Upper Receiver Spec Question. StepUp/Lip From M4 FeedRamp>M4BarrelRamp W/in Spec?

Upper Receiver Spec Question. StepUp/Lip From M4 FeedRamp>M4BarrelRamp W/in Spec?

Upper receiver M4 Feedramps appear to be either too low or too deep. This causes a lip instead of a smooth transition to the M4 ramp of the barrel.
I am sure it is the upper receiver and not the barrel as I have put this barrel into two other receivers and those had visually zero step/transition lip. I have also put an FN made barrel into this receiver with the same exact bump/step up / lip from the receiver to the barrel.

Is this within spec? The receiver mfg says it is within their spec and they do this so people can "fit" the barrel to the receiver. Which I take to mean "file the barrel ramps to smooth the transition". Is that right?
Pic below:

https://i.imgur.com/mfXeu21h.jpg

Does the barrel from this thread look the same? https://www.m4carbine.net/showthread...Something-Else

@26 INF - tried to PM you but your inbox is full

This is pretty common in all the ARs I've seen. They all vary a little. And typically the round will hit the feed ramp well above the lower receivers cut.

Quote:

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Originally Posted by joeg26er

@26 INF - tried to PM you but your inbox is full

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oops let my site supporter drop. I'll fix that.

Quote:

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Originally Posted by joeg26er

Upper Receiver Spec Question. StepUp/Lip From M4 FeedRamp>M4BarrelRamp W/in Spec?

Upper receiver M4 Feedramps appear to be either too low or too deep. This causes a lip instead of a smooth transition to the M4 ramp of the barrel.
I am sure it is the upper receiver and not the barrel as I have put this barrel into two other receivers and those had visually zero step/transition lip. I have also put an FN made barrel into this receiver with the same exact bump/step up / lip from the receiver to the barrel.

Is this within spec? The receiver mfg says it is within their spec and they do this so people can "fit" the barrel to the receiver. Which I take to mean "file the barrel ramps to smooth the transition". Is that right?
Pic below:

https://i.imgur.com/mfXeu21h.jpg

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Can you feel the lip?
That sounds like a line of BS from the manufacturer. If the lip is on the backside(round sees a step down), there is no drawback. A step up can cause issues.

Its an AR not a 1911- you shouldnt have to “fit” anything.

It is a definite step UP

so one vote says it is normal and another says it is out of spec

Headspacing checks out though so it's the feedramp geometry that is off

but would it be a huge deal to file that step down a bit? Looks like a couple thousands.

On the same topic, I am considering using this upper for my new 300BLKOUT build. I'm thinking the larger rounds would be even less likely to touch this step up and be GTG without any need for filing the barrel ramps.

My first BCM looked like that. Never had a failure in maybe 5,000 rounds before I decided to change the barrel to an ELW. I would just shoot it. If you do have issues, bring it up to the manufacturer.

You realize he already did that, right?

Quote:

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Originally Posted by jackblack73

My first BCM looked like that. Never had a failure in maybe 5,000 rounds before I decided to change the barrel to an ELW. I would just shoot it. If you do have issues, bring it up to the manufacturer.

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Not sure if it is your picture or what, but the feed ramps do not look right to me.

Quote:

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Originally Posted by joeg26er

Upper Receiver Spec Question. StepUp/Lip From M4 FeedRamp>M4BarrelRamp W/in Spec?

Upper receiver M4 Feedramps appear to be either too low or too deep. This causes a lip instead of a smooth transition to the M4 ramp of the barrel.
I am sure it is the upper receiver and not the barrel as I have put this barrel into two other receivers and those had visually zero step/transition lip. I have also put an FN made barrel into this receiver with the same exact bump/step up / lip from the receiver to the barrel.

Is this within spec? The receiver mfg says it is within their spec and they do this so people can "fit" the barrel to the receiver. Which I take to mean "file the barrel ramps to smooth the transition". Is that right?
Pic below:

https://i.imgur.com/mfXeu21h.jpg

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