Whats the purpose of a stepped barrel on an AR?

[Power Pill]

A did a search..couldnt find anything..

Anyone know why some AR/M4 barrels are stepped?

This :

 

[P90Puma]

Mounting for the M203 grenade launcher.

 

[rockenrod]

It's Stepped for a US M203 Mount.

 

[smak_daddy]

 

[Roughneck12]

That was a good question. Thanks. I had kind of wondered that myself.

 

[dizzy]

SAN barrel has a 'bulge' with a clip in it instead of the AR Step, serves the same purpose

 

[lawn gnome]

Ribbed for pleasure.

 

[icanuck]

That was a good question. Thanks. I had kind of wondered that myself.

Huh. Look at that, I learned something today. I always wondered myself. Good question.

 

[Shelldrake]

As mentioned, it is stepped down so the grenade launcher can be mounted there. You will notice that this step is on the viewable part of the short barreled rifles, but not on the 20" models. The 20" inch barrel are quite thin under the hand guards, and this is where the grenade launcher is mounted on the government profile barrels (the lower forehand guard is removed).

 

[Reaper]

SAN barrel has a 'bulge' with a clip in it instead of the AR Step, serves the same purpose

No it doesn't the grenade launcher for the Sig 550 doesn't interface with the "bulge".

The "Bulge" is actually the rifle grenade stop, the clip serves to ensure the rifle grenade is locked in place. As seen in the manual below.

http://www.mg-42.net/manuals/STGW90manual.pdf