6mm vs 7mm in the wind - Am I missing something?

Quick · Post by **Quick** » Sat Sep 07, 2013 8:34 am

Gents,

Just did some maths and worked out something regarding 6mm vs 7mm. Using my rifle and loads ballistics data, it drifts 77in in a constant 10mph wind at 1000yds, if there is a push by 1mph to 11mph, it drifts 84in, an increase of 7in of drift. So if you miss that, with the target dimensions they was they are, that will push you from centre of x ring to the 5 ring as the distance from centre of X to edge of 6ring is 5in. With a 7mm 180gr hybrid at 2850fps, it drifts 57in which is 20in less initial drift then the 6mm but when you add the push of 1mph to 11mph, it still increases 6in to 63in which still will push you to a 5 ring just 1" closer to the 6 ring. So by looking at that, you gain nothing in windy conditions shooting a 7mm vs a 6mm it seems. With both cals, a push of 1mph will still push you from centre of x ring to 5 ring. What do you reckon? It also works out the same for a 1mph drop with both cals. Got me thinking a fair bit.

I worked out the same data with a 2mph push and the 6mm increases or decreases by 14in approx and the 7mm by 11in but, when I worked out the drift with the target dimensions, you still get pushed from the X ring to 4 ring with both cals.

Gents, am I missing something?

Norm · Post by **Norm** » Sat Sep 07, 2013 9:05 am

You need to read the wind no matter what calibre you shoot!

But those small 1" differences do make a difference over a days shooting with a point here and a point there.

Just compare the F-Standard scores over a days shooting to the f-Open scores. Same conditions, but the F-Open shooters on average will have slightly higher scores.

If you want to shoot a 6mm then go for it. Its all for fun anyway.

Quick · Post by **Quick** » Sat Sep 07, 2013 9:12 am

Norm, I know it's all wind reading in the end. Doesn't matter what you shoot. I'm shooting 6mm so I am learn my wind reading better and easier using a lower recoiling rifle. My point is that it seems ballistically, on paper/computer, that the difference is negligible. I guess it also comes in where you aim in the X ring aswell can effect the results but all things being equal, it seems like the score difference will be none if the two cals are side by side and they both miss the push or drop off. Now if the 6mm shooter picks it up and the 7mm doesn't, 6mm will score high and vice versa the other way round aswell. I just thought it was interesting. I've just come off nightshift and spent 12 hours in a car watching a loaded shot so my brain had to do something

I'm just wondering if I'm missing something in this all that can effect the outcome aswell.

Chopper · Post by **Chopper** » Sat Sep 07, 2013 9:23 am

Quick, Add on to your calculations the user frieindly, recoil factors as well, this makes my mind up ,

Chop

fclass556 · Post by **fclass556** » Sat Sep 07, 2013 9:28 am

Hi Quick. I see your point and fully agree. Ballistically there are projectiles out there that give you an advantage. However that advantage is lost if you cant read conditions. ( and other variables ) Ive been to many shoots where the F Standard shooter using a .223 has equalled or bettered the big boys.

A couple of old sayings that are very appropriate "You can spend a fortune but you cant buy scores" and "Beware the man with ONE gun .. Chances are he's practised with it"

Cheers matey. Andy

fclass556 · Post by **fclass556** » Sat Sep 07, 2013 9:31 am

Hi Quick. I see your point and fully agree. Ballistically there are projectiles out there that give you an advantage. However that advantage is lost if you cant read conditions. ( and other variables ) Ive been to many shoots where the F Standard shooter using a .223 has equalled or bettered the big boys.

A couple of old sayings that are very appropriate "You can spend a fortune but you cant buy scores" and "Beware the man with ONE gun .. Chances are he's practised with it"

Cheers matey. Andy

Quick · Post by **Quick** » Sat Sep 07, 2013 9:33 am

Chop, that's a good point aswell. Recoil management I think makes a big difference. I'm keen to hear what the world champs from Ratin say about this? I'm sure they would have worked all this out.

johnk · Post by **johnk** » Sat Sep 07, 2013 9:45 am

I've concluded that all else being equal, the barrel with the biggest hole in it will shoot more forgivingly in sloppy/choppy conditions, particularly elevation wise as the distance to the target lengthens.

