Forget non-gas checked bullets unless you are sure your plain base bullets are .03 over groove diameter. For most micro-groove .444 Marlin rifles that would be .434" diameter. Also you need to keep the velocity pressure to about 1200fps/15000 psi to get away without gas checks. Forget using gas-check design bullets without the checks added as they shoot poorly no matter what velocity unless you get very lucky. Gas checks don't cost that much but add significantly to accuracy. Slug your bore and find your twixt rate so you can select a bullet design that will work for you.Veral at LBT is a great resource and top-notch mould maker. Anything he makes for yu will work in your rifle.
Pick a start charge for the 44 magnum using 2400 or 4198, and light it up with magnum primeers. If you get leading back the charge down till leading stops. Expect a maximum speed with freeedom from leading to be somewhere between 1300 fps and 1800 fos depending on bore condition, type of lube and hardness of your bullets. No other lube will match the velocity you'll get with LBT bullet lube.
If you want to make your rifle play a pretty tune, order my LFN in 300 grains with a diameter of at least .432 and GAS CHECKED. This can be shot at any velocity up to where you will hate the recoil. I shot one once driving it at 2400 fps, and capable of consistently printing one inch groups at 100 yards. I've forgotton the powder charge as it was a neighbors gun and load, and shot about 20 years ago, but bullet hardness was 20 bhn, the bullet gas checked and lubed with LBT Blue bullet lube.
I cannot claim the expertise of these fellows but I can tell you my experience. I only used jacketed in my Marlin lever action, but I have had excellent results in my 444 handi rifle with the Lee 305gr without a gas check. I cast my own using wheel weight metal that are water quenched so they are fairly hard, and moly lubed. They are 430 dia.and seated long. I am using 20gr of 2400 in mine. This is not a high speed load , I do not have a chrony but estimate it at between 1400 &1500 fps. I was trying for a load that was similar to a 40/82 BP load and think it does. It is accurate in my gun and I have taken several deer with it.
If I were trying for high speed I would certainly go with the suggestions of the others here.
Yes you can shoot plainbase in a 444, but velocities will be VERY limited compared to gas checked, and especially so if the bore is rough at all. If the bore is decently smooth and straight inside, you can expect to get good accuracy at speeds to 1400 fps, if the bore is lapped using my lap kit, and any of the LBT lubes are used, it is possible to get very good accuracy at speeds to 1800 fps, with an LBT bullet design which is large enough for your gun.
If using a mold which doesn't cast large enough for your gun, and with most designs other than LBT, don't get your hopes to high for good performance, but almost any bullet will shoot well if you keep velocity low enough.
A forum community dedicated to the great outdoors and hunting enthusiasts. Come join the discussion about hunting, fishing, survival, archery gunsmithing, optics, reviews, accessories, classifieds, and more!