I recently attended a Police Carbine Conference.  There was a rundown of aftermarket parts "they" (the speaker) felt should be installed on AR15 Carbine platforms.  Everything pretty much made sense in my opinion with one "possible" concern and that being the "D-Fender D-Ring."  Has anyone had any experience with this product.  I understand what it does it theory, but I am concerned that it may be a part that when fails could cause even more problems.  I have never used one before and can't say that I have seen a need, but I do not believe I am an authority by any means.  Please add your constructive information regarding this aftermarket part.  I am anxious to see what others have learned.

By its design (which, BTW, is virtually identical to a $0.03 O-ring) it does greatly increase extractor tension but isn't worked much and is very, very unlikely to fail within the normal service life of other parts (barrel, bolt, extractor). Having said that, if you NEED one, run it for ~3K rounds and change it.

I have O-rings in all my bolts (get a 10-pack at Lowe's) except for a couple which have D-fenders. They all work fine, but, honestly, I wouldn't add one if I didn't see the potential need. IOW, I wouldn't put one on a 20" rifle unless I had extraction problems. As it is, though, all my ARs are either carbine or midlength, so I run an O-ring or D-ring in all of them just to be sure. You WILL notice a difference in extraction force.


While you're at it, go ahead and get a heavy duty extractor spring and a black buffer to go with the D-ring. Be prepared to have a few FTE malfunctions when you first install the kit - plan on running 200 rounds through a carbine to loosen everything up, then you'll be GTG.

Be sure you get the VITON  and not the more common Buna O-rings.

VITON holds up to the heat and solvent exposure.

The Buna will turn to sh*t.

I picked up a bunch from McMaster-Carr for pennies each.

1201T16 (Mil Spec AS568A Dash 006) $4.82/pk of 50

I said this in an earlier thread.

The O-rings will last quite awhile (ie, thousands of rounds). The D-Fender will outlast your barrel.

Whether this difference is important to you, I cannot say.

I use D-Fenders in my carbines and rifles.

Me too.  All my carbines have them and I recommend them for the rifles I work on at the PD.

Did anyone mention the D-Fender has a lifetime warranty?
If you have any doubts, send it back and they will replace it free.

Yeah but for the price of one D-Fender and shipping, you could buy hundreds of O-rings that work just as well.

So what?
I have never ever heard of a D-Fender failing by falling apart.
You can send one in and get a new one "Just because."

Okay so why would spend $15 + on something that should last a life time when you can spend $3 for a few o-rings that would last you just as long? And you can buy several more o-rings for the cost of that stamp to mail your D-Fender in to get your "free" replacement.

My old Defender melted in the Hoppes.

Note to self: Do not soak D-Fender in Hoppes.

Yes, it was real. It came with the MGI buffer I bought from Brownells.

I didn't soak it long either. Several weeks later, I noticed some dark greenish goo on the bolt. I kept wiping it down but it kept coming back. So I took the extractor out and the Defender was gone and the channel was filled with the goo. I'd send it back, but I'd have to send patches back.

The trouble with soaking it without removing the extractor claw. So there was probably Hoppes still present for a long period of time.

Careful with that Hoppes and anything rubber/plastic.

You could also just buy the BCM bolt reliability kit which has better extactor spring, black insert and O ring.

A buddy of mine and I were comparing his M&P15 to my RRA Entry Tactical. His had the D-ring and mine did not. I noticed his extractor had a recess for the ring to ride in. Can I add one on my RRA even though the recess is not present on the extractor?

Also what are the sizes of these O-rings for the defender?

Or
Viton Rubber Orings # 006 50 pcs 1/8x 1/4x 1/16
$3.45 for 50 shipped

The Dfender/Oring was part of Colt's original M4A1 reliability upgrade package.  All of our SWAT guns have them.  A 400% increase in extraction.  They work well with shorties.

I think the reasoning behind it is that the D-Fender wouldn't crap out at a critical moment, where an o-ring might hit that "X" amount of rounds and fail at precisely the time you don't need it to.

