Bullet choice for 308

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pockets

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What is your opinion/experience regarding using the 155 Lapua Scenar instead of the usual 168/175 match king for long range out to 1000 yds. with a 308? If you run the numbers, the 155 with a BC of .505 comes out on top in drop and wind drift. But those are computer generated. Often real world is a different ball game.
 
I run my 175 MK's out of a 308 with a 20" barrel at around 2570 fps out to 900 yrds on a regular basis. FYI, the elevation adjustment at that range is 30 MOA. I'm seriously looking into the 155's as well after some discussion with several shooters at ALRC this year. Don't get me wrong, the 175's did their job, but I'm always looking for something better. Keep us in the loop, I've looked at the 155 palma MK's but the information you provide may sway me towards the lapua.
 
pockets, I'm curious how you got the .505 BC for the Scenar. Brian Litz' "Applied Ballistics" book says the 155 Scenar has an average G1 BC of .462, but a G7 of .236. (Litz argues in favour of the G7 measurement.) I used to use the SMK 155's (G7:214), but switched to the Amax 155 (G7:212) because I preferred the plastic tip to the ragged meplats of the SMK's.
The Amax's were a tad cheaper than the SMK's, but that wasn't really a factor. What do a box of the Scenar's go for these days?
 
The difference in BC between a heavy 175 and a light 155 - 156 bullet is not that great, yet these palma bullets - that were designed specifically for 7,8, and 900M shooting (That's what Palma IS) go way faster. A 155 doing 3k will outperform a 175 doing 2600
 
Obtunded said:
The difference in BC between a heavy 175 and a light 155 - 156 bullet is not that great, yet these palma bullets - that were designed specifically for 7,8, and 900M shooting (That's what Palma IS) go way faster. A 155 doing 3k will outperform a 175 doing 2600
Click to expand...

...unless the wind is blowing.

The old Sierra 155 Palma has a G7 BC of.214, the new 155 Palma has a G7 BC of .229 while the 175SMK has a G7 BC of.243 - so it's kinda great. I seem to recall reading that heavy high BC bullets will outperform (less wind deflection) lighter lower BC bullets in wind - the one variable that the shooter can't control. My 175 SMK's do 2700.
 
I ran the numbers in QuickTarget, using what lapua lists .508 G1 BC at 2900 fps, and what sierra lists the 175MK with G1 .505 BC for >2800, .496 18-2800, at 2700 fps. At 1000 yds. 5 mph 90 degree crosswind, the 155 has .63 MOA less wind drift, 6.67 MOA less drop, and is moving 135 fps faster. In theory. FYI Lapua lists their 170 lockbase with a BC of .525, which lands between the 175 sierra and the 155 scenar.
 
Read Applied Ballistics by Brian Litz!!!

You'll see why those G1 coefficients are total garbage and utterly useless. G1 model is the reason why so many calculators give you numbers that don't ever work in the field.

I am surprised that a sport which seeks perfection at every corner, still clings to an inaccurate drag model. G1 should only be used for flat based short bullets. G7 should be used for match boat tails.
 
what about 185 berger VLD they have a G1 BC of 0.549 and for , match ld boat tail its .553
there 30 cal 210 Grain Match Target BT Long Range has a g1 of 0.626
 
I had a similar conversation with a guy (you may have heard of him) about the 155's and the 175

The G7 value of the Lapua Scenar 155 is listed at .234 according to your May 08 article and I see you have posted two 175's I was always lead to believe the 155 Scenars had a higher BC then the 175 Sierra
…now that my world has been shattered (ha-ha) could you say approximate what the difference of .234 vs .243 is in actual terms, or what the reduction in wind drift is for each .001 is .009 statistically significant to make the switch or would I need to jump to the 175 Bergers to notice a difference

According to the measured G7 BC's for these bullets:

Sierra 175 MK: G7 BC = 0.243 lb/in^2
Muzzle velocity of 2663 fps results in 1120 fps at 1000 yards (Mach 1.0)
Muzzle velocity of 3010 fps results in 1344 fps at 1000 yards (Mach 1.2)

Berger 175 VLD: G7 BC = 0.255 lb/in^2
Muzzle velocity of 2579 fps results in 1120 fps at 1000 yards (Mach 1.0)
Muzzle velocity of 2921 fps results in 1344 fps at 1000 yards (Mach 1.2)

Lastly would you have the G7 of the 185 Scenars as shooting moly I have limited options unless I moly my own.

I have a nice little pile of 155 Scenars and might be hunting for some 175 Bergers for the up coming FT/R season.

