Ok, so, a player of mine has taken up GM'ing. This is great, I get to play for once!

Now the problem, he is a bit of a self centered ass, a lovable self centered ass, but still. We are two sessions in and he has made multiple rule mistakes and as myself and one of the other players have been trying to help him out he just starts shutting down and saying its happening this way because he wants it to even though its directly against the rules, the fluff, the current story, and the previous sessions.

He's a friend of mine, and I try to discuss the rules and his reasons with him and he wont budge from his position that He is always right.

Here is an example that is still going on, first off he said no starting with power armour unless you are a chaos marine, I am ok with that, sad my renegade cant have light power armour to start with but, what ever. But he and one of the other players home brewed a decently balanced fallen Sister of Battle class for human. Nothing over powered or under powered off the base, pretty decent job. The problem is here, in the Sisters starting gear he put in light power armour, but said that in the power armour section in the armoury Light Power Armour only gets one sub-system. This is not him deciding that in this case he is only allowing for one sub-system, he thinks that all light power armour only gets one sub-system. Now, in case i am wrong, please correct me, but light gets three just like all of the rest right? I put up a rules post in the rules forum about this too only becuase he's arguing it so vehemently that I am doubting myself and think I may have missed something.

He has also ignored skill checks, changed where things are, changed physics, (seriously, path of least resistance = blast shadow...) changed the way basic rules functions, (refractor shields need to be rolled by the player under the protection rating, a 17 means the player is safe, not hit) not all the time, but only when it suits him, which is a lot, and without any consistency, and as myself and another of my friends who have both been running games in dark heresy and other systems for many years try to help him, and correct him, or even just point out that "hey, 30 seconds ago I was several blocks down the street, how am i now standing by the truck?" he gets defensive, doesn't explain why he is doing this just quotes "rule 0" and moves along. I don't think I would care if he would at least acknowledge that he is changing the way rules function, or do it with some consistency. Especially consistency, that would make all the difference in the world if the same thing happened twice...

Anyway, my point is, what do I do? If it keeps going like this I will probably have to drop out of the game because the inconsistency and lack of workable foundation bothers me a lot. But I don't want to, I like him as a player, and a friend and I really enjoy being able to play and not plan the sessions. So i need some advice on how to deal with this guy as a GM.

As in most problems in any relationship, the only way to solve them is communication.

Make sure you tell him straight how his method of handling these situations is causing you to lose interest and pleasure in the game. Make sure he understands that unless something changes, you will leave.

To his defense I will say that being a new GM is hard, and learning a system like BCs is not easy. He might be the type that finds it difficult to handle corrections, especially if done in front of others. Loss of face, and all that. Especially if he feels it compromises his "authority" as GM. Or he might be the type who feels these mechanics are of secondary importance to the story, and he wants to drive on and not get bogged down in "uninteresting details". Again, you won't know until you talk to him. Preferably on his own.

On the flip side, inconstancy and unfairness is a very bitter pill to swallow, so I sympathize with your situation.

Find some common ground rules to proceed, or agree to disagree and go separate ways.

Most GMs will be interested in serving an enjoyable gaming experience to their players, and will be happy to implement changes based on real feedback. However, many RPGers are geeks, and many geeks have ... social issues.

Personally I am only too happy to offload some rules and mechanics processing to others around the table, and I'll happily implement any changes to rules, method and story that the table agrees to unanimously, but I will also kill long discussions with an arbitrary ruling there and then, promising to discuss in detail between sessions and agree upon a method for future rulings.

That is how force fields work though. If you roll 17 under 30, then you are safe. If you roll over, you take damage. They work just like skill checks. Roll under to succeed.

DJSunhammer, yes, that is how they work, when it came into play he said that rolling under the target number means the field did not stop the attack, hence some annoyance when we tried to point it out to him.

Darth Smeg, thank you for commenting, you are probably the most recognized name I see in the GM forums, and you are right, I really need to talk to him between sessions, which should be easy enough since we switch back and forth every week between this game and another where we are both currently players, so, I should be able to pull him aside during a smoke break or something, or better yet, just wait until the end so I don't cause drama during a different game, even though it's all the same players... But point, drama is good on the stage, not in life.

Although you brought up a good point, I do believe that a lot of what he's doing is to quickly push an exciting story forward, it seems so far like a story driven campaign and not a player driven one. I tend to run my campaigns to be a mix, but point being, that makes sense that hes more interested in telling the story than the math and mechanics. I am an engineer, I build servers and networks and domains... Data Services Engineer; I am very mechanics oriented, he is not, so that may be another big part of it...

I think I'm going to give him another session or two to see if I can adjust myself to a story driven game and not a player / mechanics driven one. I will probably still need to talk to him, but based on what you said and what I'm thinking i think I need to try to see things from his side a bit better first. "Know thy enemy, know thy friend and know thy inner self" sort of thing...

Thank you very much for the insightful response.