.308 barrel length, twist, powder burn rate, bullet gr interactions

Nik S

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I'd like to build a carry .308 that can consistently reach out to 1027yds (my range). There are going to be trade-offs for sure, so I'd like to try to get a clearer handle of what I should be looking for in an overall system that combines barrel length, twist, bullet gr, and powder burn choices to optimize ranges out to 1027yds within the parameters of a rifle that stays pretty handy. Not looking for a competition gun. My prior experience is 300WM, and 6.5CM, but I am new to .308. I probably went about my introduction to rifle backwards in that regard. I understand that .308 won't share the same BCs of those calibers.

Research I have compiled so far (please correct incorrect assumptions):
  • Basic rule of thumb: Shortening the barrel length of a .308 nets a loss of ~20 fps per inch.
  • [Edit: corrected] Fast burning powders like short barrels. Slow burn like longer barrels.
  • Slower burn powders also like heavier bullets(?)
  • Twist: 1:10 is recommended for heavier bullets.
  • Shorter barrels are stiffer. LL has shown an 18" barrel can make consistent hits at 1k. (Not sure what ammo he was using.)
I also happen to have a good deal of VV N150 on hand that I'm thinking of applying to this build, if a good idea. It's rated as "slow burn."

Are the above assumptions. correct?
If I were to use that VV N150, should I be looking at something like a 22"-24" barrel, 1:10 twist, 180 gr VLD?
 
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KZP

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You can go 1:9 twist as well. The Berger 185 juggernaut is the easy button for 1k range. I used to use them in 24" barrel, then moved to 26" for a little extra oomph. I'm sure 22" would be fine too if you really need to save length. Sometimes I would under load reaching 22" length velocity and it still worked.
 
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stello1001

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    You mention a carry 308 on your first line but what the heck is a carry 308?

    Did you mean you want to build a lightweight rifle because you will carry it so much?

    If you're tryna get to 1000 yards I would go with a 24 inch barrel.

    If you're tryna go to 1000 yards but have a handy and light rifle, I'd probably come down to 20 inch barrel!

    Look at the newer more modern projectiles. Forget about the 168 and 175 SMK. Although the 175 isn't as bad as the 168.
     

    Nik S

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    "Carry" --just shorthand for a more handy, though not necessarily light rifle that I can more comfortably carry. I have a 300WM, 26" barrel that I took on a hunt once, and regretted it. Primary interest is the range, but I don't want it a range-only rifle.
     

    Nik S

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    Newer projectiles: check.
    How would a 22" or 20" barrel interact with a slower powder like VV N150? Is it meant for a longer barrel, or still good?
     

    Rob01

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    For reaching 1037 yards with a .308 it's not a hard project. Keeping it handy comes to length and weight. You just need to get a lighter contour barrel like a Rem Varmint contour which is heavy enough to not get effected by longer strings of fire but not overly heavy like an MTU or Proof Comp contours. That way you won't have any unneeded weight.

    22" is a good compromise for length and being handy as well. You will get good velocity, enough to reach 1037 yards, and will be short enough to move around with it. 10 or 11 twist will work fine. No need to go faster and I wouldn't go slower so you can still use newer higher BC bullets. I use an 11 twist now but have used 10 and 12 in the past. I would go 10 again but not 12. The whole "shorter barrels are stiffer" stuff is from old BR. While true it means nothing to accuracy as there are plenty of very accurate 30"+ barrels as well in matches. Don't hitch your horse to that saying.

    You don't have to go to overly slow powders. Varget has worked great so powders in that burn rate should work fine for you. Even in longer barrels. I use it in my 20" and 26". ETA: VV has .308 load data on their site and it looks like N150 is a good powder for what you want to do.


    As for bullets, lots of newer good options. Some of the older options like the 175 SMK can work but why use them when you have bullets with higher BCs which will make the job easier. The Hornady 168 ELD-M is what i use in my match .308 and have shot to 1250 in matches. Has a .523 BC so a good deal higher than the 175 SMK. There are good 168-185grn weight options out there to try.

    So just put together the rifle like you want it and as handy as you need it. getting to 1000 with a .308 is not tough.
     

    spife7980

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    Fast burning powders like short barrels. Slow burn like longer barrels.
    Faster powders for lighter bullets, slower for heavier.
    It’s all about how quickly that bullet moves down the barrel making addition volume for combustion and expansion of the gases behind it and how quickly that powder burns and fills that volume behind the bullet in the bore.

    Barrel length doesn’t matter other than simply stopping the process sooner. It’s what happens before that bullet leaves which is important.
     

    Rob01

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    Hopefully just hitting some steel or paper seeing as it’s a .308.
     

    Nik S

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    For reaching 1037 yards with a .308 it's not a hard project. Keeping it handy comes to length and weight. You just need to get a lighter contour barrel like a Rem Varmint contour which is heavy enough to not get effected by longer strings of fire but not overly heavy like an MTU or Proof Comp contours. That way you won't have any unneeded weight.

    22" is a good compromise for length and being handy as well. You will get good velocity, enough to reach 1037 yards, and will be short enough to move around with it. 10 or 11 twist will work fine. No need to go faster and I wouldn't go slower so you can still use newer higher BC bullets. I use an 11 twist now but have used 10 and 12 in the past. I would go 10 again but not 12. The whole "shorter barrels are stiffer" stuff is from old BR. While true it means nothing to accuracy as there are plenty of very accurate 30"+ barrels as well in matches. Don't hitch your horse to that saying.

