D-Fender D-Ring - Page 2

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[ARCHIVED THREAD] - D-Fender D-Ring (Page 2 of 2)

Posted: 9/9/2009 3:21:20 PM EDT

[#1]

I've been using Crane O-rings that I got from Bravo Company and ADCO for several years now on my rifle, midlength and carbine gas systems without any problems.

My carbine gas system have the BCM extractor upgrade kit with the extra power chrome silicon material extractor spring, when I first installed it I didn't install the O-ring until I fired at least about 600 rounds, then after the break in I installed the O-ring, YMMV.

I run all my ARs with M16 BCG and standard buffers except my carbine gas system have a H (heavy) buffer.

I also use the D-Fender on my Steyr AUG A1 rifle and carbine, no FTF at all, it just increases its extraction force.

Posted: 9/9/2009 5:23:55 PM EDT

[#2]

Keep in mind that the "crane O ring" was out before the defender was

You are very wrong.

twl07-30-2006, 09:43 AM
"Been wanting to try this–– no spring, "D" or O-ring only, no spring. I'm thinkin' it'll work, might get a chance to try it this coming week."

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).

Posted: 9/9/2009 7:58:11 PM EDT

[#3]

Isn't that the same Jim Sullivan who publically stated he would rather issue his son an AK-47 over an M16 and then went on to sing the laurels of the Singapore Ultimak 100 which he helped design?????

Don't want it to sound like piss hitting an empty metal can, but Jim Sullivan appears to have a lot of burned bridges associated with the M16 and may be more than a little bitter over his unheeded and unheralded attempts at improving the original design.

Just asking, I still prefer D rings to O rings for the reasons stated.

Posted: 9/9/2009 8:06:31 PM EDT

[#4]

Extractor O-rings treat the symptoms of poor extraction, not the cause. Try delaying the unlocking of your bolt with a heavier buffer. That will give the cartridge more time to shrink away from the chamber walls and reduce extraction force. If you massively increase the tension on the extractor without doing anything else, the extractor may rip the rim off instead of bending/slipping over it.

Posted: 9/9/2009 9:41:20 PM EDT

[#5]

What is the measurement of the O ring that I need to buy at Lowes? Thanks.

Posted: 9/9/2009 10:16:24 PM EDT

[#6]

Quoted:

Extractor tension is indeed a parameter that quite directly relates to the function of an AR. It seems that this would be patently obvious....

Reading isn't your strong point I see. I never said that it wasn't a function of an AR, just that the O ring doesn't negativly effect it regardless of how new or used the Oring is. All the O ring does is strengthen the tension on the extractor making it more difficult for the extractor to slip off the rim of the carteridge. This in no way will make your gun foul up the extraction process.

Simply paying attention to the cycle of the firearm tells you this much.

Techincally, no, the tension on the extractor could work against the tension on the ejector spring (I say this from a mechnaical point of view, and not an experiental one...).

Then you're seeing shit or making things up. The extractor and ejector are working in entirely two different directions creating a camming action. Unless the side of your boltface rim has a burr on it that is otherwise being pushed past with a weak extractor spring, but now has enough force placed upon the rim of the carteridge to snag the burr and overcome the force of the ejector, this should not be an issue.

Like I said, if it IS an issue, then it's indicative of other issues with your firearm that should be looked into rather then depending on a "break in" period.

And yes, you're correct that buffer/buffer spring issues also effect the function of the weapon.

duh.

You've completely misunderstood what I said.

The spring, by the very nature of being a spring, will have a 'break in' period in which its tension decreases. All springs, by nature, have this. Period. The only way to avoid this is to make this break-in part of the manufacturing process, which could be done by pre-loading the apring at the fatctry - which would easily double the cost of the spring. When thias spring - as any spring will do - is finished breaking in, it still has 'extra power' compared to a standard spring.

I missunderstood nothing.

My nature, a GOOD spring will put out as close to the intended force as it can throughout its life, slowly weakening over time and the more times it's compressed.

Any spring that "puts out" advertised force and then "breaks in" to a set amount much lower then it starts out with is defective. If such were the case, then Wolfsprings would be out of business for selling shit products.

But, by all means, please provide some proof to your claims of spring tension and "break in".

I don't know what they are - but you're being ridiculous if you say they don't exist. An AR works according to principles of physics, not magic. Springs have tension, that tension is exerted on the parts the work with, and so on......this isn't rocket surgery, y'know....

