01-20-2018, 06:24 PM
My experiences in this with some different uppers.
Three receivers: BCA Side charge, PSA, BCM, FDE Aero M4E1 threaded ( did not square, posted for reference)
BCA Side charger: Acquired as set with BCG and CH, Black anodized. This upper is why I started gathering the tools and information to do this in the first place...
No pics
Geissele reaction rod was rather loose, upper could wiggle rather easily on the rod. Nothing about the finish at the face of the receiver was impressive, there were rather pronounced rough spots on the face, heavier on one side than the other. Necessity for squaring the upper was obvious. Note: This upper was bought on sale at over 50% off from someone other than BCA, it could have been a blem, though I was not told if that was the case.
Lapping done by me by hand no vise - using tool aquired from machinist friend making a rather simple turned down piece of bar stock intended to square the face of the receiver with the bore of the BCG tunnel. Used course cutting compound paste, followed by red polishing compound. Removed only enough material to enable barrel extension to make solid contact with face all the way around the receiver. There was much more material removed from one side than the other. The receiver was assembled, and was precise shooting. Accuracy was good. Function was good. Thirty minutes by hand. I would only do one of these again only if they were very innexpensive, and expecting to need to put some effort into the finish.
PSA M4: Black anodized, Acquired as individual (assembled) part.
No pics
Reaction rod was a slightly better fit inside the tunnel of the PSA, finish on face was flatter than the BCA.
Same method as above, much less time and effort required to make solid ring of contact on the face of this receiver. Was apparently of higher finish quality than the BCA was. The walls of the upper appeared thinner than the BCA. The upper seemed thinly annodized. After assembly, upper performs well, and is precise. Solid upper. Fifteen minutes by hand. I would buy for a budget build without worry.
BCM M4: Came on assembled 16" RECCE from Brownells, black anodized
No pics
Reaction rod was tight fitting, precise to the inside diameter of this upper. Face appeared to have been ground prior to anodizing. Very fine threads all the way to the face of receiver. Only reason to attempt was to compare to the above two - hey, I already did them, lets see what this one looks like. Squaring wasn't necessary.
Easiest upper of the three to square, took one mandrel turning session to remove anodized finish in an even ring around the receiver face. I doubt I changed the square condition of the receiver face at all. It is possible that this step is done by BCM prior to anodizing, perhaps this is an in house step? The finish was definately thicker than the PSA upper, also than the BCA. I wouldn't hesitate to spend the cost on this upper again. Definitely get what you pay for. Functions as expected of quality parts. Five minutes by hand. Extension to upper is very tight. I prefer this upper.
Aero M4E1 Cerakote FDE: Acquired as single stripped part to build pistol upper; Was purchased as a blem.
No pics
Reaction rod was so tight it took lube to completely pass through. Cerakote was very thick, and receiver face was as the BCM above. I learned the lesson this time and did not square the face, as it was apparent it had been done prior to finishing. I did use some compound on the RR and turned until it was a close fit when clean. 5 minutes by hand. Impressive fit between the extension and upper, no need to bed barrel. I couldn't pull the barrel out by hand after I got it into the upper, it was left together and torqued to spec. Especially considering this was a blemished piece, I would buy one of these uppers again.
Three receivers: BCA Side charge, PSA, BCM, FDE Aero M4E1 threaded ( did not square, posted for reference)
BCA Side charger: Acquired as set with BCG and CH, Black anodized. This upper is why I started gathering the tools and information to do this in the first place...
No pics
Geissele reaction rod was rather loose, upper could wiggle rather easily on the rod. Nothing about the finish at the face of the receiver was impressive, there were rather pronounced rough spots on the face, heavier on one side than the other. Necessity for squaring the upper was obvious. Note: This upper was bought on sale at over 50% off from someone other than BCA, it could have been a blem, though I was not told if that was the case.
Lapping done by me by hand no vise - using tool aquired from machinist friend making a rather simple turned down piece of bar stock intended to square the face of the receiver with the bore of the BCG tunnel. Used course cutting compound paste, followed by red polishing compound. Removed only enough material to enable barrel extension to make solid contact with face all the way around the receiver. There was much more material removed from one side than the other. The receiver was assembled, and was precise shooting. Accuracy was good. Function was good. Thirty minutes by hand. I would only do one of these again only if they were very innexpensive, and expecting to need to put some effort into the finish.
PSA M4: Black anodized, Acquired as individual (assembled) part.
No pics
Reaction rod was a slightly better fit inside the tunnel of the PSA, finish on face was flatter than the BCA.
Same method as above, much less time and effort required to make solid ring of contact on the face of this receiver. Was apparently of higher finish quality than the BCA was. The walls of the upper appeared thinner than the BCA. The upper seemed thinly annodized. After assembly, upper performs well, and is precise. Solid upper. Fifteen minutes by hand. I would buy for a budget build without worry.
BCM M4: Came on assembled 16" RECCE from Brownells, black anodized
No pics
Reaction rod was tight fitting, precise to the inside diameter of this upper. Face appeared to have been ground prior to anodizing. Very fine threads all the way to the face of receiver. Only reason to attempt was to compare to the above two - hey, I already did them, lets see what this one looks like. Squaring wasn't necessary.
Easiest upper of the three to square, took one mandrel turning session to remove anodized finish in an even ring around the receiver face. I doubt I changed the square condition of the receiver face at all. It is possible that this step is done by BCM prior to anodizing, perhaps this is an in house step? The finish was definately thicker than the PSA upper, also than the BCA. I wouldn't hesitate to spend the cost on this upper again. Definitely get what you pay for. Functions as expected of quality parts. Five minutes by hand. Extension to upper is very tight. I prefer this upper.
Aero M4E1 Cerakote FDE: Acquired as single stripped part to build pistol upper; Was purchased as a blem.
No pics
Reaction rod was so tight it took lube to completely pass through. Cerakote was very thick, and receiver face was as the BCM above. I learned the lesson this time and did not square the face, as it was apparent it had been done prior to finishing. I did use some compound on the RR and turned until it was a close fit when clean. 5 minutes by hand. Impressive fit between the extension and upper, no need to bed barrel. I couldn't pull the barrel out by hand after I got it into the upper, it was left together and torqued to spec. Especially considering this was a blemished piece, I would buy one of these uppers again.