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+--- Thread: Beating a dead horse - To Lap or not to lap (/showthread.php?tid=21334)
Beating a dead horse - To Lap or not to lap - boombatz - 05-28-2020
Hey everyone,
I know this question has been visited countless time but I was hoping for some feedback on my build particulars. I typically lap my upper receivers just out of habit, but with my 6.5 grendel build I am trying to really do all I can to pull some accuracy out of it. I have chosen to use a BCM upper as the inside diameter of the area the barrel extension sits in is machined tighter and requires heat to mate. My limited understanding is removing slop in this area leads to the most accuracy gain. Would it still be recommended to lap the receiver face? I have been reading posts and the general consensus seems to be that it only really helps if you have excessive windage/elevation to bore issues. Also - would you recommend using locktight in addition to the heat fit (I wonder if thats excessive).
Thanks in advance all
Beating a dead horse - To Lap or not to lap - Klem - 05-28-2020
Boom,
If you really want to 'pull some accuracy' then the quality of the barrel is where it is at, and the receiver join is just icing on the cake.
I can only imagine gluing the interface on a thermal fit will be a messy effort that you will have to clean up. Surely the tight fit will just displace all the glue back out. Glue is for filling the void in a sloppy fit with something that cures hard and provides support - that is the theory anyway.
If you have the lapping tool why not. It will give peace of mind and wont hurt.
Beating a dead horse - To Lap or not to lap - A5BLASTER - 05-29-2020
Having lapped several uppers. My thoughts is it does less for accuracy then beloved but it does loads for bolt life.
No need to glue the barrel if your upper is machined for a heat and shrink fit up.
Beating a dead horse - To Lap or not to lap - grayfox - 05-29-2020
^^What Klem said.
The bullet may be what translates your intentions to the target
But the barrel is what translates your intentions to the bullet in the first place.
Beating a dead horse - To Lap or not to lap - Klem - 05-29-2020
A5BLASTER Wrote:Having lapped several uppers. My thoughts is it does less for accuracy then beloved but it does loads for bolt life..
Good point A5, squaring the bolt to the extension makes perfect sense.
Beating a dead horse - To Lap or not to lap - boombatz - 05-29-2020
Thank you all for the wisdom! Certainly makes sense that if the lugs are engaging more uniformly it would reduce wear.
Just finished lapping the upper and getting to building it, appreciate you all!
Beating a dead horse - To Lap or not to lap - Mad Charlie - 05-29-2020
Not having been fortunate enough, thus far, to have found a barrel extension/receiver combo that requires a heating/freezing process to fit up, I have bedded and lapped every build. All four of the different receivers that I have required lapping to square them up, some more than others. It is not hard to do, nor does it take much time. I seriously doubt that it will hurt accuracy, and why "leave it on the table". I didn't do it to the first build but when I went back and rebuilt it I found that my groups were more consistently round and a bit smaller, fewer fliers.
Beating a dead horse - To Lap or not to lap - FLshooter - 05-30-2020
Ive installed many barrels without squaring the reciever face. Once I discovered and purchased a lapping tool,I started lapping all my uppers. and I continue to do so,because it makes sense.But have I ever noticed a difference in accuracy?I would have to say no.
As far as bedding with Loctite, I dont do it on my AR uppers. But, I have watched others do it and I have installed barrels for friends using Loctite.The reason I have never bedded my own AR uppers is because Ive never seen any proof that it actually helps with accuracy.
Beating a dead horse - To Lap or not to lap - Allen Roberts - 05-30-2020
I really enjoy all the comments. The more the better. I hope to add some appreciable notes to my quest for accuracy soon. One lesson has drilled into me. Ammo, ammo, ammo. You will struggle forever trying to group without the right ammo that matchs the barrel.
Beating a dead horse - To Lap or not to lap - boombatz - 05-30-2020
Thanks everyone for the feedback! As Klem and A5blaster predicted, there was no need to loctite with a thermal fit. In all truth it most likely would not have been possible. I used a hair dryer to heat the BCM upper extension and froze the Wilson Combat Recon Tactical for approx 30 minutes. I still faced plenty of resistance approximately half way into the receiver and needed to put some mallet work in (back of receiver not on crown):eek:. I've heard of folks baking these BCM uppers @ 350 for 10 minutes or so, but I didn't feel comfortable heating the entire receiver up.
Beating a dead horse - To Lap or not to lap - brian y - 05-31-2020
With every BCM upper I have used a heat gun and just heat it for about 5 min and the barrel will slide right in. As for lapping I check all my builds now and find some uppers need it some do not, BCM is usually pretty good but I do check them all. As for glue no need. Good luck with your build.
Beating a dead horse - To Lap or not to lap - plt228 - 06-07-2020
I picked up a Bernzomatic torch from Home Depot to use for the thermal fits. Took 5-7 rotations of the upper and the barrel slipped in. Didnt even have to put anything in a vise. Here is a video from JP rifles on how to do it.
https://youtu.be/-cOlNGxUhsk