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Discussion Starter · #1 ·
Are there any dimensional differences between a upper and lower receiver, depending or if it is chambered for 5.56 NATO or .308. Thinking about purchasing a upper and lower and starting a new project..

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The lowers for an AR-10 and AR-15 are different although some parts maybe interchangable. Uppers are also different length and there parts are not interchangable. Best visual referrence is to stand a 308 cartridge and 5.56/223 cartridge side by side. Height difference has to be accomandated in one by making everything larger i.e. magazine, bolt, housings (upper & lower), barrel, bolt, carrier etc. Additionally there is the difference in pressure each cartridge opperates at during firing with components need beefing up to withstand.
 

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Discussion Starter · #4 ·
Thanks, this site is excellent for the novice gunsmith...I noticed in my DPMS catalog that the receivers have a different part numbers. I already have a S&W MP 15 in 5.56 and a Savage 10fp-le1 chambered in .308. Thinking of going to the .308 just for the extra power. Anyone have on in 6.8 SPC, this is designed to work in the stock AR frame, right....Mi Not including Bolt and Mags,or is that wrong...




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The Shadow (Moderator)
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YES, they are different, and YES there are differences in the differences.

There are 2 different pattern 308 lowers, and the uppers CANNOT interchange. So who's lower you use, dictates who's uppers you can use.
www.ar15.com will give you the info that you are after.
 

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Discussion Starter · #6 ·
Thanks, Planning one maybe. I get mine from a friend, time you add the transfer fee, total of all the parts. and shipping. I would not really save that much as total cost. May just buy on complete, but I already have enough parts on hand to rebuild three AR's
 

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The Shadow (Moderator)
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I just helped my brother build a 308-AR platform.
You can still build a 5.56-AR cheaper than buying.
That is NOT the case with the 308 class. The reason to build there is for your paticular customization.
 

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Thanks, this site is excellent for the novice gunsmith...I noticed in my DPMS catalog that the receivers have a different part numbers. I already have a S&W MP 15 in 5.56 and a Savage 10fp-le1 chambered in .308. Thinking of going to the .308 just for the extra power. Anyone have on in 6.8 SPC, this is designed to work in the stock AR frame, right....Mi Not including Bolt and Mags,or is that wrong...

Thanks
The 6.8mm SPC was designed to fit through a M4 Carbine (AR15), at a min you would need a different barrel, bolt and magazine. Most just build a complete upper in caliber and just need different hi cap mags. You can use the 5.56 mags but will only get 5-6 rounds in for realibilty reasons (problem is the grooves on the sides of the mags) All other AR15 parts will work with it (same with the 6.5 Grendel). Steve Holland out of 5th SFGA was the developer along with folks down at AMU (Army Marksmanship Unit, Ft Benning) and Remington. I also worked with Steve on the development of the SPR (Mk12) and the Barrett M82 chambering a 25mm cartridge.

CD
 

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Im still scratching my head over the 6.8 SPC.

Yeah, I know, same platform, just change uppers.

Why not an AR10 in something oh like .243?
100 grain bullet at 2900-3000 for reach out and smack something or for more umph, 7mm08 in a rifle companies already make?

Oh well. Just something I think about at times.
 

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Discussion Starter · #10 ·
I knew what would be involved in going with the 6.8 SPC, even gave it some consideration. If you want to reach out there, you could go with .338 Federal. This my dream but the cost of ammo limits it for a weekly range weapon. Sometimes a go twice a week and .223 and .308 cost plenty..
 

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I have built two AR15 rifles over the years, but haven't favored them too much because of some bad experiences with the weapon while I was in the service. I prefer the M1A/M14 family, but I got a chance to buy a Colt AR15 HBAR NM for $600, one week before the Klinton Gun Ban went into effect.

The Colt AR out shoots the others that I had. I not sure what the price of NM AR would be these days, I know that it is up there. Mine may get convertered to the gas pistol system, some day. I plan on keep mine and maybe up date it in the future, it is very much like the M16 A2 in looks. It's a great coyote rifle at 100 yards.

As to the new calibers, I can't say, I would like to find a Stomer AR 10 when I have the money, so I would have a AR 308.
But my Springfield M1A shoots very well and it isn't that hard to shoot, I went thru book camp on this rifle.

Jerry
 

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Im still scratching my head over the 6.8 SPC.

Yeah, I know, same platform, just change uppers.

Why not an AR10 in something oh like .243?
100 grain bullet at 2900-3000 for reach out and smack something or for more umph, 7mm08 in a rifle companies already make?

Oh well. Just something I think about at times.

The purpose of the 6.8 SPC/6.5 Grendel is to give the AR15 owner more energy on target without buying a new rifle. The .243/7-08 require the AR10 platform which is a larger (none compatible w/AR15) rifle reciever and upper. Since the AR10 is non standard between companies, parts are not interchangable like with the smaller AR15. The AR15 is lighter, easier to carry, quicker into action and has more parts/accessories to custom tune your rifle for your needs.

CD
 

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I too had really bad experiences in Vietnam with the XM16 we were issued. We had a representative from DARCOM visit us several times with changes to the weapon and some new wonder lubricant none of which worked very well. Then later working with the Infantry Board I observed terrible accuracy from the M16A1. The M16A2, at that time used by only the USMC, was far superior. About five years ago I visited Knights facility in Vero beach to observe building of his fine SR-25 rifles. Later in North Carolina I had the chance to shoot one. They are a really nice and very accurate weapon. My son bought an AR target rifle about four years ago and I have found it to be so accurate (sub minute of angle) that it is almost boring. I was very very surprised since we could not get 12 minutes of angle in the post vietnam testing we did at Fort Benning. Years of refinement allowed it to approach its potential. The system is intolerant of poor routine maintenance and subject to failure when a dirty one gets hot.
 

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The purpose of the 6.8 SPC/6.5 Grendel is to give the AR15 owner more energy on target without buying a new rifle. The .243/7-08 require the AR10 platform which is a larger (none compatible w/AR15) rifle reciever and upper. Since the AR10 is non standard between companies, parts are not interchangable like with the smaller AR15. The AR15 is lighter, easier to carry, quicker into action and has more parts/accessories to custom tune your rifle for your needs.

CD
I know and understand all that, but cant help feeling it is reinventing the wheel. Cant help feel it's just another caliber and another upper when a proven system was there, just in need of someone to say it was time to standardize like the AR15 manufacturers finally did not that long ago so now different company's different AR15 parts are compatable. And as for lighter and smaller, if they are reissuing or guys are going back to the M14 for more firepower, why not the AR10 when the drills and ergonomics for it and the AR15 are very similar?

Not saying it doesn't work, just thinking there was an easier way with already proven rounds.
Just gonna keep scratchng my head over this one for now.
 

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The Shadow (Moderator)
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If anyone does go with the 6.8, and will be reloading; make sure at the least you get the SPCII chamber.
68forum will lead you to some folks and the rest of the info.
Made a big difference in my AR
 
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