as stated, you will need to find the batch that works in "your" ev2.
Jsb Exact are the most popular choice i would say.
So try a different batchers/dai. ie, you may have baught batch/dai "15" and it loves tham, but put dai "35" in it and the groups spread.
I dont tsaker any notice of head size, 4.51.52,53. Its the batch / dai number that makes the difference.
I know some ev2 owners size the exacts, some dont. depends on what works for you? the new exacts dont seem to need weighing, the older did sd there could be a wide range of weights. i once had 7.9 - 9.1 in a single tin. its why i stopped using them.
Dai / batch is the first 2 numbers (i think) on the jsb label under the tin. least, thats how i determine it.
Air arms pellets are also used by some top shooters, so they are an option.
Personally i use express in mine and apart from one batch, dai 36, all have been fine.
I have found that one of my ev2 likes them sized to 4.52, the other 4.50. sizing seems to have stopped the odd flyer.
i dont weigh express as they dont need it.
I have used or perhaps may still use Falcon / jsb RS. these are very accurate, but much harder to shoot in the wind. Good if you like a challenge!
One thing i have found with my ev2 is that the barrels need to be very clean. Every 150 pellets i use a pull through to clean the barrel.
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