.308 185 gr @ 2700 fps good enough for 1000 yds?

Discussion in 'Reloading Forum (All Calibers)' started by thefitter, Dec 27, 2011.

  1. thefitter

    thefitter

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    Is 2700 fps fast enough in a .308 to get a 185 gr bullet out to 1000 yards accurately and consistently.

    The loads ES is 18 and the SD is 7.

    Good enough or should I try and find a higher node?

    Thanks
     
  2. Turbulent Turtle

    Turbulent Turtle F-TR competitor

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    What length barrel?
     
  3. Bob3700

    Bob3700

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    If you have 2700 fps, that will get you to 1K with a 185 Berger.

    Shot those at 2620 fps out of an M14 and they made it to 1K no sweat.

    Bob
     
  4. thefitter

    thefitter

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    24"
     
  5. fullersson

    fullersson B&B Gunworks bbgunworks.com

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    I've seen that combination of bullet and speed shoot a 3" group and 900 yards. Brian Brown.
     
  6. Turbulent Turtle

    Turbulent Turtle F-TR competitor

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    With a 24 inch barrel, I don't think you are going to get much more velocity. In fact, I think you are doing pretty good right now. JBM shows that with the 185 Berger LR, at 1000 feet altitude in 70 degree weather, 50% humidity, your bullet is arriving at 1000 yards at about Mach 1.24 (1405FPS) and that is right at the beginning of the transonic disturbance area. I like to keep them above Mach 1.25 so you're doing pretty good. If the load groups well, have fun with it.
     
  7. Laurie

    Laurie

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    You don't say which 185 - there is a huge difference in the G7 BCs of the 185gn Lapua Scenar and the same weight Berger Long-Range BT. 2,700 fps MV with the latter is fine, but as others have suggested you'll be lucky (and maybe unsafe too) to get that velocity from 24". 2,775 to a wee bit over 2,800 fps is the norm from a properly throated 30" using full pressure loads, and a 6" barrel length reduction will usually knock 240-300 fps off.

    I'd always advise 24" barrel .308 Win rifle owners wanting to shoot at beyond 800yd to consider Berger's new 175gn OTM Tactical provided their barrels have a suitable twist rate. These bullets are designed to perform exceptionally well at transonic velocities dropping down through the sound barrier, but only if spun at a particular speed. This is based on the US military's current preference of 1-11.25" for its sniper / sharpshooter rifles. 1-10 to 1-12" rates will work with the OTM Tactical, although the further you depart from the optimal rate, the less effective the 'special feature'
     
  8. markm87

    markm87

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    But almost any 185 that's starting at 2700 should be super well beyond 1000 no?

    I mean... we're shooting 175 SMKs at 2550 and they stay super to about 1000.
     
  9. milanuk

    milanuk Team Savage Gold $$ Contributor

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    I'm reasonably sure thats about what Jeff Rorer used to win the 2011 FCNC for F/TR...
     
  10. thefitter

    thefitter

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    Bullet is the Berger 185 LR HPBT. Barrel is a 24" Bartlein #14, M24/M40 contour with 1-11.25" twist.

    I would really like to hear why you would choose Berger's new 175gn OTM Tactical over the 185 LR HPBT.


    Thanks
     
  11. thefitter

    thefitter

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    Do you have any links to this?

    thanks
     
  12. Laurie

    Laurie

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    I wouldn't if I really could get 2,700 fps for the 185 BTLR safely and with high precision out of a 24" barrel, but that is very, very difficult. Looking at it in muzzle energy terms, that's 2,995 ft/lb ME, the equivalent of pushing a 155gn bullet out at 2,950 fps, and that takes some doing from 24-inches in .308W.

    Having been down the 24" barrel / 1,000yd route and not liking what I found there, I know you'll definitely be well down into transonic speeds. The 185 BTLR may perform well at just above the speed of sound - it wasn't around when I was playing this particular game - in which case well and good. If it doesn't, the OTM may suit your purpose better for the simple reason it's designed to perform consistently at long ranges with a c. 2,600 fps MV even when subsonic. Its designer Bryan Litz obtained 1-MOA groups from the bullet at 1,000yd when loaded to the mild M118LR 7.62 spec and fired from a 20" barrel LaRue semi-auto rifle.

    Remember, those comparative wind drift values, simply based on the BC + MV values often don't deliver if the bullet is 'uncomfortable' at its terminal velocity. Experience shows that some designs like the 190gn and 220gn Sierra MKs perform better than they should, while others start misbehaving at what is an extreme range for them.

    Anyway, good shooting and have fun with whichever bullet model you end up using!
     
  13. thefitter

    thefitter

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    I am getting 2700 fps with 45.0 grains of N540. Chrono graph is a Ohler 35P.

    I have gone up to 46.8 with no pressure signs which is 3 grains above book max, but it is cold here (40F) so that will change in summer.

    So far the 45.0 gave me the best ES & SD on the chronograph. I'm going to try another possible node at 46.6 on Friday.

    I have been e-mailing Mr. Litz about those various bullets for my application.

    Thanks
     
  14. Turbulent Turtle

    Turbulent Turtle F-TR competitor

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    I'm not sure what pressure signs you are expecting to see, they all lie and you are simply not seeing the biggest one of them all, the chronograph reading. The Lapua site shows that you are exceeding max by quite a bit and that is a pressure sign right there and you are ignoring it.