Once again, literacy is key. I don't recall saying that they weren't there or didn't exist, I merely asked you to let us all know what they were.

but since you can't, and seem to think that it's irrelevant, the rest of your argument is as well.

If you're argueing that the addition of excess power to the extractor is going past the perameters of the deisgn, but don't know or provide the perameters that are supposedly being exceeded, then you quite frankly are pulling shit straight out of your ass and argueing just to argue.

So did mine (4 of the 5 I have dealt with) but the extra insurance does not hurt anything; it can only help, as has been proven time and again.

Proven? Really? You seem to be the only one with this issue, so let us know how you PROVED it. Lets see some test data!

It's a matter of 'too much of a good thing'.

Still not big on the whole "fact" thing are we?

I can add air to my tires to make them roll easier. I can also add too much and make them wear unevenly or blow out. The same principle applies here.

I'm sorry... does the addition of a piece of rubber under your extractor cause it to flex out of spec and cause undue wear on your bolt or barrel extension?

If not, try apples to apples comparisons next time.

The rifles I have (the 5 mentioned above), one runs an A2 stock setup, the others run carbine buffers and springs, high-quality bolts and barrels with properly drilled gas ports...I don't buy junk. They're perfectly in spec.....but the AR system was originally designed to function with a rifle-length gas system. Carbines and some midlengths, by necessity, needs ome adjustments made elsewhere in the system to offset the change in the parameters of the gas system itself. This isn't magic, this is simple engineering.

Apparently they weren't in spec. If they were, they would have run fine from the get-go.

In all honesty, I think you're missing the larger point here. Forcing a rilfe-designed spring/insert to work in a carbine system doesn't mean there's a 'latent issue' it just means that you're ignoring inherent differences in the designs.

I think the real issue here is that you're trying too hard to seem like an expert in the design when the reality is that it isn't that complicated of a system.

The only picture that i'm missing is the one where you want us to believe that something is true without providing factual evidence, technical specifications, or empirical test data to prove your contention.

The reality of it is that every part has an action and a reaction within the system that one change can effect. Through deductive reasoning and a pretty good base knowledge of the system gained by building the damn things for the last 14 years, it is easy for me to see that the addition of an O ring will NOT cause issues, but may exacerbate a pre-existing issue within the system.

Your attempts to chalk your issues up to the addition of an O ring (or D ring as the case may be) shows that you're looking for an easy excuse rather then trying to find the real issue. Especially since you can't explain exactly what is happening, nor do you know the "perameters" in which the system is supposed to be operating.

I'm actually rather disturbed that someone takes such a view of this....it's not trickery or magic, it's just tweaking one part to accomodate tweaks in another part that deviate from the original design.

Your absolutly right. This isn't trickery or magic, it's simply made up by you to go along with what you WANT to be the problem so you don't have to think about what the issue really is.

Be disturbed as you want to be. Just realize that it's because your ego is in the way and the only reason you're upset is because someone is calling you on your bullshit instead of agreeing with you.

Not that I care though because it isn't my gun.

Posted: 9/9/2009 10:19:42 PM EDT

[#7]

Quoted:
None of this plumbing shit belongs in the AR. I won't keep a gun that need a fucking plumbing part to run properly. The proper spring and insert are more than adequate to make even my SBRs run like champs.

END of story.

By that line of thinking, we'd all have no chrome in our chambers or bores because the original design didn't include it.....

Hello there whiz kid! Macnemara still hiring?

Times change and the original design specs have changed and along with it, some issues have popped up that have proven "problomatic" in the long term. Extractor "bounce" in the short barreled guns is one of them.

Either get with the times or face the possibility of having your gun not work when you need it to.

Crane came up with the O ring idea for a reason, and it wasn't to keep rubber manufacturing companies in business.

Posted: 9/9/2009 10:20:41 PM EDT

[#8]

Quoted:

Quoted:
Use the O ring if you choose.
Nobody is saying don't use the O ring.

Seriously, why anyone would spend hundreds of dollars on accessories for an AR15/M16 type rifle and then skimp on an upgrade that actually improves the feed and function of the rifle is beyond me.

That's the same flawed logic that the KNS pin goobers use. Except the KNS pins do nothing, and the O rings excessive extractor tension can actually hurt performance in some cases.

Care to back this up with proof, evidence, or facts?

Please don't pull a mark larue on this one.

