Why Are Some M4 Feed Ramps Shiny and Some Not

01-01-2012,03:03 PM

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

01-01-2012,04:12 PM

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

01-02-2012,05:54 AM

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:

01-02-2012,02:00 PM

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?

01-02-2012,02:20 PM

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

01-02-2012,08:47 PM

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.

01-03-2012,03:18 AM

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....

01-03-2012,04:14 AM

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.

01-05-2012,01:27 AM

before polish

after polish

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

01-05-2012,01:41 AM

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

01-05-2012,03:44 AM

Quote Originally Posted by henmar77 View Post

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.

01-05-2012,04:10 AM

what polishing compound are recommended?

01-05-2012,05:51 AM

Quote Originally Posted by LRRPF52 View Post

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.

01-06-2012,04:01 AM

Quote Originally Posted by txgunner00 View Post

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.

01-06-2012,04:49 AM

I've never polished my feed ramps, though I have filed them in on uppers that don't have the M4 ramps. Doing that obviously removes the anodizing, though I have noticed no ill effect. It absolutely has increased reliability though. some grendel magazines don't have the relief cuts forward of the feed lips, which can cause the cartridges to nosedive more. Adding the ramps helps there. I also use the SS CMMG followers in my 5.45 mags. the benefit there is that they are simply bent sheet steel. That allows you to adjust them to fit the mag however you like. In my case, I have them adjusted in a way that the cartridges strip from the mag straight forward, without any popup. They just run smoother that way, but they also require the M4 ramps, else they would simply just nose dive and fail to feed.

I guess the short of it is, if nothing else, I would advise at least cutting ramps in the upper if you don't already have them.

01-12-2012,12:51 AM

nice polishing job. I'll have to try it.

01-12-2012,02:12 AM

The ramps can also be polished with emery paper 600 grit and crocus cloth wrapped around a 1/4" dowel. It may not be as fast but all you really need to do is get everything smooth.The smoother the feed ramps the less amount of friction the cartridge works against on it way into the chamber. Another area to cleanup is the sharp points on the 10 o'clock lugs, this will prevent the 2 marks on the case neck when it is extracted.

01-12-2012,10:03 AM

Quote Originally Posted by 65man View Post

what polishing compound are recommended?

I've always used a Dremel tool with the felt bit and rouge. The bit is compliant enough to conform to the shape of the ramp. It can sling some rouge around, so it's best to plug the breech. Just stop every few seconds and wipe the area clean; you'll see the shine after a few passes.

01-13-2012,11:39 AM

Quote Originally Posted by rasp65 View Post

The ramps can also be polished with emery paper 600 grit and crocus cloth wrapped around a 1/4" dowel. It may not be as fast but all you really need to do is get everything smooth.The smoother the feed ramps the less amount of friction the cartridge works against on it way into the chamber. Another area to cleanup is the sharp points on the 10 o'clock lugs, this will prevent the 2 marks on the case neck when it is extracted.

Do you mean the lugs at 2 o'clock and 3 o'clock? I think the vampire bites in the AR are from the top inner edge of the 3 o'clock lug, and the bottom inner edge of the 2 o'clock lug in the barrel extension. I have heard of guys taking the edge slightly off those, but that is usually done before threading the barrel into the barrel extension, when the extension is stand alone.

As the spent case is extracted from the chamber, as soon as the neck clears the breech, the ejector tension forces it to the right and upwards, with the rim pivoting off the extractor lip until it can clear the ejection port.

Why Are Some M4 Feed Ramps Shiny and Some Not

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Polishing m4 feed ramps?

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