12.5 inch barrel vs 13.7 inch barrel velocity

[jnr4817]

Why car over Mid for the 12.5?

[tangolima]

I go by 2% difference in MV for every inch of barrel length.

-TL

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[themonk]

Why car over Mid for the 12.5?

12.5 carbine is about as reliable a system you can get.

[mig1nc]

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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[1168]

Big fan of 12.5. If I could just have one, it would be a 12.5 carbine gas with a dot and magnifier.

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, “short” gas systems seem to have less drama than longer ones. Since this is the opposite of what pretty much the entire internet feels, I’m open to being wrong. But the Crane study does seem to back this up by showing a greater RoF delta, IIRC. Either way, it’s the size of the hole, not the length of the gas tube that really matters, in my opinion as someone who isn’t an engineer.

“Same gas tube as legacy guns in current use by major militaries around the world” doesn’t market as well to tinkerers (like myself) as “we made this longer for optimized suppressed use”. 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 “wrong” with a well-tuned midlength 12.5” gun, especially if left in one configuration- suppressed or not. Though unsuppressed, it will need a blowhole to be reliable when cold and dirty.

[jnr4817]

My 12.5 mid-length runs like a top. Adding a griffin dual-lok 5 soon.


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[themonk]

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.

[jnr4817]

I teach medical applications (officer down/rescue) class and it’s 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 I’ll tune her appropriately.


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[mig1nc]

I teach medical applications (officer down/rescue) class and it’s 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 I’ll tune her appropriately.


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Can you share what barrel manufacturer?


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[jnr4817]

Can you share what barrel manufacturer?


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https://faxonfirearms.com/faxon-duty...-ar-15-barrel/

I bought this back in 2014 but never installed until a few years ago. I’ve had no issues. It’s probably not the best barrel but I didn’t know what I know now. I had all the parts laying around so I threw it together.


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