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Posted: 12/12/2025 10:44:55 PM EDT
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Are all gas blocks and all gas journals designed to leave the thickness of a handguard cap between the block and the shoulder? Is there a specification to look for? I've built upwards of 20 AR uppers, and my usual practice when building a free float upper is to, ideally, just put the gas port screw into the factory drilled dimple. If there's no dimple, I butt the gas block directly against the shoulder, and test fire it. I've never had to move a gas block forward to leave a cap thickness to get enough gas. What is the actual designed specification in various AR uppers? Are pinned front sight blocks simply "shaved off" a bit at the back to accommodate a handguard cap, or do some barrels have different distances from the shoulder to the gas port? Or is a cap width within the tolerance of a gas block port, such that it just puts the barrel's gas port further back or forward within the gas block's larger port? Thank you. |
| https://www.brownells.com/the-trigger-times/tips--tricks/quick-tips/quick-tip-ar-15-gas-block-alignment/ |
"All welchers should be removed from the EE".-Aimless
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Originally Posted By TGWLDR: https://www.brownells.com/the-trigger-times/tips--tricks/quick-tips/quick-tip-ar-15-gas-block-alignment/ Great, that's what I figured based on my experience! I just wanted to make sure I know the design intent. |
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To me that Brownells article and video seems misleading as all gas blocks do not have the same diameter hole for the gas and all gas holes in the blocks are not located the same distance from the blocks shoulder thats side is toward the upper. The print for the barrels gas hole also has tolerances it can vary. Here is an example of a manufacturer telling you how to install theirs with the leave a gap instruction bolded in the instructions. Also they mention one that does not need the gap. https://yhm.net/content/Install_Set_Screw_Gas_Blocks.pdf I found it best to measure them to be sure since they vary in more than one way. Besides the gas holes center on the blocks being located different distances I think some drill the first portion of the gas hole as big as the one for tapping a 10-32 but some blocks have holes at the sight base prints minimum diameter for that first portion of the gas hole. |
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Originally Posted By j3_: That Brownells article and video is misleading as all gas blocks do not have the same diameter hole for the gas and all gas holes in the blocks are not located the same distance from the blocks shoulder thats side is toward the upper. Here is an example of a manufacturer telling you how to install theirs with the leave a gap instruction bolded in the instructions. Also they mention one that does not need the gap. https://yhm.net/content/Install_Set_Screw_Gas_Blocks.pdf I found it best to measure them to be sure since they vary in more than one way. Besides the gas holes center on the blocks being located different distances I think some drill the first portion of the gas hole as big as the one for tapping a 10-32 but some blocks have holes at the sight base prints minimum diameter for that first portion of the gas hole. +1 Specs are all over the place from one barrel manufacturer to another, one gas block manufacturer to another. If the barrel manufacturer designs their barrel to eliminate the gap, and you use a gas block that is also designed to eliminate the gap, that is where you are going to potentially have problems with a partially blocked gas port. Unfortunately most manufacturers never state what spec they manufacture to...and in my experience, the industry could do a much better job of clarifying their specs. However, they often don't respond if you ask, or give you vague, unhelpful or incorrect information. That leaves the user to measure, roll the dice, and potentially waste money on mismatching parts. |
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Some are definitely designed to mount spaced with a .025”-.035” gap, I've found that those designed in that fashion are openly disclosed by manufacturers. There are several methods/tools available for those that feel that absolute center alignment is necessary for function. |
"All welchers should be removed from the EE".-Aimless
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