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The following is most of the information for my conversion of my Bushmaster ACR from .223 Remington to .264 LBC-AR (aka 6.5 Grendel). If you think I left something technical out of this, you are correct and I did so for a reason. I know this rifle is very friendly to users looking to customize without a gunsmith but I think doing this kind of work entails more than a bit of danger if you are just ‘winging it’ without previous training and experience in Firearms Engineering (which I possess, especially with this rifle). I don’t want a job either, Firefighting allows me to do fun side stuff like this so why would I work for someone ever again. Also, I won’t coach anybody through a build like this because of possible liability issues. When I am satisfied that the parts are safe, I do intend to make the components available to everybody that believes in this platform as much as I do. Here are the tech specs:

First Assembly Sepia.jpg

ACR All Patrs.jpg


Custom made 20” Stainless Heavy-Mid profile Fluted Barrel, .264 LBC-AR chamber
Standard ACR upper and bolt carrier group
Custom made ACR bolt for the .264 caliber (this would also fire a 7.62x39 round if the barrel was chambered for it)
Standard lower
Rock River Arms National Match Trigger group
Prototype ACR to PRS2 adapter
Magpul PRS2
C products 6.5 magazines(blue follower)
Hornady 6.5 Grendel 123 gr Amax Ammunition
Burris Optics Black Diamond 8-32x50mm Scope and Burris 30mm Signature Zee Rings
Mako Group Grip pod Bipod/Vertical Foregrip

This build has taken me about a year to assemble all the pieces with my finances the way they are and two kids(three if you count the wife). Some of the parts are irreplaceable right now so I won’t be thinking of selling any of them until I do a commercial sized run of parts. If I had to guess at the final price tag with all the engineering work, parts, and testing I would figure that I have easily quadrupled the msrp of this rifle. That’s pretty typical for this kind of work though.
I should also note that I have had advanced military training so I shoot well but I think this rifle could shoot even better in the hands of a shooter that is trained and experienced in the art of long range shooting. I can read trace, mirage and wind but I don’t make my living at it.
I have omitted the name of the barrel manufacturer because I would not recommend them to anyone(maybe someone I don’t like) and I won’t use that manufacturer for any build in the future. If you figure out who did the barrel and want to use them, good luck and you will be using a couple of calendars to measure how long it’s going to take to get a barrel out of them. I got ‘hooked up’ because I was ‘in the industry’ and it took 8 months and they doubled the quoted price at the end. The bolt was fabricated by a local machinist that is very talented and he will be the one making future bolts for me. Also, thank you to Keith at Rocky Mountain Shooters for getting some clean up gunsmithing done for me very quickly at a great price. If you are in the area I recommend him. I had no problems with the C Products magazines but they aren’t in business any longer so I consider them good enough for this build. I don’t know that I would trust my life to them yet. The only malfunctions I had with this gun were when I was working with the gas system to get the rifle gas port tuned to the action. I attribute those malfunctions to a non-tuned gas system rather than the rifle or the magazine. The grip pod was fun and may have some applicability to this platform. I wish it was a bit smaller and lighter because it is pretty huge in real life. The trigger group from RRA is good enough for me. I noticed the difference switching from the OEM trigger but I don’t think I would be good enough to tell the difference in the Geissele trigger compared to the RRA, although I would love to try it out if I had the cash for curiosity. The RRA trigger is the value buy for me on this build. Thanks to Hornady, if it wasn’t for them I would be buying Wolf. The rounds have been great every time out of the pipe. Thanks to the Burris Guys for the hookup on the Black Diamond and rings. I used to work there and I know how good that scope is from an engineering standpoint. It held up its end on this build and was more than cost effective considering the shooter. Finally a big thanks to Magpul for letting me work on the Masada in the prototype phases which gave me intimate knowledge of this platform and a solid knowledge base to attempt this endeavor. Even though I don’t work there anymore I still consider the guys and gals over there to be good friends and more than helpful when I needed some help.
I figure the rifle shoots just under 1 MOA or better which is ok for a precision gas gun and a moderately skilled precision shooter. The weight comes in at 12.4 lbs with an empty magazine according to the bathroom scale. The recoil is very comfortable and the bang is quiet enough that some people/cows over the next rise didn’t even know I was shooting until they came over. I did not notice any change in POI shift by removing the barrel and replacing it but I don’t plan to do that very often for this prototype setup because it may turn up in the longer range shots. The barrel tip is threaded because I would like to fabricate my own suppressor for this system in the future (BATF, don’t worry I know the rules for that sort of thing). In the pics to follow, all the distances are in yards even though a couple of the targets have meter designations (old habit). This rifle will shoot all day long at 600. Especially since I can turn up the magnification to 32x and the groups go to very good (I used a controversial target so I am not positing that it). The other ranges require the scope to be at 14x for the reticle to match the ballistics calculator I was using. Counting all the rounds I used for tuning the gas system, sight in, and then range days, I have about 150 rounds down the pipe. I haven’t seen any major signs of wear and tear or damage but I plan to inspect the bolt with some industry standard inspection practices to make sure there is nothing I am missing on this one.
All in all I am very happy with this build and I am also happy that I can put it down just in time for archery season. Maybe after I fill the freezer with elk and I get the 6.5 bolts done I will work on a 7.62x39 setup(I might use Wolf ammo then) and then who knows what I will add to this platform. I will post again about this stuff when I have the company formed and am ready to take preorders for the first run of bolts. Thanks for taking the time to read this.

