AR Sponsor
Posted: 8/20/2013 12:22:00 PM EDT
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I just recently completed a trade with another member here for a 300 blk upper. He assembled the upper himself. I'm not doubting the competency of his work but I'd like to make sure everything is good to go before pulling the trigger on it.
What do I need to do to make sure everything is assembled and headspaced correctly? |
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Quoted:
I just recently completed a trade with another member here for a 300 blk upper. He assembled the upper himself. I'm not doubting the competency of his work but I'd like to make sure everything is good to go before pulling the trigger on it. What do I need to do to make sure everything is assembled and headspaced correctly? Take it to a gunsmith to be checked, or purchase or borrow the gauges to check headspace yourself. You should be able to give it a visual and perform an unloaded function check to see if it's put together properly, or can have a gunsmith do that for you, too. |
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Quoted:
I just recently completed a trade with another member here for a 300 blk upper. He assembled the upper himself. I'm not doubting the competency of his work but I'd like to make sure everything is good to go before pulling the trigger on it. What do I need to do to make sure everything is assembled and headspaced correctly? -check the headspace (google it if you don't know how, there are a ton of write ups. I believe brownells even has a 'how to' on their ar15 build videos) -look for some grease around the barrel nut -check the torque on the barrel nut (remove gas tube if necessary, depends on the barrel nut used). just set your torque wrench to 30 ft lbs, that is the minimum torque value, anything more than that (up to 80 iirc) is used to get the teeth to line up with the gas tube hole. -check the gas block. make sure the allen screws are torqued properly if it's a low pro or clamp on gas block. make sure the taper pins are hammered in good if it's a FSB/shaved FSB/pinned gas block. -make sure the muzzle device is secure (you don't have to torque super hard on it, just make sure it's on there). |
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You need a set of Go and No-Go headspace gauges for 300 Blackout, if you can find them in-stock.
Take the upper off the lower and remove the extractor from the bolt (supposed to remove the ejector too, but that can be a PITA), then slip the GO gauge into the chamber and try to close the bolt on it by pushing on the back of the bolt carrier group with your hand. The bolt should fully close/lock-up on the GO gauge. Then remove GO gauge and slip the NO-GO gauge into the chamber. Try to close the bolt on it. It should not close on the NO-GO gauge. If it closes on the NO-GO, then you have too much headspace. If it does not close on the GO gauge, then you have insufficient headspace. Also, check to see if the barrel nut is indexed correctly with the gas tube and not rubbing it or forcing it in the upper receiver passage. Lastly, installer error shouldn't affect headspace, which is set by the manufacturer of the barrel, and is achieved in combination with the dimensions of your bolt. It's possible for a manufacturer to be off-spec, but that seems to be very rare. |
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