Casa 210 piston rings

[HxPaul]

How many miles should I expect to get from a set of piston rings in a Casa 210 top end kit.The rings are past the limit,top ring gap is 28 thou and the bottom ring is 25 thou.I've only done 1300 miles from new and I would have expected to do a lot more miles than that.The kit runs through the airbox so its not getting road grit into the carb.Is it possible that there is rust in the petrol tank causing the rings to prematurely wear,if that is the case I would have expected the bore to be worn,but its perfect.By the way the rings are 1mm wire rings.

Paul