Congratulations on the new rifle!!!
Your going to love it. The Prophet 2 has incredible trigger allowing you adjust it down to 3oz's. With the new balance valve the Prophet 2 has a ability build a huge amount of power. The plenum from the factory is large, but if your going to push the 44gr .30 pellets or large slugs in .22 I'd recommend adding the extended plenum. This gun can have two extended plenums add for a total of 114cc plenum space. Making this the largest plenum I can think of.
This has been the easiest gun I've ever tuned. I don't own a .30, mine is a twenty two caliber. I'm shooting the JSB redesigns at 955 fps with incredible results. The balance valve works very different from any air gun you've worked on before. It will open at the higher regulator pressure's and only use a very low hammer setting. It's crazy! It will push the heaviest pellet or slug as fast as you want. Doing it in a very easy manner. Unlike other gun's I own, it will run at the very high regulator press and sound and shot's like other guns with 50-80 bar lower regulator setting. I've personally shot the 33.9 beast in the .22 caliber at 1040 fps with no problem.
These things are POWER MONSERS. If I had the .30 cal, I'd add both plenums and start with the heaviest slug I could find. I'm guessing that you could build 150 foot pounds and get 40 shoots per fill.
Oh before I forget, The magazine is able to handle a very long projectile. It's got to be 30% wider then the Impact. In a nut shell there's room for a huge slug and the power to push it. Like I said, "It's Crazy".
Happy new gun, Mont
PS: The pull length on this gun is very short!! I personally would recommend your get on Kraford and Lypt web sight and order a butt stock right now. Don't wait, You'll love it. It's a must have for this gun!!!!