After some thinking I decided to build my own 9mm ar15, after the whole oly arms debacle (still waiting for my $...).
Anyways, I have ordered most of the parts I need. I am going the RRA style route.
On RRA's site they say that a 9mm buffer is needed, so:
1) What does the buffer do?
2) Do I really need it?
Most people that have the 9mm setup have a collapsing stock. In that case you need a 9mm buffer. Take out carbine buffer put in 9mm buffer. The 9mm buffer is heavier than the carbine buffer. Since it is a blowback system more energy is forced back vs AR15 which is a gas system. Even w/ a 9mm buffer the recoil is more noticeable in the 9mm carbine than in a rifle mode.
If you have an A2 stock then you can probally live with it. Some people change it.
The ""9MM"" buffer is a CAR style buffer that weighs very slight bit more than the std A2 rifle buffer (5.6oz vs 5.1oz).....
I prefer the std rifle stock, but due to my running a suppressor, I took and gutted my buffer body and installed a machined brass dowel to fit inside, bringing the weight to 7.0oz, this provides a delay in the opening, and reduce the amount of debris I get from the port.