At first, I used silicone O-rings, which take heat better than the black O-rings...
The silicone O-rings won't dry-out, or swell-up from solvents either...
My silicone O-rings are from a hobby shop...They are used in shock absorbers on 1/8th scale RC cars...
They are even blue like the D-fender...
My latest fix on my short barrel gun is an extra-power extractor spring, an extra-power recoil spring, and a heavy steel buffer...
Wit the heavy extractor spring, I needed no other aid with it, no O-ring, or rubber insert...It works fine all by itself, is quite stiff, and you'll have trouble getting the extractor pin in too...
The springs are from:
Wolff gunsprings...Try:
www.gunsprings.comI highly recommend them, they have online ordering, and ship right away...I had my stuff in only 2-3 days...
I use this combination in my 7-1/2" barrel Carbon-15 pistol, and it made a HUGE difference in the way the gun shoots and cycles...
I replaced the pistol buffer tube with the tube (only) from a CAR stock.(only 2" longer)
I can't use the stock with the tube, otherwise I'd be making a SBR....
Hope that helps...