Accuracy tips for building AR308

[TomBruto]

Hello, new to the forum and building first 308 ar. I would like to hear any advice on how to make it the most accurate it can be.  I will be reloading my own ammo so i am only interested on things i can do to the gun. I am pretty set on a Kreiger 20" 1:10 twist ss barrel, but am all ears for any thing else, as long as the length and twist are the same. Will be putting it in a MA-TEN Monolithic rifle length reciever with matching lower.  Have also decided on JP's enhanced bolt, possibly in a dpms, fulton armory, or young bolt carrier.

I am open to any and all information i can get for accuracy or reliability , as well as suggestions on what i should or shouldnt do.

One question i have is do people bed the recievers together? I have some devcon leftover from some boltactions i have bedded and was wondering if it has been done befor and what the results were.

Thanks in advance for any info.

[Robocop1051]

You won't need to bed the MA-Ten. They build their parts to very tight tolerances.

The next to important parts for your rifle will be a trigger, and a muzzle device.

[edgecrusher]

You won't need to bed the MA-Ten. They build their parts to very tight tolerances.

The next to important parts for your rifle will be a trigger, and a muzzle device.

agreed

[TomBruto]

I read that they have very tight tolerances, and i wasnt just gonna do it without trying it first. I was just wondering if people did it to the ar platform. I have accurized many bolt actions, but never heard of anyone doing it to an ar.

As for muzzle device, I was thinking of a surefire. So in the future when i suppress it, it will be gtg. Not sure if i want the one where the suppressor overlaps the barrel slightly or the one that just fits on the end. It will be determined by the diameter of the barrel i get.

As for the trigger, I was thinking of a RRA NM 2 stage and probably do a little work to it to lighten it. Maybe even send it off to get a NiB coat.

Is the Kreiger a good choice, well i know they make good barrels, but are there any other manufacturers that have the same quality with a smaller pricetag or delivery period?

[Jgun]

As stated by others, the MA TEN matched upper/lower will have a very tight, no play fit. If you are unsatisfied with that you may be able to find the takedown pins that expand when tightened, like the ones from Demon tactical. When tightened, they actually lock the upper and lower together. Keep in mind that the gun with optic is basically all in the upper anyway, so although I can't tolerate a sloppy upper lower fit, the fit between the two doesn't have as much to do with accuracy as you might think. As also stated above, I think the best trigger you can get will have a lot to do with how accurately YOU can shoot the gun, Good glass also. Something else, If you really want the absolute best accuracy obtainable from the gun, and are willing to have a gun that will require specific handloaded ammo, you can have a barrel made (not an off the shelf barrel) with a tighter chamber, but not so tight as a bolt gun barrel. You just have to be honest with yourself as to whether you will regret building a gun that reguires handloaded ammo but shoots onle slightly better than one with a larger chamber. If your prepared to live with the limitations as far as ammo goes, you might want to talk to a barrel maker and ask his opinion on using one of Pacific Tool and gauges  .308 Bisley AR reamers. I've just gotten one that I'm going to use to chamber the Krieger barrel in my currant M1A build.

[TomBruto]

Thanks to all of you for the info.  I like the idea of the expanding takedown pins, though i doubt i will need them, because everyone says that the reciever will fit well.  The question about bedding is more for my curiosity, i doubt very highly that I would be ballsy enough to inlet and bed my brand new MATEN, i was just wondering if it is something that people do.

Jgun, I think i will keep the chamber loos enough to where i can shoot factory ammo, though i will be shooting mostly reloads. I like to have the option.  I have some lee collet dies that i use for my 308 bolt action that only resize the neck, so as long as i use brass fired from that gun, it should be pretty tight no matter what the chamber is. Or at least that is what i was led to believe, but i have had very good results from my bolt action.  In your oppinion, is .3 moa ctc achievable with a good barrel chambered fairly tight, but loos enough to shoot factory ammo with the right load and assuming i do my part?

