"Accurizing the AR-15"

[Cool Breeze]

These are the ones I've been using:

BCM® M4 Flat Top Upper Receiver with cosmetic blemishes. Most have scratches or scuffs.

The upper comes unassembled, but complete with BCM forward assist assembly and ejection port cover door assembly.
You must assemble it. (Assembly required) (all parts, but you will have to assemble together)

THESE ARE USED/DEMO UPPER RECEIVER ASSEMBLIES. All will have several nicks, scratches, and marks on exterior finish. NO HANDPICKING.

This receiver has the M4 feedramps machined in. This is to be used with barrels that include the M4 barrel extension.

Built to the correct Mil-Specs.
(Inside Diameter for barrel extension slightly undersized for a tighter fit to the barrel and a more accurate rifle. Please use a heat gun or hair dryer to warm up threaded bore of receiver if barrel extension is too tight.)

I bought a Mk2 when they first came out, but didn't need to heat it either. Do they even make them anymore?

Great question - When I looked a bit ago, I didn't see them on their site as being sold separately but that was just a cursory glance.

[mmc45414]

Crap!!!!
People must have been reading this thread...

[DDTSGM]

These are the ones I've been using:

BCM® M4 Flat Top Upper Receiver with cosmetic blemishes. Most have scratches or scuffs.

The upper comes unassembled, but complete with BCM forward assist assembly and ejection port cover door assembly.
You must assemble it. (Assembly required) (all parts, but you will have to assemble together)

THESE ARE USED/DEMO UPPER RECEIVER ASSEMBLIES. All will have several nicks, scratches, and marks on exterior finish. NO HANDPICKING.

This receiver has the M4 feedramps machined in. This is to be used with barrels that include the M4 barrel extension.

Built to the correct Mil-Specs.
(Inside Diameter for barrel extension slightly undersized for a tighter fit to the barrel and a more accurate rifle. Please use a heat gun or hair dryer to warm up threaded bore of receiver if barrel extension is too tight.)

I bought a Mk2 when they first came out, but didn't need to heat it either. Do they even make them anymore?

Great question - When I looked a bit ago, I didn't see them on their site as being sold separately but that was just a cursory glance.

I missed the edit window on my post.

I recently bought a couple more blem uppers because I only had one left. I hadn't opened the box yet and just did so. Both uppers had a slip of paper in them explaining how to thermal fit the barrel extension. That was a first, never received those in an upper before.

If you look at the first picture where the upper contacts the lower by the receiver extension, the 'web' at the bottom looks thicker than the web at the bottom of the second picture. Maybe it's just because it's joined to a lower, IDK. No big deal, just looked unusual.

[bfoosh006]

Great shooting!

Sometimes... I can getter done, Lol

[bfoosh006]

The lapping (via the brownells tool method is the one I'm most skeptical about for the reasons you mentioned as well as me wondering if a $30 tool is really "more square/precise" than what is done by the machining of a good quality upper. If done on a lathe, that might be a different story.

FWIW... I suspect the Anodizing is the part that isn't even... not the CNC machine work.

I spoke to guys that anodize for a living and they said anodizing can easily be applied un evenly... ( IE thicker or thinner, and even dependent on the positioning in the tank )

As for the precision of the lapping tools, and I don't know if I mentioned it before, this video shows a Wheeler tool being used... My wheeler tool is crap. A VERY sloppy fit. I actually now use it to lap the insides of buffer tubes smooth.

FWIW..I also don't like to use a vice to hold the upper. I prefer to hand hold the upper, vertically with the drill and lapping tool on the bottom.

I watched a major manufacturer's worker lapping a upper, with it in a vise... and man, he was lapping like he was putting lug nuts on a semi, fully pounding the lug nuts home, with a air impact gun. Lol, not sure I will ever forget that.

My OCD makes me think a vise "could" produce unwanted binding, or maybe better said unnoticed binding.

And...the shank on a good fitting tool will burnish smooth the uppers "raceway" the BCG rides in. DO NOT USE Lapping compound inside the lower, oil will be fine.


I DON"T use the Wheeler Tool... it just seems very poorly sized. Watch this video.




A good video...Criterion's Video 3 showing the lapping with a Brownells tool... about the 55 second mark.

[TWR]

The other thing that makes me see snake oil is the fact that the bolt locks up in the barrel extension. There’s plenty of room between the bolt and the carrier and lots of room between the carrier and the upper that “trueing” the face of the upper can’t make any difference like lapping the bolt of a bolt action gun.

[stomridertx]

The other thing that makes me see snake oil is the fact that the bolt locks up in the barrel extension. There’s plenty of room between the bolt and the carrier and lots of room between the carrier and the upper that “trueing” the face of the upper can’t make any difference like lapping the bolt of a bolt action gun.

We don't have to be suspicious of this, it's a proven process vetted by Brownells selling all the lapping tools they make. I've seen the change in windage adjustment of a rear sight with my own eyes on more than one gun. If you are skeptical that lapping increases accuracy, you are right in that it doesn't. It just evens out the anodizing on the receiver face so the barrel sticks out of the receiver in a straight line. If the barrel is almost perfectly in line with the pic rail, then the windage adjustment of the sighting system will be more about the ammo used than mechanical alignment.