Gas Tube Questions

*Tried searching couldn’t find info*

I’ve been sitting on this builders set and decided to tinker around in the garage. I grabbed what I thought was just a standard rifle length gas tube but after putting the upper together the gas tube bottoms out in the key before the carrier sits all the way in the upper (pic attached)

I looked at my stash of tubes and found that I had two 15 1/8” and two 15.5” length rifle tubes.

What am I missing here? Clearly I need to put the 15.125” tube in this upper but can someone explain which application requires which rifle length tube?https://uploads.tapatalk-cdn.com/202...b440717a41.jpghttps://uploads.tapatalk-cdn.com/202...fc9494ff26.jpghttps://uploads.tapatalk-cdn.com/202...f6aff442ea.jpg


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Quick swap to the 15.125” tube and the carrier sits flush in the upper and everything appears groovy. Lemme know what these XXL tubes are for, except to make me feel inferior [emoji12]


https://uploads.tapatalk-cdn.com/202...44a5854666.jpg

AR-10 gas tubes are longer, the dogleg should be a little taller as well.

Some manufacturers just set the gas block for AR-15 gas tubes and also don't worry that it enters the gas key at an angle.

And by AR-10 I mean Armalite.

That makes sense. The dogleg did seem to impede on the barrel on the 15.5, whereas it doesn’t on the 15.125

So AR10 rifle length (true AR10, ala Armalite) and AR15 rifle length are in fast different you just have to know which rifle length your manufacturer means when building the large frame guns.

Thanks.