IanP · Post by **IanP** » Sat Sep 07, 2013 9:54 am

Quick, I think you are missing something and its something really basic in long distance target shooting!

Its not 6mm Vs 7mm its BC Vs BC!!!!!!!

Who cares how big or small the calibre is, its about the bullets and their BC's. I am now shooting 230gr Hybrids pointed for a G7 BC = 0.400. The reason I'm shooting them is not because they are 30 cal but because they offer very low drag.

If I had a 22 bullet that weighed 50gr with the same BC as the 30 cal 230gr hybrid (0.400) then it would follow the same identical down range ballistic chart, (wind drift & drop, if fired at same velocity). Then I would change over to the lighter bullet and smaller calibre because it would offer less recoil.

The bottom line is, consider the bullets before you consider the calibre. Then work out if they can be launched at the velocities needed to be ballistically superior to the other bullets under consideration. Calibre is just a means to an end which is to get the best bullet you can to win at long distance.

Of course whatever bullet you choose it must be accurate and precise which means you need to master load development and shooting technique as well as wind reading to be a winner!

Ian

Quick · Post by **Quick** » Sat Sep 07, 2013 10:07 am

John and Ian,

You bring up good points. I'm thinking I will build a 7mm anyway so I'm not at a disadvantage at the queens and alike. I think I'll learn a lot at the national teams next year in tassie. I'm gone be bugging the lot of you a ton!!!

BATattack · Post by **BATattack** » Sat Sep 07, 2013 12:20 pm

Yes BC does rule on paper. . . All things being equal. BUT generally the 6mm closes the gap on a lot of .284's because they are not equal in velocity.

Its practical to launch a 108 gr 6mm at 3100fps but there are a lot less people shooting 7mm's that are able to push a 180gr at 3100fps.

If you compare it the 6mm to say 7saum or a 7wsm doing 3050fps you might see the benefit of the bigger (read more ballistically efficient) bullet.

What does it all mean?! Flip a coin and shoot whatever blows your hair back! For what its worth I've shot more possibly with my 6.5x47 than my 7saum . . . .

Chopper · Post by **Chopper** » Sat Sep 07, 2013 2:01 pm

Flip a coin and what ever blows ya hair back :lol:

Good answer and about right :lol:

Chop

Quick · Post by **Quick** » Sat Sep 07, 2013 5:44 pm

BAT,

I think that you would defiently get a good advantage when running the 7WSM or 7RSAUM at those speeds, I chose the 180gr Hybrid at 2850fps as that would be what most would shoot overall. One thing I didnt account for is spin drift as the hybrid didnt have bullet length data in the program, and from what I know, it usually adds on 4-7' of drift overall (at 1000yds) but dont quote me. And the BC I was using for the 6mm bullet was the 107gr SMK (stepped Seirra BC's)at 3090fps which is what my rifle does. I still dont trust a single G7 BC given my experince with my 308 bullets that I have used and run calcs on. But as always im happy to be proven wrong.

Gents,

My point is not that 6mm or 7mm is better but when you dealing with a push or drop off in wind that you dont see, I've heard some say that with a 6mm it will push you to the 5 ring and a 7mm will just drop to the 6 ring and I think that that isnt the case. Given the target dimensions that we have, they will still drop into the same score ring and gain you the same score. Thats the point I'm trying to make. As always though, happy to be proven wrong.

Chopper · Post by **Chopper** » Sat Sep 07, 2013 6:01 pm

What distances are we talking here ? Chop

mike H · Post by **mike H** » Sat Sep 07, 2013 6:13 pm

Quick,
The time has come to get off the keyboard and onto the firing line,the harsh reality is that the only scores that count are fired in competition alongside other shooters. I can see that you are trying to get off to a good start,but eventually you have to make a decision and go.At the moment 7mm`s are it.Good luck.
Mike.