Thanks kindly
Trevor


Trevor,
As for your question, here's a performance analysis that shows the relative wind deflection which is the most important measure of ballistic merit for LR target shooting. The analysis assumes you can get 3000 fps with the 155's, and scales the velocity down for the heavier bullets according to an equal chamber pressure assumption. In other words, if you can achieve 3000 fps with the 155's, you can only achieve 2823 fps with the 175's with the same chamber pressure. Assuming equal muzzle velocities for bullets of different weight is not a fair comparison.
The comparison is relative, so if you can only get 2900 with the 155's, the basic conclusions of the analysis still hold, but the amount of wind deflection for each round will be a little more than shown. The important thing is the relative performance among the bullets.

Wind deflection is for a 10 mph crosswind at 1000 yards in standard conditions.

155 Scenar (G7 BC = 0.234)
MV = 3000 fps
Wind deflection = 93"

175 SMK (G7 BC = 0.243)
MV = 2823 fps
Wind deflection = 97"

175 VLD (G7 BC = 0.255)
MV = 2823 fps
Wind deflection = 91"

185 Scenar (G7 BC = 0.247)
MV = 2746 fps
Wind deflection = 100"

Analysis: When you account for the velocity advantage you get with the lighter bullet, it's hard to beat (in this case, when compared against the others you asked about). The 155 has a 4" advantage over the 175 SMK, but the 175 VLD is 2" better. In practical terms, it would be difficult to resolve that difference in terms of points (on the scorecard) when the difference is only 2" to 4" in ~ 95". The reason why the VLD is better than the SMK is because of the lower drag profile of the bullet and the higher BC that results. The 185 Scenar is reputedly a very accurate bullet, but it's got a relatively high drag profile which results in more wind deflection than the others.

Suggestion: You won't be giving up much performance by shooting with the 155 Scenar compared to the other bullets you listed.

Berger 185 BT (G7 BC = 0.283)
MV = 2746 fps
Wind deflection = 82"

This bullet requires a 1:12" twist to stabilize, and is easy to find accuracy with since it's a tangent ogive (like the SMK) and not a VLD.

I hope this was useful for you,
Good luck,
-Bryan
 
In the real world "on the mounds" I prefer the 155 Scenars. Extremely consistent ,easy to tune ,and accurate.
I've told Peter, I sent out a sampling to a friend's lab with a laser measuring tool that runs into millionths.The report back was IMPRESSIVE.
I've also "Juenked" 1000 of the 155 scenars and found ALL within 5 deviation units at the SAME node,and most within 3 DU's and less.
The results of a minor metplat repointing (no trimming needed) to a 50% reduction size,decreases the DC and increases the stated BC .

The 208 Amax at 2600 in truth, is a little heavy of a load with RL17 at 2600. Tried it and went back to 155 Scenars. However in a 300wm the 208 Amax at 3000 fps it really shines! But the Amax is stilled plagued by the 1 bullet curse.

The 175 SMK's are probably the bullet that most benefits from metplat uniforming and repointing.One just has to visually inspect the metplats to see the ragged truth.A uniform BC created by "treatment" of these will help eliminate the vertical at LR.

All that being said....your barrel will show you what bullet to use.
Gord
 
Thanks guys, that is what I was looking for. I should also mention this is for a 20" HS precision rifle, so the lower velocity won't give the same numbers. But, the differences will be the same. Where can I find/buy on of the meplat trimmer/uniformer tools? If using it on a Berger VLD hunting bullet, do you think the performance on game will be affected?
 
pockets said:
Thanks guys, that is what I was looking for. I should also mention this is for a 20" HS precision rifle, so the lower velocity won't give the same numbers. But, the differences will be the same. Where can I find/buy on of the meplat trimmer/uniformer tools? If using it on a Berger VLD hunting bullet, do you think the performance on game will be affected?
Click to expand...

POCKETS,
You will not need to metplat uniform hunting bullets as the increase in LR performance will be negligible for distances that one would hunt larger game with a 308W.
However,
When trying to place all shots into a 5 inch V bull at 1000 yards,then the full treatment of bullets and brass would be quite beneficial.
Gord
 
If shooting game at 600-650 with the 308, do you think the bullet performance (expansion) will be affected? There would be little difference in ballistic performance at the range I would think.
 
It always amazes me how different barrels along with component selection and seating depth affects that little bullet. I tried 3 different loads out of a 1:10 twist PGW Coyote with the 155's and couldn't get them to stabilize past 1000 yards. About 1/3 of them were starting to tumble and would impact the target on its side. Between the 175 smk and the 155 scenar the 155's gave me better results at 300 yards and less but after that the 175's performed better for me. I guess I could have started from scratch with the 155's and tried various other primer/powder combinations but the 175's just shot good right off the start for me with the components that I had available at the time. This isn't an attempt to say that one is better than the other....I guess you need to figure out what works well for you and learn to live with it. However, in defense of the 155's, I really didn't put much effort into getting them to work properly. The more I think about the more I realize that I'm the exception to the rule as most people that shoot the 155's really seem to like'em...:).
 
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