I have seen a picture of the dual feed ramps on the M4. Someone was selling DPMS receivers that had them. Are they necessary? How useful are they? What are their advantages, and, do I NEED these? Is DPMS the only company that has these? Can I convert a receiver without these into one that does with my Dremel? I know it seems like a lot of questions but they all condense down into a general explanation of these things. I am clueless.

Thanks for the help,


saltshaker

You dont NEED them but they may help the very rare misfeed caused by a hollowpoint hitting low.  THey are most usefull in full autos.  If you want to have it done go to the Industry Forum and ask Kurt at KKF what he charges.  He does them all the time for people.  Its not something you want to do yourself.

I have them on my Colt, and have never had a feed problem.  I think it is worth the couple bucks if you can live without your weapon for awhile.

The M4 feed ramps that extend down in to the aluminum is how we (USMC M4 Program) got through the extreme cold weather chamber testing in the mid 1980's.  Once the feed ramps were extended in that manner, the Carbine met the reliability spec for cold wx.
Unfortunately, (logistically) this leads to the Upper Receiver of the Carbine not being interchangeable with that of the rifle (Std 20-inch M16A2 barrel).  At that time, the Army (Rock Island Arsenal M16 Guys) did not want the ramps added to the rifle's tech data package for obvious non-interoperability issues.
So in worst case, one puts an A2 barrel extension into an M4 ramped Upper Receiver only to find that the barrel extension's ramp "overhangs" the upper receiver's.
On one point I agree that most probably don't need it, however, we found out later it actually speeded up the cyclic rate of the Carbine.  This told us that the original feed ramp was "slowing down" the gun, and this would be true of the rifle as well then.  And if this is true, then every round fed out the magazine and up the ramp is probablty being bumbed pretty hard on its way into the chamber.
So for shooting a variety of bullet types, and to lessen the possibility of "bullet set-back" during the ramp feeding moment, I go for ramping, especially if my gun shows signs that rounds are hitting the flat face of the upper receiver directly below the feed ramps formed in the barrel extension.
For example, I have been testing some Federal Tactical Bonded 62 grain LE ammo.  These bullets look moly coated, and this kind of hides that fact that its lead tipped.  Feeding these up a non-ramped rifle, and then extracting the round before firing, showed that the lead tips were being deformed by striking the feed ramp.  This affected grouping slightly at 100 yards, as dropped-in single loaded rounds had smaller and more uniform groups.
Firing the same ammo through a normal mil spec ramped M4 showed less bullet deformation.
Another hint,  The way I check ammo companys that submit new ammo for acceptability in our SR-25 sniper rifle system is to number and measure for overall length (OAL) of a sample of say 20 rounds.  Then load them in the magazine "by the numbers".  Immediately after each round feeds, I unload it and re-measure OAL.  If in your gun, these rounds all measure less OAL than before feeding and chambering, than they are being "set-back" when they impact the feed ramp.
In the SR-25/Mk11's, my baseline ammo for these tests is M118LR (Government Issue).  It never set's-back.  Its has the right combination of case neck tension and a waterproof sealant.
All that being said, my best hint is "if it ain't broke, don't fix it".  Or as the government so often does, "fix it until it is broke".
ColdBlue sends

So now I have a Bushy barrel in an M4 upper.(Havn't fired it yet) Will it work reliably or will bullet tips get hung up on the ridge???

Thanks for the great info Dave,

I think that clears up a lot of the mis-conceptions, false informations, and rumours regarding the M4 feed ramps!

Great post, lots of relevant info! Thanks.



Saltshaker

Kurt - I have a 20" Colt Frankenupper that I got in trade for something or the other - it has a 20" 1:7 Colt bbl with a M4 upper - I have had no problems with it but...

I think I am going to send it off to a smith up here that will copy the ramps off my M4A1 Carbine  - had the same done to my bastardly SPR

- just so i can sleep better at nights I guess

If you have "overhang" you have a "worst case"
To re-ramp the barrel extension to meet the "smiles" formed in the M4 upper, its best to pull the barrel out of the upper receiver.
If you Dremmel, do a little at a time and re-insert the barrel into upper receiver very frequently to check you progress.  Remove as little metal as possible to get the ramps lined up.
Once the barrel extension ramps line up, polish them with a felt bob and Simichrome Polish (from Brownwels), just like we did in the olden days after ramping .45's.  I always found that the polished steel finish in a feed ramp, attained with the Simichrome/bob method, was more than worth the little extra effort.
Don't polish the aluminum upper receiver "smiles" however, because if its milspec, you will cut through the hardcoat anodization that is intended to protect the underlaying aluminum.
You would only want to cut through the aluminum if you had a gun that would not work unless this was modification was performed.
ColdBlue sends...

Great Pictures!

I've run SEMIautomatic rifles with M4 barrels in generic upper receivers, and vv. for years without difficulty.  It's really not an issue in seimautomatic shooting.

In the case of an M4 barrel in a non-Colt's M4 receiver the receiver ramps can be added with only minimal attention to detail because the aluminum is pretty soft.

You can do the same with a M4 upper and a standard barrel, just takes a little more time because the steel is quite a bit harder.

With a standard barrel in an M4 upper there is a little lip but I've never experienced difficulty in SEMIautomatic firing.

-- Chuck

GreenO, your IM mail box was full.  Your answer follows a repeat of your question:  
"Were these problems caused by the higher rate of fire of the shorter barreled gun?
(or what makes the M-4 need ramps when the M-16 A-2 doesn't?)

If this is the case would lowering the rate of fire solve problems? (fat gas tube and AAC rate educer should bring even suppressed M-4's down to around 550-650rds/min"?
The problem we had (US Marine Corps attempting to "type classify/approve for service use the M4 as a replacement of the M3A1 .45 grease gun") was reliability in the cold chamber.  I,e., guns and ammo at 60 below for 24 hours "cold soak", then test firing.  By the way, the rifle passes this test, so when the carbine didn't, we had to figure out why. Also by the way, the problem did not occur in the "hot chamber".
After so many years now, I not so sure we actually identified the problem, but Colt's ramping the receiver as in the current M4 solved the problem so the program went forward.
In extreme cold, the powder does not produce the same port pressure at the gas tube as in warmer weather.  So we were getting a lower port pressure to start with.  This probably caused the bolt carrier to not only move back slower than normal, but perhaps not as far to the rear either.  This then may not have let the next round, in line to be fed, time to come up in line with the bolt to be fed in at the proper angle.
Over the years, I have observed many rifles with clear markings from 100's of rounds that "stubbed" below the feed ramps, but were subsequently "butted in" by the excessive stored energy of the recoil spring because they seemed to function ok at ambient temperature.  So perhaps in extreme cold, on a "short recoil stroke", is where the "marginal" performance shows up.
What I mean here,is that the M4, being forced to use parts more optimized (and designed) for the rifle format, just ain't going to measure up to the rifle's performance--ever!
That is why we (and others) are working on designs that may only "drop in a Carbine" for enhanced reliability, but are not interchangeable with that of the rifle's.
I am also not sure about the lube they may have used in the cold wx chamber.  If they used CLP which was all the rage back then, that could have exacerbated the issue.  When we tested the A2 in 1982-83, we used Lubricant Arctic Weapons (LAW) and the rifle functioned fine.
ColdBlue sends...