    It always seems that people have THE rifle that can be loaded way above max all the time with no ill effect. I wish I had such rifles. Better keep a hammer and some Band-aids in your shooting box.
     
  15. Keith Glasscock

    Keith Glasscock True believer - Straight 284 Gold $$ Contributor

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    I don't doubt you are able to get 2700 out of a 24" tube with N540. I can get 2730 without significant pressure signs (big, ugly things like leaking primers and ejector marks that you can catch a fingernail on) with a 26" barrel and Varget. On the other hand, I refuse to shoot that load because it is really way too hot. I have to back down a bit to 2700 and that is about as hot as I'm willing to fire.

    All of that is possible because I have a slightly larger than min spec chamber and a throat that allows me to seat the bullet out there a bit. With the 185's (hybrid or LRBT) I can seat out to just shy of 3" COAL. The increased case capacity reduces pressure and increases the possible velocity. It is about the same as having a slightly ackleyized chamber. I have more combustion room and powder capacity. The result becomes a situation where I can load as if I have a wildcat cartridge. I use the published load data as a starting point and VERY CAREFULLY work up until I see the very first signs of pressure (my rifle makes very, very slight ejector marks with Varget, but makes primer leaks with RL-17) and then I back off at least half a grain.

    As for the question of 185 LRBT's at 1000 yards - I don't know exactly what Jeff gets, but I suspect that he is closer to 2800 from his 32" barrel. Nonetheless, 2700 will perform admirably at that range and I would hesitate to go hotter. If you absolutely have to have more ballistic performance, the 185 Hybrid is a little better (about 3 to 4%) in G7 BC or you could get a bit more out of the 185 LRBT by pointing them up (I don't know how much, but indications are that it could be as much as 5%).

    A 5% increase in BC is about the same as increasing the velocity 80 fps without the added powder, brass damage, and gun wear...

    If 5% is true, then on a 32 degree day at Sea Level the 185 LRBT will arrive at 1000 yards doing about 1329 or Mach 1.223 (transonic region is typically stated to be from .80 mach to 1.20). Even with no pointing, the bullet will arrive at 1000 yards (same conditions) at 1273 (mach 1.171).

    Your best bet is to just try 2700 if the accuracy is good at shorter ranges. Worst case scenario is having to go back and try something else.

    Good shooting,
     
  16. thefitter

    thefitter

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    Thanks. I have no ejector marks just a sticky bolt. I read some articles by Salazar. He's pretty against exceeding book max. I used the JBM calculator he recommended and 2700fps is the lowest I can go and get there above MACH 1.2. I'm really not sure how I can do that without exceeding book max by a least a grain and a half. Unless I search for other powders or use another bullet. The thing is this bullet has great reviews. Damn!
     
  17. Keith Glasscock

    Keith Glasscock True believer - Straight 284 Gold $$ Contributor

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    Short barrels do make things more difficult. I have the ability to reach 1k with a 185 (barely above trans-sonic) with my 26" barrel. A 155 is a no-go as far as I'm concerned (it spends too long trans-sonic). I've found that I get better numbers with heavier bullets in the short barrel.

    For example, I can get just to the node at 2600 (my gun's node - not necessarily anyone else's) with 200 grain hybrids. 210's actually have to be slowed down a touch to 2480-2500. If you are inclined to use double-base powders (like 540) then you will probably find that you can use a 210 grain bullet and launch it at 2500 or so. I've read that most of the people using those heavy bullets are using either RE-17 or N550. I didn't look to see if you gave a twist number, but an 11 is pretty much required for the heavier bullets as is a long throat.

    Spend some time with the JBM calculator and Berger's G7 BC's (look on their website). Then take a hard look at what kind of velocity you can safely achieve. You will find a combination that will get it done. Also realize that going into the transonic range is not automatically a tumble and die event. The additional drag slows the bullet more rapidly and the changes in center of pressure will eventually destabilize it, but 1.15 at the target will more than likely work just fine. The only way to know for sure is to give it a try. You might be surprised that "conventional wisdom" is wrong at times.
     
  18. Heavies

    Heavies

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    I don't know. Sticky bolt is a sure sign of excessive pressure. Be careful.

    I once played around at the top end, and almost stuck my bolt as the temps got up there in the afternoon relay one day. After that I backed down some. Spooky. Just my $.02
     
  19. deadlyswift

    deadlyswift

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    The 185 berger LRBTs are a great bullet. However don't forget about the 175 LRBTs They will shoot well at 1000. I can't say the 175s will out due the 185s, but with your barrel length. It want hurt to give them a try. I'm shooting a 1in11 30" barrel and in the summer time I run the 185s at 2735fps with 43.6gr of Varget.

    NOTE THIS!! The 43.6gr under the 185s are knocking on the back door of excessive pressure in the summer time. Only .3gr from when pressure signs show up.
     
  20. thefitter

    thefitter

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    I have been crunching some numbers, don't know how I missed this but I will get 2700 with 47.1 of N550 which is only .3 above max. If I can find a node around there I think I'll be fine even in the summer.

    I also just discovered that the data for the 185 with 4064 I got from Berger does not match up with the IMR data too well. I think I might have some extra room that I did not know about. The Berger data is lower by 3 grains.
     

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