Thread: Best 7.62x39 subsonic loads and tips

Originally Posted by KaneB

Thanks for the tip mate, im new to reloading and still yet to test them, could you please explain the benefits of seating the projectiles to the length of the mag vs seating the projectile lower, I also have some high velocity projectiles I plan on loading once I get this rifle sorted so all tips and info are welcome. Thanks

Driverman explained the case for seating bullets pretty damn well from the point of view of dealing with the specifics of 7.62x39.

Here's my 2 cents on the broader reasons for seating bullets mag length, or deeper.

Seating bullets mag length,ie as long as you can reasonably load them, is a safe bet from the point of view of pressure. The deeper you load them, the more pressure generated inside the case. There's a margin where seating them deeper isn't gonna be a problem particularly, so it's not as if it's a no-no.

The other problem is what's called a compressed load. This is where the bullet is seated so deep that it starts to scrunch up the powder in the case.
Sometimes it can be done, sometimes it's a bad idea. It ramps up the pressure inside the case .
ADI loading tables put a "C" beside compressed loads, eg 40.5C (40.5 grains of powder, compressed load)
Too much pressure, and things like primers popping out or being pierced, cases separating inside the rifle,and other unsettling stuff happens.

Trailboss doesn't like being compressed. It may not actually be dangerous ( debatable) but the performance of the loads is said to become erratic.

The other reason for seating at mag length is that the projectile is sitting in the chamber a little bit closer to the rifling than it would be otherwise.
Rifling is composed of lands and grooves.Think of this as being like a rut in a muddy field. The lands are the high edges of the rut , the grooves are the bottom of the rut.

Once it's fired, the lands grip the projectile and spin it, making it stable.

The notion ( as I understand it) is that the shorter the jump for the projectile from the neck of the case to the lands, the better.
I think it helps with bullet stability in flight.

Each rifle has a sweet spot for seating projectiles that it responds to best. Some people swear by seating projectiles long like this, some say that their rifle works better when they do the opposite.

The main thing is not to seat the projectile so deep that there's a kaboom, and your rifle turns into a cloud of flying parts.

There's more to it than this, but that's the short version.

It would be a good idea to google "rifle case overpressure signs" and look at pictures of loads that show danger signs. I generally look at my cases when I've fired them to see if there are any indicators.