I don't use a D-Fender, and I would imagine the problem above could be solved by simply replacing your o-ring at the appropriate times. I was just chiming in on what the logic behind having one might be, aside from any enhanced performance in extraction.

I just dropped one in a small bottle of Hoppes to see what happens.
You don't even need to go to D-Fender if their part melted, Brownells will replace it.
Send a copy of your receipt/shipping order with the MGI Buffer item circled back to Brownells with a letter explaining what happened, they will ship you a new D Ring postage paid.

What makes the dring different from bravos's upgrade kit?

Well, for one, The D Ring isn't supposed to melt in Hoppes solvent or any other cleaner or lubricant for that matter.
The elasticity of the material is designed to last the life cycle of an average bolt or about 30,000 rounds, sounds like a lot of ammunition but it really isn't.
The material can stand up to heat in excess of 600 degrees Farenheight and cold to -30 F.

Like I said, I haven't seen one fail or melt so I am going to do a little test.

I have no idea what material the Bravo Co. O ring is made of having not seen or used one.

I'm not sure either but it looks like just an o ring. I'm sure you can contact Bravo on the industry page and they will send you one to do your tests on.

Can't speak for the material composition, but the the Dfender is shaped like a "D", which matches the shape of the extractor recess in the bolt.

Has it melted yet?

It has been a couple days, any word on the Hoppes test yet?

Nope.
I'm going to leave it in there a while longer.
I have a start of test pic and will take an end of test pic and post them.

Page 2 ownage to see the results of the test.

Why is that?

so is it better to have d-fender ring in a carbine or not?

Actually I've used both, and while I don't have the round counts some of you guys do, I haven't had a problem yet

Just jinxed myself.

Yes it is better for carbine length weapons which can benefit from the extra extraction force they provide.
I have D Rings in both of my carbines and two of my 20" rifles.
I don't use them at all in the 24" barrelled uppers because they are not rapid fired  and I don't shoot heavy bullet loads in them.

Will using a Defender ring offset the weaker, older blue insert? i.e. will it make up for the blue one being lame?

I'm pretty sure the insert is exactly the same.  They are just different colors to distinguish which spring they are inside of.  The rifle ones have a weaker spring (4 coil I think), while the carbine ones have a stronger (5 coil I do believe) spring.  The biggest reason for the two colors was military arms rooms where you'd have M16s and M4s, and spares for both.  Harder to confuse two different colors when reaching into the wrong parts drawer.

Well, at about 11 pm CST on Friday night I dropped the D ring in the Hoppes.
The pictures didn't turn out as well as I had hoped but,,,,if you look close at the bottle just below the cap and a little to the left, you will see out little buddy floating away in the Hoppes #9.

At 2:45am CST Tuesday I released the little guy from his prison.

I figured he must have at least swelled up a bit from the soaking so I compared him to a brand new D Ring.
Wet ring is on the bottom.

Had this test failed I imagine MGI would still replace the D Ring as the warranty is lifetime unconditional.
It is going to take something stronger than Hoppes #9 to destroy one of these.
I just might drop it in some good Scotch next,,,,,,,

Feel free to try this at home.

Anyone have one of the $.03 O-rings to conduct the same test with?

This has been the most informative batch of post ever.  From a very sincere question, someone was even willing to conduct tests!  What a great bunch of people per usual.

It takes a while for the spring/buffer/ring setup to 'break in'.

The spring will quickly lose a SLIGHT amount of its stiffness. That lost stiffness, before it's lost, can be enough to cause malfunctions.

In other words, when you do a full extractor upgrade, you're increasing tension to the very upper limits of what will work. Tension will soon fall back to within the (upper) limit of what will work, but until it does, it's possible to experience a few malfunctions.


