Been zeroing an Air Arms S200 and newly purchased S410 TDR (very nice bit of kit!)
The S200 has done nicely with Air Arms Diabolo pellets. Lovely groups.
The TDR came with half a tin of BSA pellets, they struggled to make sub 2 inch groups at 40 yards. Threw some of the AA Diabolos in it and it was hole on hole. Phew, that confirms the barrel's not bent
Now need to buy more of these AA Diabolos and i see two options: 5.51mm or 5.52mm.
The ones we've been using are 5.52. Is there any reason to try the 5.51? I'd assume not due to possibility of falling out of the fiddly little magazines, but I'd be interested in thoughts on it and why the option is there. Here's a link, more to show our American cousins the sort of prices we Brits have to suffer on the wrong side of the pond.
https://www.ebay.co.uk/itm/114130828645?var=414387472745