I got this ship from my brother. I traded some RC stuff for it. He said he only flew it once because the home made tank leaked, so it has been hanging in his garage for almost 10 years. Originally it had a Double Star 60 in it. It seems to have a short nose and a long tail moment (read heavy tail). With the Double Star 60 it was way tail heavy so I put a ST 51 in it which is a little heavier and still had to add a 1/2 oz. of lead to the nose. I was using a 12 x 5 REV-UP which seemed to be fine, 2/4 and all that. I read here that Dan Mc Entee liked the APC 12 1/4 x 3 3/4 so I decided to give it a try. I'm always open to a good prop that is over the counter and gives repeatable performance as opposed to a really really great prop thats been sanded on for 4 days and is not replaceable. Of course I was a little doubtful that a 3 3/4 pitch would pull a plane that has been flying with a 5 pitch and not doing a bad job at that. So I am here to tell you that the APC 12 1/4 x 3 3/4 is a smokin prop on the ST 51. I was really surprised to find that the ST 51 would run in a solid 2/4 break thru out the flight with lots of line tension. Didn't matter if it was in 2 stroke or 4 stroke mode. Did I mention I really like this prop. The plane still needs more trimming but it's going to be more fun with this new prop. Even more surprising is when I got home from the field today I got out the digital scale and weighed the sucker at 64 oz. I forgot to mention that the engine I'm using is a Bryan Barker modified ST 51. It's really a sweet motor. I think I sold half the guys at the field on this engine......It brings to mind how so many of us ask for advice from the experts and then when we get the answer we refuse to follow up. It seems that many of us already have our minds made up when we asked the question. Anyway thanks Dan Mc Entee for sharing your experience with the ST 51. I appreciate it.......Any other thoughts ??
Hi Greg; And I won't call you Gerg like Pratt did!!!

( HI MIKEY!!!!)I'm glad that the prop worked for you. I haven't heard of anyone yet that hasn't had at least some improvement with it in models this size. All we have to do is pray that they don't quit making it!!! ANd thanks a lot to Jim Schuett for telling me about it! H^^I'm not the best engine guy, but I think each engine has a certain power curve, and this prop lets the ST.51 get to the peak of it's power curve.
Late last year, I saw that APC came out with a 13/4 with a very similar blade shape and area. I tried one flight with that prop on my Charmer ( similar in size and weight to your model or a Magnum) and it seemed like it was just on the edge of overloading the engine. I cut one down to 12.5 and tried it again, and it resonded better. I left this prop on my Shark45 for VSC this year, thinking it might help out in the thinner air, and it seemed to. I wonder how this prop would work on a ST.60?
The only other thought I have is repitching a few of the 12.25/3.75 props to an even 4, 4.25, and 4.5 inch pitch and test those. I have a gut feeling, that with that blade shape and area, if we want to try more pitch, we might need to go down in diameter a bit. I would love to test this out, but time and life just haven't allowed it yet. Maybe this suimmer.
Good luck and have fun,
Dan McEntee