Make the switch, dump 200 rounds of plinking ammo, and unless you get a malfunction in the last few rounds, you're probably good to go. Thus far, in 5 ARs I've upgraded (2 carbine, 3 midlength) only two of them have had any malfunctions; one stopped malfunctioning at ~50 rounds, the other at ~120, and have ran flawlessly since.

I've been using O rings and the occasional D ring on my guns for years now.

I have yet to see any noticiable gain from using a D ring vs. an O ring.

I change out my extractor every 10k anyways and that includes the O ring, spring, etc. whether it needs it or not.

I'm not sure why people keep harping on some percieved need to have a "warranteed" part in a little piece of rubber.  A bag of O rings will cost less in the long run (counting shipping and whatnot for warranty issues).

I also don't know what people are talking about O rings having a limited life.  I currently have 8k rounds on the O ring in my M4 and it still works fine.  Of course as a normal course of maintinence be changed out at 10k rounds along with the extractor, gas tube, all the springs in the gun, and the firing pin.

Seems to be a whole lotta people who WANT to support a certian manufacturer out of loyalty rather then common sense.  I mean seriously.  Who the fuck wants to mail back a little rubber ring for warranty issues? Seriously? If it's so damned good, how can you bear to be without it for two weeks while it's in the mail?!!?!?!!!?!?



A cheap 3 buck bag of O rings along with normal maintinence on the weapon will do the exact same thing, just cheaper.  Unless you REALLY need to be able to tell people that you have a lifetime warranty on a little piece of rubber half the size of a dime.

Edited to add:  I've also never had this 200 round break in period with a new O ring.  I've used O rings on all guns, regardless of barrel lenght from 20 to 10.5 and have never had an issue.  I'm failing to see or understand some of the issues that some people are talking about in here.  Perhaps your guns have other issues to deal with.

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.
Guys will spend $1000+ for optics and hundreds of dollars on stocks and handguards, lights and lasers and then complain about a ten dollar extractor upgrade.

As a working gunsmith I do builds and upgrades on other peoples rifles, I don't skimp because my reputation is on the line.
I keep a number of MGI D-Fender rings on hand at all times and they are all I use.

I will gladly replace the D Ring if a customer is having a problem with it.
I have yet to do so.

When you have a rifle/carbine/whatever that has been working fine with a standard spring and blue insert, then you suddenly change to a HD spring, black insert, and O-ring, you are greatly altering a parameter directly related to weapon function.

As I said, in 3 of 5 weapons I've done this with, no malfunctions were noted, but in the other 2, a couple were (I think 3 out of 200 for each of them). It's not something that will happen every time, but then again, there may be some variables we're not aware of - specifically, which HD springs are you using? I have used different brands - Wolff and a couple of others I forget - it may be that the some springs need less 'break-in' than others. ALL springs will see a drop in tension when they're first installed, but again, some more than others - just as with magazine springs. It may be that you're using a spring type that experiences very little reduction in tension, whereas I'm using a spring that when new simply has too much tension, but quickly drops down to within design parameters.

At the end of the day 'I don't know' - but I do know that any alteration to the core parts that a weapon's function depends on should be followed by a testing phase, and a couple hundred rounds is cheap insurance. It would SUCK to build a whiz-bang rifle, change a little part, then have it fail because it wasn't broke in when you needed it.

After the 94 ban expired I "no-banned" my Bushmaster Carbine by hacking off
the AK74 brake and pinned/welded on a Phantom FH, as well as adding an M-4 tele stock.

Anyhow, as soon as I made these mods I began to have extraction issues from time to time.
Could have been a dwell time issue due to changing buffer and spring. The extractor was a little worn as well.

While researching a fix for my problem I came across the "D" ring/"O" ring concept. Since I'm in the aviation
business I came across some O rings at work. I can be a cheap bastard sometimes and did not see the point of
paying for the D ring + shipping when I can get good O rings for free or at least at little cost from the auto parts store.

Once a new extractor and an O ring was installed my carbine's extraction issue was fixed. In fact the weapon
has not had a malfunction of any kind since then. I checked this O ring again the other day and see no signs of
breakdown due to exposure to cleaning products. It's been installed for about 5 years now.

