Feedramp and Receiver Interface ... Something Doesn't Look Quite Right

[BTL BRN]

http://i61.tinypic.com/2vlmeeh.jpg

http://i59.tinypic.com/24xgfw4.jpg

http://i58.tinypic.com/2upa9tf.jpg

http://i61.tinypic.com/2zhioia.jpg

Almost as if the barrel extension sits a bit too far forward, or the ramps on the receiver aren't cut deeply enough? No malfunctions to date (only around 200 rounds) and accuracy seems to be fine; but considering the manufacturer/source (purchased as a complete upper) I was a bit surprised to see this.

Thoughts? I have not contacted the manufacturer as of yet, it hasn't impeded function or accuracy to date. However, accuracy has only been evaluated at the initial 50 yard zero and the round count as mentioned is still pretty low.

[BSmith]

As long as it's not creating a bump for the round going in, it's fine.

[halmbarte]

Looks like they were modified after being finished.

And maybe it's just me but the barrel extension looks wrong, like the cuts are too big.

H

[Iraqgunz]

Split the upper and lower. Remove the BCG and take a pic of the feedramps from underneath so we can see it better.

[BTL BRN]

Thanks for the responses so far, here are a few more; hope this helps a bit ...

http://i58.tinypic.com/doulcm.jpg

http://i61.tinypic.com/2cdbn6p.jpg

http://i62.tinypic.com/17w9qo.jpg

http://i57.tinypic.com/2a96r9w.jpg

[3 AE]

No malfunctions, accuracy fine, and by the looks of it in the last photo, all is well. Continue to fire away.

[Iraqgunz]

Looks good to me.

[BTL BRN]

Looks good to me.

Thanks again, certainly I value your input here.


My concerns are over comparing this (a known/proven quality upper):

http://i59.tinypic.com/30uecec.jpg

http://i61.tinypic.com/2s6m1k4.jpg



VS


http://i61.tinypic.com/2vlmeeh.jpg


You can clearly see how the receiver cuts are in direct contact with the feed ramps on the barrel extension, as opposed to having a noticeable gap in between.

[sinlessorrow]

Yeah I'm not seeing the issue. They look good to go imo. Besides with good sprung mags it's not like they are even needed now days.

[Col_Crocs]

I see what you mean but i too think it looks good to go. It appears to have been cut deeper + further polished than the receiver cuts but I don't believe it will ever impede function. If it really bothers you, let the mfg know.

[Slippers]

It'd be rare that the feed ramps on both the upper receiver and barrel extension line up perfectly unless they were cut at the same time (which means the upper receiver would be missing anodizing). In your pictures it's clear that the start of the ramps on the barrel extension sit further forward than the end of the ramps on the upper receiver, which is perfectly fine. If it was the other way around, then the tip of the bullet could get caught while feeding. The way yours is should never have a problem.

I've noticed that the new made-in-house BCM upper receivers are like this on several of my barrels, as are the few Vltor MURs I've had experience with. I also have a forged JP upper I got during the panic which is the exact opposite with one of my BCM barrels (so the barrel extension overlaps the ramps on the upper receiver, meaning it could catch the tip of a bullet).

[BTL BRN]

I see what you mean but i too think it looks good to go. It appears to have been cut deeper + further polished than the receiver cuts but I don't believe it will ever impede function. If it really bothers you, let the mfg know.

Yeah, it doesn't really bother me - certainly not from a cosmetic stance - and I suppose with it function 100% thus far I will just drive on.

It is a BCM factory upper, ELW-F 16" with 13" KMR FWIW.

[Phreakish]

It'd be rare that the feed ramps on both the upper receiver and barrel extension line up perfectly unless they were cut at the same time (which means the upper receiver would be missing anodizing). In your pictures it's clear that the start of the ramps on the barrel extension sit further forward than the end of the ramps on the upper receiver, which is perfectly fine. If it was the other way around, then the tip of the bullet could get caught while feeding. The way yours is should never have a problem.

I've noticed that the new made-in-house BCM upper receivers are like this on several of my barrels, as are the few Vltor MURs I've had experience with. I also have a forged JP upper I got during the panic which is the exact opposite with one of my BCM barrels (so the barrel extension overlaps the ramps on the upper receiver, meaning it could catch the tip of a bullet).

^^What he said.

Tolerances can and do build up. We try to get them as close as possible, but with as many dimensions as there are, sometimes tolerances get used up. Sometimes things look dead-nuts, other times there's a slight gap. The transition shown (receiver is proud, extension is below flush) is good to go, the other way around can cause trouble (similar to a rifle extension in an M4 upper).

[BTL BRN]

^^What he said.

Tolerances can and do build up. We try to get them as close as possible, but with as many dimensions as there are, sometimes tolerances get used up. Sometimes things look dead-nuts, other times there's a slight gap. The transition shown (receiver is proud, extension is below flush) is good to go, the other way around can cause trouble (similar to a rifle extension in an M4 upper).

Thank you very much for taking the time to reply, as long as it's functioning I am happy -- and it runs just fantastic thus far!

I do understand that the opposite would present itself as an issue; I however wouldn't expect to see that in any quality manufacturer.

[TehLlama]

It's not seamless, but the step isn't facing the wrong direction (the only no-go setup is if a round sliding against the receiver cuts can get caught 'under' the barrel extension, exactly as you're saying). If you want something that runs, that won't be an issue.