr pellets well so i loaded up a couple of magazines and shot this tree i have ranged at 65 yards. All 20 shots hit close enough to each other that there was one mark on the tree. Switched back to the JSBs and got a shotgun pattern again. So I figure bad pellets. I got a return authorization from PA and was set to return them. On a whim I decided to try some in my 22 cal Sumatra. Shot the same tree and got a quarter sized group. Loaded up 6 more and hit the same quarter size mark with all 6 pellets again. Tried them in my AT44 again and got the same shotgun pattern. I can't figure this out but decided to keep them since they are shooting well in one gun and the other 3 tins might return to normal. 
 
Sumatra have larger unchoked barrels so if they were too small I'm thinking they wouldn't shoot well in it. The skirts of diabolo pellets are alway larger than the heads anyway. This allow the skirts to seal in the rifling of the barrel. I don't know, I guess it will go in that category of why the same brand and type of pellets shoot great to terrible in the same model gun.
 
"scubajeeper"Have you mic'ed them to check the diameter? I always wonder about one batch to the next, they claim they are +.02. If they are loose in your gun it could cause them to shotgun.
I didn't. Once I discovered they shot well in one of my guns I decided it wasn't worth going through an investigative process to discovery what's going on with them. I will just shoot the AAs for now and if the next tin shoot well, i will shoot them in my AT44.
 
"Bwalton"I had a few tins that did the same, try the H&N Sniper Magnum Pellets, .22 Cal, 18 Grains they work very well in Hatsan barrels.Other then that its a toss up from tin to tin with JSB I do not know why, but some tins shot hole in hole and other tins were all over the place, this is just wit the .22 18gr
The Air Arms 16 gr shoots well. I'm not worrying about terminal performance since I'm only plinking with them.
 
Join the crowd! I've had the same issue. Pellets that were good, now aren't. The same batch that didn't group well in one specific gun, now do!

I've also discovered that measuring them with a pellet gauge doesn't always point out an issue. I fortunately have occasional use of a comparison microscope, and even then I can't always tell what is up. Same for weighing them. Now, if I just had an easy way to measure their hardness.....