gas block question

[markl]

forgive my ignorance, but why would a 7.5'' barrel on a rifle with a blow-back system have a gas block?

 

[KevinB]

doubling as a front sight?

What weapon system?

 

[markl]

carbon-15 pistol

here's a pic, sorry about the lousy quality

i wanted to get a clamp on style front sight but that obviously won't work with this barrel.

the pin sticking out was holding the last M203 type handguard in place

 

[KevinB]

No idea - it may be just their way of retaining the handguard ?

 

[markl]

that's what i was sort of thinking, it just seemed a bit excessive for the job.
i guess if it still operates without it then i can ditch it and replace it with some sort front sight if there's enough space. thanks