How can you tell if your upper receiver has m4 style improved feed ramps??

[Grendel-Gene]

That!!!

[bwaites]

This:

[RangerRick]

If you have the M4 extension and rifle feed lower (bottom right picture above) you can cut the soft aluminum of the lower with a dremmel tool to look like the top right picture pretty easily if you are careful.

It may improve feeding if you are having difficulty.


RR

[LRRPF52]

They started playing with extended feed ramps with the Colt 700 series carbines, namely the Model R0727, which people referred to as an M16A2 carbine, and was prolific among SEALs, some SF units, & SFOD-D in the late 1980's through early 1990's until the M4 evolved from it.

Basically the extended feedramps are an answer to increased cyclic rate on automatic with a carbine-length gas system, since the bolt carrier group was returning to battery a lot faster than an M16 with rifle-length gas system. This occasionally results in bolt over-ride and failure to chamber malfunctions, since the magazine spring can't lift the cartridges fast enough into position to facilitate proper feeding. The R0727 has extended feed ramps, but not as extended as the M4.

Civilian manufacturers figured that they need M4 feedramps too, and they have pretty much become standardized on civilian carbines. I've read claims by Les Baer and LaRue that high-speed filing indicates that original rifle feed ramps work better on semi-auto AR15's, but I don't know if anyone has conducted these tests with the Grendel using both types of ramps. I somewhat suspect that M4 ramps might be helpful for the Grendel since a larger cartridge is being fed into the chamber, but this is pure conjecture on my part, backed with no scientific testing. Since I have only used my Grendel barrel in my MGI system, my configuration looks like the bottom right picture.

[Grendel-Gene]

THANKS!!! makes perfect sense!!!

[Glockzilla]

Good info folks!
I've been wondering myself - since I've been experiencing FTF issues - what the chamber of my upper is. Looks like it is an M4 style ramp.
I suspect that the chamber is rather tight. I'm gonna load some new Hornady brass, run some factory ammo and see what happens.