20 inch upper + carbine buffer tube

[10mmAuto]

I'm looking at building an AR-15 with a 20 inch upper and a Mil-Spec carbine buffer tube so I can mount a collapsible stock. I know this is doable and the Canadian full length service ARs actually come from the factory this way now. Does anybody have experience with this combination and what buffer weight/spring did you use?

 

[HiBC]

I just finished putting an 18 in with a standard rifle length forend and gas system tonight.My other one is a 20 in.Both are set up with collapsable stocks,and so is my DPMS LR308L.I like the Magpul stocks.
I know one buffer is an H,the other may be an H2.One spring is a standard,the other is a Wolfe extra power because that was all that was in stock.Both work well.IMO,extra power springs might be OK going back,but along with the heavier buffer,it is like swinging a heavier hammer a little harder going forward.The BCG,cam pin ,bolt,etc take a little more beating as it slams forward.
I also think,as the gas port is farther forward,the pressure curve has dropped off some,the gas tube is longer,for a bit more delay.The 20 in bbl may well be easier on a short buffer tube than a 16 is.
The adj length of pull lets me find best position and eye relief