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Discussion Starter · #1 ·
Hello,
For my AR-15
i would like to realise a new scope upper with bull barrel in
18", 1/7 but i need information with different measure,plan...Position of the gas block, where the gas port...
Where can i found this?
Thank you
 

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There are a lot of great 18'' SPR barrels out there. I like the 1/8 chromelined with rifle length gas system myself, but some are fond of the mid length gas.

I have a CMMG medium contour chrome lined tube that is sub MOA (Daniel Defense free float tube)

I also have a Wilson stainless medium contour that is WAAA-AAAYYY less than sub MOA also in a Daniel Defense free float rail

I have a Sabre Defense 18'' mid length upper with a Troy Ind. Rail that is coming in the mail it is a 1/7 will let you know how it does.

I have played with the heavy's and the lights and have seen no evidence to support the heay is better than med con.

PK firearms is the best place for SPR type uppers that I have found www.pkfirearms.com

If you need further assistance let me know.
 

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Good morning Manu 45,

I just used a Daniel Defense 18" SPR med weight barrel on build that I recently completed. I'll have to re-measure to be sure, but I believe the gas port is up about 2" compared to a 16" barrel. I ordered the mid length (12") gas tube from Midway and used a 9" Troy free float tube that was a perfect fit with the YHM gas block folding sight combo that I used. You can still go with a longer free float tube if you use a low profile gas block. The gas port on the 18" barrel is about 10" up from the extension and about 8 1/2" from the threaded FS end. My measures are very close but not exact because all of my rifles, fortunately are assembled. Other than that, everything else was the same. I hope this helps you out a little.
 

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Discussion Starter · #5 ·
Thanks for your answer
Can you give me the diameter under the hand guard and near the muzzle?
Thanks
manu
 

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Thanks for your answer
Can you give me the diameter under the hand guard and near the muzzle?
Thanks
manu
The barrel diameter where the gas block lines up on my particular barrel is 0.750, if your wondering about the diameter and clearance for the gas block and free float tube, that would be 1.505 inside diameter of the float tube. Keep in mind that both of these diameters may change depending on the make and design of the hand guard and the barrel.
 

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For an 18" barrel, I'd suggest going with a rifle length gas system. The rifle length system will have less pressure as it's further from the chamber than the mid length and will have a shorter distance from gas port to muzzle so the gas system carries full pressure for less time. This will give the rifle more time to drop pressures before the bolt carrier begins unlocking the bolt.

Bull barrels can be very heavy. HBar or medium profile barrels will save some weight without giving up much in the way of accuracy
 
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