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Posted: 1/5/2013 7:10:47 AM EDT
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I'm building an upper with accuracy in mind. I know the barrel is important, and have one on order, but I was wondering about the upper receiver. Is there an advantage to getting a billet or specific upper, or would a normal forged upper receiver be just fine?
It might be a dumb question as most rifles come with a forged receiver, but I figured I'd ask since I have all the time in the world with the current frenzy. |
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There is no difference in accuracy potential. However, some forged receivers have been known to have a face that isn't exactly perpendicular to the upper, which can cause the barrel to have a slight cant. It is uncommon, and also usually so slight it doesn't affect much. However, if you want to eliminate this, Brownells sells a tool: http://www.brownells.com/gunsmith-tools-supplies/rifle-tools/receiver-tools/ar-15-m16-upper-receiver-lapping-tool-prod20220.aspx A billet upper, because of the way they are machined, will be less likely to have this problem.
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If you're that worried, you could always go for the Rainer Arms UltraMatch Upper Reciever.
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Some say it's cutting teeth but it is interesting reading the info on the Rainer Ultra Match Billet Upper.
Copied and pasted-- The most critical features are: Parallelism between the picatinny rail, main center bore and the centerline of the mounting lugs Perpendicularity between the centerline of the lugs and the barrel mating face (at the front of the threads) Flatness of the barrel mating face We are holding .0003 or better on all of those measurements. Competitor uppers are between .001 and .003 on the perpendicularity and parallelism. On paper looking at those tolerances it is a huge difference but I'm a machinist. In theory a more rigid receiver should be more accurate. |
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Think of an upper receiver as a scope mount to the barrel being stressed by a stock. The more rigid you can get it the more accurate you will be. I have a VLTOR an know without a doubt it is stiffer than a standard mil spec. A monolithic would also help. A one piece scope mount attached over the barrel nut will also stiffen up things. Structurally, upper receivers are a mess compared to most scope mounts and bolt guns.
Remember the original receiver was designed with a handle and iron sights. |
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Quoted: Think of an upper receiver as a scope mount to the barrel being stressed by a stock. The more rigid you can get it the more accurate you will be. I have a VLTOR an know without a doubt it is stiffer than a standard mil spec. A monolithic would also help. A one piece scope mount attached over the barrel nut will also stiffen up things. Please support this statement with data, as I would like to see how stiffness is measured. |
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Quoted:
Some say it's cutting teeth but it is interesting reading the info on the Rainer Ultra Match Billet Upper. Copied and pasted-- The most critical features are: Parallelism between the picatinny rail, main center bore and the centerline of the mounting lugs Perpendicularity between the centerline of the lugs and the barrel mating face (at the front of the threads) Flatness of the barrel mating face We are holding .0003 or better on all of those measurements. Competitor uppers are between .001 and .003 on the perpendicularity and parallelism. On paper looking at those tolerances it is a huge difference but I'm a machinist. In theory a more rigid receiver should be more accurate. to me those specs make me think you might have fewer adjustments to zero an optic, but nothing on accuracy. |
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I added some more to my earlier post.
I have not done any formal testing of stiffness on an upper. Only my opinion based on accuracy change before and after. Having an engineering background and working with multiple mechanical assemblies and firearms also form my opinion. Tests can be conducted in so many ways and variables that you can bias the outcome. Unless one fully understands the test it is no more valuable than an opinion. |
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Quoted:
Quoted:
Think of an upper receiver as a scope mount to the barrel being stressed by a stock. The more rigid you can get it the more accurate you will be. I have a VLTOR an know without a doubt it is stiffer than a standard mil spec. A monolithic would also help. A one piece scope mount attached over the barrel nut will also stiffen up things. Please support this statement with data, as I would like to see how stiffness is measured. He isn't going to find much data to back up his statement. I have built, helped build(design), and shoot comp/precision ar's. I can say without a shadow of a doubt that you take a forged and billet upper (that is in spec)and put the same bolt and same barrel into them, there will be absolutely no appreciable difference. I have tried about every conceivable combination of bolt, barrel, upper, FF tube you can image, trying to achieve the best combination. This is what I do and with the ar, I never really got into the CQB tactical side even thought it is fun. If you want to start comparing data to back up your statement we can start comparing because god knows I have enough to overwhelm myself with useless info. |
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On a bench with minimal external loads on the rifle, I am not surprised you found little difference. The rigidity helps minimize external loads from changing optic to barrel relationship.
Just to be clear I am not trying to compare forge vs billet vs non spec vs spec. I am saying a rigid receiver is a more accurate receiver. This is simple as comparing free float to conventional hand guards with side or sling loading. Receivers can flex as well. |
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Quoted:
On a bench with minimal external loads on the rifle, I am not surprised you found little difference. The rigidity helps minimize external loads from changing optic to barrel relationship. Just to be clear I am not trying to compare forge vs billet vs non spec vs spec. I am saying a rigid receiver is a more accurate receiver. This is simple as comparing free float to conventional hand guards with side or sling loading. Receivers can flex as well. and whats your vltor made out of? |
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If your theory of a more rigid receiver maintaining accuracy is false then why do people bother adding high end optic mounts that are more rigid than cheap economy ones. How does this not apply to the part that the optic mount is attached to.
The upper receiver plays a critical roll in attaching your barrel to your optic mount and finally the optic. This is also why they make one piece optic mounts to stiffen the overall assembly. This is also why you wouldn't mount your optic on a hand rail that could flex. If your idea that the bolt or carrier holds the receiver true then one could use a plastic upper and lower and expect the same accuracy. If anyone has some logic behind how it does not matter, I am all ears but a simple no it doesn't matter proves nothing. |
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