M4 configuration?

The feed ramps are different to improve reliability when firing on auto or burst.

You can swap the vast majority of parts between an full sized and carbine sized AR with no issues.

I never understood where the "M4 feed ramps" came from. Can anyone explain it to me?

The newest M4s I've encountered and used were new in '08. They did not have "M4 feed ramps" nor did any of the older M4s I've encountered. Is this something new added to newer M4s or is it a civilian thing?

The supposed "M4" feedramps are cut at a slightly steeper angle, and are cut through both the barrel and the receiver.
I have heard that they are actually put on military M-4s because there are a lot of old beaten magazines in use in the military and the "M4" feedramps improve the feed with old mags.
Apparantly, LaRue claims that if you use new, good mags, that these "M4" feedramps are not only unnecessary but they strain the cartridge in a way that might decrease its accuracy.
I don't know if that's true or not, but since we're discussing M4 ramps I'd thought I'd throw that into the mix and see what brews.

The supposed "M4" feedramps are cut at a slightly steeper angle, and are cut through both the barrel and the receiver.
I have heard that they are actually put on military M-4s because there are a lot of old beaten magazines in use in the military and the "M4" feedramps improve the feed with old mags.

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I understand that the feed ramps in question are cut into the receiver and I know what they look like.

What I want to know is when/if they added them to M4s. Actual M4s not an AR15 marketed as one.

My guess is that with a shorter gas system and possibly older/sandy mags, after firing, the bolt may already be riding home to strip another round into the chamber before the mag has proped the next round into its most reliable place for feeding, and therefor lower ramps might prevent nosediving.

If I have just expressed my ignorance, I recommend that I am better left untold directly of said ignorance.

Just kidding.

The feed ramps came about around 2001, IIRC. If you go over to the 5.56x45 Timeline at the Gun Zone, you can probably find a better history of how they came about.

My understanding from reading various sources is that the the M4 feedramps were originally part of a SOCOM program to improve M4 reliability to better meet their specific needs. One of the problems they had run into is that the M4 has a faster cyclic rate (which due to gas port erosion becomes even faster still as the weapon gets older). Lots of full auto or suppressor usage compounds the problem causing the bolt to cycle even faster.

By extending the feedramps, feed reliability was improved for rounds that weren't quite in the proper position when the faster moving bolt grabbed them. Later it turned out they also helped with feeding long OAL rounds.

Big Army signed off on a certain number of M4 improvements that they would pay for (including the feedramps); but declined several of the recommended changes. Dissatisfaction with the M4 improvement program eventually led to the SCAR, which was funded by SOCOM dollars rather than the Army.*

*I'm just a recreational shooter who read a lot of conversations in various gun/industry forums from people who were actually involved in that process. This is my rough recollection of it.

didn't we just have this conversation? http://thehighroad.org/showthread.php?t=531450

Bart responded with the NSN number, revolvingcylinder, for the "actual M4s". Perhaps you could look up the date that was issued?

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Sorry, I lost track of that thread and didn't see the response.

It's tough to tell what is a marketing gimmick in the AR15 market and what isn't with the desire for so many civilian owners to try to replicate issued rifles.

The M4s my unit was issued were previously unissued at the time('08) and didn't have them. My experience with M4s are only the ones without the new feed ramps.

That is why I was confused on the whole matter. I'm guessing the Army may not have implemented them on ALL carbines for whatever reason.

Again, it was back in '08 and I don't have the serial numbers. The unit wasn't an organic AD unit. I wouldn't know where any of those rifles are nor would anyone who was formerly with the unit. They were turned in at the issuing post and that was the last anyone of us would have seen them.

Our equipment was issued to any of the units passing through the mobilization site. They were turned in there too.

It wouldn't surprise me if the rifles were unusual. It wouldn't be the first time I was issued equipment that I thought was no longer in service. Maybe they were rifles in shifting around in the inventories a while?

Just to clarify, my only recent experience with M4s were with this batch. The rifles I was generally issued beforehand were M16A2s.

Thanks for the info, though. It helped clarify things a bit for me.

The M4s my unit was issued were previously unissued at the time('08) and didn't have them. My experience with M4s are only the ones without the new feed ramps.

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It isn't uncommon for weapons in reserve units to be rebuilds using older receivers. I recall a friend of mine with the 45th reporting that they had "A2" rifles marked XM16E1 in 1994. Could be that your M4's were rebuilds using older uppers.

The M-4 feed ramps were used by Colt as a feature so they could regain their exclusive contract status for the M-4 rifles. Because they lost their contract to produce M-16's to FN, they had to figure out a way to get some military contract royalties back and promoted the M-4. They had to make the M-4 significant enough to qualify. The low profile barrel, the flat top, collapsible stock, and the exaggerated feed ramps helped them qualify. Otherwise, FN would have just been able to put short barrels on their production line M-16A2 receivers and snatched the SOCOM contracts from Colt.

Wittzo What the heck are you talking about?

Anyway, M4 Feed ramps are there for a number of reasons. Someone already mentioned full auto fire. They also help reliably feed longer bullets. In addition it was found that the shorter gas system increases bolt speed and the Feed ramps also help with this in regards to reliability. So yes they are there for reliability reasons but there are a number of factors as to why they are used. Some of which only apply to shorter gas system lengths.

When I was in Iraq, several of the Navy (IIRC) M4s were rebuilds on M16A1 lowers.

Some of the contractor's rifles (M4 style) were apparently built by Bushmaster and seemed to do OK. Much better construction that the civilian ones I looked at when I came back.

One of the guys over on M4C is an armorer for a PMC. They issued Bushmasters and he had nothing but problems out of them. I guess bean counters screw fighting men no matter who is paying the bills.