Best BC for .308

LoneWolfUSMC

LoneWolfUSMC

Lt. Colonel
Full Member
Minuteman
Jan 9, 2008
7,377
17
Southern Indiana
www.8541tactical.com
#1
I have been using 155 Scenars and 175 SMK's,

but the question really biting at me is what it the highest BC projectile I can stuff in a .308 case? Not really worried about magazine length for this experiment.

This would just be for paper punching and steel ringing. Looking for some suggestions to play with in the ballistic calculator before trying it in the real world.

I have got to get Bryan Litz's book, but I was waiting to see if I got it for Christmas. It was on my list, but Santa missed it.
wink.gif
 
#5
Re: Best BC for .308

LW,

The 210 JLK has a published BC of .660 for the G1 model. Loaded very long in a case it can be driven to 2700f/s, but that's pushing it hard. 2650f/s is more reasonable, and the .660 BC with some modifications works pretty well in QL.

HTH,
DocB
 
#7
#8
Re: Best BC for .308

Pre-1992 Palma shooters can provide you with beaucoup data for 190SMKs from 308s. You'd have to spin it with 1:10 though.
 
#10
Re: Best BC for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LoneWolfUSMC</div><div class="ubbcode-body">Guess I need to pickup some 208gr AMAX and work up a load.

How hard do you reckon this is going to be on barrel life if I am driving them hard with RE15 or the like? It's not a primary concern (barrels are made to be burned) but I wonder. </div></div>

Aren't you shooting an SPS-V(mod)? You think the 12" twist will spin the 208s?
 
#14
Re: Best BC for .308

In 550 meter below see level DA bullets I shot from my SPS Tactical were not stable and 2 groups were 5.5 and 7.5 MOA wide. I have to test it in higher temperatures. -8°C is not the best temperature for testing so heavy bullets from 12" twist rifle
 
#15
Re: Best BC for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LoneWolfUSMC</div><div class="ubbcode-body">Guess I need to pickup some 208gr AMAX and work up a load.

How hard do you reckon this is going to be on barrel life if I am driving them hard with RE15 or the like? It's not a primary concern (barrels are made to be burned) but I wonder. </div></div>

I was wondering that too, I read through the thread posted above and some people were getting pretty impressive velocities. Would Varget do well with these heavy bullets? I'm shooting an SPS-V too.
 
#18
Re: Best BC for .308

Before RL17 came along, I had developed a load with RL15.

44.5gr RL15 in Win brass gave 2480 fps from 22" bbl.

It was stable and accurate past 1000 yards from the 1/12 Rem factory bbl. Test conditions were 4500' el, temp 40F.
 
#19
Re: Best BC for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LoneWolfUSMC</div><div class="ubbcode-body">Guess I need to pickup some 208gr AMAX and work up a load.

How hard do you reckon this is going to be on barrel life if I am driving them hard with RE15 or the like? It's not a primary concern (barrels are made to be burned) but I wonder. </div></div>

why would bullet weight affect barrel life at standard for cartridge velocities? isn't it velocity that burns up barrels? i don't understand why this question gets asked so often. 45gr of rl-15 isn't extraordinary in a 308 round, nor is 2700fps. wouldn't the only impact (if any) be at the throat? or is pressure directly related to barrel life?
 
#22
Re: Best BC for .308

Sure get a higher BC with the 208 gr bullet, but you give up the advantage the 155 have, for range estimation error, on unknown distance targets. On known distance targets they work, but the people I know found the increased recoil impulse harder to drive over 20 shot strings, they are all shooting lighter bullets now, some 170 Berger but alot prefer 155 L.

I shot a lot of 185L moly 44.4 RL15 lapua case, AIAW 7.62 chamber over 2700 fps great accuracy on KD targets.
 
#23
Re: Best BC for .308

If the 240smk was a sleeker profile, and didn't have such a ridiculously long bearing surface, I would try them. However, using G7 BC's that Brian Litz provided on JBM with a MV of 2400 (being optimistic) it's still only supersonic to barely past 1200 yards with the usual conditions around here. With the 208 Amax I can get up to 2600fps (a little too hot though in my rifle) and stay supersonic for almost another 200 yards. My needs only have me requiring supersonic travel to 1200 as that's the farthest I have access to shoot, and realistically, with my 10x scope i'm going to be limited on shots anyway on smaller targets.

I read a book recently where a ultra long range shooter believe that with the .308 case, 210 grains was about as heavy as the .308 case could really handle. Can you imagine the BC of the 240SMK if they sleeked it up to a VLD design?

