I definitely recommend an aftermarket barrel. The 10" Unported .685 bore PPS Brass I have worked very well the last day I played until the heavy rains came and made the paint a little funny. After that I went back to my Freak kit so that I had a larger bore to play with.
Barrel kits are great. You can change bore sizes as and when you need. The only down point is that they're generally expensive but you can sometimes find them cheap on forums or on eBay. If you can afford a barrel kit then it's totally worth the investment, if not then just get a single barrel that uses a good sized bore (i.e. a bore similar to the paint you generally use). As far a single barrels go the PPS Brass, J&J Ceramic and the Lapco Bigshot are probably the most recommended for the A5, generally speaking. I've owned the J&J and still own the Brass. They're both excellent. There are many others out there that are excellent too, as I'm sure others can testify to, so get as much info you can and go for the barrel that will suit your needs.

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