Posted: 9/9/2009 10:23:33 PM EDT

[#9]

Quoted:

Keep in mind that the "crane O ring" was out before the defender was

You are very wrong.

twl07-30-2006, 09:43 AM
"Been wanting to try this–– no spring, "D" or O-ring only, no spring. I'm thinkin' it'll work, might get a chance to try it this coming week."
SNIP.

That's nice. Especially comming from the folks who make the D ring.

So when exactly did Crane do the extractor "bounce" tests and follow up with the "O" ring design and when exactly did the D ring first hit the market?

Some actual dates would be nice, not just a "You're wrong" along with a claim from the folks who make a product (and who are trying to sell it) which doesn't provide dates.

I'm willing to be proven wrong, so please, by all means, do so.

Posted: 9/9/2009 10:25:53 PM EDT

[#10]

Quoted:
Extractor O-rings treat the symptoms of poor extraction, not the cause. Try delaying the unlocking of your bolt with a heavier buffer. That will give the cartridge more time to shrink away from the chamber walls and reduce extraction force. If you massively increase the tension on the extractor without doing anything else, the extractor may rip the rim off instead of bending/slipping over it.

It's not about slowing the cycle, it's about the phenomenon of "extractor bounce" as found in the shorter gas system guns.

The Mil did some tests on this (I have the slideshow somewhere on my damn computer but I can't seem to find it) and that's why extractor spring inserts came about along with O rings.

Posted: 9/10/2009 4:25:36 AM EDT

[#11]

Quoted:

None of this plumbing shit belongs in the AR. I won't keep a gun that need a fucking plumbing part to run properly. The proper spring and insert are more than adequate to make even my SBRs run like champs.

END of story.

/thread

I have a Wolff XP spring and a blue insert <gasp>. My carbine shoots any ammo I feed with no extraction problems. I'm up to 23.5k rounds now.

Posted: 9/10/2009 5:44:29 AM EDT

[#12]

Quoted:

Keep in mind that the "crane O ring" was out before the defender was

You are very wrong.

twl07-30-2006, 09:43 AM
"Been wanting to try this–– no spring, "D" or O-ring only, no spring. I'm thinkin' it'll work, might get a chance to try it this coming week."
SNIP.

That's nice. Especially comming from the folks who make the D ring.

So when exactly did Crane do the extractor "bounce" tests and follow up with the "O" ring design and when exactly did the D ring first hit the market?

Some actual dates would be nice, not just a "You're wrong" along with a claim from the folks who make a product (and who are trying to sell it) which doesn't provide dates.

I'm willing to be proven wrong, so please, by all means, do so.

Call Mack Gwinn at MGI and ask him. He still answers the phone at MGI.

If Tom Lyons says the concept was MGI's, based on his past reputation as an Industry Professional, I take his clam as authorotative over yours in absence of evidence to the contrary.

I have provided evidence to back my assertion. You have provided nothing to back yours. The burden of proof is in your court.

Posted: 9/10/2009 6:04:55 AM EDT

[#13]

Uh wow!

lol.

I don't take any position here but more of an interested outsider looking in. All this discussion has taught me more about extractor science then I thought I could have known. There is some strong debate going on here and as long it doesn't get personal I think its pretty healthy. Like I said, I've learned a lot.

Simply from a commercial point of view, I have an observation. If I were to charge $10-12 dollars for a part that conceivably costs .25-.75 cents it would be easy to offer a life-time warranty in a financial sense. Again, not taking a position, just noting the seeming economics. Such numbers could apply to any product based on the percentages.

Posted: 9/10/2009 7:11:08 AM EDT

[#14]

Quoted:
There is some strong debate going on here and as long it doesn't get personal I think its pretty healthy.

I don't really see the point in it - and wouldn't call it strong debate.

Somebody has their panties in a wad (not surprising, considering the username) and frankly I'm through arguing about it.

Posted: 9/10/2009 9:26:53 AM EDT

[#15]

Again, I would like to thank everyone for their input. I learned a lot. Please note, I did not wish to make this an issue, but a discussion. Have a great week!

Posted: 9/10/2009 3:06:36 PM EDT

[#16]

Whenever M4s are discussed all I ever see is that freakin' almighty "Chart".

The military uses 1x7 so should we all! No finish under front site base? Crap! Castle nut not staked? Buy another gun! No M4 ramps? Your weapon is only good for plinking! No taper pins? No way in hell you will be able to kill zombies!

Well, for what it is worth, the allmighty Chart does not list D, they list O.

