Anyone use these MgI Defender D-Ring.Any good or just a gimmick.
They were a good idea before Crane o-rings were available. Now, they are just an expensive extractor o-ring.
I disagree. They were purpose designed, the O-Ring is not. They also have a lifetime guarantee.
MGI has them on sale this weekend.
Why would a lifetime guarantee matter on a .50 cent item?
The D rims is not a 50 cent item. It is closer to ten dollars.
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It may be way overpriced compared to an O-ring but it is surely no less effective than the O-ring.
I know and the #60 Viton O-ring is about .50 cents. But, I also don’t use them since it’s no big deal to me. I just don’t see the value in a 10.00 O-ring.
Because it’s not an O-Ring, It’s profiled differently and shaped differently and made from a different material. It is easier to install, it does not cause stoppages from being too tight like some O-Rings will due to lack of that tiny bit of flex and it is tested to exceed the service life of the bolt.
Try one, they are only ten bucks. You can run them in rifle-length gas systems without fear of it inducing a stoppage like O-rings sometimes will.
I have tried them. Rifles and carbines built properly with correct chambers don’t need them. Never had any issues with my issued weapons or personal weapons not extracting.
Neither do mine but I look at them as cheap insurance.
$500 is also a low premium for $100,000 Meteorite insurance.
With the successes R&D have had, and the suggested improvements to the system itself implemented by quality manufacturers, the D-ring is about as relevant as a 3.5" floppy disk drive.
You are entitled to your opinion. I think it is less than useful. Ten dollars will hardly break my bank.
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Sounds like a Gov’t spending program…
On the serious side, you seem sold on this D-ring. What does it offer at twice the price above regular PM with a Colt “Gold” spring and black insert?
From a factory rep on a thread posted on another forum:
Please note that we(MGI) recommend that the D-Ring(D-Fender) have the spring in place, so as to act as a locating device to keep the D-ring in the proper place, and this would also be the case with O-rings. You are correct in your assumption that the ring takes up the primary duty, when placed in this application. In the case of the D-Fender, it is engineered to provide 4x the normal extractor tension.
During the extensive testing of these items back in the 1990’s, when Mack Gwinn and Jim Sullivan were partners in introducing this whole concept, it was found that migration of the ring could cause failures, and in some cases severe enough to seriously “tie-up” the weapon from firing. This can also happen when a ring breaks, and the repeated extractor motions move it around to where it isn’t supposed to be.
This is a main reason why Mack and Jim did not just release an O-ring, which they did plenty of testing with, and proceeded to the “D” shaped design with the wedge profile for better reliability. It was presented to Crane, and tested, and actually they never got one to fail in their extended testing.
Now, I realize that plenty of people use O-rings, and they work. They work to varying extents, and the reason Mack and Jim switched was because they found it virtually impossible to predict whether the O-ring would have an early failure or a longer life, in any given application. Some failed early, and some went along pretty well, and some went a long time, and it didn’t matter what material they tried. They were not satisfied with this unpredictability. The “D” shape is purposely made to overcome these problems, and that is why the shape is the most important part of this device.
Crane went with the O-ring because of cost, and their statement to Mack and Jim when the decision was made, was that they could just give out a pocketful of them, so if they failed, a new one could be then installed.
Now, it can be debated all day what anybody prefers to use, but this is the actual history of this type of device, that was spoken to me right out of the mouth of the guys who invented, pioneered, tested, and presented this form of device for the first time. And Mack Gwinn and Jim Sullivan are not rookies at gun design. Even if some of you might not know who Mack Gwinn is(original founder of Bushmaster, no longer associated with them, designed the M2 .50HB-QCB quick barrel change system for FN, designer of the original early Bushmaster SMG, current designer of the MGI Modular AR15 system, among numerous other things along the way), certainly you all must be familiar with Jim Sullivan, who worked at a very high position in the original AR15 design team with Gene Stoner.
