Marshall Pride 4

I am trying to chase down the likelihood of Marshall Pride 4 carrying a mutation for double muscling. I see the are many bulls of this name. The one I'm interested in was used in Canada, but any info on the bloodline in terms of double muscling would be appreciated.

What breed is this bull?

:

Sorry, he's Angus, pre 1978.
There was a suggestion that he brought double muscling into Speckle Park. I'm dubious as there is also a Limousin ancestor way back in Speckle Park, but since I dont really know if myostatin mutations were known in Angus of that vintage, or today, I'm trying to learn.

The most prominent was AAA 3447664

Marshall pride 4 was the sire of Marshall pride 256,  tiny Tim.  A lot of people used him and then the mule foot, and no telling what else popped up.  Saw calves out of him in the early 70's,  owner tried to tell us foot got cut off on a piece of tin.  Then sport came along and it broke out.  There were a bunch of them at premier in east Texas.

Thank you, Foster and cowman, for helping me out. Few things have made my brain hurt like this particular research.

Although I'm finding nothing to substantiate my idea, the first bull I thought of when wondering about double muscling in Angus Was Rito NBar. He always looked weird to me.
Not only was he the sire of 707, but he was in top and bottom in the pedigree of 6807's dam.
At least one OCC bull is an M1 carrier ( myostatin mutation), OCC Prototype 847P....but that's a different story from Marshall Pride.
There is also an Angus code for DM, Double muscling, so I guess there are two different myostatin mutations in Angus?