Im in process of planning out a 6.5 Grendel AR that will have a fixed stock, either the Magpul PRS or Fab RAPS. I would like to use a rifle length system as I already have the spare parts, and would like to try a low weight carrier and buffer setup. My intention is to try to make a A5 buffer system with a rifle length tube. Based on what I have found online:
Carbine extension: 7 - 7.25"
A5/SR25 extension: 7.75 - 8"
Rifle extension: 9.5 - 10"
Sources:
www.ar15.com
So does it a fair assumption that putting a ~2" delrin spacer within a rifle tube would give it effectively the same internal depth as an A5 extension?
Brownells has some premade options that could work, however they may add an extra 1/2" or more to convert into a carbine length rather than A5.
www.brownells.com www.brownells.com
Carbine extension: 7 - 7.25"
A5/SR25 extension: 7.75 - 8"
Rifle extension: 9.5 - 10"
Sources:
Rifle Buffer Tube Question - AR15.COM
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www.ar15.com So does it a fair assumption that putting a ~2" delrin spacer within a rifle tube would give it effectively the same internal depth as an A5 extension?
Brownells has some premade options that could work, however they may add an extra 1/2" or more to convert into a carbine length rather than A5.
AR-15/M16 BUFFER SPACER | Brownells
FEATURES: Allows for carbine buffers and springs to be used in rifle length buffer tubes Works with A1/A2 buffer tubes Machined aluminum billet cylinder Black anodized finish Spike's tactical spider logo etched on end of cylinder Does not add buff...
www.brownells.com AR-15 A2 STOCK SPACER | Brownells
AR-15 Replacement Buttstock Spacer, made from aluminum.
www.brownells.com 