[Jgun]

I have not gotten really serious about seeing what the best accuracy achievable out of the platform is yet. I'm considering my next large frame AR build to be focused on max accuracy, but to that end may elect to go with some cal other than .308. 6.5X47 Lapua, or .260 rem maybe, but from what I've read, the large  AR's built by GA precision are getting .5 MOA. I think that if you can get better than that it's an anomoly. As you probably already know, one of the problems with getting max achievable accuracy out of an auto loader is the fact that the bullets tend to take a beating during feeding, which can cause shot to shot variations. 

If you've been handloading for a bolt gun, I'm sure that you already know, the consistancy of your loads will have a lot to do with the max you can expect from the gun. Not that I've got a lot of bench rest experience to draw from (none), but from what I've read, it seems as though, much like racing, when you are trying to get the absolute best performance from your set up, what seems to happen is that the further you go with it, the smaller the performance gain is with each additional improvement you make to your platform, and will also narrow the practical use of the item.

[Robocop1051]

Jense Precision, Christensen Arms and a few other builders all guarantee sub-1/2MOA groups. You have to expect to pay out past $3k.

[Jgun]

I don't see any accuracy guarantee's on either of their websites, Where can I find them? I also went back to GAP's site and double checked their advertised accuracy guarantees, and see that I was mistaken, they guarantee 3/4 MOA accuracy from the GAP 10. They do guarantee 1/2 MOA from a number of their bolt guns, and even guarantee 3/8 MOA from their HRT bolt gun. I would expect that Jense's tube guns are getting similar accuracy, but once again, these are not auto loaders. Of interest to me was the 6.5X47 Lapua bolt gun on Jense's site. Only question for me is, would the inherent accuracy of the 6.5 Lapua rd be wasted in an auto loader? Also it looks like the steep shoulder of the rd might not feed as well as some others.

I have heard this a million times, but it's always been said that most of these guns that we are buying/building will outshoot us. We are the weak link.

On a somewhat related topic. I was looking on youtube recently, and saw a vid of someone shooting steel at 1000m with a scoped (low power) 30 06 Garand. So I think that unless you've got your heart set on shooting one hole groups on paper (bench rest stuff) I think that if you can put together a .308 AR with match barrel, and handloads that can shoot 1/2-3/4 MOA, youve got yourself a superior weapon.

[Robocop1051]

I got my info from Jense and Christensen when I called them about CF wrapped barrels. Jense specifically guaranteed a sub .4 MOA if they assembled the upper.

[Jgun]

I wonder what kind of chamber/load he uses for his max accuracy AR's, did he say anything about that?

[Robocop1051]

I wonder what kind of chamber/load he uses for his max accuracy AR's, did he say anything about that?

Magic "Lee Harvey Oswald" bullets??

A question about "bedding" a rifle. The only rifles I've seen with bedding are M1A/M14's in JAE stocks. Could an AR even be bedded? I thought the whole purpose of having a freefloat was so you didn't have to bed.

[TomBruto]

"A question about "bedding" a rifle. The only rifles I've seen with bedding are M1A/M14's in JAE stocks. Could an AR even be bedded? I thought the whole purpose of having a freefloat was so you didn't have to bed."

That is what i am trying to find out.  I would think you could bed around the reciever pin lugs, but wouldnt have to with a tight fitting upper and lower. All of my bedding experience comes from various bolt actions, but as i understand it, free floating and bedding the action are two different things. Bedding is to make sure you have a tight stress free fit to the stock so there is even pressure thruout the reciever as it is bolted to the stock. Free floating a barrel is to make sure there are no external pressures on the barrel (other than gravity) so that the barrel will have consistent harmonics.  Again that is for bolt actions, but i figured there may be some similaritys.  And also i may not be correct in my explinations on the two.

This build will be used mainly for hunting, so sub moa would be acceptable. But i would like to see ragged holes. It would make those 600+ shots a little more comforting.  Where i do most of my hunting, i cover a long canyon from a hill top and it is not uncomon to see a group of hogs at 630 yds.

