Question re subsonic 300 BLK vs. 7.62x39

[SporkInTucson]

I already load supersonic for a 7.62x39 CZ 527 and have read that loading this cartridge as subsonic can be somewhat more dangerous due to the possibility of "secondary explosive effect" (SEE).

Just recently discovered that there is a kit to turn a .223 CZ 527 into 300 BLK. I'm wondering if the risk of SEE is as great for 300 BLK. It seems like low load density increases the possibility of SEE, but I think that the 300 BLK case capacity is lower than 7.62x39, so maybe that diminishes the chances of SEE?

Really just wondering if subsonic loading of 300 BLK can be considered safer (or substantially safer) than subsonic loading of 7.62x39. Any thoughts on the matter would be appreciated. Thanks!

 

[kingmt]

Sorry but it is hard to talk about something that isn't real.

There is no proof that this has ever happened. Everyone that has tried controlled test to prove it true has proven the opposite.

You dangerous part is zoning out & putting a second charge or third in it.

 

[kingmt]

Also if that is a auto it will make a single shoot out of it. If you find someone that can do it full auto let me know.

 

[SporkInTucson]

Sorry if I'm perpetuating an urban SEE myth.

I haven't used them, but I thought that strain gauge measurements by products like PressureTrace show clear indications of secondary ignitions, when they happen.

 

[kingmt]

I have read & read on this topic & while I will say I was bias before reading them because of what I already know they have only proven it doesn't happen.

All that is happening is an explosion. Now there is tons of factors that affect the pressure & speed there is still Newtons law. When the explosion happens the pressure is expanded until it meets resistances. At that point it transfers energy to what it hits. For every action there is a equal reaction(this is happening on both sides of the bullet) so depending on how much resistances between bullet & lands how much energy is transformed into motion. The less resistances there is at a certain spot(weak spot) in this case the bullet the more energy that spot will use up taking the pressure from other spots.

I'm probably not explaining this very well though.

Any how the whole chamber absorbs pressure & flexes at the same time. The powder moving down the barrel & burning backwards causing a title wave is way out there.

 

[highlander 5]

I don't thnk you can change a 7.62x39 into a 300 BLK. The rim of the 7.62x39 is .065" larger than the 300 and the body of the 7.62 is larger and more tapered. If you got a new bolt and rebarreled yeah you could do it but it would be cheaper to buy a rifle chambered for the 300. Now if your talking duplicating the 300 by reloaing 7.62x39 accodingly that might work

 

[Fishslayer]

I have read & read on this topic & while I will say I was bias before reading them because of what I already know they have only proven it doesn't happen.

I've done a lot of reading on the topic as well & what I took away is that they have proven only that they cannot definitely prove one way or the other.

Personally, I believe some of the theories make sense. Like light bullet/slow powder .357 loads, there's enough anecdotal evidence out there that I don't think the theories are baseless.

 

[kingmt]

All the evidence I have found is someone holding a gun that is in pieces saying it most have been that thing I heard about. People don't want to admit when they make a mistake.

I believe that is how this myth started & is the fuel for the fire.

 

[SporkInTucson]

I don't thnk you can change a 7.62x39 into a 300 BLK.

I agree. I have a CZ 527 in 7.62x39 and it can't be converted to anything. But, if I buy a CZ 527 in .223, it can be converted to 300 BLK with an available barrel/stock swap. Probably not the cheapest way to get into 300 BLK, but I like 527s.

The available 300 BLK barrel is threaded and there seems to be a lot of people shooting subsonic 300 BLK so I was wondering if there's some reason why the 300 BLK cartridge is inherently better for subsonic loading compared to 7.62x39. Maybe it has nothing to do with the cartridge or subsonic load safety... Maybe it's just that the 300 BLK rifles are built to cycle when firing subsonic while most 7.62x39 autos aren't. Cycling issues don't matter to me as 527s are bolt action.