What’s wrong with me

Good morning
Well there is not a whole lot of bad having a Ballard cut Marlin. Should be able to launch cast slugs downrange fairly well if the chamber is close to specs.
Just remember the whole Ranch Dog line of molds came about due to chamber issues in Marlin's lever rifles.

Initial testing of this gun was excellent. All I had on hand was some 300gn Hornady XTPs and some 300gn Lee WFN, both loaded fairly stiff. Shooing offhand at 50, my worst group was still under 2” and my best group was just under a inch with the 300 XTPs. My other Marlin 44 would put both of those bullets sideways at that range so I am very happy with the results so far. Will have to get some kieth bullets loaded up and see how it likes those.

The RD slugs will shoot good in many rifles as long as they do not get jammed into the rifling when they get chambered.  Think of a modified heel bullet.  Fat noses.
Contenders in 41 mag have serious short lead before the rifling.

Sometime in the first decade of the 21 century Marlin made a change in the rifling twist rate of the 444 Marlin from 1/38 to 1/20. The 444 hade always been handicapper in bullet weight by the slow twist so the 45-70 was getting all the glory with heavy loads with heavy bullets.
The 444 with slow twist was built around the 265gn heavy jacket bullet and was limited to that bullet by constraints on both ends of bullet weight.
It didnt do well with lighter bullets because all lighter bullets were designed with thinner jackets for hand gun use at 1000 fps lower velocity that the 444 could be loaded to.
Going the other way to heavier bullets and accuracy would suffer. When Marlin changed the 444 twist rate to 20" they offered a rifle that could give the heavy loaded 45-70 some stiff competition in velocity and bullet weight. Theoretically both loaded with a 400gn bullet to roughly the same velocity gave a ballistic advantage to the smaller bore as the same weight bullet would have a higher sectional density this giving the 44 caliber better ballistics at all ranges with higher retained energy and a lower mid range trajectory at all ranges, as well as better penetrating ability.
I think it was a great idea and we started to see new bullet mold designs for heavy 44 caliber bullets to take full advantage of the change.
Unfortunately I think the change came too late as the 45-70 was already well established with hand loaders as well as the fact that non hand loaders could get factory ammo so loaded and add to that the introduction of the 450 Marlin mag which is nothing more than a heavy loaded 45-70 with a belted brass case.
By this time the 444 Marlin had already been relegated to second best status and apparently that label never changed. It looked good for the 444 for a short while when the twist change happened as I was beginning to get orders for 400+ gn 44 caliber bullets but as is often the case it was too little too late and the 45-70 reins supreme for the heavy hitter chambering in a Marlin rifle.
All this has little to do with Marlin 44 mag rifles accept unless at that time they made the twist change to all their 44 caliber barrels and it carried through to the 44 magnum in the model 1894 Marlins. This is something that is still a mystery to me as I am unable to pin down positively if the change was also made in 44 mag.
I am a big fan of the 44 mag cartridge and the Marlin model 1894 rifle but because of the slower twist in 44 caliber I chose the model 1894 in 45 Colt because it does have a 1/20" twist and does shoot well even with bullet weights to 400gn even when loaded to far less than maximum velocity.
Not saying the 44 mag Marlin comes up short as a 100 to 150 yard deer rifle because it does not and I say that from experience with such use but just saying it is nice to have a greater versatility in bullet weight which for me is a big +++ because I seldom cast for myself but always seem to shoot the over run from orders.

If you do get a Marlin in 44 mag stay with the same bullet weights you were shooting and all will be well. Plan on about a 700 fps gain in velocity over the revolver when loading the slower powders such as H-110 , Win 296 and others a couple positions on either side of those on the burn rate chart.

When your Mom and I lived in logging camps in SE Alaska we both had Marlin 44 magnum rifles for protection. The load we used was the Lee 310gn WFN-GC loaded to 1700 fps. Loaded full tilt the Marlin would shoot the Lee bullet reasonably well but not great. They definitely shot good enough for the job at hand.
As loads and velocity was reduced accuracy would suffer progressively.
A Marlin with fully loaded mag tube with this load shooting the 310gn Lee bullet is a lot of firepower in a small package and is why we chose it for our self defense.
You have to understand that when we were at Rowen Bay bears were ever present even in camp not just seen on occasion. When always in such close proximity the situation can get real serious real fast.
Rowan is the camp where I had a bear in the crummy eating cookies when parked in front of the office while the cutters were recording their daily log count. It is also the camp where I had to kill a bear in my strip. The situation was surreal in that when I first noticed the bear after shutting down my saw he was shredding my pack to get to food in it. He seemed preoccupied shredding my pack so I hit him across the back as hard as I could with a stout spruce limb and yelled as loud as I could at the same time. It startled him and had to hurt some too and he dashed off about 25 or so yards then stopped turned looked through to my soul laid his ears back flat showed some teeth and came right back at me,
The dash away from my pack gave me time to retrieve the 5" Ruger Red Hawk that was in the pack and get it lined up on the bear. When he reached the point of no return I fired a first shot in single action  at center mass  and the bear reared up and over backwards and as he was rolling down the very steep slope I was cutting on I fired three more shots in double action. When he piled up on the last log I had just cut about a 5' diameter spruce he didn't move but just made some gurgling sounds. I think he was well ventilated by the Keith loads the gun was loaded with the 250gn Keith bullet on 22gn 2400.
The next few minutes had me sitting by the pack quite shaken and playing the seen over in my mind. I firmed up shortly and went back to work and piled the next couple large spruce tree on the bear to end any possibility of the FS snooping around trying to make a fuss over it.
Self defense was allowed and a single frontal shot would collaborate that but 3 extra holes randomly placed while he was rolling may contradict it. I felt the SSS system was best employed for the situation and as it turned out was probably right.

I doubt there will ever be a book . I just thank The Lord that I have been able to live the dreams of a NY boy without regret. It was always interesting to me that in my years of growing up in NY that numerous times from different people mostly friends parents I was told, "" you don't belong here "" There seemed to always be things I knew without knowing how I knew them. I give my thanks to God for allowing such a life
At some point in life as age begins to overcome and the ability to make great memories is diminished I am so grateful that I was able to overcome all fears and just go and do the things I dreamed of as a boy. Those memories will sustain me book or no book until taken on to my reward! Praise God !

Your funny !

It is not the beginning but the culmination of a life that is "the proof of the investment of the time".