Mike
 

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And finally, some pictures:

Range Setup, first day.
Field Setup.jpg

100 yd shots were made in a 10 mph gusting headwind and I have seen better groups but I don’t have those targets anymore.


100.jpg

700 yds just shows that it’s not the 32x that is doing the work to get the rounds on target. All shots made contact although the third one looks pretty marginal to me. I should note that for all these distances I was shooting with a bipod on an unstable stack of gun boxes and me in a seated position to get over the grass.
700.jpg


800 yds I will take one miss at 800. Blame the shooter, not the rifle.
800.jpg


900 yds I don’t mind completely missing the paper at 900. It was starting to warm up and I wasn’t pay attention when the 2-4 mph cross breeze came up with the temperature.
900.jpg


1000 yds This was my goal distance. 60% isn’t great but I made contact with the paper on all five shots so I am happy. Especially since I was holding for the crosswinds and I was in a ‘less than the best’ seated position. I think with some more time behind this gun at the long distances I could tighten all the groups up.
1000.jpg
 

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Holy shit-balls! That's awesome. Definitely not bad hits for 1000 yds. A year is a long time for a project to come together. I hope you're happy with the final product. I think it's safe to say that you've got a one-of-a-kind rifle there. Have fun. Thanks for sharing.
 

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Excellent. Plus at that yardage a junky with a baseball bat may not prove much of a threat. But seriously excellent work. I love seeing the possibilities of this platform. The aftermarket is driven by its customers.
 

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1st off, thanks for sharing your build experience, very ambitious and I'm sure once you are totally finished, very satisfying. I have never shot anything further then 500 yards and was very happy to keep most of my shots in the torso of a silouette. Concidering this is a new build, you and rifle did very well!!

Question, I want a PRS stock for my ACR since I saw the 1st released propaganda for the Masada, is the adapter something from the Masada days, or is it a current prototype?

Again, thanks for sharing, I really enjoyed the read!!
 

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Awesome work! This is what I've wanted ever since I watched the future weapons episodes about the Masada and the 6.5 Grendel.
 

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Aweseome job! that is a beautiful looking rifle(s) you have there!
Thanks for the write up. I've been looking for a good write up on a .264/6.5 conversion for some time.

Could I commision you to make a few of those 6.5 bolts for a buddy and me?

maybe if other's are interested we could set up a group buy? would you be willing to help us out?
 

