Any thoughts,400 yards?

[farmer7]

I was shooting yesterday at 400 yards with my .308 PSS using 168 vlds,it was blowing between 12 and 17 mph at 12 o'clock and i was only managing 4" groups,normally it would do half of that or so. What i wondered was will a straight on headwind affect group size much?
I'm fairly new to this and just teaching myself and reading in places like this!
Any help or opinions would be appreciated. Thank you.

 

[J E Custom]

I was shooting yesterday at 400 yards with my .308 PSS using 168 vlds,it was blowing between 12 and 17 mph at 12 o'clock and i was only managing 4" groups,normally it would do half of that or so. What i wondered was will a straight on headwind affect group size much?
I'm fairly new to this and just teaching myself and reading in places like this!
Any help or opinions would be appreciated. Thank you.

Yes it will effect group size because of wind speed changes and even though
it appears to be comming strait at you the direction will change/swing a few
degrees left or right.

At 1000 yards I have seen the wind ( With Flags at every 100yrds )blowing in 3
different directions and still feel the same at the firing line.

This is the reason that a lot of people like BIG FAST BULLETS for long range,less
flight time, more mass and better BC's.

The lighter the bullet the more effect the wind will have on it.

J E CUSTOM

 

[Buffalobob]

To understand what JE is trying to tell you, take a look at the water in a river the next time you are out there. Sure the water is going downriver; but, it is not straight in the channel as it will move from side to side of the river channel. Secondly, it will have many localized swirls and eddies where the water is from every direction including up and down. Wind blowing up a rifle range or powerline ROW is much the same and if it is gusting up to 17mph then for sure it has lots of swirls and eddies (called non-laminar flow).

 

[MontanaRifleman]

Is it possible the wind was affecting the steadiness of the rifle? When I shoot on windy days it's a challange for me to hold as steady as on calm days. Infact, I just can not hold extremely steady in anything more than a 5 mph crosswind that is pushing on my rifle. It bounces around, not much, but enough to affect accuracy. So I do not shoot for groups in those conditions. This is on a stout portable bench with sand bags.

Also, with all due respect to JE, who is an experienced contributor on this site, weight actually has little *direct* affect on resistance to wind drift. The only two factors that affect wind resistance are BC and velocity. A .277 bullet weighing 150 gr, with a BC of .5 and an MV of 3000 fps will experience exactley the same wind drift as .338 bullet weighing 300 gr and a BC of .5 with MV of 3000 fps. They will both arrive down range at the same distance with the same velocity, trajectory and TOF.

Having said that, weight is a factor in determining BC. Generally speaking, a heavier bullet in the same caliber of similar design will have a higher BC. But a smaller bullet with a greater BC than a larger bullet, traveling at the same velocity will buck wind better than the larger bullet.

 

[RockyMtnMT]

Is it possible the wind was affecting the steadiness of the rifle? When I shoot on windy days it's a challange for me to hold as steady as on calm days. Infact, I just can not hold extremely steady in anything more than a 5 mph crosswind that is pushing on my rifle. It bounces around, not much, but enough to affect accuracy. So I do not shoot for groups in those conditions. This is on a stout portable bench with sand bags.

Also, with all due respect to JE, who is an experienced contributor on this site, weight actually has little *direct* affect on resistance to wind drift. The only two factors that affect wind resistance are BC and velocity. A .277 bullet weighing 150 gr, with a BC of .5 and an MV of 3000 fps will experience exactley the same wind drift as .338 bullet weighing 300 gr and a BC of .5 with MV of 3000 fps. They will both arrive down range at the same distance with the same velocity, trajectory and TOF.

Having said that, weight is a factor in determining BC. Generally speaking, a heavier bullet in the same caliber of similar design will have a higher BC. But a smaller bullet with a greater BC than a larger bullet, traveling at the same velocity will buck wind better than the larger bullet.

Exactly. The only benefit of more mass in a bullet is the energy delivered to the target. This is still subject to how the bullet reacts to the impact. So, shear mass does not necessarily mean better terminal performance. Bullet choice will make or break the performance of any caliber.

Given all this info, your choice of bullet is probably avail in the larger calibers, where it will most likely out perform the smaller caliber.

I would look for terminal performance, bc, and speed. In that order.

Sorry that I strayed from shooting the target to hunting, couldn't help it.

Steve

 

[farmer7]

Thanks for the replies guys, I didn't really think about wind shifts, just assumed a 12 o'clock wind all the way to the target. Its a a lot calmer today so i'll try again and see if i get on better.

 

[Michael Eichele]

JE pretty much hit the nail on the head.

I would say with the velocity of the wind you describe, 4" at 400 yards isnt bad results. Any time you can attain 1MOA at any range over 300 yards in real world conditions you are doing good. We all talk about our .25-.5 MOA rifles but that is what it takes to hit a 1-2 MOA target at long range. Just because our rifles are sub half minute rifles doesnt meen we are going to hit a half minute target. Hitting a half minute target or shooting a half minute group at distance isnt and has never been the point. Having a half minute rifle to shoot a 1-2 minute target or shoot a 1 minute group in bad conditions is the point. If youre in the 1 MOA zone in bad conditions you should be extatic, not curious.

