I have always used an adjustable plug that you tighten slightly under the dent, then peen hundreds and hundreds of times lightly using a very small brass hammer or, better yet IMO, a brass round rod of about 1/2"-5/8" diameter with a concave filed into one end that will radius the outside of the barrel. I make the radius slightly larger than the barrel O.D. so that no edge actually contacts the barrel. Then, use a very small ball peen to tap the rod (punch). The barrels are rested on several bags of lead shot, nestled into them so that there is no movement while peening.
I find I get better control like this than with using a brass hammer alone. The dent will slowly raise while you peen over it, and you tighten the plug a little more. Continue until the dent is gone. Then, clean up the brass markings on the blue and touch up the blue at that tiny spot if necessary.
Never have had the opportunity to use a hydraulic dent raiser, but understand that they have so much power that one must be extremely careful not to cause a bulge. I just feel I have much more control the way I do it, but it is a slow process.
SRH
