A few years back, a very good friend of mine did some testing of both rifled barrels and rifled choke tubes on a 12g. The fully rifled barrel consistently shot less than a 3" group for 3 shots @100, and the rifled choke consistently shout under 6" @100. He was happy to take shots out to 150-170. For the money he concluded that the rifled chokes were definitely worthwhile, easy to fit, no need for a whole barrel if your gun already has chokes, and way cheaper than a full barrel. The chokes he tried were about 150mm long from memory, and extended out the front of the barrel. Sourced from the US, shouldn't be too difficult to track down.
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