I bought a pellet sizer recently.

This one...

https://fentonshooting.co.uk/products/fenton-pellet-sizers-precision-cnc-made" rel="nofollow - https://fentonshooting.co.uk/products/fenton-pellet-sizers-precision-cnc-made

Mine is the 4.53 stainless steel jobbie.

My 9015 has a bit of a tight breech, plus the barrel is choked...which you would think would 'size' a pellet as it was fired. But I noticed that my favourite pellet (H&N FTT) took a good 'thumbing' to make it enter the breech. I thought maybe I was bending/damaging the odd skirt or two as I loaded the pellet as generally the H&N shoot fine but the odd flier was a worry.

I measured the skirt and all pellets were over 4.62 diameter...so I had to start somewhere...and bought the 4.53 sizer. It only sizes the skirt, and that's OK for now.

I have done a batch of the H&N FTT pellets, plus some JSB Exact, and Exact Heavy too. The JSB all load nicely in the breech, but I did put some through the sizer too.

The JSB's all went nicely through the sizer with just a whisker of a bright lip around the skirt edge.

The H&N were a mixture. Some pellets dropped in about 1/2 way down the sizer, others would sit up on top of the sizer's tapered entry port. They all took a good shove to move them through (harder material too maybe).  

Will have a shot tomorrow to see if there is any difference between the various sized and unsized pellets.

If nothing else it may help keep the velocity of the pellets more even if they all start out down the barrel at the same diameter.