[Jgun]

To add my two cent's to the bedding question, I've recently become involved with the M1A platform and it is my understanding that the only M1A stocks that are routinely bedded are the wood and fiberglass stocks. In fact the national match prepared guns would sometimes have the receivers modified in a manner where lugs, either one in the back (common) or one in front and back (double lugged receiver) were welded to the receiver in order to allow more points to secure the receiver to the stock. In addition, they skim coat the inner surface in order to have the inner surface of the stock precisely match the surface of the receiver. The M1A's are not actually free floated at the barrel, due to the design of the stock and the way the front band/gas cylinder attach to it, but it is common for them to be shimmed in order to preload the barrel. I think the same would apply to the bolt guns, As far as I know the receivers are bedded in a similar manner. I may be mistaken here but I have heard of bolt gun stocks being carfully relieved so that you can slip a sheet of paper around the barrel and know that it is free floated with no barrel/stock contact. I have also heard of people qlass bedding the barrels so that as you mention, there is no localized pressure from stock to barrel. I believe that a free floated barrel would be superior.  I have a JAE stock on order, and one of the beauty's of it's design is that the method of receiver mounting (using side lugs) allows a secure interface between the receiver and stock that requires no bedding, and the barreled action can be removed and reinstalled without disturbing that fit.

Now when you bring this question to the AR platform, I don't think that there would be any practical way to bed the upper to the lower even if you wanted to. As I previously stated, if you really felt the need to have a solid mounting between the upper and lower, it would be easier and more effective to make up some type of pins,bolts that locked them together, but this would make breaking the gun down more of a PITA. Now, free floating the barrel on an AR is another story. I think that it's universally agreed that if max accuracy is your goal, a free floated barrel is a must, but that's easilly accomplished with the installation of a freefloat tube/handguard.

[TomBruto]

Thanks, that cleared alot up. And i agree that a free floated barrel is a must if you are looking for accuracy. The reciever i am going to use is a monolithic upper, so it can only bee free floated, maybe you could do something to make it not, but why would you.

[survivalshop]

I have an article from Shot Gun News , where a very well named gunsmith goes over how they bed the AR's for the Army's shooting team . Give me a while , so I can find it & reprint it here as a post.

I would only use at the least , full length sizing die for reloading for an AR . Some say you never need it , but I use small base dies for all my reloading for AR's in 5.56/223 & 7.62/308, because my ammo goes into more than one AR .

[TomBruto]

Thanks, I am very curious to see how they do it. And I have a full length resizing die aswell, just thought I would give the other a try.

[Jgun]

I am am eagerly awaiting this post as well. Up until your post I had never before heard of anyone bedding an AR. From memory, do you recall if it was actually the upper/lower fit that they were bedding?

[survivalshop]

I was wrong about the gunsmith , he doesn't do work for the Army shooting team ,but has worked with them . He is building a rifle (Colt base ) for a service member going back to Afghanistan.

The Gunsmith , Phil Arrington

Having a loose fit between the upper & lower is like having the action bolts come loose on a bolt action rifle , it opens up groups by causing fliers.

If you can feel movement between the upper & lower, than for accuracy purposes, your rifle could stand to be glass bedded.

If you do not plan on swapping uppers , than glass bedding is the best way to tighten things up .

The way to achieve a tight fit between the upper & lower is to place pieces of shim stock (0.001- 0.005 " thickness)  between the upper & lower & increase the amount of shims till the the push pins become drift pins.

It usually takes between 0.005 & 0.010" in shims to tighten up the upper & lower.

The shims are positioned just in front of the rear push pin lug area . Once this is done , open the upper & remove the shims . Keep this stack of shims all together .

Now right under the take down lug at the rear of the upper receiver , degrease the inside of the lower receiver.

This is where you will use a pea sized amount of aluminum or steel epoxy putty. Apply a release agent to the rear take down lug of the upper receiver , place the shims between the upper & lower & close the upper down & drive the push pins through.

Driving the pin through should not require a great amount of force.Let the epoxy set up for twenty four hours , then open up & clean up excess epoxy and remove shims. Now the upper & lower are tight enough that a punch is needed to drive the pin out.

