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9/22/2017 12:11:25 AM
Posted: 12/17/2005 2:42:24 PM EDT
[Last Edit: 12/22/2005 11:14:32 AM EDT by TheMocoMan]
Original Post:
Talking with my friend he dropped some AR15 kung-fu on me.
"carbines are known to
be hard on the extractor spring already... this is why the "o" ring mod and
d-fender are coveted by carbine owners (as well as the "blue" bumpers and
upgraded springs)."

who can translate some of this for me? THANKS!
Doing my Homework with Google & Search
Take the bolt out of its carrier and you will see a pin that holds the extractor to the bolt.
Push that pin out, and lift off the extractor.
The spring will/should be 'stuck' to the extractor (the spring is wider where it fits into the extractor)
The o-ring/defender will go around the extractor spring to provide more oompf during extraction.
Re-assemble extractor onto bolt

Wolff Extra Power Springs

AR15 Extractor Spring
3 Pack = Product #: 657937

Sig P226 Mag Spring 5% more tension
Product #: 894650

Link Posted: 12/17/2005 6:39:28 PM EDT
Carbines are often hard on the extraction process due to their shorter gas system. The extractor is fighting to extract a case from the chamber while the pressure is still high. Beefing up the extractor spring helps it to hold onto the empty brass by multiplying the force of the spring. This is accomplished by either using a heavy-duty extractor spring or adding an o-ring to the outside of the extractor spring. The insert inside the extractor spring serves little or no purpose.
Link Posted: 12/17/2005 7:17:16 PM EDT
google is a good translator along with the search function.

the topic has been discussed greatly not too long ago.
Link Posted: 12/17/2005 10:18:20 PM EDT
I've never heard of anyone coveting or requesting the blue inserts.
Link Posted: 12/22/2005 10:22:59 AM EDT
[Last Edit: 12/23/2005 7:38:35 AM EDT by TheMocoMan]
Everything you ever wanted to know about the D-Fender.

Why? Becuase people keep asking!!!
So don't give me a lot of shot about this thread.

From: TWL
MGI Military Factory Sales
I'm from the company which makes the D-Fender.

I'll be the first to say that some of the O-rings will work to a degree to improve extraction reliability, and I don't dispute that.
In some cases they will work for quite a long time with no problems.
In some other cases they may not.

We at MGI were the first to understand that extraction could be improved with a device such as this. We tested many things, and primarily the O-rings.
After much testing and observing failure modes, we determined that for the reliability necessary for this application, a different design was required.
This spawned the inventing and introduction of the D-Fender.

The shape and material of the D-Fender is optimized for AR15 extractor applications. It has a specific increase in the extraction tension, is built to resist heat problems, has the shape to eliminate deformation and breakage/binding that plagues the O-ring, and will keep its "springiness" over the long run.

This D-Fender device has been tested at Crane NSWC in both the 35000 round test and 50000 round test, without failure. It has been accepted by SOCOM as a combat reliable item, and is in use by SOCOM, and has been for years.

We are the discoverers and the inventors of this entire concept.
We did a whole lot of testing.
We know a thing or two about it.
We make the D-Fender.

I have not said, nor will I say that the O-ring will not work in this application.
All I'm saying is that our exhaustive testing has shown that O-rings are not reliable enough to use in this application in the long term. The time of failure is not predictable, and when it fails it is likely to be a catastrophic failure.
If you use the O-ring, changing it regularly will be your best bet.
Our testing has shown that when an O-ring fails, it is prone to migrate to a spot which binds up the extractor and takes the gun out of action.
We could easily have marketed O-rings, since we were the first on the scene with this idea.
It would have been alot easier to sell $1 items that we could buy for pennies in bulk.
We decided after testing that we couldn't go to market with them, due to reliability concerns, and so we went a step further to design the D-Fender.
It's your choice.

