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Thread: First Look at BCM's NEW M4 Upper Receiver

  1. #31
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    Grant, do you happen to know if the Brownells upper receiver lapping tool will still fit the BCM upper?
    "That thing looks about as enjoyable as a bowl of exploding dicks." - Magic_Salad0892

    "The body cannot go where the mind has not already been."

  2. #32
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    No NEED for lapping with the new upper I hope!! )
    Have you had to lap stuff in the past? (I only ask because, as I mentioned--but perhaps it was deleted--I had a canted BCM upper, which is why I'm SO glad they are having their own made to spec...I even wonder if that small group of people who had issues is the reason WHY they created their own.

  3. #33
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    What I really like is that all of the BCM uppers that I own, Paul assured they were inspected.

    The fact that he feels this is the nest option, suggests it is a LARGER problem than most want to admit.

  4. #34
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    Quote Originally Posted by evi1joe View Post
    No NEED for lapping with the new upper I hope!! )
    Have you had to lap stuff in the past? (I only ask because, as I mentioned--but perhaps it was deleted--I had a canted BCM upper, which is why I'm SO glad they are having their own made to spec...I even wonder if that small group of people who had issues is the reason WHY they created their own.
    Never had to. I just like to lap to ensure that the face of the upper is as close to 90 degrees from the centerline of the bore as possible. However, I have the tool so I use it.

    Some uppers (like my most recent BCM) will wear perfectly evenly as the lapping tool works its magic. Others will wear entirely on one side...indicating that the shoulder of the upper receiver where the barrel extension would rest was grossly out of alignment. Meaning that you're gonna need a ton of windage on the rear sight to get a zero......or (in really bad cases) that you can't get a zero at all.

    On my last build (using a BCM blem upper) I only had to move the Magpul MBUS gen2 rear sight 4 clicks off of the mechanical setting from the factory to get a 50m/200m zero using my Rainer Arms 18" Mountain series barrel. I like that I'm operating close to mechanical zero, though that has little bearing after the gun is zero'd. Much like a handgun with the rear sight drifted all the way to one edge of the slide....it may be ugly (and triggers my OCD like a mother), but as long as you have a zero, it's just as effective.

    I have found that BCMs have been more consistent in this dimension than any other brand aside from Colt (which means, when I use the tool, it takes the anodizing off in a near even fashion around the entire circumference of the upper receiver face). The above stated improvements can only help to further enhance this quality.

    My worst receiver was a DPMS. Looked like a half moon. I was removing my buddy's FSB and going with a FF troy rail and troy GB. He nearly used all the windage on his troy rear sight...until I disassembled and lapped the receiver. He only needed 3 clicks off mechanical center after that (an enormous improvement) to achieve the same zero.
    Last edited by BufordTJustice; 02-01-14 at 21:09.
    "That thing looks about as enjoyable as a bowl of exploding dicks." - Magic_Salad0892

    "The body cannot go where the mind has not already been."

  5. #35
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    Personally, I think that BCM is moving to the forefront of quality and availability in this industry in the civilian market. They are not reinventing the wheel. They are simply listening to their customer base, and taking an active interest in quality assurance. Even though their customer service is handled superbly, they are taking steps to lessen the need for customers to need it. Many companies out there want to be the best or think that they are the best. How many are actually listening to their customers and taking action and making decisions to prove it?

    I am anxiously awaiting their delivery. Good for BCM and us.

  6. #36
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    I am really impressed with BCM's products, and the Milwaukee PD incident (https://www.m4carbine.net/showthread...PD-to-stuff-it) confirmed that Paul was NOT all about the bottom line. I will continue to support BCM!
    Thanks for the rifle Grant, it's been great!

  7. #37
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    Will these be on all new BCM rifles/ uppers?

  8. #38
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    Evidently so (ETA: Grant says so on page 1).
    Last edited by evi1joe; 02-02-14 at 01:10.

  9. #39
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    Quote Originally Posted by evi1joe View Post
    Evidently so (ETA: Grant says so on page 1).
    Definitely don't see that stated anywhere.

    He only mentions "limited distribution" ...

  10. #40
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    Looks like they are already using these on new uppers. I purchased this new 20" upper receiver assembly a week or so ago from BCM, and it is marked BCM4:



    “Live free or die; death is not the worst of evils.”
    - General John Stark, July 31, 1809

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