    You don't have to go to overly slow powders. Varget has worked great so powders in that burn rate should work fine for you. Even in longer barrels. I use it in my 20" and 26". ETA: VV has .308 load data on their site and it looks like N150 is a good powder for what you want to do.


    As for bullets, lots of newer good options. Some of the older options like the 175 SMK can work but why use them when you have bullets with higher BCs which will make the job easier. The Hornady 168 ELD-M is what i use in my match .308 and have shot to 1250 in matches. Has a .523 BC so a good deal higher than the 175 SMK. There are good 168-185grn weight options out there to try.

    So just put together the rifle like you want it and as handy as you need it. getting to 1000 with a .308 is not tough.
    This is excellent, thank you.
     

    Rob01

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    Hit steel. Try to stay outside transonic.
    You don't have to stay outside of transonic. You just need a bullet that goes transonic without issue. That is why the 168 SMK sucks as a long range bullet as it gets real squirrely going transonic. Pick a newer higher BC bullet and you will be fine.
     
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    Totoro

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    Funny this thread came up, I am in the midst of doing something similar.

    Going with a 20" 1-9 fluted Sendero steel tube.

    178 Hornies + Varget + CCI + Norma

    Sorta like a Remmy LTR.
     
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    Rob01

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    The 178 Hornadys will shoot fine in a 20" 11 twist as well. Have shot thousands through mine. 9 shouldn't hurt anything but that fast of a twist is not needed for them.
     
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    Nik S

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    Faster powders for lighter bullets, slower for heavier.
    It’s all about how quickly that bullet moves down the barrel making addition volume for combustion and expansion of the gases behind it and how quickly that powder burns and fills that volume behind the bullet in the bore.

    Barrel length doesn’t matter other than simply stopping the process sooner. It’s what happens before that bullet leaves which is important.
    This is good to hear. I was under a misconception on burn rate, and as a result, under a mistaken impression that a slow burn powder in combination with a short-to-medium length barrel would not work so well.

    Corrected in the OP.
     

    Bungi

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    Which of the newer (more modern) bullets do you like for 308 ?

    I have some Lapua 155 scenars, but I have not loaded any yet.
     

    Totoro

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    Hornie 178 ELDM/ELDX for me; be it animal/steel/rock whatever, it won't know the difference.

    @Rob01, you're absolutely right about the 9 twist; 10-11.25 outta work just fine too.
     

    VargmatII

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    I have shot the 308 for years. Had a 20" 1:10 twist that shot great with Hornady 178 grain A-Max. The last 2,5 years Ive shot with my TRG 22 which has the 26" 1:11 twist barrel, shoots 175 grain Scenar L and 175 grain SMK with ease, been out to 1200 yards on steel.

    Next barrel will be 24" and either a 1:11 or 1:10 twist, depending on what is available at that time. I would not bother with a faster twist than that.
    Ive had great results with Norma 203B / Reloader 15 powder. But Im down to my last two cans of it and will switch to VV N140 in the future.
     

    ma smith

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    I have shot the 308 for years. Had a 20" 1:10 twist that shot great with Hornady 178 grain A-Max. The last 2,5 years Ive shot with my TRG 22 which has the 26" 1:11 twist barrel, shoots 175 grain Scenar L and 175 grain SMK with ease, been out to 1200 yards on steel.

    Next barrel will be 24" and either a 1:11 or 1:10 twist, depending on what is available at that time. I would not bother with a faster twist than that.
    Ive had great results with Norma 203B / Reloader 15 powder. But Im down to my last two cans of it and will switch to VV N140 in the future.
    what kind of speeds are you getting out of the TRG ?
     

    granite wagon

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    Mine is right around 19" & 11twist. It does just fine with 155.5 berger @ 2770ish & 175 berger @ 2640ish.
    Both are in transonic flight at 1000 & both handle the transition without drama.

    When its new barrel time I will be fine w/ 10 or 11 twist .
     

    DJL2

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    I’ve come to appreciate 20” as something of a sweet spot for me. They balance nicely and carry well, even when they’re portly. I’ve got a 6.5 setup at like 11.75 lbs with bipod and suppressor and it carries very nicely. My Delta-51 is a little chunkier, still carries very nicely.

    An adjustable cheek piece does a nice job offsetting weight from a bipod/suppressor. If you’re gonna tote it with bare muzzle, skip the adjustable cheek (unless it’s the Manners screw on bits or their new LRH). I’m generally a stock over chassis guy, especially for carrying.

    My 20” .308 clocks 2595 fps with FGMM 185 Berger Juggs, 2725 with Hornady 168 ELD-M, haven’t tried the Superformance match. Either of the above should get you where you want with no drama. Factory ammo seems to leave a lot on the table performance wise, with the exception of the Juggs. Hard to imagine 1:10 (or even 1:11) being inadequate for anything you’ll launch out of a .308 (barring some sort of 200+grain single fed target load).
     

    Alaska

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    175gr Berger OTM is your bullet !
    And it will stabilize in a 1:12 if needed !