.308 win long range problem

[Dano86]

So I have worked up a 168gr SMK load that my Savage 10FCP absolutely loves (consistent 6 shot dime sized groups at 100yards)

Well I took the rifle and that load out to my local range and I noticed that it shot 1.5-2 inches to the right at 200, no biggie, I chalked it up to flinches and/or a warm barrel ( I was Chronoing new loads and took a break, cooled it off, and shot some of my known loads)

I pushed it back to 600yards and we were shooting 18" x 24" steel plates. After my first shot mt spotter called out about 2 feet to the right. once I corrected the hold for that 2 feet it was dinging steel with every follow up shot. The wind was only 2 maybe 2.5 mph, pretty calm day and not quite a full value. either way a full value wind at 2mph, in my experience, should only be 6-8 inches at 600 yards, not 2 full feet.

I am very meticulous when mounting scopes but I did not lap the rings on this particular rifle. Could that make that big of a difference at 600yards or am I just being too picky?

 

[USSR]

Dano86,

Differences between POA and POI that are imperceptible at 100 yards become quite apparent as the distance increases. Perfectly normal.

Don

 

[rcmodel]

+1
You can't be sure of Exact Zero at 100 yards.

And a 2 mph wind at the firing position may be a 10mph cross-wind at 400 yards, and a 5 mph cross-wind going 45 degrees the other way at 600.

rc

 

[Dano86]

Would you guys just chalk it up to how the rifle shoots and Dope it out any time I shoot at those ranges?

What would you guys do?

(Keep in mind prior to this 600 yard range opening I have been limited to 100 and 200 yard ranges, so this is a new problem for me)

 

[Ridgerunner665]

I'd figure out where the problem was...thats what I'd do.

First place I'd look is my scope mounting and how well it is all aligned....first clue would be if you had to adjust the windage of the scope by a large amount to get it zero'd.


If not that, I'd wonder if the barrel was screwed on straight.


For what its worth...spin drift will shift impacts to the right, but not by 2 feet at 600...maybe 1.5 inches.

 

[Laphroaig]

I assume that you are dialing in the elevation as you shoot at longer ranges.

A couple things that come to mind are crosshairs not 100% vertical, canting your rifle, and/or inaccurate internal scope adjustment that also moves right as you change elevation.

One thing to try is to get your 600 yd. no wind zero. Leave your 600 yd. dope on your scope and shoot a group at 100 yds. on a relatively calm day. I'm guessing you'll be about a foot high. Try to be sure you aren't canting. Measure how far the group is off center in inches (right) and that will be your 600 yd. correction in minutes.

Its not unreasonable to have to make a windage adjustment for long range work. Although 2 feet (4 minutes) sounds like a lot.

Laphroaig

 

[herkyguy]

+1 on the crosshairs not perfectly vertical. I am sorry to hear about the issues.

With my Rem700 SPS in .308, I zeroed at 100 then opened up to 600 yards with no problems, but I was meticulous about mounting the scope. Leupold mk4 rings with my leupold mk4 scope and it required very little wind age.

 

[Dano86]

First off I appreciate the input.

I think a long range day is in order. I just loaded up 50 rounds and I will probably load up about 25 more tonight

 

[Vern Humphrey]

I assume that you are dialing in the elevation as you shoot at longer ranges.

A couple things that come to mind are crosshairs not 100% vertical, canting your rifle, and/or inaccurate internal scope adjustment that also moves right as you change elevation.

That's one likely cause. The other is the scope isn't tracking properly.

First, shoot at 600 yards, but with a backer about 8 feet deep below your bull. Don't adjust your sights at all, shoot with your original 100 yard zero. If that group is in line, but you're out of line when you adjust for the range, your scope is the problem.

Next, shoot the square at 100 to 200 yards -- fire a group on a large target backer, then crank in about 48 clicks right windage, shoot another group, then add 48 clicks, shoot a third group, then crank in 48 clicks left windage, shoot another group, then subtract 48 clicks and shoot the last group.

Your target should be perfectly square, and the fifth group should be right on top of the first group.

