I need some educating.... 7.62x39 vs 300AAC

[SteveK]

I love the 7.62x36 cartridge. I have an Russian SKS and a Colt Sporter that shoots 'em well. I am of the opinion that the 7.62x39 cartridge is one of the finest whitetail rounds out there and have harvested many a deer with 7.62 over 20 or so years but, I have a recent burning question I can't find a good answer to.

Why in the hell does the 300 AAC, a round created by necking-up a 5.56x45 cartridge, shoot heavier bullets than the larger 7.62x39?

Thanks for your assistance.

Steve

[john hayslip]

Simply because we're using heavier bullets. The 7.62 is designed for gas guns and fairly low pressure ones (for gas guns) at that. The 223 runs at higher pressures. With the same weight bullet they are practically ballistic doubles.

[fryboy]

originally the 300 acc was designed as the 300 whisper ( or perhaps refinement of the 300 whisper may be a better term ) ,in order to be effective it had the need for a heavy sub-sonic projectile as the lighter ones lost energy too quick ,hence the 300 has a longer throat/leade designed for longer projectiles , the m-43 round ( 7.62x39 ) can be used with decent results with 150 grain projectiles but because of a shorter throat case capacity starts to suffer when heavier bullets protrude into the case space

[Rangefinder]

originally the 300 acc was designed as the 300 whisper ( or perhaps refinement of the 300 whisper may be a better term ) ,in order to be effective it had the need for a heavy sub-sonic projectile as the lighter ones lost energy too quick ,hence the 300 has a longer throat/leade designed for longer projectiles , the m-43 round ( 7.62x39 ) can be used with decent results with 150 grain projectiles but because of a shorter throat case capacity starts to suffer when heavier bullets protrude into the case space

^^Pretty much sums it up. BUT, I get very good results with 147gr. steel core pulls loaded over 27gr. H335 to 2.20 OAL through my MAK. Just barely fits the mag, cycles well, and great accuracy (so far). Haven't stretched the distance much, but checking POI on my 50yd back yard range was well within 'ragged-hole' results.

Compared to the 300 AAC, it's nearly the same animal. I've loaded 220gr. cast in x39 (PC'd to help minimize gas cutting from seating so darn deep), have a non-cycling load that sounds like a pellet gun, and a cycling load sitting right on the edge of sub-sonic that is about like a 22lr. It just takes a bit of playing to get the right combo for your rifle that will cycle those heavy pills and still stay below the 1050fps. line.

[Jupiter7]

I guess we also should add that 300blk was designed to run in an M4 magazine in an M4. Some of the objectives were to replace the mp5 suppressed with more power and accuracy with same manual of arms and 7.62x39 power with a barrel change only. If I was already invested in 7.62x39, 300blk would be a lateral move. The bullet weight is needed to cycle the action in an AR.

[Bullshop Junior]

It has to do with the twist. The SKS and AK rifles have a fairly slow twist. My handi Rifle singleshot has a 1/10 twist and I shoot the 200gn Lee RN in it.

[Bullshop Junior]

originally the 300 acc was designed as the 300 whisper ( or perhaps refinement of the 300 whisper may be a better term ) ,in order to be effective it had the need for a heavy sub-sonic projectile as the lighter ones lost energy too quick ,hence the 300 has a longer throat/leade designed for longer projectiles , the m-43 round ( 7.62x39 ) can be used with decent results with 150 grain projectiles but because of a shorter throat case capacity starts to suffer when heavier bullets protrude into the case space

The throat can be fixed though. My handi rifle has suck a long throat I can drop a 220gn RN jacketed in it and close a sized case behind it without it touching.

[bruce drake]

The guys have already mentioned the barrel-twist rate and the throating so I'll just say +1

I own AR uppers in 7.62x39 as well as 300BLK. Both get loaded with 125gr boolits and shoot equally well with 150gr bullets also.

I don't shoot or load the heavier subsonics in either. I consider both to be fine woods cartridges for deer or smaller game.

Bruce

[Bullshop Junior]

I don't believe is subsonic. My standard weight bullet in my 7.62x39 is a 150gn.

[HARRYMPOPE]

The 7.62 x 39 with a 1-12 twist in a custom Mauser had a .205(or so) 5 shot group record at 100 yards that stood for a number of years in the CBA with a 190+g bullet.In a bolt gun or single shot its a better choice than the 300 Whisper/AAC IMHO.The only advantage the AAC has is common magazine parts and bolt faces to the AR platform(and tacti-cool name)

[bruce drake]

Most 150gr bullets can easily be kept supersonic in the x39 cartridge with a number of powders. The 300BLK is do-able with H110 as well as AA1680 but the x39 has a better powder selection for the cartridge if you are running a gas system rifle.

Bruce

[supersniper]

Bullshop,

You might not believe in subsonics..... but they do exist. :P

Twist rates on SKS and AK is about 1 in 9.5" - which is plenty fast enough to stabilize the heavier boolits.

[Ed in North Texas]

Bullshop,

You might not believe in subsonics..... but they do exist. :P

Twist rates on SKS and AK is about 1 in 9.5" - which is plenty fast enough to stabilize the heavier boolits.

Hmmm. I think Dan is going to have to clarify. While I was wondering exactly what he thought IS not sub-sonic ( I tend to read what is written, which is not always correct), you thought he didn't believe IN sub-sonic (which would make sense, given the sentence construction). With the widespread use of spell check, we can't always tell if a thought was incomplete, or it was a typo.

Dan - please clarify which you intended.

[Bullshop Junior]

I don't use subsonic loads. I prefer about as heavy of a bullet as the cartridge will allow at the fastest speed I can reasonably make it shoot.

[supersniper]

Thanks for the clarification.

I was just teasing you a bit is all. We all have different preferences and requirements. I have always enjoyed experimenting (Research and Development).

[JeffinNZ]

There is a really good video on Youtube by a guy explaining the .300 BKL and why it came about. Can find the link sorry but it's very good.

[Artful]

This one?

[Artful]

Or maybe this one?

[JeffinNZ]

Or maybe this one?

Yeap, that's it. .300BLK for dummies. Really good.

[badbob454]

ill stick to my rusky sks i shoot 173 gr boolits real well , plenty of power for target shootin ... which is what i love best