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Javi
09-21-2011, 12:26 AM
So I'm fairly certain I'll be going with a 1 in 8" twist barrel from BCM for my AR-15 build. Apparently it comes with M4 feed ramp barrel extension on it. The upper(s) I was looking at don't mention anything about it having those small cuts that continue the ramp into the upper receiver. I sent them an email asking if they do but if not, is this a problem?

MrPlink
09-21-2011, 12:34 AM
only if you have a full auto lower, and even then its a subject of much debate.

If you want more details, search the forum, this has been an endless topic of discussion.

IMO, wont matter

Javi
09-21-2011, 12:41 AM
Cool. I read a good amount into it through some M4 carbine thread which explained M4 feed ramps very well. I just wasn't sure if the combination of the feed ramps on the barrel and lack there of on the upper would create feeding problems. Was thinking I may have to have a gunsmith or someone make those small cuts in my receiver.

Edit: Did do a vague search for "M4 feed ramps" before hand and nothing relevant came up.

MrPlink
09-21-2011, 2:35 AM
I just wasn't sure if the combination of the feed ramps on the barrel and lack there of on the upper would create feeding problems.


I think I may have jumped the gun and not fully read your post, that may be a different scenario when they are mismatched.

Ive read it is better to not have them at all (which is what I originally thought you meant) than to have them mismatched or poorly cut.

Ive never been in that scenario personally, anything Ive had either had em, or didnt.

Maybe try running it and see what happens? If it aint broke, dont fix it

coq
09-21-2011, 5:29 AM
Your scenario sounds OK. The rule of thumb that seems to be repeated over and over...mismatch is OK if extended cuts are in barrel but not in receiver. NOT OK if cuts are in receiver but not the barrel. You can imagine how this would create a lip that could possibly cause feeding issues.

When I had a situation like this a couple of years back, I upgraded on the receiver to make a match, just because.

dieselpower
09-21-2011, 6:42 AM
There is a picure at ar15barrels.com. go look at it. your upper will be the OK pic.

Lancear15
09-21-2011, 7:35 AM
http://operatorchan.org/k/src/k309010_feedramps.jpg

Metal Magic
09-21-2011, 9:07 AM
I think if you go with with BCM you will be ok, Every model I have seen has the proper cut on the barrel and upper receiver.

intheknow
09-21-2011, 9:52 AM
nice! pics really help understand what youre all talking about hehe

Javi
09-21-2011, 2:07 PM
I think if you go with with BCM you will be ok, Every model I have seen has the proper cut on the barrel and upper receiver.

As far as BCM, I'm only getting the barrel from them, not the barrel & an upper. I got an email back from the guys that make the upper I want and they do have those grooves for M4 feed ramp barrels so that's good. If they somehow were mistaken, I'd be okay with "OK" then :) Which is great because the upper I'm looking at is perfect for me, was a pain to get exactly what I wanted.