Knowledge sought 308 supersonic at a grand

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Markit

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I am just getting back into the mid to long distance game and was hoping to source some info / knowledge from experienced 308 long distance shooters.

The question is, is it possible to load a 308 such that it will maintain supersonic to a grand out of a 20” tube.

I have a used savage 10tr with 20” barrel 5R rifling and am debating rebarreling to a 6.5 creedmore if this is not possible out of the rifles current configuration.

All my prior long distance shooting was with a 300 win mag but I have a lot of 308 reloading experience mainly for gas guns out to 600m or so and hunting, nothing for long distance.

Any info and or load suggestions would be appreciated.

Marc
 
A pretty quick google search yielded this result on another forum. (Don't think I'm allowed to hotlink to other gun forums?)

h ttp://www.sniperforums.com/forum/cartridges-calibers/32340-308-supersonic-load-1000-yards-out-20-inch-barrel.html
 
Markit said:
I am just getting back into the mid to long distance game and was hoping to source some info / knowledge from experienced 308 long distance shooters.

The question is, is it possible to load a 308 such that it will maintain supersonic to a grand out of a 20” tube.

I have a used savage 10tr with 20” barrel 5R rifling and am debating rebarreling to a 6.5 creedmore if this is not possible out of the rifles current configuration.

All my prior long distance shooting was with a 300 win mag but I have a lot of 308 reloading experience mainly for gas guns out to 600m or so and hunting, nothing for long distance.

Any info and or load suggestions would be appreciated.

Marc
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Yes, no problem, so long as you use a suitable bullet with a good BC.

Work up, testing for accuracy and velocity. Accuracy is the more important variable.

I have done a fair amount of shooting at 1200 yards with 308 ammo that was not super-sonic. Have never seen anything unusual about the shooting results, other than that a small wind change made a big difference on the target.

Is something bad supposed to happen when a bullet goes sub sonic?

I say that with tongue in cheek because we shoot black powder 600 to 1000 yards, and our bullets are subsonic by 300 yards.
 
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Transonic Flightis the portion of the bullet’s flight where the speed has dropped to around Mach 1.1 and continues to around Mach 0.9. In simple terms, that guys like me can make sense of, it just means the bullet is transitioning from supersonic to subsonic flight. The part to remember is when you fire a rifle and hear the crack what you just heard was the bullet breaking the sound barrier. It’s jumped to a point where it’s traveling faster than the speed of sound. That’s roughly 1100fps and varies according to environmental conditions.

While the bullet is supersonic it is moving faster than the sound it produced when it was fired. However, as it slows down over time and distance the sound will eventually catch up. When that happens the sound wave, shock wave, whatever you want to call it…will catch up and pass the bullet. When that happens it tends to destabilize the bullet’s flight. The bullet no longer flies predictably and accuracy typically suffers greatly.
 
Eynhallow said:
Transonic Flightis the portion of the bullet’s flight where the speed has dropped to around Mach 1.1 and continues to around Mach 0.9. In simple terms, that guys like me can make sense of, it just means the bullet is transitioning from supersonic to subsonic flight. The part to remember is when you fire a rifle and hear the crack what you just heard was the bullet breaking the sound barrier. It’s jumped to a point where it’s traveling faster than the speed of sound. That’s roughly 1100fps and varies according to environmental conditions.

While the bullet is supersonic it is moving faster than the sound it produced when it was fired. However, as it slows down over time and distance the sound will eventually catch up. When that happens the sound wave, shock wave, whatever you want to call it…will catch up and pass the bullet. When that happens it tends to destabilize the bullet’s flight. The bullet no longer flies predictably and accuracy typically suffers greatly.
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I have heard this before. What I would like to see is some evidence.

As I mentioned, black powder bullets leave the muzzle super sonic, but are sub sonic long, long before 1000 yards. I have not see any sign of "destabilisation".

Can you refer me to a paper on this issue? I am sure it has been tested.
 
Ganderite said:
I have heard this before. What I would like to see is some evidence.

As I mentioned, black powder bullets leave the muzzle super sonic, but are sub sonic long, long before 1000 yards. I have not see any sign of "destabilisation".

Can you refer me to a paper on this issue? I am sure it has been tested.
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Not all bullets experience the transonic zone the same. Some are barely affect, some like the 168gr SMK go bananas. The Berger 185gr Juggernaut was specifically designed to be highly stable in the transonic region.

Pretty sure Litz has a chapter on this in one of his books, I'll look tonight.
 
Remember there are shooter who comfortably shoot a 308 to 1500yds and 2000yds. There are a number of 30cal bullets that don't care about flying subsonic.

Pick one of these and send it...

100fps isn't going to make or break the end result if using the right bullet.

Jerry
 
Alpheus said:
Not all bullets experience the transonic zone the same. Some are barely affect, some like the 168gr SMK go bananas. The Berger 185gr Juggernaut was specifically designed to be highly stable in the transonic region.

Pretty sure Litz has a chapter on this in one of his books, I'll look tonight.
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I am familiar with the Sierra 168. It was designed as a 300 yard match bullet. The stability problem, as I recall, is a time issue, which just happens to be around the time the bullet is subsonic in some calibers.

I know I have done a lot of shooting at 1200 yards with ammo that went sub at around 1100. And I have done some accurate shooting at 1600 yrds with several calibers (22-250, 308 and 6.5x55) and I assume all were sub sonic by then. I have not given this issue much thought, but my own experience suggests that going subsonic, in itself, is not necessarily a big deal.

