Anyone had luck priming in a Z position or should you get in as tight as an A frame as you can?

got a 40z 4.5 boom pipe i prime in a z just not a tight z i also use slikpak but only on certin mixes

Yes you can prime in a Z form, the machine structure is fine either A or Z , tight pattern or flat.

The difference is your mud. Will the material separate on the trip through the boom?

Some parts of the country only A frame with a 5 inch tip hose makes it, some other places anything goes "almost"

The big secret is, Are you reliable priming in the morning ? If so you are doing something correct, priming in the morning is also about clean out last night, If you are having problems priming then either your prime routine or your cleanup routine is in need of Tweeking.

I want to try out a z boom sometime. the schwing 31 is cool, but I feel like a true z would be interesting to run

I always prime A frame. This allows me to prime various mixes because basically I only worry about it going up. 

yeah I always a-frame , watched a putz tech try to prime in Z when the pump was being put in service and plugged up , learned my lesson , I always a frame unless I have grout.

I prime the 40Z I run in the Z, I have had it plug once between C and D section elbow it happened last winter one day after I had already pumped a job before that ! It might have been  the temperature that day. I like that its so much faster than rolling it out into the A. But I guess it's whatever works for you and what your comfortable with.

We prime the 32 5z sermac in z no worries! traveltech is 100% right about a good wash up the day before making all the difference 

We use bullet pigs and they're full proof , a good clean pipeline and a decent mix and you shouldn't have a problem , but when you have not so clean pipe or a rocky or marginal mix , I would A frame , it should work 99 out of 100 times , its that 1 time that is gonna be a pain in the ass , on a high profile job with high early concrte and a impatient customer that is gonna make you say damn I'm gonna take the time to A frame .