I have a 1973 vintage 94 in 44 magnum that is more patterning than grouping. It worked very well for years and then one day it didn't. No major falls or drops didn't get run over nothing unusual. I've completely disassembled it, checked the barrel for looseness in the receiver, checked the receiver for cracks all seems good. It would shoot everything you put in it no problem now factory, reloads, 180gr, 240gr nothing shoots accurately ever.

Has anyone else ever encountered this problem and if so what did you do about it? Am I missing something what's left to check? Sights were a Marbles tang which was fine until the rifle went out. Went back to the Lyman receiver peep and no improvement. Had even tried a scope for a while and that wouldn't zero. Any Help would be appreciated.

The marked rounds are from the Winchester. It's way worse than it looks here the pattern is roughly a foot and a half around but there's no way to fit a real picture from a good phone camera on this crappy antique platform.

Perhaps a good barrel cleaning?

It was as clean as it can get and now has only 14 rounds through it.

Is it possible the barrel is “shot out” after 50 years?

Definitely not. I bought this in 1984 it was only 11 years old and seemingly unused then. I hunted with it but never exclusively using other rifles also depending on the circumstance. This has been my brush gun and I have taken 2 deer with it but wouldn't hunt with it now since it went bad. I doubt it has 2500 rounds through it and if that much. No Winchester is going to wear out with that kind of round count on it.

I've been reviewing what Jericho said and I think I'm going to do a breech plug bore soak just in case the throat is heavily fouled and I can't see it.

Update:

So I found out sort of lefthandly that years ago when my brother borrowed my 94 to complement his collection of lever guns for a range trip he had run lead head 44 specials through my 94. Oddly enough this corresponds with the accuracy issue. We all know that should never had been done so now I have it completely disassembled to clean the throat effectively from the rear as it's a fouled out mess looking like a smoothbore in there. Will update after I get it to the range.

Well I found some pitting issues forward of the chamber. I don't know if they are the source of the troubles I've been having but they are definitely there.
Now this barrel has never rusted in the time I've had the rifle so this was there before I bought it or it's a manufacturing defect. What's odd is none of this is visible looking down the barrel from the muzzle only from the breech.
This is the best shot I can get using extreme magnification. If you look closely tool marks are still visible on the lands so this barrel is far from worn.

Did you happen to put a little ding in the crown cleaning it? I did that once and had to redo the crown. If the bore looks good and accuracy suddenly diminishes, that was the first thought to pop into my mind.

The crown is fine no dings. A tiny spot of bluing loss at around 1 o'clock but that's it.

Looks like it may still be some lead remaining in the bore.

Best thing I have found to remove stubborn lead is some fine bronze or copper wool wrapped around a bore brush and soaked in solvent then passed several times through the bore.

What 470Evans said!

So the indepth disassembly and lead removal cleaning actually worked very well. The rifles throat was so blocked with lead there was hardly any rifiling seen. It now groups extremely well with 240gr bullets but is still terrible with 180gr. I'm fine with that as it's a brush gun hunting rifle and should be using the heaviest bullets possible anyway. Thank you all for your helpful suggestions. Bill