I think the area he is referring to is right behind the rear lug on the upper , where it meets the lower . The epoxy will fill the void & tighten the receivers up . When removing the shims , you get the necessary amount gap to open & close the upper & lower. The shims are in placed in front of the lug , when you start placing the shims , you will see where they make a difference & where they do not .

I have been planing to do this with a DPMS upper & lower 308 I have ,but want to shoot a before & after to see what results I get .

Use this method at your own risk .

I say that because I have gotten rifles where those who thought they could do a bedding job only to find out they didn't put release agent in all the right places. Hate to see that in an AR .

Good luck , it will be a couple of weeks before I have time to play with bedding .

[TomBruto]

Wow, good info!  I would definately try this on my ar15 first. The upper and lower dosent match, and there is plenty of movement between the two.  However, it is still very accurate, and not really set up with a big scope to get tiny groups at long distances.  It has a 3.5x scoope on it which is rock solid and more than enough, most of the time. I may have a scope laying around to mount to it to test group size before and after bedding.  I have bedded many rifles, and am very aware of the potential problem of not using a release agent. It will not be overlooked. Now just to find time to do it.

Btw, did it say anything about bedding the front pin lug?

[Jgun]

I think, the method outlined by the gunsmith, which sounds much like a better version of those little rubber acuwedges they sell, is pretty clever, and would probably be pretty cheap/easy to execute, but, just for the sake of discussion, I would like to mention what my experience has been building small platform AR's. I find that I am often building guns with uppers and lowers from different companies. I usually am using more expensive, billit parts, so this may not be the case with the forged stuff. I'm partial to the Vltor uppers, although I've heard that the Rainier ultramatch are just as good. Anyway, I've found that the holes in the billit lowers I've used, have all measured almost exactly .250", while most standard pins I've measured are anywhere between .246" to .248". This may not seem like much, but when I've tested the uppers and lowers for fit using the standard pins, the fit is often sloppy. This has become so common for me that I almost always use the oversize NM pins that Armalite sells (which I think measure .251") I usually have to polish them to fit using fins emery paper. My experience with this method is that I get a tight, no wobble upper/lower fit, without any gap between the upper/lower mating surface, as you would get if you bedded it with shims between the two. I certainly think that the epoxy method sounds easier, and cheaper, just not sure if it's quite as good. I've never done this with the large platform receivers because I've been building with matched sets, but I presently have a POF lower/ MOLON LAVE upper that I plan to assemble this way. the only problem is that I don't know if Armalite sells  NM AR 10 pins, and even if they do, if they  will work on your upper lower set, if not it would require making a set from scratch.

[survivalshop]

You asked & received  & nothing about the front pin.

He did say that the Army team went to the wedges because they switch from 22lr uppers for practice .

I think you will find that the tightest matched uppers & lowers , will loosen up when round count gets higher . They set them selfs when broken in . Bedding the rear lug almost stops this movement, it gives another anchor point to absorb recoil . The accuwedge works in the same way , just not as precise.

[NoFail]

Doesn't a tensioning screw accomplish the same thing as the bedding idea? But maybe that will leave a gap between receivers  <dontknow>

[TomBruto]

Everybody, great info, thanks. 

I bet whith the bedding and the tensioning screws or the NM pins, the upper and lower would have a rock solid fit and hopefully contribute a measurable gain of accuracy.  Usually I will see group sizes cut in half after i bed a bolt action. I dont think it would be quite that significant on an ar platform, but i wouldnt be surprised to see a noticable improvement.  I believe that a perfect fit of action to stock is or can be just as important as barrel, or scope, when precision is the goal.  Needless to say i will be experementing with this pretty soon.  And to get rid of any gap between the recievers, assuming there are still some even though i plan on using oversized pins, I would just clean the top face of the lower reciever, and put some release agent on the upper, and bed them together.  Which may even get rid of more play in the fit. Only down side, the lower will be completely dedicated to that particular upper.

[histopicker]

I have a lower made by sun devil mfg. in mesa az. these folks put a tensioning screw up through the lower to contact the rear pin. you can adjust the pin tension through the grip and it removes all the play between the upper and lower. Great idea sun devil.