If some have noted a problem (say with the Sierra 168) it would take some testing to see if the problem is related to sub sonic or something else.

I look forward to hearing what Litz has to say.
 
Yes, OP, you can make 1000yds supersonic with the right bullet.

I've been working toward the outer limits with my .308 18.5" bbl, and my data suggests I should be able to get there too. Unfortunately for me I'm having trouble finding a high BC bullet the 1:12 twist in my gun will shoot well.

If you have a 1:10, I would suggest RL-17 under Hornady 168gr ELD-M.

As more experienced shooters have pointed out, some bullets retain stability better than others through transonic, but I have little experience in this area, and thus nothing of value to contribute.
 
Ganderite said:
I have heard this before. What I would like to see is some evidence.

As I mentioned, black powder bullets leave the muzzle super sonic, but are sub sonic long, long before 1000 yards. I have not see any sign of "destabilisation".

Can you refer me to a paper on this issue? I am sure it has been tested.
Click to expand...

http://www.accurateshooter.com/ballistics/transonic-effects-on-bullet-stability-bc/
 
Thanks all.

The members of this site are a wealth of knowledge - thanks for sharing.

I will try the powder (I have RL17 and some others) and the projectile Hand Skills and Alta Tactical (Rick?) recommends.

For my gas gun with a 1:10 18.5” tube I have been using 155 and 168 gr AMAX as well as 168gr Hornady BTHP Match out to 500 and just beyond, but i dont think these projectiles have a good enough BC for LR from a 1:10 bolt gun.

Cheers,

Markit
 
Markit said:
Thanks all.

The members of this site are a wealth of knowledge - thanks for sharing.

I will try the powder (I have RL17 and some others) and the projectile Hand Skills and Alta Tactical (Rick?) recommends.

For my gas gun with a 1:10 18.5” tube I have been using 155 and 168 gr AMAX as well as 168gr Hornady BTHP Match out to 500 and just beyond, but i dont think these projectiles have a good enough BC for LR from a 1:10 bolt gun.

Cheers,

Markit
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If you can get 2850 from the 155s you should be ok to 1000. Try 44 to 47 gr of Varget. I would try something like the 168 Amax, too.
 
When using Silver Mountain targets, which use the shock wave of the bullet (the small supersonic boom) to register the shot on target, I have found that it's "hit and miss". Sometimes it will register and sometimes not. But that's You may have to use a 155 gr bullet loaded fairly stoutly to keep it super at 1000.
 
Example is an exercise we do for fun sometimes to test our skills and load limits: 26" Barrel in my Stealth II with 168gr SMK I can (inconsistently) hit 2L plastic bottles at 980m but put it at a mere 20m farther and I have yet to touch it with these bullets (knowing they are not recommended past 600m) . Point is.... the right bullet combined with the right amount of velocity and you will hit consistently at 1000m.

While accuracy is ultimately everything in precision shooting (that's the point right?) when you really stretch it out you will find that you may sometimes need to sacrifice some accuracy points to boost velocity so that you can be effectively on target at EXTENDED ranges.

Long distance shooting is a science / passion and half the fun is getting there... after that, hitting your target is the easy part. Enjoy, stick with it (don't get too frustrated) and most importantly have fun.
 
Many years ago I loaded some Sierra Matchkings the 220 grain bullet to the maximum for the 308. It took 2 or 3 goes to get the powder into the case and one or two of the cases deformed but I was shooting really well at 1000 yards mainly due to a brilliant wind coach. I used a rebarrelled P14
 
Eynhallow said:
Transonic Flightis the portion of the bullet’s flight where the speed has dropped to around Mach 1.1 and continues to around Mach 0.9. In simple terms, that guys like me can make sense of, it just means the bullet is transitioning from supersonic to subsonic flight. The part to remember is when you fire a rifle and hear the crack what you just heard was the bullet breaking the sound barrier. It’s jumped to a point where it’s traveling faster than the speed of sound. That’s roughly 1100fps and varies according to environmental conditions.

While the bullet is supersonic it is moving faster than the sound it produced when it was fired. However, as it slows down over time and distance the sound will eventually catch up. When that happens the sound wave, shock wave, whatever you want to call it…will catch up and pass the bullet. When that happens it tends to destabilize the bullet’s flight. The bullet no longer flies predictably and accuracy typically suffers greatly.
Click to expand...

Bullets are not just destabilized when their own sound wave catches up to them. I have never studied this, but in fact I would suggest that a sound wave impacting a bullet in flight would have virtually no effect at all.

Otherwise shooting ranges would be filled with bullets getting knocked all over the place by other peoples sound waves.

As a bullet plows through air, it creates waves. At supersonic speed that wave is created behind the bullet exclusively. At sub sonic speed the wave is emitted in all directions. With the waves exclusively behind the bullet, the pressure behind the bullet is higher than at subsonic speed, and results in the Centre of gravity of the bullet being slightly further towards the rear. When the bullet drops below subsonic speed, that wave formation transitions through the bullet immediately, the pressure behind the bullet reduces, and the CoG of the bullet shifts forward. That shift in CoG is what destabilizes the bullet and causes it to tumble. Different bullet geometries will be more or less vulnerable to this shift. Brian Litz describes this effect more scientifically then I can, but I just wanted to point out that the trans sonic shift happens immediately, regardless of whatever head start a bullet might have on its own sound wave.

I am sure you can get a 308 bullet subsonic out to 1000, but that 20" barrel is a serious handicap.
 
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