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Posted: 5/8/2008 2:54:31 PM EDT
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OK, I've searched and read and I haven't seen a single build (besides mine) where anybody did anything beyond slapping some parts together and calling it a rifle. So, for the experts out there, what do you do besides starting with quality parts, to squeeze the last iota of accuracy out of your rifle? (I'm just asking about the rifle here, the ammo is a whole nother subject) When I put mine together I lapped the face of the upper receiver to achieve 90% contact with the shoulder of the barrel extension, but that was about all I could find to really do to it accuracy wise. What else can I do to make it better? What does it actually mean when a manufacturer sells a "fitted" bolt with their barrel? Do they just grab a bolt and a barrel and check to make sure the headspace is OK? Is that bolt lapped and adjusted for minimum headspace and a perfect engagement of all the lugs? Hopefully if we get enough info in this thread it'll become sticky worthy. As a build your rifle 201 "Advanced tweaks" sort of thing. |
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The most important accuracy work is done when the barrel is manufactured. So long as that is done properly everything else really is just picking the right parts and assmbling them correctly. As for a matched bolt, I don't see that is solves anything that isn't also solved by loading the ammo specifically to work best in that barrel. |
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To a certain extent yes. The barrel manufacturing tolerances and tailored handloads definitely are the most important factors. Also a good trigger. But in the world of precision bolt guns, a those items are just the start. Truing the bolt face, lapping the bolt lugs, and a myriad of other tweaks go into making a good gun into a tack driver. I'm trying to find out what can be done to turn a run of the mill .5MOA gun into a sub .25MOA gun. |
Find a semi auto that truly shoots .25MOA and we'll both ask the guy who made it. |
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I wasn't aware there was such a thing as a "tack driving" AR15. Only ones I have ever heard(never seen) of were bolt actions and single shots. When you say "tack driving" you are meaning caliber size hole @ 100yds 10 shot group, right? Even for a bolt action with experienced operator this would be a hard feat. |
I agree that this subject, while extremely interesting, might be a moot point with the AR platform. I suppose that if a consistant .5 MOA AR15 isn't good enough for you, than you need to switch up to a bolt action.  I've never heard of a .25 MOA AR15...but if someone here is cabable of building one, I would love to find out how it's done. Watching this thread with interest, although I don't know how much will come of it. |
| Bushflyr, I like you have squared the face of the upper receiver. But in hind sight, I quess when I got my barrel I should of checked into a matched bolt. The bolt, in my opinion, should be square to the bore and all lugs lapped to the extension and the chamber finish reamed (if this is feasible). The barrel I got is the Oly SUM. It's a 24" SS broach cut 4 land to AMU spec. Also the Y/M NM chrome BCG. It shoots sub MOA and has on occasion shot some .25" 5 shot groups @ 100yds. The other day I was able to place 5 shots into 1.1" and another 5 shots into 1" @ 200yds. It shoots good, but I wouldn't call it a tack driver. I just want more. |
Well I'll give Les a call and ask him. I'm sure he'll spill his trade secrets for the rest of us. Thats very impressive though. |
Yea he will, for about 2 grand 
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LOL yeah, Les is a wee bit pricey.  I guess we should ask Bush to clarify his stipulations a little. Should this .25 MOA AR-15 be chambered in .223/5.56mm, or do other chamberings count, like .204 mentioned above? Can this be a custom-made gun like a Les Baer, or were you talking more along the lines of things that WE can do, as builders in our own shops, to achieve that kind of accuracy? |
I don't really want to delve into the relative merits of round x vs. round y in this thread. I'm only concerned here with what we as builders can do to wring the utmost in repeatability from our rifles. Having said that, I, and many other other home builders/hobbyists, happen to have a decent little metal lathe in my shop. So turning, truing, and other minor milling operations are well within the realm. Building my own barrel is WAY beyond my skill level, but maybe not for others, so if someone happens to be willing to instruct us in the black art of barrel making then hell, throw it out there.  |
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I would think if you are going to the expense of mod'ing up an AR, I would do it with an ar10 platform, probably in Rem.260 or some other ballistic optimized for long range round. I would think that the lessons learned would transfer from big to little, and I guess it would be cheaper to work with ar15 parts. As to applications, I would think the Military would be interested in a consistent 2.5 inch group rifle at 1000 yards. That's twice as good as the SASS, right? Is the AR system so inherently accurate that the effort to go from a relatively easily obtianed .75-.5 MOA rifle to a .25MOA rifle is a huge PITA, for not much real gain? Maybe as an aside, it seems there is a movement to piston operated gas systems. I thought that piston systems has issues with accuracy because of variatons in the operating rod and its operation? I thought M1A guys had to try random rods till they got one that shot well. |
| Accuracy tricks in a standard AR build with quality parts is a non issue. Squeezing every bit out of it would only be of value if you are starting with a 223 MATCH chamber to begin with. All of my ARs are built with 5.56 NATO chambers. I don't mind sacrificing a bit of accuracy to know the weapon will digest every type of ammo I run through it. |
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Read these: Black Magic: The Ultra Accurate AR-15 The Competitive AR15; The Mouse That Roared The Complete Guide to AR-15 Accuracy AR 15 Complete Assembly Guide Between them, they contain about everything you can controll when you assemble an AR15 from parts manufactured by someone else. |
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The heart of accuracy rests with the three B's: barrel, bullet, brass, in that order. Buy a high quality barrel, from a company that shows representative groups shot with their barrels. A matched bolt can be two things: a bolt that was only checked for headspace after the barrel was made, or a barrel whose chamber was cut specifically for a particular bolt. The latter should be the tighter chamber. Tight chambers lend themselves for better accuracy. The AR can have lapped bolts to a particular extension, but it is not worth the time and effort. Any accuracy gains are minimal, if even measurable. You did well in lapping your upper receiver. This is one thing that is readily overlooked by many match builders. Assembling quality parts will produce a good shooting rifle. Fitting quality parts will produce a superior shooting rifle. There are several other tweaks, but as another poster stated, builders do not freely share their knowledge. Edited to add: The above referenced books are excellent. |
The barrel extension on the AR handles most of that. On a bolt gun the locking lugs are in the receiver and they much be square and true to the barrel. On the AR that is handled as part of making the barrel. Having a short bolt that rides inside a bolt carrier allows more movement than a long bolt that locks up against several points in the receiver. That bit of movement helps it "self adjust" if the barrel isn't perfectly square but it can also make the level of precision reached on a bolt gun unreachable. And then you have to consider the amount of time required. An AR bolt and barrel extension have a lot more lugs to fit than a bolt gun. |
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