I'm interested in purchasing a new barrel for my 16" AR-15, but I've come across a bunch of things that I'm ignorant about.
1) What twist would be best for me?  I'll be purchasing a light weight 16" barrel with a mid-length handguard.  My current barrel is 1/9 and that seems to be fine.  I'll be shooting 55gr FMJ or 62gr FMJ, nothing heavier.  Does the 1/7 twist offer any advantage in my situation over the 1/9 or does it really not matter.
2) I've noticed something called a wilde (sp?) chamber.  What is this and what advantages does it offer?
3) What does the "F" on the front sight posts mean?
4) Is there anything else that I should know or ask that I have not?

Quoted: I'm interested in purchasing a new barrel for my 16" AR-15, but I've come across a bunch of things that I'm ignorant about. 1) What twist would be best for me?  I'll be purchasing a light weight 16" barrel with a mid-length handguard.  My current barrel is 1/9 and that seems to be fine.  I'll be shooting 55gr FMJ or 62gr FMJ, nothing heavier.  Does the 1/7 twist offer any advantage in my situation over the 1/9 or does it really not matter.

If you never shoot anything heavier than 62gr then unless it is some really experimental weird 62gr that is abnormally long, you won't get any benefit out of 1/7.

2) I've noticed something called a wilde (sp?) chamber.  What is this and what advantages does it offer?

It is a match chamber a bit between 5.56mm and .223 SAAMI. The idea is it offers better accuracy than 5.56mm while not sacrificing reliability as much as a tighter .223 chamber.

3) What does the "F" on the front sight posts mean?

It means it is designed to be used with a flattop/detachable carry handle

Thanks for educating me.

It means it is designed to be used with a flattop/detachable carry handle

How and why is it different?

F front sight bases are taller.  On some non F FSB you have to use a longer sight post and it will stick up between the ears of your front sight post to get a propper 50 yard zero.

Be careful putting an older style lightweight barrel on a flat top upper receiver.  A non F marked front sight does not always work with an extended post-- according to a major Colt dealer, that fix only works about 5 percent of the time.  There can be subtle variations in the manufacture of the FSBs which can make it impossible to zero even with the extra long post.

CMMG and a couple others put out LW barrels with F sight bases.

OK, two more questions.  What is a "T" marked upper?  What is a MOD4 barrel?

T marked upper has marking that denote Top.  The number denote which slot number you are looking at.  This is supposed to aid in reinstallation of optics to the same location for those who have trouble with know where the top is and cant count higher than the fingers on one hand.

MOD4 is what CMMG calls their copy of the M4 contour of their barrel. M4 used to be patented by Colt and no longer is after Colt tried to sue over it.

You're really helping me out.  I do have another question if you're not getting sick of me asking.  How do M4 feedramps differ from regular feed ramps?  I saw this in a post in the EE.

They are extended and require a matching cut into your upper.  Some one will link a pic shortly.