Branden
 
#25
Re: Best BC for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Unsichtbar</div><div class="ubbcode-body">Sure get a higher BC with the 208 gr bullet, but you give up the advantage the 155 have, for range estimation error, on unknown distance targets. On known distance targets they work, but the people I know found the increased recoil impulse harder to drive over 20 shot strings, they are all shooting lighter bullets now, some 170 Berger but alot prefer 155 L.

I shot a lot of 185L moly 44.4 RL15 lapua case, AIAW 7.62 chamber over 2700 fps great accuracy on KD targets. </div></div>

I suppose it's difficult to find the right balance. I'm good at range estimation/calculation/cheating (laser rangefinder), however I suck at wind SWAG. I like the heavies as they don't deflect in the wind nearly as much as the lighter bullets, however if the area you are shooting has very little wind, the point is moot.

I been kickin' the idea of shooting 155's, however I don't know if I can get the 2900fps from my 20" barrel, I suppose it's something I just have to try.

Branden
 
#26
Re: Best BC for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dust_Remover</div><div class="ubbcode-body">Where can those "JLK" bullets that I hear so much about be bought? Can they be used for hunting as well?

Branden </div></div>

JLK bullets The 180 jlk lbt may be the best ticket in a 308. I have not yet shot any but at the speeds we can push a 180 and a predicted bc of .575-G1, it's worth a try. Unfortunately I don’t think Bryan Lintz has tested these for a G7. Gramham has used them with success and I think he is getting near 2700 fps. Using JBM standard presets shows 345 inches drop and 80 inches of drift (10mph) at 1k w/ a 100 yard zero.

I emailed swampy and he advised if you want in, you need to act fast as he is ordering jackets and making these in the next 3 to 4 weeks and that will be it until May or June.
 
#27
Re: Best BC for .308

In looking over this thread I find it amusing (in an actually humorous way) that we are discussing the selection of a single caliber of bullets from a weight range over 50% (155g to 240g) that all seen go go subsonic right about the same point. That point being somewhere in the range of 1200-1300 yards.

Thus we have a banquet of superlatives!

{Donning flame protective suit}
or as the French would say: "Vive la difference"
 
#29
Re: Best BC for .308

If they all go subsonic at the same relative point (give or take 100 yards perhaps, maybe less), the only real difference between them (excluding drop which is redundant as we have to either hold over, or dial it in regardless) becomes wind deflection susceptibility. You could also include downrange energy in there as well if you so choose.

I found that most of good bullets in 155 or 175gr range will make it to 1100, the 168's will if you push them REALLY fast. Once you get above that you can get a little further until you get to the 200+ grainers, and then you have 1200-1300 yards, depending on how fast you can start them (i.e. how long is your barrel).

Branden
 
#30
Re: Best BC for .308

Exactly. Wind is what will kick your ass. As I was reading through this thread I kept jumping back to Ballistic FTE to check wind drift with a FV 10mph wind at 1K. There is a big difference. I don't so much care about where the bullet goes transonic. It might or might notbe a problem depending on the design. 168's suck when they go sideways at 900+, but if my wind call is on then the 1000 yard target is still going to get a dose of pain. Now it might make a difference in F T/R, but I don't know becuase I don't shoot F-Class.

What will make a difference to me is what I can jam in my magazine. I am looking at the 208's and such for long range slow fire where single
loading is not a big deal. For closer in, I just run 155 Scenars or 175smk where speed on the bolt is going to make a difference.

I just like having options. The real beauty of this is it may allow me to extend tha capabilities of my duty rifle until I can afford another expensive piece of
glass for a pure competition rifle.
 
#32
Re: Best BC for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Niles Coyote</div><div class="ubbcode-body">The 180 jlk lbt may be the best ticket in a 308. I have not yet shot any but at the speeds we can push a 180 and a predicted bc of .575-G1, it's worth a try....Gramham has used them with success and I think he is getting near 2700 fps.</div></div>I shot the JLK 180's at the Terry Cross/Jim Clark match the first week of December. It was 45-50 degrees and they were at 2730fps from 24" bbl. I entered a straight BC of .580 in Exbal to get the correct dope: 45 degrees and 30.53hg was 9.6 Mils to 1000yards and 2.4 Mils in a full-value wind @ 10mph. Impressive for a .308.

Oh, and Swampy only makes them maybe once or twice a year. He's just finished a run, and as of 12/31/09 they're all gone until next time.
 
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