The OS engine is ABN, which is the same as ABC for all intents and purposes. OS juse uses Nickle instead of Chrome.

A new ABC/ABN engine SHOULD "get stuck" at the top of the piston stroke when cold. The piston and liner have what ammounts to an interference fit at the top of the stroke. Once the engine is warmed up, the liner expands more than the piston, and the fit is correct. If you losen up the fit while the engine is cold, you loose compression once the engine is running at temperature.

You should also try to avoid running the engine overly rich or at low RPMs before it has warmed up, and avoid extended cranking with an electric starter. Both of these will tend to wear the piston/liner fit more than you really want it to be worn.

As for throwing the prop, you might want to get rid of the spinner and go with a spinner nut, as it makes it easier to take a look at things. Generally, though, it sounds like you just aren't tighening down the prop nut enough. If it continues to be a problem, you can add a second prop nut as a jam nut. A lot of 4-stroke engines use this, as they are prone to throwing props when they backfire.

Which brings me to the possibility that your engine is backfireing. If the glow plug you are using is too hot, or you have too much nitro in the fuel (or a few other things too), the engine can fire too soon, and kick backwards, throwing the prop. Since your engine is brand new, and sounds like it has a lot of compression, this is certainly possible. Try this. Set the electric starter aside for the moment, and use a chicken stick. Prime the engine, put the glow starter on the plug, and then flip the prop BACKWARDS against compression with the chicken stick. The engine might "backfire", which in this case means fire in the correct direction, and start up.