How do QD adapters work?

jjgow · Post by **jjgow** » Tue Sep 09, 2008 11:07 pm

I did a search, and found several threads relating to homemade QD adapters, but everybody said to just buy a can that could use one. I looked at some centerfire and rimfire QD adapters and here are my questions:

1. On the YHM Mite QD adapter, are they just really large threads (not sure if that's the correct term)? What makes that better than 1/2x28? Is there any reason a mount like this would not work with 5.56?

2. On most centerfire rifle cans, the mounts look very complex, but they too appear to incorporate the larger threads. What's going on with these?

3. Does any one have a diagram of how a 3-lug works? I understand the basic concept (twist to lock into place), but can't picture in my mind how the two pieces go together.

4. Is there any feasible way to make my own QD mount? I saw that Griffin Armament offers a QD mount kit, but it's a bit pricey, especially because you can't individually buy muzzle attachments. I'd also prefer the pleasure of having made something myself.

Thanks in advance!

David Hineline · Post by **David Hineline** » Tue Sep 09, 2008 11:47 pm

28 threads per inch, means 14 full revolutions to put on or take off a silencer if 1/2" of threads.

5 tpi coarse threads means 1.5turns to do the same thing.

If you have ever connected a BNC video cable up the 3-lug works kinda like that.

The Gemtech QD 22lr that is no longer made hooked up kinda like an air chuck going into an air hose.

Feel free to design your own system

jjgow · Post by **jjgow** » Wed Sep 10, 2008 6:11 am

Thanks for your answer!

About the 5 tpi thread: Does it hold the can on better than a 1/2x28? I was reading through the forums earlier and people were saying that if you didn't want a can to unscrew while you fire it, you should get a QD can. Is there just more surface area to contact, so it holds better?

And just to make sure: if I wanted to make a 5.56 QD, could I just use a similar 5 tpi thread? I wouldn't need a complicated looking flash hider?

Conqueror · Post by **Conqueror** » Wed Sep 10, 2008 6:12 am

The larger threads mean it's faster to screw on or off. But that's not the main benefit of the QD system:

The important bit is that ring at the base. It has four teeth on it, and the ring is spring loaded with forward pressure. When you screw on the can, the teeth "latch" into a number of slots on the rear of the can. That means the can is "locked" onto the mount and cannot vibrate loose. THAT's the real benefit of a QD system - they all have some sort of latching or locking mechanism which prevents the can from loosening while you're shooting it.

jjgow · Post by **jjgow** » Wed Sep 10, 2008 6:15 am

Oh, okay. Thanks for the quick response!

I guess with .22lr there's little danger of that happening, but with 5.56 the added recoil can shake it loose?

Mtdew · Post by **Mtdew** » Wed Sep 10, 2008 7:31 am

jjgow wrote:Oh, okay. Thanks for the quick response!

I guess with .22lr there's little danger of that happening, but with 5.56 the added recoil can shake it loose?

ALL thread on cans will come loose. Some just take longer than others.

Thread fit is a huge part of it.

jmorris · Post by **jmorris** » Wed Sep 10, 2008 12:03 pm

Iâ€™ve seen one that used interrupted threads as a method of attachment (probably the least desirable). I want to say it was a prodigy, but that doesnâ€™t seem right, anyone else?

Same concept http://en.wikipedia.org/wiki/Interrupted_screw

jamis · Post by **jamis** » Wed Sep 10, 2008 12:08 pm

I have the YHM setup like in the picture Conqueror posted on one of the 9mm XL cans. I like the fact that its a lot easier to thread on the the standerd 1/2-28.

Its got its good points and bad points. I have noticed even after screwing the can down all the way I still can feel some play. YHM told me that was normal but it concerns me.

jjgow · Post by **jjgow** » Wed Sep 10, 2008 4:10 pm

Well, I guess I can make some QD adapters just for convenience and just have a nomex (or something) glove and tighten it every now and then.

