My information and experience for over 35 years.
1. For some reason, the 336 Marlins seem to always shoot the 170 grain loads better (more accurately). Maybe it has something to do with the Micro-groove rifling that they started using in the late 1950s. But, you are shooting a carbine, and you've got to realize that 4 inch groups at 100 yards are regarded as the norm, and that 2 inch groups at 100 yards are regarding as very good. (I have seen some 1 inch shooters though.)
2. As far as variable scopes, I have now gone strictly to the Leupold Vari-X II in 2x7. They are a perfect blend of lightweight, compact, good light gathering, and solid reliability. If you just go to a few gunshows, you will find these in used, nearly excellent condition, for $125 to $150. If you buy one like this, and there is any problem, ship it back to Leupold and in all likelihood they will fix it for free and send it back in 7 days. You just can't go wrong with a top of the line Leupold. I have a few that are 25 years old, and they remain perfect.
3. As far as 150 grain bullets, no deer that is well hit with a Remington 150 grain core loct, or a Winchester Power Point, is going anywhere. There will be no substantial difference on the game in using the 150 grain vs. the 170 grain. The 150 shoots a little flatter, so if coyotes are in the mix, and your rifle shoots the 150 grain factory loads well, you don't have to worry about having enough power on deer out to 150 yards. I have shot two deer, at 125 yards, using the 150 grain Remington core locts, broadside behind the shoulders, and in both instances, the bullet went clean through and out the other side, leaving a 50 caliber exit hole.
4. The 30-30 is a superb deer round, out to 150 yards. I would wager that lever actions in 30-30 ruled the roost in Georgia for more that 70 years (before the .270 became popular) and nobody thought they were undergunned! (Ask your dad.) They just didn't take shots beyond 150 yards. Even after more than 100 years, tens of thousands of new 30-30s are sold every year! There is a reason for this. THEY PERFORM.
5. About two years ago, one of the big ammo makers (Remington or Winchester) released to a sports writer the number of boxes of centerfire ammo it sold during the year, for the top ten sales. Most people thought it would be the 30-06 or the .270. Wrong, the 30-30 Winchester was number 1 by a large margin. Then, I think, followed the .30-06, the .270, the Rem 7 Mag, the .308 Winchester, and the .300 Win Mag.
6. The real world plus that the .270 gives you is shots out to 250 yards, across those bean fields, using 130 grain bullets. So if you plan to shoot beyond 150 yards, be a good sportsman and leave the 30-30 behind.
Hope this helps.
Big Paulie
