This is not a sex question- no jokes please.

For example: If you have a carbine and put a 20" heavy barrel upper on it - should you change out the carbine buffer for a heavy barrel buffer?  Could using the old buffer cause problems? I didn't realize there were options till I saw the site linked below.

www.biggerhammer.net/ar15/buffers/

DAMN!

DOUBLE DAMN ! [sex]

A carbine buffer and stock should work with any upper.  However, they tend to be less tollerant of other things that can affect reliability.  Such as rough or sticky chambers, gas leaks, or gas port size.

If you have a cheap plastic bb filled carbine buffer throw it out and get a metal one.

Otherwise, if it works don't mess with it.

TRIPLE DAMN!

Just remember that a car buffer (short) works with a car stock to limit the amount of travel.  If you install a full size buffer in a telescoping car stock, the carrier will not come all the way back.  On the same note, if you drop a car buffer in a full size stock, the carrier key will impact the back of the receiver and do some damage, due to the carrier travel not being limited out by the longer buffer.

P.S. There are two types of buffers, the short for the telescoping stocks, then the full for fixed stocks. The barrel lenght has nothing to do with the lenght of the buffer.  

Thanks.  That makes sense after looking at the pics on biggerhammer again.  When I read "carbine" vs "Heavy barrel", I was thinking barrel/overall length.

No worries.  

Regarding the weight of the Car buffers, you will notice that the 9mm SMG is the heaviest listed.  This is due to the 9mm being a blow back action (non-locking).  This extra weight slightly delays the action/carrier from coming back as the round is fired (mass and inertia).

On the standard weight car buffer verses the M-4 heaver buffer, the same effect takes place and this added stall/weight allows the barrel to loose a little more pressure which allows the chamber pressure bound case to be easier extracted, and the greater mass of the buffer slows the cycle rate (rounds per minute in full auto).

Hope this helps.

Now that you've gotten your answer, I'd like to add:

Size doesn't matter!

To all of you how have been told this, they now have a pill that can help you out.

P.S. Never send a boy to do a man's job!!!!