I've got to agree that the unisizer and ATS barrels have worked exceptionally well for me. When I had a custom barrel done up I used a stock AT-4 barrel with unisizer as the base for the work. I guess if the paint is extremely small or large you may have problems but at some point you run out of range with Freak inserts as well.
Northern Command has pre-freaked barrels for sale.
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Pre-Freaked is that even a word? LOL