AR15 Spacing Issues
 

http://imgur.com/JUZcILU

I just installed a BCG and charging handle but as you can see in the picture, my BCG is leaving scratches on the buffer connector of the lower. It also rubs and leaves a scratch on the stock you can see. How would you go about adjusting this ? It seems like my BCM Ambi handle is a tad too big, think I can file it off ?

Nope. That's normal.

This is an example of someone that doesn't fully understand their weapon, but is trying to brainstorm a way to tune out a "problem" that is normal function. The top of the lower is the positive stop for any charging handle.

If you file down the top of your lower extension mortise, or file down the bottom of your charging handle, you'll just get more slop, and it'll make the same marks again.

Remove your upper from the lower, unlock the charging handle, pull it about 2" rearward, then you'll see how the charging handle can pivot downward with no resistance. That's because the rear of the charging handle is not supported by any trackway - it is designed to ride on the extension bridge.

The "knobs" on the charging handle near the front lock into the track in the upper, but there is no such alignment lug at the rear - hence the belly of the charging handle HAS TO RIDE ON THE LOWER EXTENSION BRIDGE!!!

Very good to know, interesting because I was told the lower I purchased was on someone else's rifle but when purchased it didn't have any marring or signs of use. By "positive stop" on the top of a lower what do u mean ?

As I mentioned in my last post - take your upper off of your lower, then pull the charging handle about 2" rearward, then press down on the charging handle. There's no flexion, but you'll see the displacement of the charging handle.

The lugs on the charging handle keep the FRONT end held up into the track in the upper. The rear end, however, doesn't have any lugs, so it's able to float a little up and down.

You can even see this by simply pulling the charging handle fully rearward and locking the bcg open. There's a lot of tailplay in the charging handle. If a guy always pulls back and up on the charger, it won't drag its belly, but if you ever exert any downward pressure - common with AR's wearing a scope - then you'll drag those two track marks across the rear of your lower receiver extension bridge.

Those marks on the top of your lower bridge are a lot like cylinder rings on revolvers. A lot of neat freaks and newbies think it's an indication that their firearm is misbehaving - but it's just an indication that it's functioning as designed. It's "character." Guys that buy cool basketball shoes might have white sneakers that stay bright white. Guys that actually play basketball might still buy white shoes, but you can tell that they actually PLAY because the sneakers tell the story.

Eventually your buffer tube will get tracks from your telescoping stock, your dust cover will leave a mark on your lower, and vice versa, your charging handle will get stripes worn down its sides and top, your upper will get a line worn where the charger latch rides, your mags will get streaks, your safety might even spin a ring on the side of your lower... Let alone if you're actually shooting the rifle and getting nicks and stratches and scrapes...