Air Arms Owners Club

I have an S510 in .22, which I bought new...... Initially when I started using it I started using AA Field in size 5.51. I will call this tin A The rifle seemed to like this tin of pellets so I reordered two tins of the same make and size from the same supplier, call these tins B and C..... When I started using tins B and C, on checking with the chrono I discovered that my average fps was down by 15. My output had dropped by 0.6 lbs. These readings were consistent for both new tins. I then tried a new tin of AA Field in size 5.52, i.e tin D. Output when using tin D was back to the same as the original tin A of 5.51. Questions going through my head...... was the original tin A labelled wrong and was actually in size 5.52 and not 5.51 as labelled. Perhaps the other two later tins B and C of 5.51 were correct. Confused I would not have thought that a 100th of a mm would have such a difference in fps. Being relatively new to the world of PCP rifles it would seem that buying a tins of pellets is a lottery as far as consistency in fps is concerned...............Any thoughts anyone.

Most people who have studied this in detail say firstly the size on the tin is BS and secondly its the die number you should go by. That is if you buy pellets that give the die number on the sleeve.
There's loads of forum posts where folk have actually measured pellets and its not exactly what it says on the tin.

I just put them through a sizer, 4.52 or 5.52 and don't stress myself over it. Rog

Dont forget you was also leading the barrel as you went along.

BBF

Thanks for the feedback concerning leading the barrel. I was aware of this, but I have tried firing alternate gauge pellets through the rifle, one shot with 5.51 and then the next with 5.52, so fourth and so fourth and the difference of 15 fps is still there. The pellets from the tins marked 5.51 and consistently slower than the pellets from the 5.52 tin. In my mind there must be some engineering physical difference between the 5.51 and 5.52 for this 15 fps drop of to occur. I kept the gun at the same pressure at around 170 bar. Still confused.

The stated sizes aren't reliable. I'm guessing the pellets are from different batches. It's quite usual to get 10-15fps difference between JSB-manufactured pellets from different dies. The die number is the first number on the label on the bottom of AA tins. For JSBs it's the first or first two digits depending on whether the batch number is 7 or 8 digits.
I only measure 0.177 pellets so can't comment on .22 dies. See example in "Pellet sizes" thread:
viewtopic.php?f=5&t=5038