First Look at BCM's NEW M4 Upper Receiver

[Eurodriver]

Are the feed ramps different on these? I swear they looked a little "improved", for lack of a better term. (And I actually mean the word improved in a positive sense)

Also, what's the deal with "M4" and "BCM4" on the front of the receivers? Are they the same, or not? What do the different markings suggest?

[C4IGrant]

Are the feed ramps different on these? I swear they looked a little "improved", for lack of a better term. (And I actually mean the word improved in a positive sense)

Also, what's the deal with "M4" and "BCM4" on the front of the receivers? Are they the same, or not? What do the different markings suggest?

My understanding is that the ones stamped "M4" above the GT are not made or controlled by BCM. The BCM4 stamped receivers are made by BCM and are sold stripped to the consumer (and what we stock). The receivers that have the white BCM logo on the side are made by BCM and used when BCM builds an upper or rifle. The BCM uppers that are stamped "BCM4" and the ones with the logo are the same.



C4

[wake.joe]

Then you should know what tolerance stacking is.

Go use it some and it will feel smooth in no time.

Sent from my Nexus 7 using Tapatalk

Why bother, if a different upper works right away?

Are we accepting "break in periods" now?

I'm sure the upper will work fine on another gun. It just happened to not work well on my new manufacture noveske lower. Sorry to diss your brand, bro.

Sent from my SGH-M919 using Tapatalk

[Obscenejesster]

Why bother, if a different upper works right away?

Are we accepting "break in periods" now?

I'm sure the upper will work fine on another gun. It just happened to not work well on my new manufacture noveske lower. Sorry to diss your brand, bro.

Sent from my SGH-M919 using Tapatalk

Why not try another charging handle?

I've always excepted break in periods with certain things. I like when everything is nice and tight in the beginning.

I know BCM uses a dry lube coating in their upper receivers and this wears away after a few cycles. The coating might be what's causing it to be tight.

Sent from my SM-G900T using Tapatalk

[luckydube56]

I bought a 13.7 parallax tactical barrel some time ago which i had planned on using in conjunction with a KX3. I never did pick up a KX3 and since i have this barrel laying around i decided to finally mount on one of the BCM stripped uppers.

Holy sh*t. It took a rubber mallet and piece of 2x4 and about 30 minutes of pounding to get it to fit. I tried stripping the coating off the barrel extension and freezing the barrel to get it to shrink. It did not help. It fits very very tight. So tight I thought the barrel extension might expand the dimensions of the receiver extension. So I test fitted a barrel nut on it and it went on smooth as butter.

In the process of hammering in the barrel (more accurately I hammered the receiver onto the barrel), the receiver kept rotating slightly to where the pin would not align with the notch so I kept having to back it out which accounts for why it took 30 minutes of pounding. Each time i backed it out, I observed the inner diameter of the receiver extension. I saw no marring or misshaping on the inner surface and it remained smooth with no obstruction. Even the internal coating remained unmarred. Strange huh? The barrel looks straight as far as my eyes can tell. I will probably never be able to remove the barrel. I feel like it would not come out if i tried to shoot it without a barrel nut.

I think between the tight tolerance of the BCM Upper and, perhaps, slightly out of spec PXT barrel (???), I might have experienced some tolerance stacking which caused the barrel to not fit. In any case, what was alarming at the outset for me is now kind of gratifying. I cant wait to complete it and test it.

[mtdawg169]

I bought a 13.7 parallax tactical barrel some time ago which i had planned on using in conjunction with a KX3. I never did pick up a KX3 and since i have this barrel laying around i decided to finally mount on one of the BCM stripped uppers.

Holy sh*t. It took a rubber mallet and piece of 2x4 and about 30 minutes of pounding to get it to fit. I tried stripping the coating off the barrel extension and freezing the barrel to get it to shrink. It did not help. It fits very very tight. So tight I thought the barrel extension might expand the dimensions of the receiver extension. So I test fitted a barrel nut on it and it went on smooth as butter.

In the process of hammering in the barrel (more accurately I hammered the receiver onto the barrel), the receiver kept rotating slightly to where the pin would not align with the notch so I kept having to back it out which accounts for why it took 30 minutes of pounding. Each time i backed it out, I observed the inner diameter of the receiver extension. I saw no marring or misshaping on the inner surface and it remained smooth with no obstruction. Even the internal coating remained unmarred. Strange huh? The barrel looks straight as far as my eyes can tell. I will probably never be able to remove the barrel. I feel like it would not come out if i tried to shoot it without a barrel nut.

I think between the tight tolerance of the BCM Upper and, perhaps, slightly out of spec PXT barrel (???), I might have experienced some tolerance stacking which caused the barrel to not fit. In any case, what was alarming at the outset for me is now kind of gratifying. I cant wait to complete it and test it.

As Iraqgunz tells every student that goes through his armorers course, don't force anything. If it required that much work to install the barrel into the upper, something is not right. Too late now, but if I had been in your shoes, I would have stopped and taken measurements of the extension and the upper receiver to determine which part was out of spec. Then contact the appropriate party for replacement.

[VIP3R 237]

I bought a 13.7 parallax tactical barrel some time ago which i had planned on using in conjunction with a KX3. I never did pick up a KX3 and since i have this barrel laying around i decided to finally mount on one of the BCM stripped uppers.

Holy sh*t. It took a rubber mallet and piece of 2x4 and about 30 minutes of pounding to get it to fit. I tried stripping the coating off the barrel extension and freezing the barrel to get it to shrink. It did not help. It fits very very tight. So tight I thought the barrel extension might expand the dimensions of the receiver extension. So I test fitted a barrel nut on it and it went on smooth as butter.

In the process of hammering in the barrel (more accurately I hammered the receiver onto the barrel), the receiver kept rotating slightly to where the pin would not align with the notch so I kept having to back it out which accounts for why it took 30 minutes of pounding. Each time i backed it out, I observed the inner diameter of the receiver extension. I saw no marring or misshaping on the inner surface and it remained smooth with no obstruction. Even the internal coating remained unmarred. Strange huh? The barrel looks straight as far as my eyes can tell. I will probably never be able to remove the barrel. I feel like it would not come out if i tried to shoot it without a barrel nut.

I think between the tight tolerance of the BCM Upper and, perhaps, slightly out of spec PXT barrel (???), I might have experienced some tolerance stacking which caused the barrel to not fit. In any case, what was alarming at the outset for me is now kind of gratifying. I cant wait to complete it and test it.

I have also had problems with PXT barrels being extremely tight. My brother bought a complete upper which we then took apart and cerakoted. When we put it back together we had to freeze it and use a rubber mallet to get the barrel back in. And yet we taped the contact surfaces so no Cerakote was on the barrel extension or inside the upper. However it is a tack driver and consistently posts sub moa groups.

[dentron]

BCM upper and Parallax Tactical barrel, hmmm wonder what the problem was....

[C4IGrant]

BCM upper and Parallax Tactical barrel, hmmm wonder what the problem was....

I am sure it was BCM.



C4

[luckydube56]

I am sure it was BCM.



C4

I am under no illusion that it was BCM at fault. I've bought their products from them (and from you) including complete rifles, uppers, lowers and misc parts for my own builds. Never had problems with any of them.