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Vertical stringing

 
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  #1  
Old 09-15-2009, 10:09 PM
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Vertical stringing

I have a 7mm RUM that I pillar bedded into an A2 stock. The bedding job seems pretty neutral with almost no movement when you tighten down the action screws. The barrel is free floated and I don't let it get hot any way. It has a V port muzzle brake from Straight Shot Gunsmithing (308 nate). It has shown a definite tendency towards vertical stringing with 150 gr BT's loaded to magazine length. I haven't chronographed a series of rounds to check my ES yet but at 100 yards groups will be under 0.5" with horizontal spread in the 1's and I shot her at 200 yards the other day. 3 shots into 0.6", again with horizontal spread of around 0.1". All groups shot off sand bags and using a Leupold 6.5-20 SF scope. Ideas?
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Old 09-16-2009, 07:31 AM
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Re: Vertical stringing

So, you are saing that your are getting groups 0.1" wide by 0.5" tall @ 100yrds, and 0.1" wide by 0.6" tall @ 200yrds? Sound pretty good. I don't see how your going to know anything concrete without knowing velocity spread. That's what I would guess, but you won't know for sure until you measure. I was having the same problem (bigger group size though) where the groups looked like a football. I finally broke bad and bought a chrony. Great investment, but I don't know how much help it will be in this situtation, since your talking about a change in velocity that will mostly be within the tolerance of your testing capability (unless your firing from a vise, that is bolted down, and your target doesn't shift "any" on impact). My Chrony at best is within 0.5% accurate. Just something to consider, since that is 15fps @ 3000fps.
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Old 09-16-2009, 08:18 AM
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Re: Vertical stringing

That is not much of a vertical spread but it could be a number of things. Like has been said it could be velocity spread but you will not know till you check that. It could be that a different primer will clear up that problem. It could be something as simple as your shooting form or hold. Work on only one thing at a time to fix your problem though. One other thought. Have you de-burred the inside flash hole of your cases? This really helped smooth things out in many of my loads years ago when I started doing this.
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Old 09-17-2009, 09:43 AM
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Re: Vertical stringing

It looks like it is shooting well, .6 groups at 200yds!. To really determine the vertical spread you need to get out and shoot at 500-1000yds. Whatever the longest ranges you intend to use the load(hunt) at.
Then you can really see how the load performs.
I get an initial load and then do a long range ladder to fine tune.
There is a good link to the 1000yd ladder test in the reloading forums.
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Old 09-17-2009, 12:35 PM
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Re: Vertical stringing

Not claiming 0.6" average at 200 yds, that was actually the only group fired at 200 yds. She does seem to want to shoot for sure, though. I need to shoot through the chrony next time I'm out there. I have not uniformed the flash holes and haven't tried any different primers. I've been using Fed 215 match primers. If I don't get it figured out before my trip to Colorado for mule deer, I'm not going to sweat it too much. It is still punching some pretty small groups and I'm probably going to limit my shots to 600 yards.
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  #6  
Old 09-17-2009, 01:03 PM
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Re: Vertical stringing

Sometimes when loads are too hot they can start to string vertically. I shot one the other day with my 260. Four shots all in a straight line. Perfect straight line at 300 yrds. Probably 3-3.5 inches long. MV was too high and the brass had some extractor marks.

One of the more intersting groups I"ve ever shot.

Not all of my rifles do this but they ALL act funny with max and over max loads.
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  #7  
Old 09-18-2009, 08:44 AM
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Re: Vertical stringing

Sambo 3006,

Read Jerry Teo's load developement article on the home page. It should help you out.
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