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Posted: 12/13/2006 12:45:58 PM EDT
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Does the D-Fender o ring cause any problems & doesit work as advertised. My rifle runs perfectly now but a little extra insurance can't hurt. Who has experience with these. |
| It does what it's supposed to, also a #60 o ring does the same.. but both are intended to help out a weak extractor - so the best insurance is to change out your extractor spring as a regular maintenance item and make sure you have the proper insert in there. If those don't help and you need more oomph, go to a stonger spring and/or D ring, IMO. |
+1 you aren't having any problems with your rifle now. if ain't broke don't fix it. what "insurance" do you need? no offense, but in the off chance your extractor fails, you lose a day at the range, not your life. if you plan on defending your home with an AR15, you should consider a change of address. |
You mean your spring doesn't have a little rubber nipple thingy in it? It should.. part number 12 on this diagram, fr00t! www.brownells.com/aspx/NS/schematics/schemmfg.aspx?schemid=802&m=3&mn=Colt%c2%ae&model=AR-15+Bolt+Carrier+Assembly+All+Models |
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i just had my first experience with a crane o-ring... just built an SPR in 6.8mm (i'll have pics/range report when i get home). the bolt wouldn't lock forward all the way. i assumed that maybe the round was hanging up in the chamber (very strange for a noveske barrel). low and behold the extractor is not hooking onto the round. take it apart only to find that there is a stupid o-ring making the extractor so tight that it won't even chamber a round properly. remove the o-ring. rifle is doing well. i now have firsthand proof that these o-rings and magic pieces of rubber are garbage. |
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thats what i"m thinking, apparently I've been running mine w/out the little rubber buffer inside the extractor spring for the last oh 4-5000 rounds or so w/ no failures to extract or eject. All i'm doing is getting a pack of ext power wolf recoil springs & the rubber inserts that are supposed to go in there. I still dont know, I swear mine never had one. |
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Well, now that the experts have had their say, let's hear what the military people from Crane and US Army Developmental Test Command have to say on the subject. The MGI D-FENDER has been issued a US Government Military Certification for COMBAT USE, This DTC Safety Certification was issued May 7,2001, and states on US Department of the Army letterhead as follows: "Memorandum for SOPMOD........... Conclusions and Recommendations: The D-Fender D elastomeric rings/washers have been used extensively on 3 configurations of the M16 type weapons and have ALWAYS BEEN FOUND TO AID RELIABILITY, WITHOUT NEGATIVE EFFECTS according to the test data provided by NSWC Crane Division. This has been described ato be a simple, easy method to ensure weapon extraction and functioning. Based on the test information provided by NSWC Crane Division, a DTC Safety Confirmation is issued for the use of the D-Fender D-Rings on M4/M16 series weapons............ Alan L. Yankolonis Chief, Tank Automotive Armaments Division Directorate for Test and Technology" |
Why on earth would you NOT use the most effective tool at your disposal??? Here's an idea! You know that nice automobile you have in your driveway. Drive it, but just not to work. Ride your bike. Sounds stupid, don't it? 
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 Most likely out of spec ammo. |
yes because Silver State Armory Sierra Match Kings are out of spec ammo. get real. i could barely strip the bolt that's how tight it was with the rubber o-ring. after the o-ring came out... i fired 20 rounds without a problem... |
Well, in all my years of using and working on AR-15's, and in my Armorer's Course, YOU are the only person I've ever heard of having a problem that can be attributed to a properly sized o-ring type device on the extractor spring. |
And will continue working. Until it doesn't. D-fenders work well but are pricey. So is piece of mind. Got life insurance?  The factory insert is recommended on the package with the Wolff. A crane o-ring is a lower cost, but acceptable, alternative, particularly if you have several bolts and limited cash.
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show me a document that specifically states the dimensions of a piece of rubber that doesn't belong in the bolt. this was in a 6.8SPC bolt, not 5.56. i don't know if CMT is using a different insert/spring or what. but all i know is that the o-ring DID cause problems in my bolt. even after i pulled it apart, CLP'd it, and reinstalled the o-ring. i was all for giving this little piece of rubber a try. but it has created more aggrevation than it was worth. |
Well... 6.8SPC is not an AR-15 technically anyways, so I'll let you have the point. 
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fair enough. i guess we've reached a stalemate. 
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OK, here's my take on it: Upon extraction, there are other forces at play that can vary greatly from rifle to rifle. Namely, chamber dimensions, gas system configuration, and ammo. A tight chamber and higher residual gas pressures upon extraction can dictate increasing the strength of the extractor. But you can go too far, and boost the extractor strength to the point that it has a hard time getting over the rim on feeding. Consider the typical 20" set-up - stock spring and blue insert. 16" - stock spring, and stiffer black insert If that still doesn't cut it, then a stronger spring, such as a Wolff (my preferred) or a O-ring. Still not cutting it? Then both. But don't just slap them all in just to do it. Only do it if your rifle needs it. Many may add the O ring and get no adverse affects, but it may not be doing much good either. The trick is to only increase the extractor strength if it needs it, and not any more than it needs, otherwise you may get feeding issues. My $.02 |
Been there done that. Save yourself time/aggravation, get a chrome lined barrel from a different maker. |
+1 This has been the best approach with my particular guns as well. Almost all of them are just fine with the standard spring and blue buffer, actually. None are full auto though. If one gives trouble, I jump up to the Wolff spring first and keep the standard buffer. This has always been enough in any of mine. If I had a military M4 though and used it like the military does, I would snag a D-fender and put it in, but that is a completely different application than most folks' semi-auto 16's and 20's. My $0.02 |
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