MGI Military Factory Sales Manager
Call 1-800-307-0728
or email twlyons@juno.com

The difference between the Crane O-Ring and the D-Fender are the materials and the shape.

The shape is designed in a wedge profile and "D" shape, which is suited to the application and doesn't do the asymetrical "squishing" that the O-rings do, which leads to the breakage.

The material is designed to have a specific(4x) increase in extractor tension in the AR15 extractor system, that has been determined thru testing to be the desired tension increase needed to enhance carbine extraction.

The overall design is made specifically to overcome the inherent weaknesses in the O-Rings that were identified in tests as needing improvement.

Testing showed that this set of design criteria solved the reliability issues that were cropping up with the O-Rings that were first tried. It has resulted in a very reliable, long-term solution to the carbine extraction issue that has been time tested, Crane tested, and combat tested over the last 5 or more years.

We invested a large sum of money in special molding and tooling to make this product, to say nothing of the time and efforts and innovation that were involved.

We are very proud and happy to have been able to be leaders and innovators in this area, but we want to be sure that people are aware that there are differences in these items, and the reasons why we make what we do.

Again, we take no issue with those who want to use O-Rings instead of D-Fenders.
We simply want to point out that we did not stop at the simple answer of the O-Ring for a reason, and went on to address the issues that came up with the O-Ring, so that we could have an even better product that went beyond that in performance and reliability.

We know it costs more, and people sometimes take issue with that.
We're very aware of that.
But, we're also aware that many people want to have the best performance possible, and are willing to pay more to get it.
That's where our product is targeted.
We went beyond the norm in performance, and it cost more to do it.
We know the difference, and we are providing the best solution, but not the cheapest one.

It's up to the individual to decide for himself what he wants to use.
We simply make the product available to those who want it.


I dropped in on a semi-private machinegun shoot held today at a farm in Wythe County, VA.

A older guy there who had just bought an M-16 (He did not know how to break the bolt down so he had no experience with his toy) had a ultra short pistol length upper (7 inches?) he was trying to get to run.

He was getting around two dropped extractions per magazine.

I had a spare D-fender in my range bag.

His ultra shorty now runs like a 4 legged sunuvabitch .

The D-fender fixed his new expensive toy, I am now one D-fender short and 13 bucks richer.

He is happy as he can be and I got to play with a couple of M-16's as a reward for my foresight.

The D-fender works with no BS. It is worth 13 bucks easily IMO especially considering he spent at least 30 bucks worth in ammo trying to figure out his problem before I butted in.
Link Posted: 12/23/2005 6:47:53 AM EDT
[Last Edit: 12/23/2005 7:41:16 AM EDT by TheMocoMan]
Disclaimer: This is simply a quote from HTH pulled from the archive.
Sorry for the confusion. I'm *still* trying to collect all this damn data with regards to all this shit that has to do with the f*** extractor. It's a pain.

Quoted from the archive. It has good information about O-Rings. Edited to remove the D-Fender bashing.

"Here's the real deal on O-rings.

Both Silicone and Viton are good material choices for O-rings. I prefer Viton for its better wear properties.

Go to McMaster-Carr - a wholesale hardware supplier and try the following part numbers:

1201 T16 : Mil-Spec Viton O-Ring $4.82 for a pkg of 50 O-Rings.

6540 K116 : Double-Seal Viton O-Ring $10.24 for a pkg of 50. These are exactly the same as the "X-Ring" sold by DSA(?).

9396 K11 : Silicone O-Ring $6.90 for a pkg of 100 O-Rings.

The O-Rings you can buy at your neighborhood plumbing supply outlet are probably Buna-N rubber and not very good in the long run.

With all due respect, bigbore, you have failed to identify the material of construction of the O-Ring you sell other than to say it is NOT Viton. If not Viton, then I can only assume it is an inferior material.

The Mil-Spec Viton O-Rings above are less than $0.10 each. Buy a bag of 50 and pass them out to your shooting buddies!