Not that I give a damn, I run 55gr exclusively, in semi-automatic only, so I prefer 1x9 and don't give a damn about feed ramps. But I do like BCM Extractor Spring Uprade Kits with Mil-Spec Crane O-Rings.

Posted: 9/10/2009 4:47:30 PM EDT

[#17]

I just cant' take anyone seriously who uses a Defender.. as they probably endorse the accuwedge as well....

There bandaids for fixing the real problem.

Posted: 9/10/2009 7:10:33 PM EDT

[#18]

Quoted:
I just cant' take anyone seriously who uses a Defender.. as they probably endorse the accuwedge as well....

There bandaids for fixing the real problem.

I can't take anyone seriously who would make such a remark as that.

Oh tell us, fabled wise one, what exactly the "Real problem" is??????????

You see, I use D rings in most of my own rifles and whether it be luck, good building, grace of god, or maybe the D ring, I just don't have extraction problems with the rifles.
If a bandaid prevents esanguination then give me a box full.

Posted: 9/10/2009 7:51:45 PM EDT

[#19]

Your a working gunsmith...... you tell me with your wealth of AR experience.....

And I have a scratch on my lower receiver... can you fix it.....

Posted: 9/10/2009 8:47:30 PM EDT

[#20]

Quoted:
Call Mack Gwinn at MGI and ask him. He still answers the phone at MGI.

If Tom Lyons says the concept was MGI's, based on his past reputation as an Industry Professional, I take his clam as authorotative over yours in absence of evidence to the contrary.

I have provided evidence to back my assertion. You have provided nothing to back yours. The burden of proof is in your court.

Proof? Really?

What proof?

You provided the word of a source who is obviously not unbiased and have provided no verifiable dates.

I'm sorry, if this is what passes for "evidence" to back your assertions, I hope you were never in the debate club. Losing sucks.

Posted: 9/10/2009 8:51:21 PM EDT

[#21]

Quoted:

Quoted:
There is some strong debate going on here and as long it doesn't get personal I think its pretty healthy.

I don't really see the point in it - and wouldn't call it strong debate.

Somebody has their panties in a wad (not surprising, considering the username) and frankly I'm through arguing about it.

It's easy to make snide remarks and back out of a discussion when you can't logically back your position.

Yay you!

Posted: 9/10/2009 8:52:25 PM EDT

[#22]

As opposed to the big fat cup o' nothing you have contributed to this thread. Like I said, if you have better informtion post it. If you want better info, call MGI and ask to speak to Mack.

So far, all you have offered this thread is unsupported speculation and an ill attitude. Whatever criticism you have of what I have offered, it is head and shoulders above the pure speculation you have brought to the table.

Here is more of TWL's post:

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.

We just received payment Friday for a large D-Fender order to the British SAS unit.
I spoke with a SF soldier from the 5th Group in Ft. Campbell yesterday, and he verified that his unit is using D-Fenders, to me by phone just yesterday morning, during his order for another different product from us.

Our D-Fender is not "totally pervasive" throughout the militaries, but it is in use by the thousands, and has been for a number of years. It is usually procured by individual unit discretionary funds, and mostly by the special-ops groups.

We don't make these guys buy our stuff, and apparently they want it. They can get the O-rings as issue, which would not cost anything to them specifically. They replace these O-rings with our D-Fender.

So, we have a good product that is getting some recognition and use.
We also realize that the O-ring works, and for many people it is a perfectly good choice for their range work or training activities, and it is much less costly.

Mack is a SF 5th Group vetaran of MAC-V-SOG, and highly decorated with many tours in VietNam. His son(Mack III) who also works with the company is a veteran of the SF 7th Group, as a weapons man for 15 years, and sniper instructor. They know what it means to depend on your weapon. They are the company owners.

Personally, it makes little difference to me what any person wants to use in their gun. I primarily posted this stuff here, because I watch these discussions take place, time and again, with all kinds of speculation, and questions about what polymer should be used, and which # O-ring they should by at the plumbing store, etc.
I thought that a little firm information from a historical perspective, with how's and why's would be helpful to the members.

Posted: 9/10/2009 8:53:31 PM EDT

[#23]

Quoted:
Again, I would like to thank everyone for their input. I learned a lot. Please note, I did not wish to make this an issue, but a discussion. Have a great week!

It's not an issue, it's still a "debate".....ish.

Glad we've helped.

Posted: 9/10/2009 9:25:46 PM EDT

[#24]

Quoted:
Your a working gunsmith...... you tell me with your wealth of AR experience.....

