The Oehler 35p is the only way to go. It has the option of increasing the distance between the screens to gain a better accuracy reading. The further apart they are (to a certain extent) the better your readings will be. This comes into play when you get into high velocity rounds such as the 300 Tomahawk and others of comparable size.
The one I used had a problem with it the proof screen wasnt working properly but since I sent it back (fixed for free try that with any other brand) it works excellent.
To compliment the Oehler chrony a very high quality ballistic program such as NECO's QuickLOAD would place you at an advantage that would be hard to duplicate with other set-ups.
QuickLOAD allows you to design experimental widlcats and examine the design features without going through loads of work just to see your design not own up to what you wanted it to do.
Just my 2 cents.