I want to replace an AR 15 A2 rifle stock with a AR 15 Carbine collapsible stock. Do I need to replace the rifle Buffer and Buffer Spring to do this? Thanks to all who respond.

Yes sir. Gotta replace the buffer, spring, and buffer tube. Bravo company has the complete kit for like $60. They can be had from PSA for a little cheaper. if it were mine, I'd use a mil spec tube made from 7076.

Mi shooter556 has it pretty well laid out, however he neglected to question what barrel length and gas system is installed on your upper. You really need either tune the gas system or select a buffer appropriate for your barrel length and gas system. Otherwise you may end up with a buffer too light for the barrel/gas system resulting in an excessive recoil impulse and a bit of battering to the firearm or too heavy a buffer with a result of possible unreliability or a failure to lock the magazine back on an empty magazine.

Issues like this are why I have now installed a Syrac Ordinance adjustable gas block on all 3 of my AR's. It allows me to tune the gas system to a specific load. As a result none of my rifles run more gas than what is required and as a result the uppers clean up quicker and there is a noticeable reduction in the recoil impulse.