All three of our ARs wear the O ring now, even the new 20" that never had an extraction issue.
My Bravo Company BCG in the middy came with one installed.

For AR's I am a firm believer in two things: The "O" ring and the P-Mag.

Decent ammo is nice too....

Hows about we got to the point where we could spend thousands of dollars on our rifles and optics by not wasteing our money when we don't have to?

It's easy to throw out comparisons of equipment costs and then call people stupid for not going along with your line of thinking, but seriously, PROVE to me that a defender works better then an O ring.  C'mon, lets see the proof.

I've used both and cannot tell any difference whatsoever in the performance of a gun running an O right or a gun running the defender.

Keep in mind that the "crane O ring" was out before the defender was and that the Crane O ring is issue on many rifles in the militarys inventory. I don't see a sudden rush to the defender because it's measurably better in any way, shape, or form.



And I've been building or working on guns from AR's/AK's/HK's/SA's to Glocks/1911/Sigs/HK's/S&W's/IMI for the last 14 years.  Just working in the "industry" doesn't give one a better grasp on a subject.  Methinks that the end user has more insight into a discussion like this so throwing out there that you're a "gunsmith" is irrelevant.



And i've not "had" to replace an O right either.  I just do as part of my regular maintinence because I can.


Really people.  Lets have some proof besides the fact that you can spend 50 times the worth of the actual part to send it back to the manufacturer for warranty issues "if" you actually have any issues.

Lets get something straight though.  I'm not saying the D ring doesn't work, just that it doesn't work any better then an O ring, and certianly isn't worth the extra price comparitivly.

The addition of an O ring or D ring does not negitivly impact any "parameter" of the function of the system in a way that could cause extraction issues.





The whole point of adding a ring of any sort or an upgraded spring  is to place added preassure on the extractor to ensure that there is no extractor lift during the extraction phase of operation.

The ONLY way this could negativly impact your firearm is if you made it so strong that the extractor did not snap over the rim of the cartridge during the chambering phase of operation. If this is an issue, perhaps you need to look at either your buffer weight or your buffer spring.

Quite frankly, if you're buying equipment that is sold as "extra power" and then "quickly drops down to within design parameters.", i'd be asking for a refund.  The whole point of buying these things is to place, and then maintain EXTRA FORCE upon a function of the firearm.  If it quickly goes away, then what's the point?  

And by the way, what are the "design perameters" of the extractor?  What's the "minimum" spring weight and what's the "max" weight?  Exactly how much force does an O ring or a D ring add to that?   Since you bring up the "design perameters", i'd like to know what they are.

To answer your question, I use the same springs and inserts that come with the gear (CMT and Fulton Armory), and I replace with factory replacements.  No wolff gear, no extra heavy duty springs, etc.  Just factory springs, inserts, and a cheap assed O ring (with no warranty I might add), and my guns run perfectly.  Even when beat on, dirty as shit (with real dirt too, not just carbon buildup!).




At the end of the day, I can look at the logical aspects of a machine, the interaction between the parts, the hows and whys and easily surmise that if adding an extractor ring causes problems, there's other issues to look at because no extractor ring addition should cause problems, it should only help fix them.

What you call "cheap insurance", I call causing excess wear on some part of your rifle to make up for something else being out of spec in the hopes that the system will just "wear" itself into working order.  

While this may work.....ish, it doesn't fix the original issue to begin with and i'd me more worried of that rifle failing when it was needed then a rifle that just worked regardless.  To you, it may be "cheap insurance".  To me it means I can't trust the gun because of latent issues.

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.

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.

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



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...).

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



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 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....






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.




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

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.



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.





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'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.

No, not the end of story - I'm glad your SBRs run, but that's too small of a sample size to be statistically useful.

my Mk18mod0 clone had extraction problems due to the faster bolt cycle..

I installed a D-fender, and now it runs like a charm !!!