Converting a 5.56 to 308

[bluetrane2028]

Probably will go with 7.62 by 39 as I don't want to reload and it's cheaper than a 300 blackout.

If it's just the cost of ammo, I'd still go 300. Same mags you have now and 7.62 uppers can be very finicky from what I've seen.

[ExFlyinguy]

Probably will go with 7.62 by 39 as I don't want to reload and it's cheaper than a 300 blackout.

If that is your choice, Empty Mag can probably help a lot. He's got a few threads here about his x39 build

Here's one of them: http://forum.pafoa.org/showthread.php?t=352379

[bamboomaster]

below is a list of calibers that work in a Ar15 lower. There are some bolt action uppers that fit the lower but they will not feed through the mag well, i.e. 50 bmg.
Rimfire calibers
.17 Mach 2
.17 HMR[1]
.17 Winchester Super Magnum[1]
.22 Long Rifle[2]
.22 Winchester Magnum Rimfire[1]
Centerfire calibers imperial measurement
.17 Mach IV
.17 Remington Fireball
.17 Remington[1]
.17-223[3]
.20 Practical[4]
.204 Ruger[1]
.222 Remington
.223 Remington
.22 PPC
.22 Nosler
.224 Valkyrie
.224 Kritzeck (Shortened .223 remington neck)[6]
.223 Winchester Super Short Magnum[5]
.243 LBC[3]
.243 Winchester Super Short Magnum[5]
.25 Winchester Super Short Magnum[5]
.25-45 Sharps
.277 Wolverine (6.8×39mm)
.30 Carbine[1]
.30 Remington AR[7]
30 American[8]
300 OSSM[5]
300 AAC Blackout (7.62×35mm)[7]
.300 Whisper[7]
.350 Legend[9]
300 HAM'R - Wilson Combat[10]
358 Yeti - Wildcat[11]
375 SOCOM
.40 S&W[12]
.45 ACP[13]
.450 Bushmaster[1]
.458 SOCOM[14]
.50 Action Express
.50 Beowulf[15]
Centerfire calibers metric measurement
5.45×39mm[1]
5.56×45mm NATO
FN 5.7×28mm
6×45mm
6.5mm Grendel[1]
6.8×39mm (.277 Wolverine)[16][17]
6.8mm Remington SPC[7]
7.62×37mm Musang
7.62×39mm[7]
7.62×40mm Wilson Tactical[7]
7.92x33mm Kurz
9×19mm Parabellum[2]
10mm Auto[13]
9x39mm[18]

I'm not surprised that 9.3x74R isn't on the list...

But .45-70 should be...

9.3x74R.jpg

[akley88]

[QUOTE=bamboomaster;4135583]I'm not surprised that 9.3x74R isn't on the list...

But .45-70 should be...

i havent seen that in an ar 15 platform but phoenix weaponry does make a 45/70 AR based on a 308 lower, but its pricey. i would think 45/70 might be a little to long for a standard ar15 lower.

[R L Suehr]

I'm not surprised that 9.3x74R isn't on the list...

But .45-70 should be...

9.3x74R.jpg

[QUOTE=akley88;4135588]

I'm not surprised that 9.3x74R isn't on the list...

But .45-70 should be...

i havent seen that in an ar 15 platform but phoenix weaponry does make a 45/70 AR based on a 308 lower, but its pricey. i would think 45/70 might be a little to long for a standard ar15 lower.

458 socom mimics it ballistically pretty well.

[Emptymag]

If it's just the cost of ammo, I'd still go 300. Same mags you have now and 7.62 uppers can be very finicky from what I've seen.

That's internet fiction.
It used to be true before extended firing pins and the introduction of C-Products Defense mags.
No longer.

The only real potential issue with a 7.62x39 AR is the bolt.
Since it uses the same bolt as a 5.56 with the bolt face machined to fit the larger case, the bolt face is thinner, creating the potential for breakage.

I'm not reading anything to suggest it's a common issue - just that it's a POTENTIAL issue.

Buy a spare bolt.

[akley88]

458 socom mimics it ballistically pretty well.

My socom is one of my favorite rounds.

[DukeConnor]

below is a list of calibers that work in a Ar15 lower. There are some bolt action uppers that fit the lower but they will not feed through the mag well, i.e. 50 bmg.
Rimfire calibers
.17 Mach 2
.17 HMR[1]
.17 Winchester Super Magnum[1]
.22 Long Rifle[2]
.22 Winchester Magnum Rimfire[1]
Centerfire calibers imperial measurement
.17 Mach IV
.17 Remington Fireball
.17 Remington[1]
.17-223[3]
.20 Practical[4]
.204 Ruger[1]
.222 Remington
.223 Remington
.22 PPC
.22 Nosler
.224 Valkyrie
.224 Kritzeck (Shortened .223 remington neck)[6]
.223 Winchester Super Short Magnum[5]
.243 LBC[3]
.243 Winchester Super Short Magnum[5]
.25 Winchester Super Short Magnum[5]
.25-45 Sharps
.277 Wolverine (6.8×39mm)
.30 Carbine[1]
.30 Remington AR[7]
30 American[8]
300 OSSM[5]
300 AAC Blackout (7.62×35mm)[7]
.300 Whisper[7]
.350 Legend[9]
300 HAM'R - Wilson Combat[10]
358 Yeti - Wildcat[11]
375 SOCOM
.40 S&W[12]
.45 ACP[13]
.450 Bushmaster[1]
.458 SOCOM[14]
.50 Action Express
.50 Beowulf[15]
Centerfire calibers metric measurement
5.45×39mm[1]
5.56×45mm NATO
FN 5.7×28mm
6×45mm
6.5mm Grendel[1]
6.8×39mm (.277 Wolverine)[16][17]
6.8mm Remington SPC[7]
7.62×37mm Musang
7.62×39mm[7]
7.62×40mm Wilson Tactical[7]
7.92x33mm Kurz
9×19mm Parabellum[2]
10mm Auto[13]
9x39mm[18]

That is very informative. Thanks for posting that.

[Emptymag]

That is very informative. Thanks for posting that.

Yeah, now we all know what to do with all those 80% lowers we have laying around!

[R L Suehr]

My socom is one of my favorite rounds.

Yeah, I keep meaning to build one. Something always comes up and I get side tracked. One of these days though.