Hey everyone, this is my first dip into the AR15 world....... my first rifle being the M&P15 Sport 2. The last time I shot a rifle, it was the M16-A2 in BCT. Feels similar to the M16 but I'm not familiar with the particular part differences.

Looking at some options on replacing the factory stock. Does any one know if M&P 15 Sport 2 comes with a carbine buffer and spring? If so, what's the difference between the M4 carbine buffer and spring and the AR 15 buffer and spring? Searched on the forum but found nothing on this subject.

Thanks in advance

First and foremost, the M4 is the designation for a select fire military firearm that we civilians are prohibited from owning.

1. The M&P 15-Sport is issued with a standard buffer spring and a carbine buffer.

2. There is no dimensional difference between the mil spec carbine buffer found in the 15- Sport and in a military M4.

3. The label "carbine" is to distinguish the buffer type between what is used for the collapsible stock M4 pattern AR-15 v.s the M16 A1/A2 style fixed length rifle stock. The buffers different between the two.

4. For us civilians, we have access to carbine buffers that diverge from the mil-spec weight. We can run from a standard carbine buffer, to H, H1, H2, H3. As the number increases, the weight increases, increasing the static mass the energy the combustion gasses must overcome to cycle the action.

We also have access to hydraulic buffers which provide progressive resistance to cycling of the action which dampens the recoil impulse and bolt bounce.

Welcome aboard. You've started to dip your toe into the deep end of the pool.

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-John

If you are looking to replace the stock only, what does it matter what the buffer and spring are? A direct butt stock swap doesn't need any mods. Are you asking if it's a milspec or commercial tube?

If you are looking at replacing a rifle stock with a collapsible stock, you most likely will have to replace the buffer tube and spring. The collapsible stock engages detents in the carbine buffer tube.

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Judge control not gun control!

Awsome! Thanks John...very much what I was wanting to understand. One thing about the deep end. Either you sink or learn quick how to swim. Thanks again for the info.

Directly from Magpul sight.

"An M4 carbine buffer and spring are required for use with the UBR and are not included.
7.62x51 ARs may require the use of a custom short buffer and spring."

Very true, however, what type of stock you wanted to use wasn't mentioned in your original post. Research the stocks you are looking at as best as you can. Check YouTube for reviews as well. The gen 1 ubr is heavy. The gen 2 is 20% lighter and is less expensive. I think they are shipping the black ones now with other colors available "soon."

If Magpul says that, presumably they know their own product. When they say "M4 Buffer Tube" , that translates as Milspec buffer tube.

What that all means - Milsec and commercial spec buffer tubes are all the same ID, and use same dia buffers. The milsec tubes have thicker walls, and hence slightly larger OD.

Why two standards ? Since most civillian shooters don't usually use the butts of their carbines to buttstroke soviet ballistic helmets or smash thru walls, some mfgs felt they could use thinner tubes that would be plenty strong for "normal" use and save them a few cents per unit material costs. Many aftermarket are available for either flavor, but they are not interchangable.

More useful information....much appreciated.