And I have a scratch on my lower receiver... can you fix it.....

Oh, I get it, and for a price, I can fix anything.
Couple of my rifles have Accu Wedges in them too.

Posted: 9/10/2009 9:41:20 PM EDT

[#25]

Quoted:
I just cant' take anyone seriously who uses a Defender.. as they probably endorse the accuwedge as well....

There bandaids for fixing the real problem.

Not been paying attention have we?

The Extractor bounce (lift) issue is a chronic problem that's inherent with the carbine length gas system guns. Admittedly it's only been actually observed in 14.5 inch guns that I know of, (don't recall them doing high speed filming of 10.5 inch barreled guns), but it IS a real issue. It's not created by a deficiency in the manufacturing of the various parts or the gun itself. The design, as specified in the mil-spec has this inherent issue.

I finally found the power point presentation that was made in 2003 regarding the issue. It can be viewed at the following location: EXTRACTOR LIFT (bounce)

Call it a bandaid for the "real" problem, and if this is what you think, please fill us in as to what you think the "real" problem is.

As the Mil already figured out, extractor lift is the problem when fouling or other issues that might impede extraction are present. Whereas in a "clean" gun, it will extract fine, add too much fouling in the chamber or a "dinged" case, or something that affects extraction in a similar manner, and the otherwise non-issue of extractor lift becomes a real problem.

The O ring and D ring are designed to overcome this inherent issue that an otherwise perfectly "in spec" system can experience when fouled or used in combat conditions which can be very dirty and can introduce forign material into the system that may adversly effect the operation.

So, once again please tell us the "real" problem.

Posted: 9/10/2009 9:59:09 PM EDT

[#26]

I have no idea what a d-fender d-ring is...

Posted: 9/10/2009 10:16:56 PM EDT

[#27]

Quoted:
As opposed to the big fat cup o' nothing you have contributed to this thread. Like I said, if you have better informtion post it. If you want better info, call MGI and ask to speak to Mack.
So far, all you have offered this thread is unsupported speculation and an ill attitude. Whatever criticism you have of what I have offered, it is head and shoulders above the pure speculation you have brought to the table.

And yet you STILL lack any evidence other then the word of someone trying to sell a product. Still don't get that whole "debate" thing, do you? I asked you to prove me wrong and you still havn't.

Don't get me wrong, they might be the greatest guys in the world, but independant, verifiable data is all I ask. Not constant deflection to contact someone who is in the business of selling a product.

You accuse me of bringing nothing but unsupported speculation and an ill attitude. Hello pot, meet kettle. If you can't look at what you've offered and see the irony of your statement, I will start lowering the expectation of having a resonable and rational conversation with you. Mind how I said "conversation" and not debate. That's because i'm not trying to prove you wrong, I just want PROOF, real, verifiable PROOF, not just sputtering and lame attempts at re-direction to someone else to explain what you apparently cannot.

I'm not saying you're wrong, I'm just saying that you have yet to prove your point satisfactorily.

Lets see some more.......

Here is more of TWL's post

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.:

:

Keep the part in red in mind, i'll reference it again.....Especially considering that they are trying to sell a product themselves.

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.

Wait, what? They poo-poo others for not doing "reliability testing", yet they cannot be "more exact then that"????? Sounds like they weren't doing any reliability testing either. The whole idea behind "testing" is that one measures performance and does so in a repeatable manner that anybody else can then repeat the same test and come to the same conclusion.

I don't see this happening here.

Also, I need some clarification,..... they say that they tested the O ring, prior to moving into the D ring design.......? Prior to moving ON TO, or prior to moving into designing the D ring because they thought the O ring was a failure? I don't get the wording. It's vague and doesn't tell us if they are claiming that they made the D ring in response to failed O rings, or if they tested the O rings first and then moved onto testing the D rings.

It looks to me that they tested O rings, thought they sucked, and decided to make a "good" version and came up with the D ring.

This being the case, it says the O rings were around first.

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.

Still no confirmation as to which came first, the O ring or the D ring.

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.

That's right, blame the end user for "improper installation"....seriously...how do you install a D ring improperly? I challenge you to install one backwards.

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.

Then again, what exactly do they consider "failure"? Does the ring have to come apart into little pieces or does it have to flatten out and just not place any extra force on the extractor anymore? Would you not consider both instances as "failures" of the product?

Something tells me they are only considering self destruction of the D ring as a "failure".

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.

