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Discussion Starter · #1 ·
Gun shop wisdom has claimed that you can. The overall length for both cartridges is relatively the same, and they both function from the same lower receivers and mag wells. Let's look at it a little closer though.

The 6.8 case is obviously larger in diameter. Loading the larger 6.8 case into the narrow recess causes binding of the stack and exerts outward force that bulges the magazine. In the chart below, I loaded 6.8 rounds into 2 5.56 mags until they wouldn't take anymore. The GI mag held a few more but was binding heavily before I quit trying. The measurements were taken just below the mag well.

Mag Bulge Comparison
Unloaded5.566.8
CProducts LLC 6.8.906"NA25 rds / .912"
D&H 6.8.871"NA25 rds / .872"
GI 5.56 (Sanchez).902"30 rds / .905"13 rds / .978"
PMag.882"30 rds / .883"10 rds / .907

Interestingly, except for the CProd, each mag only grew .001 when fully loaded with the proper ammo (Cprod grew .006). However, jamming the 6.8 rounds into the 5.56 mags grew them .076 for the GI and .025 for the PMag. This indicates that the stack is trying to force itself outward instead of upward, and will be problematic to feeding.

5.56 Magazines with correct load.



6.8 in 5.56 Magazines.



It is also discussed that a 6.8 follower can be inserted into the 5.56 mag for better function. Maybe, I find the benefit unlikely, but neither the CProducts or D&H 6.8 followers would fit in the GI or PMag. It should also be noted that D&H's follower is made by MagPul but stamped 6.8.

Finally, it could also be argued that the 5.56 mag feeds fine if downloaded to 5-6 6.8 rounds. Sure, especially the PMag, both magazines didn't have much binding until 8+.

In conclusion, it is generally accepted that the primary cause of an autoloader's failure is the magazine. This is an area where reliability is a big concern so I would rather not risk function for convenience. In the long run, 6.8 magazines are not rare and are comparably priced with their little cousins. Can I use a 5.56 mag for 6.8 SPC? Short answer, no.
 

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Nice post, well illustrated and logical...but someone, somewhere is getting ready to type their first post and will ask if they can use 5.56 mags in a 6.8.
 

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Sticky!!

or

Maybe we can get Paulo to add it to his 6.8 spc guide...and then when a new member registers on the forum, the confirmation email comes with Paulo's guide!!

Since it answers 99% of the basic new to 6.8 questions
 

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Thanks for the information, well put together.
 

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Great information.

Since all the other stickies work so well. (Sarcasm). Lets see how this one works.


Sent from my island villa by carrier pigeon.
 

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Discussion Starter · #11 ·
Since all the other stickies work so well. (Sarcasm).
I know, right. At least someone can just link to it and skip the drama.
 

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First off, thanks for this. Answered a lot of my questions concerning magazines for the 6.8
Second, I found it all by myself by searching, instead of wasting bandwidth asking in a separate thread, and getting told to search. :)

Found answers to some other things I was wondering through searching too (about Magpul's 6.8 mag only for LWRC, and about a simple follower change wouldn't work).

Just ordered up a couple PRI 15 rounders tonight
 

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Gun shop wisdom has claimed that you can. The overall length for both cartridges is relatively the same, and they both function from the same lower receivers and mag wells. Let's look at it a little closer though.

The 6.8 case is obviously larger in diameter. Loading the larger 6.8 case into the narrow recess causes binding of the stack and exerts outward force that bulges the magazine. In the chart below, I loaded 6.8 rounds into 2 5.56 mags until they wouldn't take anymore. The GI mag held a few more but was binding heavily before I quit trying. The measurements were taken just below the mag well.

Mag Bulge Comparison
Unloaded5.566.8
CProducts LLC 6.8.906"NA25 rds / .912"
D&H 6.8.871"NA25 rds / .872"
GI 5.56 (Sanchez).902"30 rds / .905"13 rds / .978"
PMag.882"30 rds / .883"10 rds / .907

Interestingly, except for the CProd, each mag only grew .001 when fully loaded with the proper ammo (Cprod grew .006). However, jamming the 6.8 rounds into the 5.56 mags grew them .076 for the GI and .025 for the PMag. This indicates that the stack is trying to force itself outward instead of upward, and will be problematic to feeding.

5.56 Magazines with correct load.



6.8 in 5.56 Magazines.



It is also discussed that a 6.8 follower can be inserted into the 5.56 mag for better function. Maybe, I find the benefit unlikely, but neither the CProducts or D&H 6.8 followers would fit in the GI or PMag. It should also be noted that D&H's follower is made by MagPul but stamped 6.8.

Finally, it could also be argued that the 5.56 mag feeds fine if downloaded to 5-6 6.8 rounds. Sure, especially the PMag, both magazines didn't have much binding until 8+.

In conclusion, it is generally accepted that the primary cause of an autoloader's failure is the magazine. This is an area where reliability is a big concern so I would rather not risk function for convenience. In the long run, 6.8 magazines are not rare and are comparably priced with their little cousins. Can I use a 5.56 mag for 6.8 SPC? Short answer, no.
Best & and most complete answer I have ever seen to this question!
 

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Tried this today with a Lancer 10 round. Nice steel feed lips, smoke body, you get to see exactly why it's not working right on top - the ribs are too close internally and the stack of rounds push them out. More than five, you get into difficulties fitting the mag well, and the first rounds won't always chamber. The internal friction is too high.

Wilson was machining Lancers IIRC to fit their proprietary cartridge. The exterior of the rib isn't highly recessed, possibly more room could be made. Or - you could run reliable factory mags instead of home shop versions, and not have to worry about it.

I tested three different make rounds in the 110-115 range, Federal Fusion, Hornady VMax, and Remington Express, loading to maximum of 8 to 9 rounds - which wouldn't easily insert in the magwell. After down loading to 6, it would fit, but chambering the first round was problematic. With 5, it would at least chamber and cycle ammo thru by hand. Anecdotal posts here all seem to indicate only 5 rounds seem to be reasonably reliable as a load.

So, to sum up, can you use one of these, no. Can you load it and get them to cycle a few rounds, maybe. Should you rely on it, not if your life depends on it. Am I taking it deer hunting next weekend, well, I won't confirm or deny it. Should you? Can't say.

Should be pretty clear.
 

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Yup. Buy the cpd 6.8 mags, none of the 556 mags will work.

Sent from my DROID RAZR using Tapatalk
 

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Try posting a wtt in the equipment exchange. You never know.

Edit- just noticed you are less than 50 posts, a little conversation and you will get there, then post in the ee.

Sent from my DROID RAZR using Tapatalk
 
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