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Rotary, 1044, and BigD,
I plan to make those bolts available once I have done a couple of tests on my bolt. I will let you guys know when I am ready to accept preorders. My plan of action goes something like:
1) Finish testing/analysis on the bolt
2) Form company
3) Finish needed drawings/specs
4) Get quotes on bolts
5) Offer preorder
6) Make Bolts
7) Sell Bolts


OIF, please make sure you do your homework and work very closely with all the mfgs you use if you pursue this project.


APWR, I wasn't taking a shot at you in my disclaimer. I hope you are not offended but I have been in the firearms industry long enough to know why they have disclaimers and warnings like the one I posted. I have had at least 2 guns blow up on me and I would hate to be responsible for that happening to someone that didn't know what safety precautions to have in place so they actually got hurt or worse.


Everyone else, thanks for your comments. I like to hear if people here like what I have to offer and what they think I could improve on. I will consider the 6.8 bolts after I do the 6.5 bolts but I know this is on the radar for BM so there may be better parts to chase rather than that caliber. If BM can't do it right I will take a closer look at it. The nice thing about the 6.5 bolt is that you can use it for the 'bad guy' equivalent of the 6.8 which is the 7.62x39. I know the ballistics at medium distances are slightly better on the 6.8 but you can't deny that they are in the same realm when it comes to mass, and the ak round is way cheaper. Just my thoughts.

Mike
 

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for the bigdog only send me any ar sytle barrel and i will design produce the bolt for you for free given that you let me keep the specs for my co.really been shoping for the tokarev so people can shoot for cheapo,it currently the cheapest mil surplus round out there and its wicked cool up the in the fiveseven,.357 sig, 25/20,and 30 luger for rifle coolness in a pistol cartridge.
o snap, i'm gonna buy another barrel soon for ya lol
let me check around for stuff and get some dollars together for the new project
 

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This thread is full of win.
 

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I need to read up on this cartridge. Im building a .308 ar but I may need a new project.
Oif, long story short, 6.5mm (.264") bullets are a long-favored European hunting caliber (back to the dawn of smokeless powder rifles around 1890) with some military application. The 6.5x55mm Swedish Mauser is one of the oldest living Euro hunting loads. This particular bullet diameter strikes a bit of a ballistic sweet spot for balancing diameter with weight and useful velocity, allowing cartridges to be loaded with long, sleek, heavy-for-their-width bullets while still retaining useful muzzle velocity and very mild recoil, and while still providing enough bullet diameter to carry useful payloads against large game and people. W. D. M. Bell killed several elephants with a 6.5 in addition to his favored 7mm. With the 6.5 Grendel and the 6mm Benchrest industry, this caliber has seen something of a "rediscovery" in the USA. The high ballistic coefficients achievable within the practical limits of a 6.5mm bullet reduce drag-related deceleration and wind drift, allowing the comparatively light-weight, light-kicking (relative to other 1000-yard cartridges) round to retain a consistent trajectory and useful velocity at long range.

The Grendel in particular takes advantage of this (and modern bullet design) in pursuit of a cartridge which satisfies the size and chamber pressure limitations of the AR-15 platform while retaining supersonic flight to ranges beyond 1000 yards. The Grendel is a 6mm PPC case necked up to 6.5mm. The .264 Les Baer Carbine is the same thing, but with names changed to protect the innocent. The latter arose almost entirely out of the stringent licensing control enforced on the Grendel brand by Alexander Arms.

Chief benefits of these cartridges are full access to the .264 bullet selection in an AR-15 platform, for after a hundred and twenty years of refinement, what was always a good caliber now benefits from a host of technological advancements in bullet design and manufacture, as well as a wide array of bullet weights and shapes. The OP has demonstrated its accuracy potential at a rate of 1000 words-per-picture.

Chief knocks against it relate to the use of the PPC case design, which features a short, fat body and a steeply constricted neck. These features have been shown to contribute to poor feeding reliability in repeating arms, which makes them less than desirable for military or other hard-use applications, such as hunting afield, regardless of action type. The 6.8mm SPC uses a longer, less severely choked .30 Remington case to avoid these problems.

