Thread: Reloading and sonic crack questions

So to say I know sweet stuff all about either would be overstating it.

First question, I know that a bullet going super sonic creates a crack, does the faster the bullets going or the larger it is make it a bigger bang?

Secondly, could I for instance take a factory 7.62x39 round, rip the existing projectile out an ram a heavier one in? and if so what gear would I need to do it? or is it one of those jobs you need the full kit and start from scratch?

Cheers

Don't ever do that for your own safety. Too many people jump into reloading by getting the kit first, you need to buy a few books first and understand how to stay safe before getting into it.

Originally Posted by big_foot

So to say I know sweet stuff all about either would be overstating it.

First question, I know that a bullet going super sonic creates a crack, does the faster the bullets going or the larger it is make it a bigger bang?

Secondly, could I for instance take a factory 7.62x39 round, rip the existing projectile out an ram a heavier one in? and if so what gear would I need to do it? or is it one of those jobs you need the full kit and start from scratch?

Cheers

Well I can tell you that a jet going super sonic makes a lot more noise than a .22

Originally Posted by big_foot

So to say I know sweet stuff all about either would be overstating it.

First question, I know that a bullet going super sonic creates a crack, does the faster the bullets going or the larger it is make it a bigger bang?

Secondly, could I for instance take a factory 7.62x39 round, rip the existing projectile out an ram a heavier one in? and if so what gear would I need to do it? or is it one of those jobs you need the full kit and start from scratch?

Cheers

I used to do to .303 bullets what you are contemplating with your 7.62...I survived but know now that it was not the smartest thing to do....303 rifles are very forgiving. I wouldn't dream of doing the same thing to my 7 mm...I don't think it would be as forgiving.

Fair enough, might be something I take on later in life when Ive got a bit more spare time

Originally Posted by big_foot

So to say I know sweet stuff all about either would be overstating it.

Secondly, could I for instance take a factory 7.62x39 round, rip the existing projectile out an ram a heavier one in? and if so what gear would I need to do it? or is it one of those jobs you need the full kit and start from scratch?

Cheers

Actually asking the above question here before trying it was very smart might have even saved your life.

I'm pretty sure the crack won't get louder the faster its going, size of the projectile would effect it as it would be making as the shockwave size would be dependant on projectile size.

However the muzzle blast may be bigger because more powder was used.

And if it exited the barrel at just over the speed of sound then the it would only make the crack for the first part of its flight. But then it becomes unstable when passing back through the sound barrier.

Does any of that make sense, it barely does to me and it's just my yr13 (7th form) physics im leaning on.

Originally Posted by Chupacabra

Actually asking the above question here before trying it was very smart might have even saved your life.

I always extensively research an idea in thoery before under taking the practical

Ive just spent hours trying to find the correct valve lash setting for my suzuki before i get the spanners in there pretty sure ive got it right

the bigger the diameter of the projectile, the bigger the sonic crack will be.
a .17 sounds very quite when suppressed, even tho it is traveling supersonic, but to quieten a 500 s&w is most practical to run it sub sonic as the sonic crack it relatively loud.
back to the original question.
when you drive a car, it is safe to assume that a heaver car will consume more fuel, so the logic that a heaver bullet will need more gunpowder is a common misconception.
the reality is the opposite.
what you need to understand is that the cartridge has a set capacity. if you seat a larger bullet into the case, then it will take up more internal capacity than a smaller projectile. it go's further into the case.
given that a heaver projectile will need more energy to move, it will cause more pressure to build behind he projectile before it starts to move from the case and up the barrel.
add to that, the heaver projectile taking up more space means there is less room so the powder burning will raise the pressure levels more rapidly, there will be a combined effect within the chamber of decreased capacity and increased resistance, causing increased pressure levels.
the reality is that we are working with a set pressure level that a given chambering can handle.
so if you care to look at some reloading data from powder manufacturers, you will see a decrease in recommended powder charge with an increased projectile weight.
they want you to remain within the recommended pressure levels of the given chambering for a given bullet weight. so you don't blow up the gun.
to decrease the velocity, you may need to decrease not only the powder charge and increase the bullet weight, but change the burning rate of the powder and possibly the density of the powder.
this may sound complicated, and I suppose it is a little. but it is not beyond most sensible people. the best bet is to read and research before starting out into reloading.
better still. find someone who will take you under their wing, and set you onto the right path to reloading safely.
if I can help, I would be glad to.
greg

Originally Posted by greghud

the bigger the diameter of the projectile, the bigger the sonic crack will be.
a .17 sounds very quite when suppressed, even tho it is traveling supersonic, but to quieten a 500 s&w is most practical to run it sub sonic as the sonic crack it relatively loud.
back to the original question.
when you drive a car, it is safe to assume that a heaver car will consume more fuel, so the logic that a heaver bullet will need more gunpowder is a common misconception.
the reality is the opposite.
what you need to understand is that the cartridge has a set capacity. if you seat a larger bullet into the case, then it will take up more internal capacity than a smaller projectile. it go's further into the case.
given that a heaver projectile will need more energy to move, it will cause more pressure to build behind he projectile before it starts to move from the case and up the barrel.
add to that, the heaver projectile taking up more space means there is less room so the powder burning will raise the pressure levels more rapidly, there will be a combined effect within the chamber of decreased capacity and increased resistance, causing increased pressure levels.
the reality is that we are working with a set pressure level that a given chambering can handle.
so if you care to look at some reloading data from powder manufacturers, you will see a decrease in recommended powder charge with an increased projectile weight.
they want you to remain within the recommended pressure levels of the given chambering for a given bullet weight. so you don't blow up the gun.
to decrease the velocity, you may need to decrease not only the powder charge and increase the bullet weight, but change the burning rate of the powder and possibly the density of the powder.
this may sound complicated, and I suppose it is a little. but it is not beyond most sensible people. the best bet is to read and research before starting out into reloading.
better still. find someone who will take you under their wing, and set you onto the right path to reloading safely.
if I can help, I would be glad to.
greg

Cheers mate that put it quite simply, its not something I was going to rush out and do but this year I was thinking about getting a bolt action 7.62x39 and reloading sub sonics for bush hunting as most of my hunting is 10-30m visibility I figured it would be a bit more economic and practical than the .308 not to mention easier on the ears.

You could run the 308 subsonic and have a few full power in your pocket for a shot across a slip or cut over.

Originally Posted by veitnamcam

You could run the 308 subsonic and have a few full power in your pocket for a shot across a slip or cut over.

I was thinking about that, I didnt follow the .308 sub sonic thread how did it turn out?

Only problem with that is it doesn't include buying a new gun

308 subs have to be shot to fully appreciate how great they are.
on my mates rig on the rifle but he's got the holdover for subs and normal written on it.and he just colours the subs black

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Originally Posted by big_foot

I was thinking about that, I didnt follow the .308 sub sonic thread how did it turn out?

Only problem with that is it doesn't include buying a new gun

Spanners is producing what i think is/will be a very effective 30cal subsonic projectile, or he will be if he stops renovating the house and gets in the loading room