ar-15, 5.56x45, 7.62mmI was looking at building a AR-15 style rifle chambered in 300 AAC Blackout (7.62x35mm). The cartridge is designed to feed from a standard 5.56mm STANAG-compatible magazine and lower receiver. The twist rate of a Blackout barrel is 1:8”, while I have seen 7.62 NATO usually has a twist of 1:12”.
My question is this: I know you can easily convert from 300 AAC Blackout to 5.56 NATO by simply changing the whole upper assembly and using the same magazine, now loaded with 5.56 ammo. But can you change the lower receiver and use a 7.62 NATO (i.e. AR-10/SR-25) lower and magazine and shoot 7.62 NATO out of it?
EDIT: After further research, the 300 AAC Blackout round uses the standard M4 (5.56mm) upper. So converting it to 7.62 NATO would necessitate changing the upper and lower. But can 7.62 NATO be shot through the 300 AAC Blackout barrel?
No. The bullet is the same diameter, but the chamber (the portion that the loaded round is inserted into) is entirely different. This is a feature that is machined in to the barrel. The 7.62 NATO will not fit in the 300 AAC chamber. Additionally, barrels made for 7.62 NATO AR-style rifles use a larger barrel extension, to mate with a larger bolt than the 300 AAC.
7.62NATO CartridgeABSOULUTELY DOES NOT FIT INTO THE CHAMBER! This cartridge is an A10 designed Automatic Rifle Cartridge is Also Known As 308 Winchester for non military chamber rifles with 100 to 220 grain weight bullets available. NATO is military specification for pressure, powder, and bullet design for defense. The 300aac blackout is a .308 Diameter bullet in a 5.56/223 CASE that is cut down, shouldered to 35mm Length,Case Neck formed to fit the chambe’s shoulder thus a 7.63x35mm CARTRIDGE. A .308 bullet diameter to pass through a .300 rifle bore that accomidates the rifling grove diameter to allow the bullet to pass through. Light bullets need a SLOW twist like 1:12 for 50 graine an lighter bullets in the 5.56/223. 30 caliber bullets use 8:1, 9:1, 10:1, to stabilize heavy bullets 150 to 220 grain weights @3000FPS & 11:1, 12:1 for lighter weight bullet stabilzation. Any bullet can be fired in any twist BUT ACCURACY MAY FAIL!! The 300AACBlkOut is a 30 caliber bullett in a 5.56/223 case! The AR is primarliy a short range hard hittingMax Penetration SubSonic Designed for low Sound Supression in short barrels. & can be shot SUPERsonic for tough Game at short ranges Like BigBoarHogs! You cant puta 7.62 NATO roud in a 300AACblkOut Chamber PERIOD! If this doesnt make sense to you then DFWI!
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