Lapping receiver

I am thinking about lapping a receiver on an AR that I put together a while back. I pulled the barrel on my stag model 3 and replaced it with a Green mtn 20" stainless barrel. I also replaced the handguard with a free floating rifle length handguard. My accuracy didn't really improve after the swap. With the 16" barrel I was getting 1 1/2" 5 shot groups with handloads at 100 yds. With the new barrel I am getting 1 1/4" 5 shot groups after testing many different powders, seating depths, bullets, etc. I have even tried different scopes and rings just to rule that out for my accuracy problem. My next question is could it be that my receiver isn't perfectly square? And could this be causing my issues? I haven't had this problem with any of my AR's so I'm left scratching my head.
 
I agree with Eugene, I can shoot a really nice 3 shot group. I will screw up a 5 shot group every time.
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I am not one to be happy with good 3 shot groups. I have built a few AR's and all have ended up shooting under 1 inch, 5 shot groups with handloads. One of them will post 1/2"-5/8" 5 shot groups consistently. I also have several bolt guns that I can consistently put 5 shots under a quarter at 100. I do not claim to be an expert marksman but with a solid bench and a good rest I can do much better than what this rifle has shown me. Like I mentioned in my original post this is a 20" Green Mountain Stainless Fluted barrel. The reviews on the barrel have been a lot different than what I am seeing but I understand that all barrels are not the same. I was happy to see the 1/4" improvement, but I figured that the improvement would be greater when going from the government profile 16" chrome-lined barrel to a heavier and longer stainless barrel. And the trigger on this rifle is a Geissele SSA-E trigger which is pretty sweet. Even if I measure my best 3 out of 5 they are still not that great of a group.

Thanks for the responses so far.
 
I hate to tell ya to start all over, but, buy you a New Daniel Defense Barrel (Most under $275 on GunBroker) and your 5 shot groups will be 1/2 the size of the groups you mentioned above.
I have three, 2-16" pencil barrels and 1- 18" barrel each shoot 1/2" to 5/8" groups with very little load development.
 
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I ordered a BHW 20 practical barrel a few weeks ago to replace the GM barrel. I was just wanting to try to find anything else that I could do in the mean time to salvage the GM barrel.
 
When I hear someone complain about AR accuracy I think a couple of things in addition to the old solid rest and shooting position details. First is whether it has a quality barrel and free floated hand guard. You sound like your are good on both accounts. My second is the trigger. A bad trigger can turn a sub MOA gun into a 2" real fast.
Sorry, just saw your post about trigger. You have that covered too.
 
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Just happened to think about primers. I have always had pretty good results with regular WSR primers but I was wondering if perhaps some other sort/brand of primer might help my groups. Would it be worth a shot to try maybe Rem 7.5's or maybe some benchrest primers? What do you guys like to use?
 
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I picked up 100 Rem 7 1/2 primers today and loaded up 4 rounds with varget and 69 gr SMK's. I wanted to load 5 but I only had 4 pieces of brass left that were already sized and primed. Ended up getting a 4 shot 3/4" group at 100 yds.



Hopefully with a little tweaking it will continue to get better.

Thanks for everyone's responses and recommendations!
 
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lapping the receiver i dont think does anything for groups. It does square the barrel and gets the bore line central to the axis. Accuracy nothing from what i can tell.
 
ICU22-250 I have loaded 50 gr nosler bt's, Hornady 55 gr sp's, Sierra 69 gr MK. I have tried benchmark and varget powder so far but I'm hoping to find some IMR 8208 XBR soon. I have decided not to worry about lapping the receiver. I'm just going to keep trying different loads until I find something that it likes.
 
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