444 Marlin with trail boss

I’m looking for a load for my 444 Marlin, using a 300 Gr Cast bullet and Trail Boss powder. Just trying to get a light load. Thanks in advance

Load a 45-70 with 12-14 grains of Trail Boss. Shot in a H&R Handi Rifle. Have shot 50 rounds at one setting at the rifle range. Trail Boss is very good for light loads.
My wife shoots her 38 Special Revolver loaded with a 125 grain cast powder coated bullet loaded with 3 grains of Trail Boss.
Try a case about half full of Trail Boss just make sure the powder is not under compression with the bullet seated.
I use Trail Boss in 308 Win with a 117 grain cast bullet, my 10 year old grandson shoots the 308 Win with the Trail Boss a lot.

I don't have a 444 so can't speak from experience. I did look at your cartridge with QuickLoad and it says a full case (100% load density) would happen at 16.5 grains TB and right at 1300 fps and still be well under 30k psi. So bstone5's 12 to 14 grain suggestion would be totally reasonable to try.

I would worry that the 300 grain boolit might not stabilize in the Marlin's slow twist at those low velocities. But I'd bet a 200 (I shoot a lot of these made in a 6-cavity Lee in 44/40 and 44 mag rifles) would be a wonderful light load boolit if the 300 gives stability/accuracy troubles.

TB in 444 Marlin: 1) Load TB to touch bullet base but NOT be compressed. Weigh Load. That's your max load. 2) Multiply by 0.7 That's your minimum load. Work up from there for accuracy. In my experience with TB, lower extreme velocity spreads in straight walled cases and most consistency in top third of load density. YMMV. Enjoy!

https://imrpowder.com/wp-content/upl...-loads-r_p.pdf

My experience with TB is that the minimum load is closer to 80% of max. Anything below 80% resulted in extreme variations in velocity on my chronograph. A 95% load density (just a little below the base of the boolit) resulted in an MV of 60% of the max load with standard smokeless powder (for instance, if the max load for a standard powder results in an MV of 2200 fps in the 444, then the 95% LD load of TB with the same boolit will be about 1320 fps). My favorite light load in my 444 is 19.5 gr. of 5744 with a 260 gr. SWC-PB giving an MV of about 1150 fps and it is a delightful accurate load I can enjoy shooting all day long.

i like to use 23.0 - 25.5gr of alliant 2400(with a pinch of dacron) under a 300gr saeco fn in my 444.

i've used TB with mixed results. 250gr kieth, 275gr ranch dog, 280gr wfn gc and 280gr lfn gc. i think it went 1/2 - 4" groups at 50 yards.

Thanks everyone I bought 100 bulletts from a guy just to see if they will work, more for plinking then anything else, I’ll let you know

Just as a FYI (only limited in application here as it's a bottlenecked case), but the preferred Trail Boss loading in my .350RM was at only 56% loading density.
Outstanding accuracy, averaging 0.4" 3-shot groups @ 50 yds; ideal subsonic velocities of 1080 to 1090 fps.

So u tried 12 grs and it shot not to bad, the primers where high after shooting. If I remember right it’s a sign of low pressure. I’ll bump it up to 13 grs and try again