Stepping outside the world of modern military combat rifles for a moment: Additionally, the constraints of the AR platform prevent any cartridge from taking full advantage of the 6.5mm bullet's potential, which is best shown when longer cases and slightly higher pressures and velocities are permissible, such as in the Mauser and Mauser-derived bolt actions for which the popular 6.5mm hunting cartridges have been developed. While it is not necessary to drive a 6.5mm bullet at greater than 3000 feet per second at the muzzle to achieve lethal results, most modern hand and factory loads for 6.5mm cartridges exceed 50,000 cup and 2600 feet per second. (The notable exception is the 6.5x55 Swede, which is SAAMI limited to 45,000 cup due to the weakness of some of the vintage Mauser '96 actions for which the Swede was originally developed. An 1898 Mauser or later action can handle hotter Euro and hand loads in excess of the SAAMI spec without trouble.) These cartridges, both new and old, take full advantage not only of the ballistic properties of the 6.5mm, but also of the wide range of bullet weights and shapes available in this caliber, from 100-grain target and varmint bullets to 156gr penetrators designed for large game such as Scandanavian moose and polar bears. (Or, if you are as manly as Karamojo Bell, elephant skulls.) These cartridges also for the most part favor longer, less severely necked, more traditional cases.

On an editorial note, I first became exposed to this cartridge while researching the (at that time) brand new Grendel. Investigating the one, I discovered the plethora of other cases from which the 6.5mm bullet could be delivered, and the advantages of doing so for one not constrained by a STANAG magazine. As I was at the time looking to refit my Mauser '98 rifle, I was free to choose any compatible case. The rifle was formerly chambered for 6mm Remington, but I wanted something just a hair larger and more versatile. I eventually settled on the Swede (AKAs: 6.5x55mm Swedish Mauser, 6.5mm Swedish, or just 6.5mm SE; it's beem around long enough to have several names), as this round allows me to take good advantage of the ballistics and bullet selection mentioned above, and has a traditional, vintage flavor, to boot. (The action is itself vintage, a WWI prize.) You can even find old, tattered boxes of Swedish Army sniper FMJ floating around, if you look. My Oberndorf Mauser action is more than strong enough for modern powder loads and chamber pressures. (The 6mm Rem. is SAAMI spec'd at 60,000 cup, if I remember right.) As I type, this rifle is on its way back from the gunsmith with its new 25" fluted Lilja barrel, and I expect it will be able to thread needles at 900 yards. If only I could. Moreover, and perhaps more importantly, it will ALSO be able to accurately deliver 156 grain penetrator rods out to MPBR.

Would I be interested in a 6.5mm adaptation for a modern combat rifle? Yes, but not until after 6.8mm SPC, 7.62x39mm, and even .300 BLK. My priorities for a combat rifle cartridge are reasonable accuracy out to MPBR, reliability, efficiency, and availability. As my accuracy needs are already met and exceeded in a bolt gun that takes better advantage of the caliber, and given the issues with the PPC case design, the Grendel/LBC target cartridges are a low priority option. Also, while I'm sure numerous instances can be cited of PPC cases cycling without failure, their stigma exists for a reason. I will wait until the fat-case revolution has silenced all doubters. (In case you can't tell, that's sarcasm. I mentioned this was editorial content.)

All of that said, DSM is absolutely right. This thread is full of win, and what the OP has achieved makes me proud to be an Ah-MUR-ican. Well done, and my hope is that you will complete your plan and turn out hundreds, if not thousands, of bolts to a content-starved ACR aftermarket.
 

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.................................................................................................All of that said, DSM is absolutely right. This thread is full of win, and what the OP has achieved makes me proud to be an Ah-MUR-ican. Well done, and my hope is that you will complete your plan and turn out hundreds, if not thousands, of bolts to a content-starved ACR aftermarket.
+1 and thanks for the info!!
 

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Ancient, cjt50, DSM and everybody else in this thread,

Thanks for the encouragement. This is what I wanted to hear before I start a business based partly on this platform.

Mike
 

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ok,this is awesome news.
 
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