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If I had a bulged barrel, I'd install a full-length tub in a smaller gauge inside the barrel - as the tubes themselves are strong enough for modern ammo, even if they weren't installed inside a barrel.
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I'm sure I'm the oddball in the crowd, but I would never do that. Not that it isn't a viable alternative, it is, but I have never understood why someone would want say, a 12 ga. gun in weight and appearance, that shoots 20 ga. shells. If I had a barrel that bulged I would scrap it, or sell it for parts if possible, and either find another barrel (or barrel set), or sell the whole gun for parts. I'm not belittling the idea, it's just not for me.
The only reason I would have for sub-gauge tubes is sporting clays competition where I could use my 12 ga. gun with a carrier barrel for all the sub-gauge events.
Bulged barrels are the kiss of death, IMO.
SRH