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1/25/2018 7:38:29 AM
Posted: 1/15/2006 5:38:29 AM EST
Hey everybody, what a great place for info and help.hase
Thanks for any help.
Link Posted: 1/15/2006 7:36:42 AM EST
= bolts should be kept with the barrel, i would at least but carriers can be used on all. the bolt mates to the barrel not the upper.

= different barrels will need different sighting in and will probably need re-sighting in after removal/install.

=to use with the mgi upper? probably just bbl.,fsb,gas tube, muzzle device.

here are some mgi threads, twl is the ar15.com mgi rep







there's a search button up above on the tabs use it to find topics already discussed.
Link Posted: 1/16/2006 6:50:10 PM EST

I'll address the sighting part of your post, as the previous post is right on.

The barrel will have an extension that the bolt locks into. On top of the extension is the index pin which will fit into a corresponding notch within your QCB. This pin is also used to index the front sight, to keep things lined up. Randall at AR15Barrels.com is a good guy, and builds good products. The front sight base that he installs will line up pretty well with your rear sights. It is a matter of the barrel builder properly indexing the FSB against the index pin on the barrel extension. All of my index pins fit snugly into my QCB.

Once you get a second barrel, you might find a slight amount of adjustment that you will have to make on your rear sight to get the new barrel shooting to the proper poi. These are normal variations of the few thousandths that occur with the width of the index pin, and the mounting of the front sight. If you really want to get persnickity about keeping all of the barrels lined up with the same setting on the rear sight, you can go with the type of gas block that is held on with set screws. You will find that you have a small amount of rotation that you can make on this type of sight, and still have the FSB over the gas port on the barrel. Rotate the front sight slightly to get it to come in line with your first barrel and rear sight setting. Of course a lot of folks here do not like set screws, but that is an entirely different matter.

I have found much less than a MOA of adjustment needed when switching barrels on my QCB. Keep the entensions clean, and the mating surfaces inside the QCB and you will be good to go. And stay away from any cheap barrels that may not have the FSB properly indexed.

I have three barrels that all line up within 1 moa with a single rear sight setting, and one that is a bit out.


P.S. Drop me an IM or e-mail if you want to talk about anything else QCB.
Link Posted: 1/17/2006 5:24:43 AM EST
Link Posted: 1/17/2006 7:56:28 AM EST
That's cool. Like the design of 249 front sights only the army never gets around to actually zeroing those to individual weapons.

It seems that given enough time MGI might think of everything.

What's the deal with the "midlength" Is that in addition to carbin length or is the std system just going to be midlength now?
Link Posted: 1/17/2006 9:02:17 AM EST

If I don't scream kick and fuss about the non-backwards compatibility issues of the original QCB with the new units, can I get put on the list to beta test the front sights

Man, just ponder the possibilities if Mack had all of the financial and personnel resources to design at his top speed.

Link Posted: 1/17/2006 9:19:25 AM EST
[Last Edit: 1/17/2006 9:24:32 AM EST by twl]
Link Posted: 1/17/2006 9:33:36 AM EST

You guys are killing me. Every time I figure a work around, you guys work around my work around. I am trying to keep all of my barrels at Carbine configuration, for the reasons you posted. My latest from Marty will be a 24 with carbine that I will use an adjustable gas block on. This is gonna be the 6x45, and I am not really concerned about iron sights. It's gonna look a lot like the old space gun with that much barrel hanging out there, but I am fine with that. Once I decide if the 24 is gonna work, or it needs trimming, we might have to talk about the front sight base.

Not to totally hijack this thread, but your post has me pondering my next pistol barrel length. How about the new sight/gas port location on a pistol barrel? Now we are talking carbon fiber here also.

Link Posted: 1/17/2006 9:49:23 AM EST
Link Posted: 1/18/2006 12:42:43 AM EST
Thanks for the info guys. That is what I love about this forum.

Bearbait1 I will probably email some more questions to you later. Thanks.

twl is there a certain bolt carrier that you guys recommend to use with this system? I was told in and earlier post that I just needed to change the bolt as I change each barrel and keep them together as a set. Also with the barrel when I order it I just need to get the barrel, gas block and gas tube correct? I do not need the barrel nut because of the camming system used to tighten the barrel, correct?
Link Posted: 1/18/2006 5:07:27 AM EST
[Last Edit: 1/18/2006 11:21:54 AM EST by twl]
Link Posted: 1/18/2006 11:18:01 AM EST
Link Posted: 1/20/2006 6:49:58 PM EST
hey tom i was just wondering if you have heard anything on my upper receiver and when i should be receiving it thanks Adam Natwick
Link Posted: 1/21/2006 1:46:07 AM EST
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