peppertx:
NEF made 2 Ultra-Comp's...the 30-06 & the 270 for a few years.They stopped selling them in 2002-2003 and are in the process of selling off their remaing inventory of barrels this year.I believe they still have a few of the 270 barrels left to be sold,but are out of the 30-06 barrels.I have both calibers in them,and they have a 23" barrel with a 1" threaded ported sleave attatched.Some folks have a problem do to one reason or another because of the extra noise associated with them,but for shooting in the open you won't notice much difference in the noise level,however...those standing 90 degs. off to one side of you certainly will to them they are extreamly loud,,,they aren't designed to be shot in an enclosed space.They were designed as a compensator to reduce muzzle rise,with the side benefit of having reduced recoil.Marlin NEF's parent company also had some of their various big bore lever rifles with ported barrels...I owned a couple of their 1895 GS that were ported...and with some of my heavy 45-70 loads...they worked great...these didn't have a threaded compensator..they just had the ports cut straight into the barrel,and they didn't do as good a job on cutting the ports that way...They did succeeded on both counts of reducing muzzle lift and recoil though.On the NEF's,they work and work well reducing muzzle lift by over half and recoil about the same...especially with heavier loads.
The custom 257 Roberts was Fred M's creation,and if you do a search on his post I'm sure you can find it,so far I think he is the only one who has done this one.
Mac