Once again....what kind of failure are they looking for? I have yet to see them say anything about measuring the amount of force required to move the extractor being used as a test. According to all I've seen here, so long as the D ring doesn't shred itself, it doesn't matter if it is flatter then a pancake or soft and squishy and no longer imparts any extra force on the extractor, then it's "still viable". How about some weight measurements on the extractor after every 500 rounds to set a baseline for performance.

We just received payment Friday for a large D-Fender order to the British SAS unit.
I spoke with a SF soldier from the 5th Group in Ft. Campbell yesterday, and he verified that his unit is using D-Fenders, to me by phone just yesterday morning, during his order for another different product from us.

Our D-Fender is not "totally pervasive" throughout the militaries, but it is in use by the thousands, and has been for a number of years. It is usually procured by individual unit discretionary funds, and mostly by the special-ops groups.

We don't make these guys buy our stuff, and apparently they want it. They can get the O-rings as issue, which would not cost anything to them specifically. They replace these O-rings with our D-Fender.

So, we have a good product that is getting some recognition and use.
We also realize that the O-ring works, and for many people it is a perfectly good choice for their range work or training activities, and it is much less costly.

Mack is a SF 5th Group vetaran of MAC-V-SOG, and highly decorated with many tours in VietNam. His son(Mack III) who also works with the company is a veteran of the SF 7th Group, as a weapons man for 15 years, and sniper instructor. They know what it means to depend on your weapon. They are the company owners.

Personally, it makes little difference to me what any person wants to use in their gun. I primarily posted this stuff here, because I watch these discussions take place, time and again, with all kinds of speculation, and questions about what polymer should be used, and which # O-ring they should by at the plumbing store, etc.
I thought that a little firm information from a historical perspective, with how's and why's would be helpful to the members.

Now it just sounds like a whole lot of name dropping and attempts to be validated by name recognition.

Once again, not saying the product doesn't work or that the folks at MGI are crooks, but i'm STILL not seeing any DATA, just a whole lotta talking around the issue.

Test data people. It has a place, and HERE is that place. Remember that part about "reliability testing"? I still havn't seen reference to any measurable test, just testing that says, yup the product is still in the gun and hasn't broken into pieces. To me, that's not "performance" testing, that's structural integrity testing. The two do not necessarily equate.

Lastly, please remember that the issue of extractor lift (bounce) was and has been an issue since the first M4 was fielded. I'm not sure if they knew it was extractor lift that was the issue for a long time, but they knew that added extractor strength was the solution. I don't think they figured out that extractor bounce was the issue until later and finally got around to trying to measure this issue in 2003 with some real testing.....hence, both the O ring and D ring were out before they finally figured out that extractor lift was the issue (if I remember correctly).

I remember that people were complaining about spent casings being stuck in the chambers of A2 series rifles going way back and that was the origin of the spring inserts, but it wasn't until the enhanced issues with the M4 that the O ring was added.\

Gotta keep the timeline straight to figure this stuff out properly.
<b

Posted: 9/11/2009 1:33:06 AM EDT

[#28]

And yet you STILL lack any evidence other then the word of someone trying to sell a product. Still don't get that whole "debate" thing, do you? I asked you to prove me wrong and you still havn't.

When you make a serious attempt to prove your assertion right, then we can discuss why the burden of proof is on me. All that is required to couter gratutious assertions is another gratutious assertion. I provided you far more than that. You claim to want data and you have yet to provide any to back your initial assertion. Once you do that, then you can aargue for better data on my part. Untill then, you are attempting to hold me to a higher standard than you are capable or willing to meet yourself.

You claim to understand debating and yet the simple concept of burden of proof eludes you.

Again, untill you establish your credibility to be equal to or better than a well-regarded industry professional or first at least make a compelling case, I have zero reason to accept your raw speculation over their narrative. If you have any evidence MGI has ever misrepented their product, pleas present it. Otherwise, that is simply more unsupported speculation on your part.

I am satisifed with MGI's claim, it is certainly wholly plausable in the absence of any supporting data from you.

Posted: 9/11/2009 8:12:30 AM EDT

[#29]

Quoted:
I have no idea what a d-fender d-ring is...

Until I read this thread I didn't either .

I can see how they can serve a purpose in some weapons but I haven't had this problem .

I'd be interested in hearing the makes and models of the carbines used by those insisting they are necessary .

I'd also like to know if any of them reload their own ammo .

[ARCHIVED THREAD] - D-Fender D-Ring (Page 2 of 2)

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