The "problem" with the .444 from it's beginning has been the use of light-for-caliber bullets. While it's true that the current bullets normally used are a bit too lightly constructed (designed mostly for pistol use)....even with tougher bullets the fact remains that when you give up bullet weight, you also give up penetration.
The key to the success of any of the big bore, moderate velosity rounds is the use of heavier bullets to give penetration and "killing power" without hyper velosity. This DEOES result in a bit more arching trajectory, but at the ranges such roiunds are intended for (under 250 yards) this is not significant.
The "idea" of light weight bullets at relatively higher velosity to "flatten" trajectory was tried as far back as the late 1800's with the so-called "Express" loadings loaded with black powder... such as the .45-70 with 270-300 grain bullets at 1800-2000 fps.
These loads DID flatten trajectory a bit, but not a significant amount at "normal" ranges, and gave up a LOT in killing power and penetration. They soon disappeared and "failed".....with hunters going back to what had always worked (heavy bullets at reasonable velosity.....and shooters learning the trajectory of their weapon). Some pretty fancy "long-range" shooting was done with those old 450-500 grain bullets at 1300-1500 fps despite their "rainbow" trajectories.....and they killed well when they arrived.
The .444 marlin has always been hadicaped by the use of light bullets at high (relatively) velosity. Where the .444 really begins to shine is with 325-400 grain bullets at a more sedate 1600-1800 fps. With those loads the .444 becomes a powerhouse killer very close to the .45-70. The shooter must learn his rifle and trajectory, but once again, at under 250 yards (where a big bore, moderate velosity round should be used) this isn't a big problem.
If you "must" shoot lighter bullets at higher velosity, you must accept that it will NEVER perform as well as a heavier bullet loading. It WILL work on lighter game and with very good shot placement, but never a good as a heavier bullet for all-around use. Better bullets CAN help, but not really solve the problem (a sow's ear is still a sow's ear.....even with lace around the edge).
The 300 grain .45-70 loadings suffer the same fate. They WILL work if properly placed and with good bullets, but never equal a 400-500 grain bullet for all-around use.
