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Discussion Starter · #1 ·
Recently acquired a 6.8 AR with the barrel stamped M1S 6.8 SPC. Removed the flash suppressor and found it was threaded 1/36. Not sure of the AR's history other than it is at least several years old and was in like new condition. 1/36 barrel threads are uncommon but they do exist. A few companies online sell flash suppressors with 1/36. My questions is: Are 1/36 threads possibly an indication of when the barrel was produced. Maybe in the early days of the 6.8's introduction? I plan to call M1S and ask. Thought I'd float the question here first.
 

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1/2-36 threads? YHM uses the same thread pitch. Model 1 barrels have a Saami chamber with 9.5 twist. Worst specs available for 6.8. Upper end performance can not be acheived compared to better spec'd barrels. As for the thread pitch, a thread adapter can be used to change the threads to 5/8-24. Available from Brownells.
 

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I have one, bought it off another forum member here. It's a 1:10 twist, 16 inch barrel and shoots all factory ammo very well. It had the Spec1 chamber but I had it reamed to SpecII dimensions. I plan on cutting it down to 11" and doing away with the threads all together.
 

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Discussion Starter · #4 ·
What's it cost to have the Spec II chamber ream done? Does it just increase runout/lead? I shot a box of factory ammo at an indoor range just to get started and it did fine. Once I get some brass I'll start working up my own loads. Will push performance a bit over factory but nothing crazy. Have other smoking fast flat shooters for that. Haven't done much research yet. Assume there's a Spec II die?
 

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No spec 2 dies....all ammo in 6.8 has the same outside dimension specs--- its just the chambers that are different

Did you know that 223 and 308 are the same way? Multiple chamber designs but all ammo is same spec. Not to pick on you, just noting that people have a hard time understanding the slight differences in 6.8 but they often have no idea there are at least 18 different chamber designs in the "308win/7.62x51" class
 

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Discussion Starter · #8 ·
All good info. Thanks. I am a long time hand loader so I will get a handle on things. Just need to find the time to do the research. Definitely going to be measuring my chamber and scoping the throat to have a look at things. I have used Tubb's bullets before, so I may go that route.
 

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Also the M1S barrel with the 9.5 twist will possibly do better with the heavier bullets like the 130 Berger. It has been found that much of the problem with barrels is the land to groove ratio, if the M1S barrel is 50-50 then that will be the limiting factor.

This is not to say it will not do well with the lighter bullets but if interested in using the heavier bullets it may work a bit better than an 11 twist.
 

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Discussion Starter · #10 ·
I will give 130s a try, Steve. Just installed a float tube, new gas block, and Magpul MOE rifle stock...and mounted a Leupold VX-R on top of a Burris PEPR mount. Only thing left is to ream the chamber and then get some bench/trigger time. Any issues running an aluminum gas block on a 68? I have a mix of steel and aluminum on several 5.56 ARs but steel on my 300.

Though never really fired, this gun was a build by someone at least several years back. It's amazing how heavy some of the parts were that I traded out. The gas block was quite beefy steel and weighs nearly 7 ounces. The ELCAN optic with mount was 1 lb, 8.5 ounces! The ARMS handguard was 1 lb, 4 ounces. The plain Jane adjustable carbine stock was nearly 11 ounces, as compared to a current equivalent adjustable stock at about 7 ounces. My how things have gotten lighter over the years.
 

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Discussion Starter · #11 ·
No spec 2 dies....all ammo in 6.8 has the same outside dimension specs--- its just the chambers that are different

Did you know that 223 and 308 are the same way? Multiple chamber designs but all ammo is same spec. Not to pick on you, just noting that people have a hard time understanding the slight differences in 6.8 but they often have no idea there are at least 18 different chamber designs in the "308win/7.62x51" class
I was not aware of all those 308win chamber designs, and I've been shooting them for several decades. How is one to know what design they have? I assume there's s common or standard design in professionally manufactured guns? I measure headspace and runout but that's about it.
 

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I'd stay with steel gb--- you'll gas cut an alumninum one fairly quickly
 
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