i use a lee dies in my dillon and drop the loaded rounds in my chamber to check. I like to check each round in the chamber fo rhte gun im using especially for a big match so i reduce the chance of malfunctions.
i picked m&p in production. You have been shooting it in ssp and it is something you are familiar with. But you will get hooked and end up buying more guns thats what happened to me.
You may want to think about a g35 it gives you the most options. You can relaod for minor power factor for production, or you can reload to major power factor and shoot it in limited or limited 10.
Go for it, i shot local matches for about 6 months before my first major match and it was awesome. Major matchs are a great way to see how you stack up againxt the big dogs.
Ive tried some unknown brand fmj i got from a local gun store, these were not as consistant in weight as the montana golds. The price and availability of montana gold is what sold me on them and they work well for me in my glock.