What AR alternative calibers fit standard metal GI mags without modification?

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Have an extra illuminated scope lying around that I think I want to build a non-223/556 upper for. What higher power cartridges fit in a standard metal mag without having to cut anything or bend up feed lips? Have a bunch of "pre-ban" standard capacity mags that I want to utilize and not damage... Was thinking vanilla 300 blk, however I'm not sure it's much of an "upgraded" caliber, and I think I've read somewhere that the 6.8 rounds require cutting and/or bending... Suggestions?
 

teamRR

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Mags for ARs are kinda the cheapest thing, especially when you get into the boutique calibers.

6.5 Grendel would be where I'd go for AR15 alternatives but they take different mags, however also you only need 10 rounds for that really since it's generally for distance and not dumps... if it's a different caliber for dumps you want well 300 blk is the ticket.
 
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Mag dumps are lame. I have a bunch of older mags already. Limited capacity mags are typically expensive, are they not? Also, does the 6.5 use the standard 556 bolt/buffer?
 

Mountain

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+1 for .458 SOCOM. Barrel swap (including gas block and gas tube) plus bolt will do it. Of course easier just to swap out a BCG but you can save a little via only replacing the bolt. This caliber is insanely fun at the range and was devastating on pumpkins back in the NES Pumpkin Shoot days. Ammo is very pricey but once you buy the brass it can be reloaded on the cheap. My go to is 300 grain Hornady JHP's and 4198 powder.

I bought my upper years ago from Radical Firearms. Was fairly inexpensive at the time- seems like their price is much higher now. 16'' 458 SOCOM Complete Upper with FHR Mine is very accurate and has operated flawlessly.
 

CrackPot

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458 Soccom fits 10 rounds in standard 30 round mag. Couple gotchas. Does not work in 223/556 PMAG or equivalent since they out a ridge down the middle of the front to help with separation. That is right where the bullet tip goes for 458. Second is the follower is less than ideal and worth replacing.

If you get 458 marked magazines, you can buy them new. They LOOK like a 30rd mag, but have a 458 follower and only take 10 rds.
 
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Mags for ARs are kinda the cheapest thing, especially when you get into the boutique calibers.

6.5 Grendel would be where I'd go for AR15 alternatives but they take different mags, however also you only need 10 rounds for that really since it's generally for distance and not dumps... if it's a different caliber for dumps you want well 300 blk is the ticket.
You can get 8-9 to feed in standard ar mags
 
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HERE YOU GO. Just change the mag. Problem solved!



RC
 

xjma99

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300BLK is fun. Versatile, cheap, plentiful. That’s a good combination.
I wouldn’t say cheap!! Atleast not the subsonic stuff!
OP, what are you looking to do? 300 blackout is more a cqb round than a reach out and touch you round.
 
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Personally, I'd lean towards the .20 Practical.


.17-223

.19-223
Features of the CZ 527 chambered in the 19-223 Calhoon include:

  • ballistics of a 22 caliber, velocities of the 220 Swift, yet low fouling and low recoil
  • expect velocities of 4050 ft/sec with a 32gr bullet, 3850 with a 36gr, 3750 with a 40gr, and 3650 with tthe 44gr
  • the 19-223 Calhoon easily matches the velocities of the 17 Rem but with a considerably heavier bullet (eg: 19-223 Calhoon shoots the 40 gr at 3750 ft/sec. while the17 Rem shoots the 30gr at 3600 ft/sec )
  • broad range of bullet weight choices ( 32gr, 36gr, 40gr, and 44gr), making the 19-223 Calhoon an excellent rifle for everyone from the varmint / pelt hunter to the game hunter.
  • typical accuracy of 1/2 minute or better
  • Pac-Nor Super Match, handlapped barrel in varmint or sporter contours, in 2 barrel weights, .750" at 26" or .650" at 24"
  • the CZ 527 is a true 223 sized Mauser style, dual front-locking lug, action with a compact .585" bolt diameter and 6" overall length
  • bedded receiver with a free floated barrel
  • barrel channel venting just like the target rigs
  • 20 ounce trigger with a set trigger feature that will go adjust down into ounces
  • low recoil and very flat shooting
  • 5 round detachable magazine or single shot follower
  • special appealing insignias to add collectability
  • factory loaded ammo or brass


.20 Practical

Not sure:
30 AR? / AR 30? (Remington)

the cartridge finally established the AR-15 as a true big game rifle

A .30 caliber cartridge designed specifically for the AR-15 platform.

"By now you might be asking yourself, why bother? Remington already has the R-25, and why buy a rifle chambered for a .300 Savage-equivalent cartridge when the R-25 is available in .243 Winchester, 7mm-08 Remington and .308 Winchester? I can think of three reasons worthy of consideration. For one, the versatility of the R-15 is easily increased by switching out its upper for one in .204 Ruger, .223 Remington or .450 Bushmaster, an option that's not possible with the R-25. For two and three, the R-15 is lighter and less expensive than the R-25."




.277 Wolverine?
"The .277 Wolverine is a wildcat cartridge. It is a multi-purpose mid-power cartridge with increased ballistic performance over the AR-15's traditional .223 Remington cartridge requiring only a new barrel to upgrade/convert any 5.56-based firearm to .277 Wolverine "






.17 Remington?
.17 WSM (Franklin Armory rimfire upper)
 
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