Anybody using this ?
www.fulton-armory.com/D-Fender.htm

Unless your rifle is exhibiting extraction problems due to inadequate tension on the extractor, I'd skip it.  If you want one anyway, go to your local hobby shop and buy a foot of high temperature fuel line for model airplanes.  It is made out of the same stuff as this gadget.  A foot of fuel line will cost you about $2.  Then take a razor blade and slice off little rings from the fuel line and install as you would the D-fender.

I got it, and I have been using it for about 2 years. I bought it as part of the Counterpoise system.(ARMFORTE.com) I started noticing an improvement with the extraction with 5.56 rounds that had serious abuse from repeated stripper clip usage. As for a home made version the D-fender is kinda tapered so you would have to cut the material on an angle trying to "rig it." A waste of time (my opinion).

JerrY

I use a #60 O ring from ace hardware does the same thing and only costs .25 cents

I've got a parts gun with a cut-down barrel that was having extraction problems.  Actually, they were more like ejection problems.  The bolt was cycling far enough to eject the spent case and feed the next one from the magazine, but the spent case wasn't making it all the way out and was jamming up the action.  Happened once or twice every 100 rounds.

I was ordering some other parts and ordered a DFender along with it.  I took the gun to the range yesterday and had no problems in 200 rounds.  Time will tell if this was fixed it, but the early results look promising.

It's a good product. It or something like it is practically necessary if you've got an M4 barrel (14.5") or shorter.

I use a D-Fender and I've got a couple of thousand rounds through my 11.5" upper (registered, of course!) with only a couple of failures to eject (one just yesterday, in fact), and no failures to extract.

I've never heard of the o-ring trick, but it sounds cool. You can also get the black M4 extractor insert instead of the standard blue one.

I use the blue one, too, in both my M4 barreled uppers & they work great - FA firing w/ no FTEs.

 I have a 11.5" Bushy upper.  Install heavy duty extractor spring and O-ring. Went for a test drive today--no problem.