Polishing m4 feed ramps?

[Grendel-Gene]

I have read that some people like to polish their feed ramps..... Can anyone elaborate on just how exactly this is done? Do they also polish the portion of the feed ramp that is on the upper receiver? How does that affect the hard coating on the aluminum upper?

Just want to be sure I get this right...

So much to learn.

Thanks

[Hoot]

The biggest factor is that there is as little if not no step up from the aluminum receiver ramps to the steel extension ramps. If you have a rotary tool like a Dremel, there are rubber polishing points that unlike the solid stone kind, take off material painfully slowly. Painfully slow is the speed you want to go with this. Anyway, those rubber polishing points are heavy on the rubber and light on the abrasive. They're great for "melting off" a barrel extension that is damaging your brass. Not for the short of patience type personality though.

I do not remove the anodizing from my receiver, though if you do, it's not the end of the world. You just have to keep the exposed metal lubed from that point forward so it doesn't corrode. Folks running larger thumper caliber ARs mill out the ejection port and no harm comes from removing the anodizing from that.

Aside from the convenience factor, there is no need to limit your purchasing to just Dremel brand polishing points. There are many sources for them out there, some of which are better than what Dremel chooses to market.

Hoot

[LRRPF52]

What Hoot said. When I do a barrel extension meltdown and polish, I use the green rubber polishing tools from my Ryobi kit. Main reason is to minimize damage to the brass, and assist with smooth feeding. Here's an example:

[Grendel-Gene]

But a portion of the ramps extends onto the aluminum receiver... that's the part that i am most concerned with. And shouldnt it be polished as an assembly to get a smooth transfer from the aluminum to the steel?

[stokesrj]

It's only important that the steel is lower than the aluminum, so that there is no edge for the bullet to catch on. If the rifle and magazines are set up to feed correctly, there is no need for the feed ramps to begin with.
Bob

[Grendel-Gene]

Thanks

[ndawoods]

The rubber points are called cratex and you can purchase large quintiles on ebay or from sinclair's, or midway. There are many different grits and also they will conform to the shape you are polishing.

[Grendel-Gene]

Well I used a regular dremel stone to turn down the sharp edge that was actually protruding above the aluminum line and tested the feed afterwards and it worked flawlessly. Now i will go back with these smooth grit rubber cratex deals to polish to the max. I didnt have the patience to go for hours on end of slow fine polish to work down what i knew had to come off....

[LRRPF52]

The extended feed ramps into the aluminum upper are a band-aid that arose from issues with full auto in carbines, since the short gas system was cycling the action way faster than the rifle-length gas system, resulting in bolt over-rides, where the action beat the magazine's ability to raise the cartridges in time. On the Colt Model 727's that were in use among NAVSPECWAR and certain SOCOM units, the use of AUTO during break-contact drills drove the requirement to get the carbine functioning more reliably, which is the last carbine model variation before the M4 arrived. I'm not sure how important M4 feed ramps are for the Grendel in SEMI auto, as they are not necessary in 5.56/SEMI.

I would really be interested in hearing Bill A. weigh-in on this one, since he has done a lot of testing both on SEMI and AUTO with the Grendel. All that said, the aluminum extensions should not need much polishing, if at all.

[smoke13]

before polish


after polish


used a dremel with small polishing wheel & compound to remove the burrs

[henmar77]

doesnt look worth doing unless the ramps on the extension are protruding..

[Whelenon]

doesnt look worth doing unless the ramps on the extension are protruding..

I disagree, polishing feed ramps and other mating parts helps form, fit and function. When custom shops charge big dollars for there guns, your paying for skilled labor to making sure all parts and components fit and function together perfectly. Attention to detail is the difference between a top quality gun and a production gun.

[65man]

what polishing compound are recommended?

[txgunner00]

The extended feed ramps into the aluminum upper are a band-aid that arose from issues with full auto in carbines, since the short gas system was cycling the action way faster than the rifle-length gas system, resulting in bolt over-rides, where the action beat the magazine's ability to raise the cartridges in time. On the Colt Model 727's that were in use among NAVSPECWAR and certain SOCOM units, the use of AUTO during break-contact drills drove the requirement to get the carbine functioning more reliably, which is the last carbine model variation before the M4 arrived. I'm not sure how important M4 feed ramps are for the Grendel in SEMI auto, as they are not necessary in 5.56/SEMI.

I would really be interested in hearing Bill A. weigh-in on this one, since he has done a lot of testing both on SEMI and AUTO with the Grendel. All that said, the aluminum extensions should not need much polishing, if at all.

I hadn't thought about this until now... does larger diameter of the 6.5 case put the mepat of the bullet at a slightly lower start point relative to the barrel than a .556? If so, that might be an argument for M4 feed ramps.

[Variable]

I hadn't thought about this until now... does larger diameter of the 6.5 case put the mepat of the bullet at a slightly lower start point relative to the barrel than a .556? If so, that might be an argument for M4 feed ramps.

Yes. I couldn't say definitively that they are required though, as I'm sure someone somewhere will chime in that they have a Grendel that runs fine without them. Either way, M4 feed ramps can only help if done properly so I personally wouldn't build a Grendel without them.