I'm thinking of adding a 450 bushmaster. Looking at the ruger American 22 inch bolt. I have a very accurate marlin with the 1/20 twist. Is the any advantage

I'm going to take a wild stab at it and say the deer wouldn't know the difference, at least within the normal operating range of both. I'd also guess that, given similar shoulder fit, you couldn't tell the difference in recoil.

My rough guess is that the 444 Marlin is going to have a better bullet selection.

sounds about right

Back in the day the only 444 ammo was Remington with a 240 handgun bullet.
I shot a buck with it one morning fro a Marlin.
He dropped to his chest so fast and hard he nearly bounced. He popped up, turned right and ran 20 yards, fell down, stood up and turned around, ran another 10 yards and fell again.
He then lifted his head and blew a stream of blood out of his nose then fell dead.
I had hit him on the ball of the shoulder in out the 3rd rib.
To say I have never seen one act so unearthed, so stunned by the shot.
It was like he was phased on stupid.

The 450 Bushmaster is taking off and new ammo offerings keep popping up. The 444 Marlin (which I love) is headed in the other direction. It is on the wane and has long ago been supplanted by the resurgent 45-70. You have two cartridges that are headed in opposite directions. One would think that would have to play in to your decision making.

The 450 bushmaster in the Ruger is a fine rifle for the money . I have an H&R 444 with the 16tw barrel - loaded some 240gr. flex tip Hornady's it shot 1'' at 75 yards - sighted in at that range since it's 65 yards to the hog feeder . It's my night hog rifle - 4x12-50 L VXR .

I don't see any lack in ammo for the 444marlin and that cartridge isn't going anywhere because the parent case is the 30-06 case with a rim - straight off the press . No shoulder or neck added , if the 30-06 goes away so will the 444marlin .

I wouldn't fret over performance or availability in either case. Pick the rifle that appeals to you, go forth and slay. Watch out for transitional Remlins (the Marlin forum can help you with that). Starline makes brass for both, so if you're worried about feeding it, lay in 250 cases for about $150 and you're good.

That was the standard hunting load in muzzleloaders here in NJ with a lot of guys for quite a while. 80-100gns pyrodex 240 grain xtp. It just works really well.

The 265 Hornady flat point bullet is THE bullet for the .444, The Hornady SuperPerformance ammo is very accurate in my .444 and the bullet performs great. It might be a little too much for whitetails - it would be perfect on elk and moose. I've shot a couple whitetails now shooting through 1" saplings and when the bullet hits the deer it just destroys them. The last doe I hit at about 35 yards after the bullet hit a thumb size bush left a fist sized hole through the deer, and she STILL ran, but the blood trail was 5' wide to where she dropped after a 30 yard run.