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Old November 9, 2012, 05:05 PM   #1
Sweet Shooter
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Shooting in the snow...

I just went to the range and my SIG M400 once again turned in some impressive groups—an inch at the largest but actually that one included two turret clicks to the right. I was not expecting tight groups as it was snowing heavily and I'm using up some 40 gr V-max (in a 1x7 !!!). Has anyone noticed an effect in the snow on group size? What are the physics I wonder of a bullet traveling 100 yards at ~3400fps through falling snow.

Also since I had the rifle apart the other day to do a deep clean the groups had moved to the left by about half an inch (hence those two click mentioned above)... is that to be expected? If so, we could never know where a deep cleaned rifle is going to hit. Thoughts?

-SS-
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Old November 9, 2012, 05:51 PM   #2
Saskhunter
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I have never noticed any effects from snow, or rain for that matter.
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Old November 9, 2012, 06:11 PM   #3
FrankenMauser
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Snow won't affect the bullet's flight in any measurable way.

It will, however, have an affect on the shooter and the shooter's view of the target, and the temperature may change the behavior of the firearm and ammunition.


A few years ago, we had a 2-page discussion about the affects of heavy rain on a bullet's flight. In the end, it was agreed that the odds of a bullet hitting a drop of water, even in rain as heavy as 2" per hour, were low enough that it didn't matter. In the case of the bullet actually hitting a rain drop, the influence on the bullet would be insignificant -- to the point that it is essentially imperceptible at the target. Snow, of course, would have even less of an influence.
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Old November 9, 2012, 06:17 PM   #4
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Living in an area without snow 363 out of 365 days every year....

Cold weather tends to throw off my aim a bit, but its more of my aim being thrown off by my body being cold.

No idea how much snow might affect a bullet, but I bet it affects it less than drops of rain would.
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Old November 9, 2012, 08:48 PM   #5
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I shoot year round in Wisconsin as long as it is above -20 and the winds are less than 20mph as long as I can see the target. Group size no difference, number of groups are less because I'm not out there as long. Only a guess but I will bet you concentrated harder because of the snow and reaped the reward with a tighter group.
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Old November 9, 2012, 09:05 PM   #6
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Snow like rain effects the shooter more then the bullet. Except for the temp swings you get with snow conditions, there well be some elevation changes going from a warm day to a cold day. That's temp not the snow.

Even then starting at 3400 fps to 100 yards, it's gonna take a big swing in temps to notice.

But snow per se doesn't affect the bullet.
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Old November 9, 2012, 09:24 PM   #7
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A clean bore will effect velocity for a few shots until it gets dirty again. You may see this as vertical stringing on the target. Knocking some crud off the crown, or more likely wearing the crown with the cleaning rod will also move your point of impact.

Most likely you tweaked your zero by moving something as you were cleaning.

Snow doesn't matter, but temperature affects the powder burn rate and air density, and thus changes in velocity cause a vertical shift again. But you won't see much at 100 yards.
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Old November 9, 2012, 09:58 PM   #8
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I would guess that humidity could have an affect and it may have been dry, but I doubt that you would see the effect at only 100 yards.
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Old November 10, 2012, 10:14 AM   #9
sc928porsche
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Temp will effect POI, but usually not group size. As we know, temp effects powder burn. Also, if you are using pressure method instead of free floating, the material touching the barrel will change. Thus effecting POI. Mind you, these are not large amounts.
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Old November 10, 2012, 11:16 PM   #10
big al hunter
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You took your gun apart and reassembled it. Yes that will affect the poi. Especially if the torque on the action screws is different or if the stock and action mated in a new location ever so slightly. Some rifles will shoot to different poi for a few shots and come back to the original poi as the action seats into its old spot. Bedding the action will help reduce this, or you can just adjust poi each time.
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Old November 12, 2012, 11:59 AM   #11
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Thanks chaps. @big al hunter the SIGM400 is an AR. But I do get what you're saying. This basically illustrates the need for a tight, repeatable lock up between an upper and a lower... which many say is not important.
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Old November 12, 2012, 09:39 PM   #12
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On an AR, it is more likely you disturbed the scope. There are plenty out there that shoot well despite being really loose.
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Old November 13, 2012, 11:30 AM   #13
arizona98tj
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Quote:
This basically illustrates the need for a tight, repeatable lock up between an upper and a lower... which many say is not important.
Can't agree with that statement. You are comparing apples to oranges, IMHO.

A standard rifle has the barrel/action attached to the stock....and so the action screw torque plays is important. The fit between the barrel and stock is equally important. Anything loose there will put you all over the target.

On an AR platform, the barrel is attached to the upper receiver. So it is important to have those two properly torqued. The barrel does not interface with the lower receiver and so the fit between the upper and lower makes no difference. I agree that a sloppy fit is annoying...I don't like it and won't put up with it. But it is not an accuracy issue like a loose barrel in the upper receiver would be.
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Old November 13, 2012, 12:51 PM   #14
Sweet Shooter
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Quote:
arizona98tj
Can't agree with that statement. You are comparing apples to oranges, IMHO.
That's okay I don't need you to agree.

I hold the lower and have the upper moving in relation to it every time I pull the trigger, even when benched.

It might be marginal but I'm interested in eradicating margins... mostly everyone who is interested in a 1MOA gun—given that 1MOA is not match standard these days—is trying to do the same thing. Why ignore that one thing to which there are several simple fixes?
-SS-
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