When dry fitting most times they only go in about half way. Prefit the pipe using soapy water to get full penetration. It's still hard to get it to fit up but you have to do this to get a trued up and square installation with good penetration at each fitting. Then when everything is square mark the edges of each fitting with a pencil. Also mark a perpendicular line from the pipe to the fitting. Use a pencil not a magic marker since the glue will dissolve anything other than a pencil. When you glue the fittings line them up with the marks. The pipe will be perfectly square and look like a pro did it!
Once you prime it and apply the glue, the glue should act as a lubricant and allow you to ram it all the way in there, just be prepared to push hard and give it a twist immediately after putting the glue on, that stuff bonds fast
PVC pipe goes all the way to the bottom of the fittings in most cases. If you are getting it in about halfway (which is average) then you are good to go. Remember to use cleaner, primer, AND glue so you geta good solvent bond in addition to the chemical bond!
I have always used the "face" to "face" measure then add in the total make up (socket depth) in this case 3". Depending on your measuring and cutting technique you will need to further adjust that measure (after a few tries you will have a ver dependable standard). You can use a few scrap pieces as gunners (as in I'm not really gunna use that piece) to hold it together to get the actual measures. This only works when you use a tool that gives a nice square cut.
If you have a table top compound miter saw, you’ll get the best cut (use a slow speed). A hand saw and miter box will do to, but your arms are going to get a work out. Always face & clean your cut edges to make a nice smooth fit.
+1 to pencils ... every craftsman should have a pencil, a level, and a speed square.
Thank you folks, all good info and food for thought. I have added the requisite pencil to the two other items listed and retired the sharpie. Whoever installed the original piping has it absolutly dead level. That is my target. We'll see how it goes.