I like the Microgrove Marlins they the real Marlin factory came up with it to save a few bucks but still make a good shooting rifle,I have found and this is my opinion, Micro barrels shoot better than the old Marlins with Normal rifling with a normal ie Sierra, Hornady Speer ext bullet,. Then the cast bullet guy's started to complain! But then what only 10% of shooters use cast bullets I use them and love to cast my own too and the Micro Grove works just as well. The only case I can see is with the ''older''real Marlins in .444 with that silly 1/38 twist it just does not like the slow moving easy on the shoulder cast loads with a 300+ bullet but push the same bullet at max vel it just might work.
Nothing wrong with Micro Grove in a 30/30 or 45/70 I find they shoot great or better, in my case than Ballard Rifling.
Now I just have to find a 35 Rem I can afford I think most are marlin rifling? that = Micro.
My 81 Marlin 30/30 can handle cast bullets as well as my 788 both can Drive tacks at a 100yrds and too be honest I was shocked my Marlin could shoot as small a group as my 788 Rem except when it gets hot then the group wanders but if you need more than three shots to kill a Deer you might as well take up another hobby!!!
Nothing against the normal rifling it has worked and worked well since the begening but dont't turn down or say anything bad about Micro grove barrels they will work fine even with cast bullets.
My ony complaint is the 1/38'' twist of the .444 had they made it a 1/24'' I bet nobody would complain.