Started having a sort through the tin of 4.52 JSB 'Exacts' tonight dividing them into 4.44 and under on one side and 4.46 and larger on the other (the verniers are accurate to .02mm).  I haven't made a lot of progress as you can see but the ratio is about 2:1.  The smallest is 4.42 and the largest 4.48 - a long way off the 4.52 stated on the tin regardless.

To further demonstrate my thinking re the Air Chief challenge gun, a pic of a 4.42 JSB sitting nicely inside the barrel and another of a 4.52 Sig that won't enter without being forced in.  To my way of thinking the 4.42 is going to shoot straighter in this gun than the 4.52.

I'm impressed with the RWS Superdome! 

I have never really considered too many brands to be "good". JSB has always been my go to, and I consider H&N to be good (the Germans usually do things right), but most of my guns prefer JSB's to H&N's. All other brands I've usually considered to be cheep and substandard, but i'll have to look into these RWS Superdomes.

Nunga I was pretty sure I had checked skirt sizes before I started and found they were somewhat larger so I just did the same check on the JSB skirts and nope, that's not the case.  Again, a hell of a lot of variance that I wasn't expecting from this manufacturer.

Now that I've gone as far as I can with the MIC project gun I though I'd buy some smaller 4.50 JSB Exacts to try in place of the 4.52 I've been using.  The logic being that a smaller pellet might perform better in what seems to be a tight bore.  So I measured some of the 4.52 from a new tin and got some very strange results.  Initially I thought it might be my MIC digital calipers so I swapped to my MIJ Mutitoyo vernier calipers and got the same results.  

I was led to believe from the factory visit video I viewed on Utube recently that the JSB's are sorted in the packing centre to very exact sizing, hence the 4.50, 4.51, 4.52 packs. I'm either missing something obvious or that was a complete crock!.  Perhaps their QC has gone down the sink since Covid but what I recently bought as 4.52 are nothing like it.  

So to confirm my suspicions, I checked four different brands in .177, taking 10 pellets from each tin in sequence and measuring them with the Mutitoyo calipers.  I don't have full details of the Sig pellets, they're just some that Dave Simms gave me to try a while back.  The differences are astounding as you can see from the results attached and in the future I won't be so keen to buy the JSBs - although having said that I may buy a tin of the 4.50 and select the smallest from them to try (assuming they will actually be smaller than the 4.52 average of 4.44).  I'm guessing they'll be just the same mix with a different size written on the tin!

I have plenty more that I could check but it's pretty brain numbing so I leave it at that for the moment.