I have shot a lot of lead through my microgroove barrel. Works fine, terrific accuracy. Here is a good link on the subject. I realize that you are not talking about the .444 Marlin caliber, but the same advice still applies. Of course the price is terrific. I might even buy it one for that price. My local dealer has one on the rack for $250 and I thought he was giving that one away.
http://www.beartoothbullets.com/tech_notes/archive_tech_notes.htm/17
"In new production guns both the .444S and .444P now employ a Ballard-style cut-rifled barrel with a 1:20" twist, whereas the older .444's had Micro-Groove barrels with a 1:38" twist. The new style barrels are more forgiving with poorly fit cast bullets, and shoot well with properly fit cast and jacketed bullets as well. However, the older Micro-Groove barreled guns had an undeserved reputation for not shooting cast bullets over 1600 fps. This was and is pure hogwash! The fault lies with the bullet and bullet fit! When these Micro-Groove barrels are properly fit with a well designed. hard, gas checked, with a strong front driving band, cast bullets will rival or even out perform jacketed pills at any velocity range reasonably attained with the .444 Marlin. (More on this in the load development segment of this multi-part article) Both new and old productions .444 Marlins are notorious for their outstanding accuracy potential. Both the original Micro-Groove and the newer Ballard-type barrels will deliver MOA accuracy in nearly all rifles with even modest load development, and throughout a whole host of bullet weights and designs."
