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Discussion Starter #1 (Edited)
Still planning on doing a carbine length barrel but the funds said that's still a little while down the road yet so I chopped the barrel back and kept the mid length system. Went with 12.75" and had them open the gas port an additional .010". I've seen that some 12.5" cycled pretty hard and ended being over-gassed from too much gas port tweaking. Here was my experience...

- Rifle would not cycle on "S" with both old and new regulators. Case didn't eject, bolt was forward and locked.
- Both regulators cycled fine on "U" of course.
- Ejection pattern was between 4-5 o'clock and pretty strong, compared to 2-4 o'clock with a pinned 14.5"
- Felt recoil was comparable enough between the two that I couldn't tell the difference.
- No accuracy work, just plinking to test function but didn't seem overly affected given the bowling pin on the 50yd berm was dancing around.

My thought is that it is still a little over-gassed. Not by much, but still too a little too energetic. Seeing how it behaved when shooting I'm seriously wondering if the barrel is cut to 12.75" and the gas port left alone it would still work normally and as advertised. The gas port on the factory ACR barrel is miniscule so the rifle is very efficient on how much gas it needs. Pics to follow later...
 

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Looking forward to pics my man,,,,,,,

Just curious, did you happen to measure the barrel gas port before you had it cut?
 

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Discussion Starter #3
.060 if I recall correctly.
 

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.060 if I recall correctly.
Thank you sir, now where are the pictures!!!!!!! (tap tap tap..............);)
 

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good report. Always interesting to see what you'll get done, DSM. +1 pics
 

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Discussion Starter #8
 

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That's tight.
 

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Discussion Starter #10 (Edited)
You guys were ragging for pics and then nothing? C'mon now... ;) j/k


This is still kind of transitional yet. I put that YHM Phantom on there to have something on the threads and because I was too lazy to open the vault to get an 18T mount out. I do, just happens so, to have an additional stripped ACR barrel (thanks Dana!) that I'm thinking (read: planning to) of cutting back as well and doing some barrel contouring. For being an SBR it's still got some mass that I think I can drop. This time I won't touch the gas port and try my theory out.
 

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I like that, I like that alot. Very nice!!!!

Thanks for picture.....
 

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Discussion Starter #12
Thanks! I'm still amazed at how much more I like something when it's SBR'd. It's something I recommend to all who are fortunate to live somewhere it's allowed.
 

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Discussion Starter #14
Did it myself in the duracoat match.
 

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Discussion Starter #16
Eventually. My first excursion was to see how it ran. I think I'm gonna cut that other barrel first and test my theory on the gas port.
 

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Discussion Starter #17
Update: Work order is in to get the other barrel chopped. Won't be doing anything to the gas port this time to see how if it'll work. If not, it's easier to make the port bigger than making it smaller.
 

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my tests indicate a 12.5 " barrel with no mod to the gas port runs MK 262 77 grn. OTM great but will not cycle Tula steel cased rusky ammo -go figure
 

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Discussion Starter #19
Interesting. And while my pocketbook doesn't support very frequent shooting of Mk262 then it should be fine for cycling 5.56 ball and my various handloads. The extra millisecond of gas pressure that the additional 1/4" of bore provides might be worth it. :D

I wonder if it would cycle the steel cased ammo with a lighter recoil spring on the piston?
 

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Very nice rifle,
how long did it take to get your SBR stamp and what is the cost minus the gas port expansion and what company chopped your barrel?
 
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