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Discussion Starter · #1 · (Edited)
This information is MOSTLY for Type 1 Gas Systems.

It may be applicable to Type 3 as well in terms of sizing to get you in the ballpark, but I have NO IDEA if that's the case. It's just a guess.

***EDIT*** I've started including some Type 3 dial size info as well****



XCR Factory Bbl Port Specs for Type 1 Gas System:
5.56 XCR 16” bbl: .070"

5.56 XCR 9" Mini bbl: .086"

7.62x39 XCR 16” bbl: .116”

XCR Factory Gas Block Port Specs for Type 1 Gas System:

5.56 XCR w/16” and 9” bbl: .136”

7.62x39 XCR w/16” bbl: .136”


Factory 5.56 XCR 16” bbl Gas Dial specs for Type 1 Gas System:


S=.046”
1=.059”
2=.063”
3=.070”
4=.120”

Factory 7.62x39 XCR 16” bbl Gas Dial specs (same for 6.8 SPCII 12” bbl) for Type 1 Gas System:

S=.046’
1=.067”
2=.081”
3=.093
4=.120”

My Stnd.10.5”& Mini 8.3125” bbl’d 5.56 XCRs: Gas Block .140” (9/64), Bbl Port .098” for Type 1 Gas System

Gas dial sizes for the 10.5” and 8.3125”:
.140" or .136” (5.56 #4 dial position)
.093" (5.56 #3 dial position)
.081 (5.56 #2 dial position)
.067" (5.56 #1 dial position)
.046” (5.56 S dial position)

Bought a used 10" 5.56 Type 1 gas system pistol with a mini length gas position:

Gas Block: .136" Bbl Port: .086"
Factory Gas Dial Sizes (AFAIK):

.120" (5.56 #4 dial position)
.067 (#3 dial position)
.059 (#2 dial position)

Didn't bother with 1 and S positions.
 

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Discussion Starter · #3 ·
Thanks Sean K for posting this is very good and useful information.

By chance do you have or know where to find the port and regulator specs for the 12" barrel ?
Unfortunately, the only 12" gas dial numbers I had, I posted for the 6.8 SPC.

It *seems* the 16" 7.62x39 and 12" 6.8 SPC II dials work well in shortened 5.56s.....I accidentally bored mine out to almost the exact same specs and my 10.5" 5.56 and 8.3125" 5.56 are running 100% on any ammo without cleaning or oil.

HTH,
Sean
 

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Discussion Starter · #4 ·
BTW, the posted information is NOT set in stone. It's what I found when I measured the dials and bbls/gas blocks I had. There was some variance...some of that may be due to port erosion, or getting clogged up.....these are just general guidelines.

Hope you find them useful to your project or diagnosis. :)

Sean
 

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I picked up a 16" barrel that had been cut back to 12" with pinned and welded CAR15 flash suppressor for 16.125 length measured from closed bolt face.

Barrel gas port was .070 function was less than 100% on setting #4

Barrel gas port was drilled out with a #44 drill bit and is now .086

The intent was to drill the port out to .760 with a #48 drill bit first, test and go up in steps as needed to .086

A moment of distraction and the wrong bit was in the drill chuck resulting in a .086 port right off the bat.

On setting 1 function is 100% with XM193 ejecting and landing in a 3 foot circle 8 to 12 feet away steel case at 4 to 10 feet.

I got lucky this time.

----------------------------------------------------------------------------------------------------------------------------------------------------------------


Might be possible to tap the gas passage/ gas port in the front sight base gas block and use a set screw that has been center drilled as a gas bushing to choke down the gas in cases when needed.
 

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Discussion Starter · #7 · (Edited)

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Discussion Starter · #8 · (Edited)
7.62x39 Factory Bbl Port Specs for 10" mini:
.111

didn't measure gas block port

7.62x39 bbl Gas Dial specs:
4= .120
3= .063
2= .059( can't get the bit all the way in so maybe .055 also)
1= .055
s= .040
 

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Very good information in this thread. Can we sticky it?

It would be great to develop a list/spreadsheet of detailed specs -- measurements for barrel profiles, etc.
 

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Discussion Starter · #14 ·
I have an 18 inch heavy barrel. From the info Sean provided the hole on the #2 position is twice as large as any thing he listed. Time for a new gas dial. My thanks for all the replies and information. I'll be contacting Navelbeaver shortly.
I don't have ANY 18" specs....so maybe that's normal....though I'd guess not...based on the the fact that the longer bbl *could* theoretically have a smaller port than the 16".
 

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Discussion Starter · #15 · (Edited)
Got a Type 3 Dial and Gas Block (actually I got two....but I'll go over the other one later and update the post) from Nate.

He wasn't sure of the caliber, gas length or bbl length....but it was "small hole"

The Gas Block hole is a .128".

Position 7 = .067"
6 = .063"
5 = .059"
4 = .052"
3 = .046"

Didn't check positions 2, 1 or 0.

This will be going on the factory 10" 5.56 pistol with mini length gas system (mentioned at the bottom of the first post) to bury it inside a standard length upper...so I'll have to open it up.

I'll update with how much I open the first few largest ports and whether or not I monkey with the gas block to get it running 100%.
 

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Discussion Starter · #17 · (Edited)
Are you going to try it before you open it up?
Hmmm....new posts didn't show this.

I am planning to open it up before trying it. Why? B/c I'm not convinced the past owner(s) of this thing knew if it worked or not. The catch wasn't even notched to seat properly.

What I don't want is to drag it out to the desert and have it not run at all.

The ports on the Type 3 are tiny....too small IMO for them to work on a 10" bbl....but, there's also the timing issue of the dwell time with the slightly longer bbl port to muzzle distance in the mini length gas position to consider.

At the very least, I'm going to open up position 7 to .110" so at least I know it *should* run on the highest setting for sure.

Said fuck it...and opened up:

7 = .110"
6 = .093"
5 = .078"
 

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Discussion Starter · #20 · (Edited)
Got you on a wasted trip. Is this for suppressed shooting? If so, I haven't seen one that's needed to be opened up.

If not suppressed, disregard.
Not just suppressed.....but the lower settings weren't (and probably won't be) messed with.
 
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