Modifying AR feed ramps for 7.62x39mm

[cmshoot]

AR’s in 7.62x39mm aren’t known for their reliability. Feed ramps that were designed for the skinny 5.56 cartridge don‘t work quite as well for the buxom Russian 7.62.

Customer brought in an AR pistol chambered in 7.62x39mm. It was having feeding issues, and chambered rounds were showing gouges on the bullet and casing. Burrs in the feed ramps were the culprits.

I went over options with the customer, and we decided to remove the center divider between the two feed ramps, to assist in feeding. This would also remove the burrs.

Original feed ramps.

 

[cmshoot]

Preliminary removal and reshaping

 

[cmshoot]

Nearly done. Full removal complete, and some hand polishing done.

I will finish it up in the shop, using extra fine Cratex bits, followed by felt bobs with increasingly finer grades of polishing rouge. I’ll take more pics as the process moves along.

 

[57fairlane]

The 300blackout barrels we did at Remington had .308 feed ramps in the barrel extension. Might look into that

 

[NewLeaf]

Great Info!!! Thanks again CM . I noticed Tandemkross sells some bits that are supposed to work very well?? I don't think it would really matter as long as what you got works.

 

[Blue bio balls]

Nope..

 

[cmshoot]

Nope..

Care to expound?

 

[Jeddak]

Looks good! Similar to AK feed ramp, one wide ramp. Should work great.

 

[cmshoot]

I didn’t invent this “modification”. The first time I became aware of it was when Bushmaster started selling 7.62x39mm AR’s that had a reputation for reliability. Bushmaster did two things differently in their upper; large gas ports (I’ll have to do some digging to come up with the size they used), and a single, large feed ramp in the barrel instead of two separate ones.

Look at the differences in the size and taper of the 5.56x45mm vs the 7.62x39mm, and you’ll see why the 2 small M4 feed ramps could cause issues.

I’ve done this barrel extension modification on 3 previous AR’s in 7.62x39mm with great success.

 

[Jeddak]

That would explain why my Bushy worked well. I never paid attention to the ramp.