9mm FSB with standard hand guard

[boss_hawg]

So if I wanted to have a 9mm upper with a front sight base and standard CAR hand guards, what should I use to keep the hand guard cap from rotating?

Note that the 9mm doesn’t use a gas tube because it is straight blowback. Also my 9mm BCG is incompatible with a carbine gas tube.

Does any company sell a piece to extend backwards and hold the cap in place? Should I just use a pistol length tube (barrel journal is carbine length)?

I am not looking to:
-switch to a free float rail
-tap the FSB gas port for a screw

I currently have the whole upper built without any tube but I noticed that there is some play with the hand guard.

 

[1776]

Why not just chop a gas tube down ?

 

[dial1911]

-tap the FSB gas port for a screw

This was going to be my first suggestion.

And I think @1776 is onto something with the "sacrificial" gas tube... just cut one off so it's long enough to span between the FSB and maybe 1/4" into the upper receiver (assuming the upper receiver has a hole for a gas tube).

 

[boss_hawg]

good suggestion

any difference between chopping a carbine gas tube and just leaving a pistol length tube hanging inside the hand guard?

 

[SouthernSlammed]

good suggestion

any difference between chopping a carbine gas tube and just leaving a pistol length tube hanging inside the hand guard?

I would think, as long as your not in the upper to make contact with the bolt you will be good. Of course be sure to pin it so it's not wondering!

 

[Red Dawn]

Just have the tube stick a little past the handguard cap or ....
Get the Mad Machineist at Macon Armory or @permaneo vox to build you a gas impingement AR9