So you can pay your money and take your chances with whatever you want to use. I at least can say that you are all now duly informed on how these items came to be used, what the history of the development was, and the conclusions that were arrived at after testing by the inventors(who probably know just a little bit about this subject).
twl-“Better reliability…” In Mack and Jim’s reliability testing, what did they determine the MTBF of the D-ring to be compared their (hopefully comparable Crane-type) O-ring? Hype and fear (you pays your money and takes your chances) are marketing tools, not reliability testing. With these numbers, sample size and testing protocol, we see how the inventors came to their conclusions and have the same level of confidence as you. Then we can decide if increase in reliability, if any, is worth the additional cost.
The O-rings tested by Mack and Jim, prior to moving into the D-Ring design, had an unpredictable MTBF, between several dozen rounds, and several thousand rounds. I’m sorry that I can’t be more exact than that, but I can’t get Mack on the phone right now. The issue that was perplexing them was that they could find no way to determine accurately when the things were going to fail, because they didn’t seem to exhibit predictable behavior in these circumstances. That’s why they went the route that they did.
According to the DTC certification letter dated 7 May 2001 that I have here on the D-Fender, it states that reliability was “ALWAYS improved” and “with NO negative effects”, when “extensively tested on 3 forms of M16/M4 weapons”, by Crane. According to Mack, the Crane tests proceeded over about a year’s time, during which time they tested the D-Ring to several tests of over 30k rounds each, and never did get a failure. Apparently they decided that about 100k rounds of ammo was enough to expend on this testing. That’s the information that I got from Mack.
To be on the conservative side, we recommend changing the D-Fender when you replace your bolt. We have seen very few, but there have been a few, D-Fender breakages, and they were sent back to us, and unfortunately the users could not give us any round counts, or other circumstances which may have led to the few failures we have seen. We generally attribute these to an improper installation of putting the spring on top of the D-Fender, instead of thru the hole in the D-Fender. We replace D-Fenders if there are any breakages with them, at no charge.
But, to answer your specific question, no MTBF for the D-Fender has ever been determined, because nobody to date has reached enough rounds to make a repeated determination that it will fail at that round count.
As I mentioned above, we conservatively rate it at the life of the bolt, and recommend changing then.
Anyone who wants to try their own test to wear one of these things out, just make sure that you have plenty of ammo on hand.
The quote from the DTC Certification letter states, “Documented use of these rings has occurred at NSWC Crane over the last year in an attempt to develop the limits of their performance”. It seems to me that the words, “in an attempt”, backs up Mack’s statement that the attempt to find the limits was not reached, and the recommendation to SOPMOD was generated. There were no limits reached in the test that were mentioned in that DTC certification letter, and I have the letter sitting here in my lap right now as I’m quoting off of it.
I was at a shoot once and there was a guy with a 7.5 inch DPMS upper on a registered Colt M-16 lower. He was having tons of extraction failures with that piece of crap. I gave him a D-Fender and afterward, it ran like a raped-ape.
Yeah, I’ve seen that, its like 6-7 years old. Seems everybody has moved away from the o-rings and gone to HD extractor springs instead. Except in extreme cases like the FA Kitty Kat you mentioned. Thanks
Thanks Guys
I wonder if the killer app would be a Springco 4 coil or Colt copper washed spring with a d-fender D ring?
Not sure if it matters, but Colt Canada is selling all of it’s LE guns with the D-ring installed in them. For that matter they also come with the accu-wedge also.
Boltgun
A DFender made a 7.5 inch upper run reliably in my case.
Sample size of one and I have O rings in other bolts.
The O-ring came about due to extraction issues with the M4A1 early in the 2000’s and the beginning of the war. It was not till 2006 Colt got off their asses and got their enhanced copper colored extractor spring out in wide usage, and even later for the civilian market(easy to get $3.95 springs now though).
Now M4A1’s do not come with O-rings, just the copper washed extractor spring and black insert. It’s worth remembering they went from a COTS 5 coil spring with O-ring, to colts copper spring with no O-ring.
As for dfender, well it’s a $10 extractor insert that is no longer needed compared to MILSPEC Viton #6 o-rings that cost .10c fromcertain websites(of which I have 50 because they were dirt cheap).