Jgun

The configuration looks as though it would be a really perfect carbine for a LEO. I know I'm really partial to the 14.5" guns. Not sure if I would go shorter for an all around multi use carbine, even if there were no NFA considerations. Of course that my be more self serving than fact simply because SBR's aren't legal for civilians in my state. I've got to say, my 14.5" .308 is by far my favorite AR. I have found that I'm able to consistantly hit 12" steel plates at 200M with it, using an unmagnified mini red dot. The 300BLK carbine may become my new favorite over the .308, once I've put a 14.5" 300BLK upper together, but that remains to be seen. I also have found that I prefer the full length rail/hanguard on the 14.5" guns, wish I had done that with all of my short AR's, don't know if I'll ever get around to going back and switching out my shorter rails though.

I have the PRI low pro adjustable steel GB on my 300BLK rifle. I went with an adjustable for this build because i selected the Youngs machining Superlight bolt carrier group. While I really like the PRI GB, I'm not sure if it's the best choice for your application. IMO you'd be better off with a gas block that has specific settings like the Noveske switchblock or similar, instead of something with an infinite screw adjustment like the PRI. Doesn't Armalite also offer a GB with a three position switch? I would suggest you do a search of those vs the type like the JP/PRI that, as far as I know are more intended to be set and left alone than readjusted every time you take the can on and off.

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.

Yeah, but correct me if I'm wrong, isn't that pinned Brake the AAC that mounts a suppressor?

I haven't personally built on the Armalite receivers, but IMO the quality of the Mega receiver set (which I own) is superior to that of the DPMS receiver sets which I have bult on. I have not run into any problems as far as parts fit goes, with any DPMS type parts that I have used to build my MA TEN.

For my (an i'm sure some others) education, perhaps you could post what the sizes are for the DPMS and TM pins once you've got both in your possesion?

Have you turned it around to see if the "head" of the pin is correctly threaded so that you can screw it into the receiver? If not, Maybe you can try to find something laying around the house that does thread into the receiver so you can figure out if the problem is the pin or the receiver. I've not worked on these receivers but I'm thinking that ideally you'd like to have it threaded to the correct standard size, so if it turns out the receiver is the problem you may need to carfully drill and tap it. If you have to, be sure to put plenty of tape on the side of the receiver to protect it while you do the work.

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?

These look pretty nice. I think if they had a 14.5" I'd be placing an order right now. www.spikestactical.com/new/z/barrels-300-blackout-barrels-c-210_211.html

Unless I'm mistaken, thats the stock that POF was listing on their site a few years ago. I remember that I was intersted at the time, but when I looked into it later they had stopped offering it. Have you tried contacting them?

I like that!. I don't know if it would be an option, but I might relieve the handguard so that the front sight would fit without removing the back post. Are the Magpul handguards much lighter than an aluminum rail?

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.

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

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.

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.

After reading your post, just out of curiosity, I weighed some parts I had laying around here. I weighed a POF lower (12oz), a butt stock with buffer tube , not the lightest (1lb 4 oz), and a grip, light weight buffer and spring (10 oz). I don't have a trigger to weigh but from the looks of it, it sounds like you may end up with a gun weighing in at around 7 1/2 lbs, without optic,. That will certainly be one lightweight .308 AR.

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.

Is your GB made of aluminum? If so is it possible that the threads are oversize? I have not personally done this because I have not used any adjustable aluminum gas blocks, but perhaps, if you find that the GB threads are worn, you could install a steel thread insert. If this looks like it might be a viable solution for you, I might suggest that you go with one of the solid ones instead of the Heli coil "spring" type. If you find that the threads in your GB are intact, You might try installing a longer screw, that protrudes from the side of the GB and then you can put a nut with the appropritae thread on it. You then adjust the screw using an allen wrench, and, while holding the screw with the allen wrench You tighten the nut against the side of the GB, works as a lock nut.

Only thing I might add to the above reply is that you will have to make some provision for access to the gas block in order to make adjustments while dialing in your gas system, that could mean selecting a hanguard that could be installed without disturbing anything, after you get the gas system adjusted. as far as fitting your GB under the handguard, you might want to take a look at the low pro adjustable steel GB from PRI, it's basically the smallest adjustable out there and pretty much the same size as the smallest non adjustable GB's on the market.

That GDI mount looks to be of very high quality. I'd love too hear a review once you pick it up. I must say though, I'm not sure what more your getting for your money with it that would justify it's costing 1 1/2 times what the AD mount costs. I've been using the Ad Recon and have found that it works exactly as I expected. I haven't done any return to zero testing by taking it off and remounting to see how well it retains the zero, but so far it has been rock solid for me and I have had no zero shift, or loosening after 100's of rds on both my 14.5" .308 and my 300. I would certainly hope there is some fonctional superiority of the GDI, I'd hate to spend an extra $300+ for a mount just because it was prettier.

The likelyhood is that YOU will be able to see some signs that the GB was changed, will anyone else, maybe,maybe not, depending on how meticules you are when removing the old one and installing the clamp on. inevitably,any surfaces where one of the GB's doesn't cover where the other was mounted, will show signs of the others mounting.

Perhaps someone with first hand knowledge will post to confirm this, but, from a manufacturing prospective, I believe that the most likely, and logical way that something like this would be done would be that the front sight (without any holes drilled in it) would be placed on the barrel using a jig or fixture of some type to locate it in the proper place and radial orientation, and then, either using a manual machine or CNC (if combined with other operations) will drill and ream the holes through both the front sight and the lower edge of the barrel. This is how they assemble AK's which are almost fully pinned/riveted together. It would be impractical to attempt to machine a crescent half hole on the bottom of the barrel and then try to get the holes drilled through the sight to try to line up. I would be shocked if you find those crescent relief cuts on the bottom of your barrel, unless it previously had the type of sight you want, already mounted. If I were you I'd go with one of those clamp on sights that Robocop posted.

I've also read that if ultimate accuracy is your goal from the AR, the set screw mount type GB's are not ideal, because they create localized pressure at two points on one side of the bore. I'm not sure how tight you need to torque the set screws on the GB's so this may not really be an issue, but I think that the clamp on, or Noveske's pin on mounting method are probably superior.

In my case the incentive to make the barrel nut was that I already had the Larue rail, which I consider to be of high quaity with a very strong mounting design, it was exactly the right length to just cover the rifle length GB, and I didn't feel like spending almost $400 for the DD Lite which was not the right length, that and to see if i could do it, but I would agree, there are so many good handguards on the market these days, you should be able to get almost anything you want without resorting to machine work, (unless you enjoy it, like me).

Does the SPX have an 18" barrel?