I have considerable (though dated) experience with AR type rifles (M16 Viet Nam 1969). However, not so much with the current trend AR's. O.K., I'm old but I'm building my first current era AR.
My question - is the collapsible carbine stock buffer spring length the same as the rifle length spring. I know the buffers are shorter and will probably use an H or H1, just not sure about the spring

Interesting question. I have built a couple and I just bought the buffer tube, buffer and spring as a package. This way they were all matched.

Even so, I'm curious to hear what others say about this.

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http://www.kdeguns.com/ar-manual/M4%...23Pchange8.pdf

TECHNICAL MANUAL
ARMY NO. 9-1005-319-23&P
AIR FORCE TO 11W3-5-5-42

RIFLE: 11 3/4 Inches (29 85 cm)
minimum to 13 1./2 inches (34 29 cm)
maximum

CARBINE: 10 1/16 inches (25.56 cm)
minimum to 11 1/4 inches (28.58 cm)
maximum.

I have the Spikes ST-T2 buffer. Weights about 4.5 oz. and is Tungsten powder filled. I'm still using the standard buffer spring that came with the Sport.

With the old buffer my casings were ejecting about 10 ft. at about a 45 degree angle (right and rear). With the ST-T2 buffer they travel about 3 ft. with less recoil. I like it.

Thanks, nice read... all 436 pages

CTRL F - search function is your friend! Not sure how we ever got by when all we had was hard copy.

We learned to use the table of contents and index along with the correct part names.

In this case, the spring in question is the Action Spring. I found it by looking through the table of contents until I found the heading, "Inspection of Action Spring." The word "inspection" clues me into where a specification might be.

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Wow... you must be old!

Actually, that is how I found it too... searched on spring, got the hit in the table of contents and went from there.

Thanks for the help guys. This is what makes the S&W Forum so great - someone out there has an answer for almost any question us amateurs have.

I installed a Spikes ST-T2 buffer and a Dave Tubbs buffer spring in my M&P15X. Runs so smooth!