In the movie "Rules of Engagement" the Marines tappped the back of their magazines against their helmets to seat the rounds further back in the mag?  Does anyone really do this?  Is it necessary? If I load a mag with the LULA, do I have to do this?

No its not necessary but some mags DO require it like AK74 mags.  The failure rate of the M16/AR15 magazine from not tapping it is extremely low but it does not hurt and soldiers often do weird things to enhance the reliablity of their weapons like under load mags when they dont need to or press the forward assist after charging even when its not necessary.

It seems like everybody with military experience (including me) taps the mag after/during loading it.  I took a marine buddy of mine to the range last week, and he slapped the magazine against his BARE, SHAVEN HEAD.  Old habits die hard.

Agreed.  It's standard Army doctrine to knock the back of the mag on your helmet to fully seat the rounds.  I imagine it is more of a necessity for the military because of the rough treatment and knocks loaded mags take in the course of being carried on your web gear.

Even though I'm a civilian now, I still knock the mags either with my off hand or on my thigh...heck, I even do this with my handgun mags.

As a side note, I thought it was a good, realistic touch for them to do that in the movie.  Small details like that are a rarity in Hollywood.

for the AR I only really do it on failure to feed.

With my sloppy chinese ak mags, it's necessary to do it before inserting the mag almost every time.

Always do it when loading a 1911...

Quoted: I've seen too many nose-down mag feed failures to skip this step with ANY mag. It may seem like a waste of time to some folks, but MY guns rarely have failures of any kind, and I attribute that to ALL of the things I do to keep them running right.  Ensuring that the ammo is properly seated in the mag is just one of these steps. -Troy

What are all the things that you do?  Please describe your "ritual."  This doesn't just apply to Troy.  Anyone with a routine, please share.

first i kill a chicken and drip the blood......

Quoted: first i kill a chicken and drip the blood......

Cool. however when they start flapping around and clucking like crazy it freaks me out.  So, that's out.

Speaking of:

Do you know the difference between kinky and perverse???

Kinky: I use a feather.

Perverse: The whole chicken.

Quoted: It seems like everybody with military experience (including me) taps the mag after/during loading it.  I took a marine buddy of mine to the range last week, and he slapped the magazine against his BARE, SHAVEN HEAD.  Old habits die hard.

Yes indeed they do: I avoid, as best I can, the "bare, shaven head mag-tap," but instinctively tap the spine of any magazine I load against "something" a bit harder than my hard head in order to firmly seat the rounds in the mag at their base.  After reading the posts here, I realize that, almost simultaneously to setting a good cheek-weld, I also consistently and unthinkingly tap the forward assist on my way to the pistol grip and trigger assembly.  I cannot remember if this was drilled into me by a PMI at Parris Island or acquired by hard experience throughout my 0311/0321 experience.  Resultantly, I believe, I cannot recall experiencing, then or know, hang-ups of any kind due to irregularly positioned rounds in a magazine (this includes using the pre-green-follower, 30-rounders).  (An added benefit of fully loaded mags with firmly seated rounds is noise elimination.)  Just my $.02.

O'DubhGhaill

I was taught to shoot the AR by a former Ranger, who got me into the habit of slapping the mag to make sure the rounds were seated as far back as possible. He also got me into the habit of an additional slap upward on a seated mag before charging the weapon. I do both without really thinking about it.

Unnecessary? Maybe. But I've put 4K rounds through my AR without a single FTF.