Thanks for the responses, guys

JohnnyO · Post by **JohnnyO** » Wed Sep 10, 2008 4:11 pm

Here is one I made to use with a YHM 9mm QD flash hider, you can do the same with the 5.56 flash hider that Conqueror showed.

jjgow · Post by **jjgow** » Wed Sep 10, 2008 10:27 pm

Well, I've thought about it, and I think that for simplicity I will do a 5.56 3 lug mount, as I can easily get a muzzle attachment, and I believe that I can get someone to make a female end, or buy one to screw into the can I am planning on making. Does anyone have any experience with doing custom work like that? I would sort of like to do it myself, but I think that I'd be going in way over my head with that sort of thing.

So:
1: If I buy a Trident 9 3 lug end from Major Malfunction, would I be able to thread the end of my can to put it on?

2: If that isn't possible, where do you think I could get a female 3 lug to male 1/2x28 and what do you think it would cost me?

Conqueror · Post by **Conqueror** » Thu Sep 11, 2008 2:18 pm

1) Yes, it's possible, but you'd need balls of brass and brains of mud to shoot 5.56 through an aluminum 3-lug mount.

2) These things aren't off the shelf components. If you want a 3-Lug 5.56 can you're going to have to machine the can components yourself, pretty much.

jjgow · Post by **jjgow** » Thu Sep 11, 2008 3:39 pm

Yes, I thought the strength of the coupler would be an issue, and while thinking about it today, I'd more likely do that same idea, but with a 9mm AR. When I said "where can I get one," I meant where I could have one made for me and what the price of such a commission would be. I still want to do a 5.56 QD, but I'll probably just stick with the fewer tpi design rather than anything fancy.

I was thinking about doing something like the KAC 9mm can, but I don't know exactly how it works. Obviously, there are slots on the sides of the barrel for the pins to engage, but I have 2 questions:
What stops the can from wobbling a bit? It seems like it would with that design.
How does one push the pins back out? It looks like there's a spring involved from what I see, but I'm not entirely sure.

Mtdew · Post by **Mtdew** » Thu Sep 11, 2008 4:37 pm

Conqueror wrote:1) Yes, it's possible, but you'd need balls of brass and brains of mud to shoot 5.56 through an aluminum 3-lug mount.

SWR's are made of SS not Al.

jjgow · Post by **jjgow** » Thu Sep 11, 2008 4:43 pm

Mtdew wrote:
SWR's are made of SS not Al.

The plot thickens... I'm still not sure I'd like to fire 5.56 for something not designed for it, though.

pneumagger · Post by **pneumagger** » Thu Sep 11, 2008 5:50 pm

I think a 3 lug mount is every bit, if not more, robust than the Gemtech Bilock.

Give it a go... you be fine.

jjgow · Post by **jjgow** » Thu Sep 11, 2008 5:54 pm

I guess I'll give it a try, but I won't be moving to the United States for at least 2 more years.

pneumagger · Post by **pneumagger** » Thu Sep 11, 2008 5:57 pm

??? Where the heck are you?

Henry Graham · Post by **Henry Graham** » Thu Sep 11, 2008 5:58 pm

Our 3 lug mount is mostly aluminum. Do not use it for 5.56mm. I guarantee something bad will happen.

jjgow · Post by **jjgow** » Thu Sep 11, 2008 8:25 pm

pneumagger wrote:??? Where the heck are you?

New Jersey

Thanks for the heads up, Henry

jjgow · Post by **jjgow** » Fri Sep 12, 2008 4:39 pm

All right, now that I think I've settled on the idea of just making a 5 tpi mount for 5.56, and maybe a 3 lug for a 9mm in the future, I'm curious as to how I can reduce POI shift with either the can itself or the QD mount. Any tips when starting up (other than making sure everything is concentric)?

I presume that I may have to make the can and then make minute adjustments to something before it works properly, but I'm not quite sure what.