.308 question

O

OctaRon1

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Sussex, New Brunswick
I had Sean put together a .308 last year and I'm finally getting to shoot some distance.
Question, I'm getting 4" to 5" 5 shot groups out to 600 yds. when I go to 700 yds the group is 10" to 12"
I know it could be the shooter but would a heavier projectile help?
I load Sierra 168 gr. HPBT with 44 gr. of Win. 748

thanks Ron
 
It's the bullet. 168 matchkings don't handle going transonic very well. Switch to 175s or another brand of 168 and your problem will go away most likely.
 
The 178 Hornady Match always shot great in my old 12 twist barrel, but as mentioned if I was in your shoes I'd either go lighter (155, lots of good choices here) or heavier (175 SMK is very easy to work with, or 185 Berger BTLR). Personally I shoot 200 Berger Hybrids in the 308 F-TR rifle Sean built me but I won't recommend them because I don't want anyone else buying up the supply.

What twist is your barrel?

Scott
 
FTRRookie said:
The 178 Hornady Match always shot great in my old 12 twist barrel, but as mentioned if I was in your shoes I'd either go lighter (155, lots of good choices here) or heavier (175 SMK is very easy to work with, or 185 Berger BTLR). Personally I shoot 200 Berger Hybrids in the 308 F-TR rifle Sean built me but I won't recommend them because I don't want anyone else buying up the supply.

What twist is your barrel?

Scott
Click to expand...

I have a 12 twist, won't I be better to go heavier I thought a 155 gr would be affected by any wind more.
 
OctaRon1 said:
I have a 12 twist, won't I be better to go heavier I thought a 155 gr would be affected by any wind more.
Click to expand...

its a trade off, lighter bullet you can push faster= less time to target = less effect by the wind. heavier bullet is less effected by wind but - slower velocity - more time to target = more time to be effected by wind
 
175 SMKs are also a good choice for you
You might try 185 Bergers but with only 1:12 - they might not shoot well for you unless you run a real hot load.
 
Berger 168 Hybrid Match Target is my choice out to 1k, great BC to make it out there without going transonic, still light enough to get good velocity without an overly hot load.
 
ultimate_monkey said:
its a trade off, lighter bullet you can push faster= less time to target = less effect by the wind. heavier bullet is less effected by wind but - slower velocity - more time to target = more time to be effected by wind
Click to expand...

At 700 yards they aren't going transonic..

The above is correct, but depends what you want to do. A 200+ Gr bullet will be going faster than a 168 or 178 grain at 1000yards and delivery more force when it gets there. It also bucks the wind better.

For reference, my mild load on a 208gr AMAX will delivery over 1000 ft-lb force at I believe around 1400 FPS at 1000yards. The 178 or a 168 won't come close to matching either of those numbers. Yet when that AMAX leaves the barrel it's going a modest 2485 FPS in a very safe powder charge vs the 2700+ out of a 168-175ish with moderate powder charge.

Really depends what you want to do. Have fun doing what you are doing. Reloading is a lot of fun when you consider the variables and what you want to do with them.

My last outing this weekend was 5/5 shots at a 10" gong at 850 yards in gusty wind conditions! I was stoked! Not spectacular by any means but rewarding none-the-less.

Some day I would like to try the 155 scenars though.
 
Shibby! said:
At 700 yards they aren't going transonic.
Click to expand...
It might be. The transonic zone is generally considered between Mach 0.8 and Mach 1.2.
With an estimate of 2650fps velocity based on 44.0 gr of 748,, and running these numbers through JBM then this baby enters the zone at 700m.
The consensus is that the 168 SMK doesn't handle the transonic zone very well, other designs of similar weight may do better.
Best to avoid it altogether and either go lighter/faster, or heavier/slower to stay supersonic throughout the range you intend to shoot to.

Calculated Table
Range Mach
100 2.151
200 1.968
300 1.795
400 1.63
500 1.472
600 1.321
700 1.178
800 1.044
837 0.999
900 0.947
1000 0.901
1100 0.864
1200 0.831
 
Last edited:
Thanks for all the info gents, it helps a lot.
I'm thinking I'll order some 155 Scenar and 185 Scenar try both and see what results I get.
Good to know the 168 SMK is my problem and not just my poor shooting.

Thanks Again
Ron
 
"...It's the bullet...." Yep. You might want to think about using a different power too though. IMR4064, for example.
"...have a 12 twist..." That'd be unusual for a .308. 1 in 10 is the norm.
"...believe the 155 Palma (sierra) was..." Yep, but the Palma rifles are heavy barreled single shots. Fourteen or 15 pound beasts.
 
Shelldrake said:
It might be. The transonic zone is generally considered between Mach 0.8 and Mach 1.2.
With an estimate of 2650fps velocity based on 44.0 gr of 748,, and running these numbers through JBM then this baby enters the zone at 700m.
The consensus is that the 168 SMK doesn't handle the transonic zone very well, other designs of similar weight may do better.
Best to avoid it altogether and either go lighter/faster, or heavier/slower to stay supersonic throughout the range you intend to shoot to.

Calculated Table
Range Mach
100 2.151
200 1.968
300 1.795
400 1.63
500 1.472
600 1.321
700 1.178
800 1.044
837 0.999
900 0.947
1000 0.901
1100 0.864
1200 0.831
Click to expand...

That seems like a nice program for calculating mind telling me were you got it?
Ron
 
sunray said:
"...It's the bullet...." Yep. You might want to think about using a different power too though. IMR4064, for example.
"...have a 12 twist..." That'd be unusual for a .308. 1 in 10 is the norm.
"...believe the 155 Palma (sierra) was..." Yep, but the Palma rifles are heavy barreled single shots. Fourteen or 15 pound beasts.
Click to expand...

Actually 1:12 is very common. 1:10 is more rare in the long range world. Standard twist rates for Palma shooting in Canada is 1:13. Shooting 155s does not call for anything faster. FTR guys like 1:11 for the 185s.
 
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