Why car over Mid for the 12.5?
I go by 2% difference in MV for every inch of barrel length.
-TL
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12.5 carbine is about as reliable a system you can get.
Is that for unsuppressed? I would think 12.5 mid is perfectly fine if running a can.
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This. Or a 1-4x/1-6x.
As for carbine vs mid, it just works. Has for a long time. I somehow have yet to test this with a MG lower and shot timer, but when switching from suppressed to unsuppressed and back, āshortā gas systems seem to have less drama than longer ones. Since this is the opposite of what pretty much the entire internet feels, Iām open to being wrong. But the Crane study does seem to back this up by showing a greater RoF delta, IIRC. Either way, itās the size of the hole, not the length of the gas tube that really matters, in my opinion as someone who isnāt an engineer.
āSame gas tube as legacy guns in current use by major militaries around the worldā doesnāt market as well to tinkerers (like myself) as āwe made this longer for optimized suppressed useā. Since few people own suppressors, and few people will experiment while keeping variables to a miniumum, the internet is largely how people get informed about this topic, for better or for worse.
On the flipside, I doubt anything is āwrongā with a well-tuned midlength 12.5ā gun, especially if left in one configuration- suppressed or not. Though unsuppressed, it will need a blowhole to be reliable when cold and dirty.
My 12.5 mid-length runs like a top. Adding a griffin dual-lok 5 soon.
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Not saying you will have an issue, but I would interested to see you do a two-day class @ 1k rounds and see how she is doing on day two.
I teach medical applications (officer down/rescue) class and itās 2 or 3 days depending on the customer. Round count is usually 500-600 rounds per day, rifle and or pistol. Never had an issue. She gets pretty dirty, but is loved and clean regularly. I run a bcm mk2 buffer and h2 equivalent. When I get my suppressor Iāll tune her appropriately.
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Can you share what barrel manufacturer?
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I bought this back in 2014 but never installed until a few years ago. Iāve had no issues. Itās probably not the best barrel but I didnāt know what I know now. I had all the parts laying around so I threw it together.
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Cheers , that would be cool
Would be extra cool if they are both from the same series from the same manufacturer.
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I have a 12.5 and 13.9 criterion coreā¦I can get you velocities as soon as this lousy Michigan weather breaks.
sweet 
American Eagle M193 average velocities
12.5 criterion core average 5 shots 2854
13.9 criterion core average 4 shots 3062
Chrono 15 feet downrange
Donāt bank on reproducing that with 2 other barrels, but thanks for sharing your results.
That is pretty impressive difference for 1.4ā spread.
The 13.9 only had 200 rounds down it when tested. Was a new builds. The 12.5 had about 500. 13.9 was shot suppressed yhm turbo t3. 12.5 shot cold u suppressed
13.9 handloaded 62gr gold dots 2.260 oal. Light crimp arplus 24.0 gr. 2766 fps avg
So, this is completely unscientific, but today my buddy chronod his 13" X95 SBR and averaged 2919 with American Eagle 55gr 60 degrees at around 400 feet elevation.
Same weather my 13.7" ballistic advantage did 2865 with M855.
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My elevation was about 820.