I think every serious Pumper must have a selection of barrels with different bores or a good kit.
Even if you stick with one line of paint it will vary from batch to batch.
That's the secret to accuracy.
You have to match your paint to bore PERIOD!
Get a good kit Panda.
I have several options. First I use the LAPCO barrel sizers. They have a good bore spread to choose from and I just match them with any of my OG favorite barrels. You can buy each one indivudually from their website.
Next is my CCM kit.
Do not rely on just one fixed bore barrel!