Is there a difference in Buffer tube springs

[thom]

Is there a difference in the springs of AR buffer tubes? Can a spring for a pistol tube be used in a mil-spec tube without causing problems? I have a mil spec tube and want to use a pistol recoil plug and spring for use with a pistol upper. It will not have a 6 position stock on it. Thanks for any help.

Thom

 

[G34]

Yes and no. Before you have issues or cause damage
1. Weigh the buffer
2. Count the coils and or measure the spring
3. Compress the buffer and spring inside the tube and see if the bcg travels rearward enough to strike the lower.

 

[YNOTAZ]

There are two different length (and coil count) springs for a standard AR:

Standard Carbine Spring – Measures 10.5” with 37 to 39 coils
Standard Rifle Spring – Measures 12.75” with 41 to 42 coils. I have never seen a AR pistol spring.

There are different spring rates you can use for different cartridges i.e. .450 SOCOM or .500 Beowulf but a standard carbine spring should work for your application.

One question, you mention a “pistol recoil plug”. Do you mean a buffer spacer for pistol calibers like the picture below? Are building a Pistol Caliber Carbine, like a 9mm, 40, 45, or 10mm? If so, spring rate and buffer weight come into play for the blowback system.

 

[delta6]

Standard Carbine Spring – Measures 10.5” with 37 to 39 coils
Standard Rifle Spring – Measures 12.75” with 41 to 42 coils. I have never seen a AR pistol spring.

And standard AR10 (308/7.62x51) buffer spring is 9 3/4". Spike's makes a 11 1/4" spring and SR25/M110 buffer spring is 13 3/4 (longer lower receiver extension).
Mil spec minimum for a M16/M4 variant is 12" for a rifle and 10" for a carbine.

The "plug" or buffer spacer (good picture by YNOTAZ) is generally used on PCC guns to lessen chance of breaking bolt catches by limiting the rearward travel of your blow back BCG (which slows the velocity on the return). If your gun has a bolt hold open feature this is important. Some folks use quarters in their extension to limit travel and they do make buffers that are a bit longer to achieve the same result.

 

[thom]

I have counted the springs that I have and most are 10.5 inches or less. I have 2 different buffer weights for this 9 mm upper that I bought at the less Phx gun show. The seller said that I would need the 8.0 oz weight to make it work properly. I also got a spring from the seller that is almost 11 ".
I put the upper on this lower and it worked good. But the problem is that I want to make a dedicated lower for this upper or change out the brace. I can't seem to get the rubber brace off of the buffer tube.

 

[YNOTAZ]

The 8.1oz buffer looks like it is already elongated for a PCC, eliminating the need for the plug.

An "almost 11" spring is most certainly a rifle length AR spring. While that will work in a carbine, which yours with a collapsible stock will be, I'm not sure it will run, or at least run well on a 9mm.

9MM AR are not that hard to get running. I would use the 8.1oz buffer, the length will help protect the bolt catch as Delta6 described, and a standard carbine length spring to start out with.