Anyone Currently Shooting a Savage Model 12 LRPV ?

[Dave Hoback]

Not just for yours Charlie. That’s how it is for every gun. It’s not weight that dictates twist needed, it’s bullet length. And while the norm has been that typically the heavier the bullet, the longer it is, there have been several lighter bullets in a specific caliber, that are longer than their heavier counterparts.

As Charlie mentioned, those Berger 155 Full Bore’s are a perfect example. Very long for for a 155 30cal. So if that is your specimen for example, that answers why. But in the world of firearms, these contraptions do some strange things at times that defy logic. Just something to ponder.

[charlie b]

There is sound physics reasons for all of this. The simplified stability equations work most of the time, but, others require the use of the more detailed equations that take into account the specific aerodynamics of the bullet being used.

And sometimes it can be atmospheric conditions. The bullet stability depends on the density of the air. Most of the time we shoot when it is closer to std conditions, but, if we go out when it is very cold then some of the loads we use might not work.

The manufacturers recommend certain twist rates based on the extremes. They have to. If Sierra made their Match Kings and recommended a twist rate that would not work at below freezing temps, they they would be turned away from military contracts (and many hunters). So, they are very conservative.

[jkv45]

Thanks guys.

One more question - is a 175 superior to a 155 in terms of wind deflection?

[Palmafiddleman]

In general the advise is to use the heavier weight bullet for its caliber for its ability to resist wind deflection. The 155's were chosen to create the maximum test for a rifleman/competitor in wind reading and adjustment before executing the next shot. When shooting "2 or 3 to a mound" you will have a limited time to break your shot when it is your turn. You may not have the luxury of waiting for your preferred condition to re-appear. By the way, .308 FTR shooters use the heavy, 200, 220 grs etc. class of bullet weights.

[charlie b]

Blue is the Lapua 155gn Scenar factory load
Green is the Lapua 185gn Scenar factory load

Note the starting velocity, I suspect from a 24" or 26" barrel. I picked a zero range of 300yd

You can notice the wind drift differences in the two bullets. This was for a 5mph wind

Range	Drop (inches)		Velocity		Energy		Wind drift (inches)		Time (milliseconds)
0	-1.4867	-1.4837	2822	2477	2740	2520	0.0156	0.0178	0	0
200	4.9646	6.0442	2471	2280	2101	2135	1.3035	0.9238	228	253
400	-11.5335	-13.2674	2145	2091	1583	1796	5.5292	3.7925	488	528
600	-58.5207	-64.4834	1843	1911	1169	1500	13.3760	8.8903	790	828
800	-146.8517	-153.9021	1566	1740	844	1243	25.7532	16.5333	1143	1157
1000	-292.6009	-289.4278	1310	1577	591	1021	43.9179	27.0994	1562	1519
1200	-520.7133	-481.2653	1099	1422	416	830	69.5685	41.0601	2066	1920
1400	-862.0448	-742.0185	1013	1275	353	668	101.0725	58.9821	2637	2366

I can say I like shooting the 175SMK's at 1000yd more than the 155 Bergers. I can adjust for wind easier. I also think the heavier bullets make for a lower ES/SD for me, which results in smaller groups. The only thing I have to overcome is the recoil. I am not consistent enough with hold (12lb rifle) over a long string. Which is why my 1000yd gun is a 6BR these days. :)

[Dave Hoback]

If that ain’t about the most confusing chart I ever done seen! So, “A” (Blue) is the 180gr.. but it’s in green columns? And since when is a 180gr going to be higher velocity than 155gr? Sure those aren’t reversed?

[charlie b]

Dave,

The cut and paste messed up the A and B heading. Pay attention to the color.

Fixed it. :)