End Quote

Link Posted: 12/23/2005 7:02:08 AM EDT

Originally Posted By TheMocoMan:
Here's the real deal on O-rings.

The D-Fender ring is a quality ring, but it is no better than standard O-rings made of the appropriate material.


I'm not quite sure what you are saying in your post. When you post on 12/17/2005, you have no idea what the topic is about, but you post again on 12/23/2005 to tell us there is no difference.

I am more than a little curious as to how you mastered these items, and how you conducted your testing in such a short period of time.
Link Posted: 12/23/2005 7:11:55 AM EDT
[Last Edit: 12/23/2005 7:13:04 AM EDT by eklikwhoa]
i get the d-fender free so i use them.

didnt have extraction problems before it and didnt have any after it.
Link Posted: 12/23/2005 7:13:20 AM EDT
Link Posted: 12/23/2005 7:20:47 AM EDT
Sorry for all the confusion. I forgot every time I add to my own persnal reference I end up BUMPING this thread. MY BAD! Sorry.
Link Posted: 12/23/2005 7:22:56 AM EDT

Originally Posted By twl:
Well, I'm not sure exactly what is being postulated here, but I'm quite sure that nobody on this board knows as much about this topic as Mack Gwinn and Jim Sullivan, who designed the D-Fender, and invented the entire concept of this kind of extraction enhancement and tried all the various other things during the development process.

I certainly hope that this is understood.

I confess I'm not sure what this thread is supposed to be either, but I doubt anyone ability to go from zero to expert in days. I can't help but wonder if the original poster is simply cut and pasting things for some reason, perhaps to get yet more discussion going on this topic.
Link Posted: 12/23/2005 7:25:36 AM EDT
How about a nice sale: "Buy an MGI Buffer and get a few free D-Fenders". I'd go for that.
Link Posted: 12/23/2005 7:34:25 AM EDT
"the original poster is simply cut and pasting things for some reason reference, perhaps to get yet more discussion going on this topic.a thread for my own purposes, since I got only a few resposnes but not a lot of information and backround.
Link Posted: 12/23/2005 7:35:22 AM EDT
Link Posted: 12/23/2005 7:35:25 AM EDT
I'd prefer to buy a couple of D-Fenders and get free MGI Buffers
Link Posted: 12/23/2005 7:39:54 AM EDT

Originally Posted By Kisara:
I've never heard of anyone coveting or requesting the blue inserts.

Aren't the Blue inserts the Carbean inserts? Ken at S.A.W. broke it down for us once, but the Dunder heads on this site ran him off.

I think my Colt carbean came with the Blue insert.
Link Posted: 12/23/2005 7:41:57 AM EDT
Link Posted: 12/23/2005 7:44:44 AM EDT
I can't find shit on this whole Blue insert thing. Damn friend won't call be back either.

Some dude made a blog...
"Normal" springs feature a blue plastic insert, Colt strong springs have a black insert.

G** damn internet
Link Posted: 12/23/2005 7:46:37 AM EDT
[Last Edit: 12/23/2005 7:53:28 AM EDT by Stickman]
Why not call TWL as he suggested? I'll bet the info would be a bit more credible than some "dude with a blog".

Instead of cut and pasting isolated pieces out of a thread, you could relate your own information based off the questions you asked TWL.
Link Posted: 12/23/2005 7:52:41 AM EDT
+1 on calling twl for info.
Link Posted: 12/23/2005 7:53:16 AM EDT

Originally Posted By tvone:
I'd prefer to buy a couple of D-Fenders and get free MGI Buffers

+.......man i dont know just a lot
Link Posted: 12/23/2005 7:56:26 AM EDT

Originally Posted By Kisara:
How about a nice sale: "Buy an MGI Buffer and get a few free D-Fenders". I'd go for that.

i get my "free" d-fender this way.

run the mgi buffer and included d-fender in all my ar's
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