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2" x 12" groups?

 
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  #1  
Old 08-23-2012, 08:03 PM
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2" x 12" groups?

So I am developing a round for a friend's 7mm RUM. Worked some loads up at 200 yds. shooting well around 89 and 91 grains of Retumbo 180 Berger HVLD. COAL 3.650.

I just did two rounds of each the first time, this time I made four of each .5 grains in each direction of these.

I am shooting with a bi-pod on the front and a rear bag. The scope is a 3X9 and has no parallax adjustment. I know this is not ideal but it should not be as bad as it was I don't think.

Shot the loads at 400 yds. today to alleviate some of the parallax issue. Was taking my time dry firing between shots to keep myself from flinching. I used two of the 88.5 gr. loads to get on paper at 400 (they were both short) then the next two fell about 1.5" apart at about 10 and 4.

The rest of the loads had good vertical spreads ( about 1.5") but would be spread from one end of the paper to the other (about 12"). The wind was blowing full value at about 5-7 and we were watching the mirage pretty close so I expected better.

My question is, is the barrel just grouping them like this or am I doing something else really wrong? (aka trigger pull)

My next step is to obviously shoot some more 88.5 gr. loads, which I will try to do later this week. But in the mean time any suggestions would be greatly appreciated.
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  #2  
Old 08-23-2012, 08:58 PM
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Re: 2" x 12" groups?

if you had 1/2 moa vertical at 400 and 3 moa horizontal it was most likely one of 2 things.
Your lack of wind reading or a gun handling issue. Try a rabbit ear bag with a heavy fill so it really holds the back of the gun from moving side to side, don't forget to remove the rear stud.
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  #3  
Old 08-23-2012, 09:44 PM
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Re: 2" x 12" groups?

Also chech your Natural Point of Aim. Once your on target, all ready to pull the trigger, take your finger off the trigger and close your eyes for 5 seconds. see where you are on the target. If your off the bull, reposition and try again until your smack on the bull.

I doubt that your getting your but kicked that bad at 400 yards by a 5-7MPH wind. also, do you have a scope level? If your canted it can throw you badly, but usually you will have vertical stringing also.

Make sure that your not muscleing the gun, especially in your grip. you can be pretty sloppy and get away with alot, but haveing a super flexed grip will through you every time.

Also check your bi-pod. If its not secure you can have issues.

could you have someone else shoot it to compare?
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  #4  
Old 08-24-2012, 04:43 AM
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Re: 2" x 12" groups?

Are you using a bi-pod?
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  #5  
Old 08-24-2012, 05:14 AM
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Re: 2" x 12" groups?

Quote:
Originally Posted by Bullet bumper View Post
Are you using a bi-pod?
"I am shooting with a bi-pod"
__________________
"I'm gonna make a Marine out of you if it short dicks every cannibal in the Congo!"

Ralph L. Ermey
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  #6  
Old 08-24-2012, 06:25 AM
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Re: 2" x 12" groups?

OK this is typical bi-pod grouping that comes about with poor recoil control and poor grip and butt control of the gun. The bi-pod will skate around from side to side under recoil . The vertical will be fine but the horizontal not so good. You are shooting a 7m RUM not a 6mmBR so you have to hold it firm otherwise recoil will push you and the the bi-pod all over the place .
Make sure you load your bi-pod by pushing it forward slightly after each shot especially if shooting from the dirt .
Make sure the butt is in your shoulder and not going under slightly with recoil , which helps the bi-pod skate . The latest sniper technique of laying very straight behind the gun is prone to poor holding if you are not young fit and agile so don't use it .
Make sure the bi-pod connection to the stock forend is as rigid as you can get as some tend to be not so rigid and flex about from side to side under recoil making horizontal even worse and helping the bi-pod skate from side to side.
Heavy guns with heavy recoil need much more than a bi-pod attached to a single sling stud it just is not rigid enough.
Recent experiments I have done with an 18 pound alloy chassis rifle and a Harris bi-pod have confirmed these issues . Some other brands like Atlas are a bit better I feel. In the end I had to epoxy resin the American defence rail adapter to the bi-pod permanantly to stop sidways flexing . Not the rail adapters fault but the single point pull of the Harris bi-pod is just not rigid enough and can rock about around that single point .
A bit of wind is in there also to one side I reckon but if the group is pread left and right of the center then it can't be all wind , bi-pods are great at controlling verticle but need help to control horizontal .
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  #7  
Old 08-24-2012, 11:14 PM
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Re: 2" x 12" groups?

Sounds like we're all in agreance here. It's probably not the load, I just can't shoot! I will try some of these things and let you guys know. Thanks for the input!
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