 

[300WSMMAD]

We all talk about our .25-.5 MOA rifles but that is what it takes to hit a 1-2 MOA target at long range. Just because our rifles are sub half minute rifles doesnt meen we are going to hit a half minute target. Hitting a half minute target or shooting a half minute group at distance isnt and has never been the point. Having a half minute rifle to shoot a 1-2 minute target or shoot a 1 minute group in bad conditions is the point. If youre in the 1 MOA zone in bad conditions you should be extatic, not curious.

Just what I needed to hear I think, Ive been struggling to repeat past performances with my Lapua, NZ at the moment has been sorta hot,30 C
in the shade, 25-85 % humidity not the nicest conditions to shoot groups in
and in all my trying I cant repeat them, very frustrating.

Sometimes we just need to see things from a different seat.
Thanks.

Regards 300WSMMAD

 

[Michael Eichele]

No problem.

Sometimes we expect too much. We do something amazing and want or think we can do it all the time. We cant. Thats why kill zones are 8-20" on most big game animals in north america. But if you can take a half minute rifle and hit a 1-2 MOA target in the real world then youre on the right track. The better the accuracy potential of your rifle and your abilities the better your chances for a clean harvest when conditions arent perfect. When conditions are perfect we expect to shoot half minute groups on small targets. Unfortunatly conditions are rarely perfect. It maybe lighting, wind, mirage or a whole host of other factors that affect our shots. When these conditions are present and we hit a 1 MOA target, we're happy!

Ask yourself. Was the 4" group at 400 yards good enough to take a deer?

 

[J E Custom]

Is it possible the wind was affecting the steadiness of the rifle? When I shoot on windy days it's a challange for me to hold as steady as on calm days. Infact, I just can not hold extremely steady in anything more than a 5 mph crosswind that is pushing on my rifle. It bounces around, not much, but enough to affect accuracy. So I do not shoot for groups in those conditions. This is on a stout portable bench with sand bags.

Also, with all due respect to JE, who is an experienced contributor on this site, weight actually has little *direct* affect on resistance to wind drift. The only two factors that affect wind resistance are BC and velocity. A .277 bullet weighing 150 gr, with a BC of .5 and an MV of 3000 fps will experience exactley the same wind drift as .338 bullet weighing 300 gr and a BC of .5 with MV of 3000 fps. They will both arrive down range at the same distance with the same velocity, trajectory and TOF.

Having said that, weight is a factor in determining BC. Generally speaking, a heavier bullet in the same caliber of similar design will have a higher BC. But a smaller bullet with a greater BC than a larger bullet, traveling at the same velocity will buck wind better than the larger bullet.

This is not ment to be argumentative so don't take it that way .

It is a good subject to debate and we can allways learn something from others if we listen.

You are dead on about the wind drift under your conditions BUT your numbers are not apples
to apples.

Most ,277 dia. 150 gr bullets are from.450 to .530 BC.

A 300gr .338 bullet will be in the mid to high .700 BC ( 300 SMK is .768 BC).

So with a 150gr .277 dia bullet @ 3000 ft/sec drop at 400yrds would be 18.7 "
Wind drift @ 400 yrds would be 10.2"

And with a 300gr .338 dia. bullet @ 3000 ft/sec drop at 400yrds is 16.9"
and wind drift is 6.4"

At 1000yrds the .277 150 gr @3000 ft/sec mv drops 275.7" and drift is 79.7"
The .338 300 gr @ 3000 ft/sec mv drops.217.0" and drift is 45.4"

So compairing the two is not very fair to the 270 .

The point to my reply is that with weight comes BC and ( the higher the weigh in
a given dia. the BC will go up as long as it is the same basic shape ( Not spitzer to
Round nose ).

This is The reason that most long range shooters try to get the Highest BC and velocity
there rifle is capable of and weight is the key to higher BC's

Just my point of view
J E CUSTOM

 

[RockyMtnMT]

Or what the bullet is made out of. Increase length = increase bc, w/o increasing weight = faster = even less drop and drift.

So, same bc bullet of less weight in the same cal. will out run the the heaver bullet at any distance.

Beyond that comes the difference in speed vs the difference in bc out to what distance.

For example I am running the 180g E-tip instead of the 200g accubond out of my 30cal because it out performs to about 1000yrds.

Just my .02

Steve

 

[MontanaRifleman]

JE, I completely aggree with you. Maybe I should have used a more real world example. A lot of folks think that weight is a direct factor in bucking wind and my point was that it depends on how that weight is packaged. The only two factors plugged into the wind drift calcs are velocity and BC. I wanted to use two exagerated examples to illustrate that. Weight does play a role in BC and to what degree depends on shape and projectile surface.

In a more real world case, a 7mm 180 gr VLD, with a BC of .659, fired @ 3250 fps will edge (No pun intended) out a 300 SMK fired @ 2850 fps, at 1000 yds by about 1" in drift and 45"of drop. Beyond the 1000 yd mark the SMK passes the VLD in bucking wind because of it's higher BC.

So yeah, in most cases, with the bullets we shoot, the heaviers ones are better for bucking wind. In some cases a smaller bullet will out peform a larger one to some degree.

Cheers