 

[taliv]

if the reticle in your scope has holdover points, you could use it as well to diagnose

 

[Slamfire]

I talked to guys who shot on Larry Moore’s Long Range rifle teams. This is the same Larry Moore on the cover of this Dec 1956 issue of Guns Magazine.
http://www.gunsmagazine.com/1956issues/G1256.pdf

Larry tested every potential service rifle as a Government Employee at Aberdeen Proving Ground, some of his reports are still Offical Use Only, but they have been quoted in a couple of books on M14's, FAL's, and M16's. Larry wrote a number of articles for the American Rifleman. He also was a competitive small bore shooter and won the Wimbleton Cup (1000 yard match) at Camp Perry.

If Larry picked you for his long range team, one of the first things he did, was make you go out to the range and prove that your rifle sights/scopes were plum. I found about this from two gentlemen who were on his team. Imagine talking to two mature shooters, sitting next to each other on a bench, guy’s who individually had won matches and championships, and Larry made them go out to the range and shoot on paper. Both of the gentlemen who relayed their experience looked like sheepish school kids as they recounted the experience.

Larry had you shoot at 100 yards at the bottom of a typical range target: six foot by six foot. You hit your aim point with your 100 yard zero. Larry would hang a plum bob aligned on the center of the bullet hole. You went up to your 1000 yard zero, aimed at the bullet hole, and let fly. If there was any cant in scope or irons, it was obvious as the bullet impact was going to be left or right of the line.

I think this is a great idea.

 

[Sunray]

A great deal depends on how you're shooting. As in off a solid bench or prone with or without a bipod. It doesn't take much shooter error to throw a bullet off by 2 feet at 600 yards. And you're starting 2" right.
If you think in terms of a straight line between you and 200 yards, 2" right of the bull, then extrapolate the line a further 400 yards. It'll be much more than 6 to 8 inches. There is math to do this. Don't ask me what it is though.
If that 1 to 2 inches at 200 was a consistent group, you might have a bedding issue. Operative word bedding 'might'.
However, I wouldn't use 18 x 24 inch steel targets to judge a group size or accuracy. A hit anywhere will knock a target that big over.

 

[jehu]

As said before,canting is a big factor. Make sure your scope is mounted plum and level and then put a scope level on it so you can make sure your rifle is level with every shot.

 

[MtnCreek]

After the shot is fired, where are your crosshairs?

 

[MistWolf]

After correcting the windage at 600, did you shoot at 100 to check POI at that range?

 

[Dano86]

As said before,canting is a big factor. Make sure your scope is mounted plum and level and then put a scope level on it so you can make sure your rifle is level with every shot.

I have not been to the range again but today I went and bought a Wheeler Pro level, pulled the rifle apart and made sure everything was as plum and true as I could. I will have to see what it does hopefully tomorrow.

 

[1911 guy]

For shooting at ranges up to 300 yards, having a scope dead nuts isn't an absolutely critical thing. But once you pass that mark, it an absolute necessity. I hang a plumb* and align the reticle with it after I level the rifle itself. Then it's on you to hold the rifle level when you shoot.

* A plumb is a string with a weight on the end. It hangs dead straight down due to gravity.

 

[Dano86]

Well I believe I may name my first child Wheeler Pro! I used it to level out the scope on my .308 and I was cogniscent of keeping my rifle level while shooting and here is the result of a 4 shot group at the 600 yard line.

Again I appreciate all the info and help!

 

[Jim Watson]

A LR shooting friend uses a "thermometer target." It has a regular aiming bull near the bottom of a tall target and a vertical stripe going up the target. He hangs it with a level.
He aims at the bull at 100 or 200 yards and adjusts to hit the stripe at the proper level for the come-ups to longer ranges.

In calm air this assures a mechanical zero for windage and checks for sight or scope vertical.

 

[Legionnaire]

Nice shooting, Dano86! Thanks for posting the update and the pic.

 

[murf]

have you eliminated scope parallax?

murf

 

[cowtownup]

Having same problem... Gonna try some stuff mentioned here