AR Sponsor
Posted: 11/13/2006 11:18:28 AM EDT
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I'm not talking about a lighter Match or 2-Stage trigger, but I've repeatedly heard that some AR manufacturers have "tighter tolerances" between their Upper & Lower Recveiver & how this helps make a weapon more accurate. I am no gunsmith, but I've built half a dozen AR's for myself & friends. The extent of my building experience has been buying a stripped lower & putting the parts together from different manufacturers in hopes of building a decent AR (LMT SOPMOD Stock, LMT Upper, KAC, Magpul PRS, Ergo Grip, etc...). From my understanding of the basic mechanics of the weapon operation, I would think that the accuracy of the weapon would depend just on the barrel, & matching bolt. I don't understand how having a tighter lower receiver will affect the accuracy. Products like the AccuWedge claims to do just this. Basically the way I see it, the only part of the lower receiver that affects the initial discharge of the weapon is the hammer as it hits the firing pin & the round goes boom. This is probably a dumb question, but can someone help me out & educate me? Thanks! 
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it doesn't. it CAN on a weapon where the rear sight is mounted to the lower and the front sight is mounted to the barrel/upper (think FAL). in that instance, the "play" between receivers can change the position of the sights relative to eachother. in an AR platform though, all sighting equipment is mounted to the upper. |
| I guess a lot of people believe the play in the assembly of the two receivers affects accuracy. I believe this has been disproven in the case of the average play which is not significant, because the bullet is long gone before the gun recoils. After all, the sights are on the upper half. It's similar to the slide play on a 1911 pistol in that the barrel and sights are part of the upper half, so the average slide play does not adversely affect accuracy. Barrel lock-up and bushing tolerance are much more important on the pistol. If the upper in either case is so loose that a consistent sight picture is not possible, then you would have a problem, but this is rarely seen. If it bothers you, use an Accu-Wedge which does work as-advertised to tighten up the fit to rock-solid. I've had good luck in trying different uppers on a lower to get a better match, and I suppose some fitting is possible. I know manufacturers do this to satisfy the perception of 'quality', because most of us will grab the rifle and check the play the first thing when we pick it up. A well-fitted AR assembly is nice and certainly doesn't hurt a thing, but unless it seems about to fall off the rifle it probably is a non-issue. I'm sure there are other opinions, and I'm always open to learn something I hadn't considered. |
Thanks for the help. I'm a military guy so how it feels doesn't matter as much as compared to how it performs. My previous builds have me M4 type AR's. My next project is a precision SPR so I was just making sure that my old Bushy lower would be fine for the project.
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| It doesnt in no way,accuwedges are a waste of money and on 1911s the most important thing is barrel to bushing fit and barrel hood to breach face for accuracy.On ARs its all in the upper..the only thing for a lower as far as fit is properly machined for weapon function with the upper.On ARs its proper head space and bolt to barrel and extension lock up. |
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At best an accu wedge will upgrade a rattley feeling loose fit to a rubbery feeling loose fit. They are a complete and total waste of money. If you really want a tight fit, get an offset pin such as the one made by JP or shim the upper and lower receivers. Personally I like a solid feeling rifle, especially when using a sling or bi-pod. It probably has little physical effect on accuracy, but I think it improves your ability to make very small adjustments to the sight picture as you are moving the rifle, not taking up slop and then moving the rifle. |
i'm no bolt-gun guy, but doesn't glass bedding typically run underneath the barrel too? if that is the case, it probably changes the harmonics more then anything else. if is just where the receiver mounts, then i would guess it is more for "repeatability". wood probably creeps quite a bit due to a million different factors like heat, moisture, use/impact, etc. |
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Although I agree accuwedges do nothing for accuracy, they do eliminate receiver play. I've run with and without them, and I prefer without just for the ease of dissassembly. It's funny how many people will tell you what a waste of money the accuwedge is. But if you see a pic of most guns on this sight, there's a shit load more money being wasted on much dumber shit. 
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Nope, they buy the lowers & I put everything else together for them. I don't sell it to them. I just suggest parts from different manufacturers, they buy them & I put it together for them. |
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Glass bedding isolates the barrel from the stock by creating a perfect match between the receiver* and the stock (e.g. barrel does not touch and receiver is perfectly fitted to the stock). With this perfect fit, there is a strong enough coupling between the receiver and the stock for the combination to act as a single unit. In the AR system, the barrel is torqued onto the upper, and when free floated is free to do its thing (just like a glass bedded bolt gun). |
Basically because a bolt gun has a 1 piece stock that the receiver is bolted too. An AR receiver is kinda of floated on the takedown pins. I've seen USAMTU M16s with glass bedded pads in the pin areas. They don't shoot any better than not having them IMO. They just give the shooter more confidence, because his upper isn't wiggly anymore. Also An AR bolt doesn't lock into the receiver like a bolt-gun. It locks into the barrel extension. I think the new low-buck special bolt-gun from Remington actually apes an AR in this regard. At least 90% of the accuracy potential of an AR is in the barrel. You can sometimes gain a little by truing the receiver at the barrel junction, depending on how true it is from the factory. There may be a very small amount to be gained by the fit of the barrel extension into the upper also. M9 |
Though some very light barrels are bedded as you describe, its not typical. Some light barrels are bedded in the receiver area & the barrel floated except for the forend tip, some light barrels shoot better with a pressure pad in this area. On a HB target or varmint rifle though, its typical for the receiver & 2 or 3 inches of barrel in the chamber area to be bedded. A relativley new twist is to install a bedding block around the barrel just in front of the receiver & bed it into the stock & then float the rest of the barrel & the receiver. Finnish sniper rifles based on the old Mosin-Nagant have used this method succesfully for years. M9 |
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There is no accuracy benefit to a tight upper and lower receiver fit. None, zip, zero, NONE! Accuracy & precision are mechanically achieved by the line of sight being as close possible in relation as much as possible to the line of the bore (excluding ammunition, etc.). Therefore, if the sights are mounted to the barrel (which in an AR they effectively are) their relationship is going to be the same every time the rifle is taken apart. If the sights were mounted to the lower receiver (like you see with crappy scope kits for rifles like the SKS and on shotgun receivers and not on the barrel) you'll find you will need to re-zero every time. Glass bedding of a bolt rifle stock is basically pouring in cement (for lack of a better term) and filling in all the places where an action might be able to wiggle. The action is laid in with a seperating compound so that the "cement" can form around it. When hardened, the barreled action is removed and final fitting is done to relieve the bedding from the barrel. You want NOTHING to touch that barrel. Since the stock bolts to the action and not the receiver, there's NO need to contact the barrel at all (see AICS and McMillan stocks, e.g.). The only "modification" to the receiver fit that is done by accuracy shooters (AMU for Hi-power, e.g.) is to put basically plumbers putty between the two receivers. Is this for accuracy improvement. No. It's mostly for piece of mind that everything is going in the same place. Same for the Accu-Wedge. I use them. Not because it imporves accuracy. It just makes everything feel better...to me and maybe to you. Any performance gain? None mechanically. Rich |
+1 it doesn't unless it's a Full Auto lower 
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If your lower/upper receiver holes are so warped to where it would 'cause a "cant" then either those receivers are beat (and I really don't know how since they're non-wear areas) or you got sold a bill of goods. Rich |
| And sight picture is the same every time, because its all on the same piece of the weapon, the upper. Now, if you fitted the thing to some kind of ransom rest and the upper to lower fit was really sloppy, maybe there would be some inconsistancy, but for a rifle being sighted and fired by a human with functioning eyes, who will shoot to the same sight picture every time, it won't make a damn bit of difference. |
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