Quick question on .308 velocity

[Pappy83]

My daughter wants to shoot in a 1000yd prone match in a few weeks. I have been reloading for her savage precision carbine with 14.5 inch barrel and fixed muzzle break(She is only 95 pounds)for over a year now. She can usually shoot sub 1 inch 5 shot groups at 200yds with it(100yd goups are consistently .425 to .600). I have a 180smk load that is 2610fps on average at the muzzle(this load shoots very well but is hot, and she has problems shooting anymore then 20rds). Will this be good enough for 1000yds or should I switch to either 175smk, or 155. I can push a 130gr barnes tsx to 3050fps without any pressure signs(and is comfortable for her to shoot) so I was hoping maybe I could push the 155 fast enough without beating her up to bad. Thanks for any help.

 

[uncleduke]

Well; I think you'll have a hard time with such a short barrel. A 155 weight bullet needs all the length you can get for 1,000 yds. Going up in weight might get you there ie.(200smk). You would need a 10 twist bbl. You might consider a longer pre-fit bbl. just for 1,000 yds. and the extra weight would help with the recoil. Since two weeks is not much time to get a new bbl. try as heavy a bullet as possible. The 180 smk will not shoot as fast as a Berger 180 or JLK. Post some details about the twist rate of the barrel and see who chimes in. Good luck.

 

[GermanS1]

The muzzle brake isn't rules compliant in an NRA match and the barrel is way too short to generate the MV you'll need to keep that bullet above the transonic range at 1000 yd. You can't get there from here with that setup.

 

[Kenny474]

If you really want to try and make it to the match, you might want to try and talk with Jim Briggs of Northland Shooter Supply. He has a lot of Savage barrels in stock and may have something that will get you to 1000yds, and you may be able to get one overnighted. The bad news there is the shop is closed until August 3rd.

A longer barrel is really your best bet, and finding one in 2 weeks will be tough. Though you may get lucky.

Good luck
Kenny

He does have a few Shilen stainless Pre-Fits in .308 listed with 28" and 30" lengths.

 

[Pappy83]

Thanks for the replies, so what MV do I need to stay supersonic out to 1000yds with 175smk, berger, jlk bullets. I have the stock 20 inch tube. both barrels have 1 in 10 twist. Rifle has been used out to 700yds on steel with great success with the 14.5 tube. thanks again for help.

 

[Steve Blair]

Terminal velocity must be above 1300 fps, 1400 is better. It is not sound velocity, but shock wave buffeting the bullet receives as it slows to transonic that causes problems. Some bullets are more affected than others but it is still best to stay above this region.

With the 175 Berger, that means a minimum muzzle velocity of 2760 under standard conditions.

 

[Pappy83]

I wont get there with the 14.5 tube best I have gotten is 2700 or so with 168's. I lost around 100 fps on average with each load going to 14.5 from 20. I did push 155 palmas today to 2880 average 45.8gr of IMR4895(were accurate). The 14.5 tube and chamber are fast, I dont know if it is worth trying the 20 or just buying a new barrel. thanks for the help

 

[nockhunter]

"transonic" is transitioning trough the speed of sound, a 308 rifle bullet is either subsonic or supersonic (for this discussion). All bullets start at subsonic and go through supersonic at about 1100 fps give or take a little on altitude and air temp. Breaking the sound barrier is what disturbs a bullet in flight, once going supersonic and once coming back subsonic(two sonic booms). The bullet is affected more at lower speed (going subsonic) than going supersonic.

Mike

 

[Steve Blair]

"transonic" is transitioning trough the speed of sound, a 308 rifle bullet is either subsonic or supersonic (for this discussion). All bullets start at subsonic and go through supersonic at about 1100 fps give or take a little on altitude and air temp. Breaking the sound barrier is what disturbs a bullet in flight, once going supersonic and once coming back subsonic(two sonic booms). The bullet is affected more at lower speed (going subsonic) than going supersonic.

Mike

Mike,

That is not correct. The transonic region is generally accepted to be 0.8-1.2 mach. The quote below from Bryan Litz states the problem clearly.

QUOTE
Transonic Flight
In the transonic region, the most important thing that happens is the center of pressure shifts forward as the bullet slows. That shift affects the stability of the bullet. If the bullet is not well stabilized, it cannot remain point forward thru the transonic region. However, even if the bullet has sufficient stability (static and dynamic) to be able to fly thru the transonic region and stay point forward, it is still affected. The erratic and sudden CP shift can cause dispersion, even if the bullets flight becomes well behaved again when it slows down.
-Bryan
UNQUOTE

 

[nockhunter]

Right, trans--sonic. Transition from one to the other.


Whitcomb area rule.

Severe instability can occur at transonic speeds. Shock waves move through the air at the speed of sound. When an object such as an aircraft also moves at the speed of sound, these shock waves build up in front of it to form a single, very large shock wave. During transonic flight, the plane must pass through this large shock wave, as well as contending with the instability caused by air moving faster than sound over parts of the wing and slower in other parts. The difference in speed is due to Bernoulli's principle.


Mike

 

[Steve Blair]

Mike,

I am not trying to pick a fight, but this is not an etymology question. Transonic is an aeronautics term that refers to the velocity region from approximately 0.8-1.2 mach. Citing the Whitcomb rule does not change the definition. If you think that bullet behavior is unaffected until it reaches ~1120 fps, act accordingly.

How about if I change the post to read "transonic region"? Would you regard that as more accurate?

 

[earl39]

I have a 180smk load that is 2610fps on average at the muzzle(this load shoots very well but is hot, and she has problems shooting anymore then 20rds). Will this be good enough for 1000yds or should I switch to either 175smk, or 155.

if you are getting a true 2610 with the 180's then switching to 175mk will get you to 1000 yards with just a few fps to spare (maybe 50 depending on conditions and altitude). but that short of barrel altho easy to tune really just isn't made to push a bullet to 1000 yards. I don't think you will be able to push the 155 hard enough in a short barrel to get there and don't even try 168's as they are almost a sure thing to go haywire somewhere around 800 yards even out of a long barreled 308. with a 175 berger vld you may be able to drop your speed to around 2550 and still make it to 1000 yards but that also would be a close call.
whatever you do i wish her the best of luck. 1000 yards is not as easy as a lot of expert keyboard shooters want people to think it is. and for the record i do shoot 1000 yard f-t/r altho my scores are not great. normal score is in the 170's.
German is probably correct that you can't get there from here with that setup but i think he is stating the norm where your 2610 is anything but the norm. No offense intended German love your articles