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Old May 18, 2008, 09:48 PM   #1
rifle59
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horizontal stringing

I am working up a load for my .375 H&H. I am using a lead sled rest. Other than wind, what other causes for horizontal stringing?
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Old May 18, 2008, 10:00 PM   #2
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Your horizontal stringing is possibly the barrel gremlin "walking" the barrel in the stock. With the lead sled the rifle is transferring the recoil to a solid rest instead of recoiling into your shoulder as it would naturally. Any looseness in the bedding or barrel channel will allow the barreled action to flex a bit when the rifle hits the brakes on the rest. Try shooting it with your shoulder a few times and see if the stringing stops or increases. Make sure your teeth are firmly clamped together; a 375 does kick a bit! It's not in the realm of a 340 WBY or the brutal .378, but very stout. Check the stock bolts and make sure they are torqued to spec. When you shoot it in the sled be sure that you position the rifle exactly the same for each shot. Good luck.
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Old May 19, 2008, 12:00 AM   #3
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If you were firing quickly enough to start warming up the barrel, it could be the cause.

Changes in barrel temperature typically cause the barrel to begin walking sideways. You'll usually see a bit of vertical movement as well.
As the barrel cools down, it slowly returns to the original POI.

If you were firing quickly enough to actually get the barrel hot, I would say it is absolutely the cause.
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Old May 19, 2008, 12:01 AM   #4
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What primers and powder are you using?
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Old May 19, 2008, 07:03 AM   #5
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I have heard that you don't want to use a higher recoiling rifle like the 375 H&H and the 300 Win Mag on the lead sled, especially with a wood stock. The sled is so stiff that it transfer's all the recoil back into the stock which can give it cracks in the buttstock as well as around the action. Just a thought that might save your rifle from harm.

As far as the stringing I think you will find that it won't happen off of the shoulder. It is probably too much pressure on things with the sled.

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Old May 19, 2008, 02:23 PM   #6
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Examining targets while working up loads, you observe that at some point accuracy is at its best. As the charge increases beyond the most accurate load, I have quite often noticed (but not always) that vertical stringing begins. It must have to have something to do with the barrel harmonics.

In addition, as has been referred to in this thread, a load worked up at a medium temperature may exhibit horizontal stringing at a 20-30 degree higher temperature. That is similar to the increased pressure from “over max accuracy loads”.
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Old May 19, 2008, 05:16 PM   #7
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Without getting into the methods of working up a load for accuracy (look for yourself here where Shoney's observation is explained, and at this site for a newer and, for many, easier approach), you can test the temperature walking theory by shooting at a very slow rate, leaving the bolt open and letting the gun cool for five or ten minutes between shots to see if the problem lessens or goes away? It is normal for the few shots to differ while initial fouling builds up, if you start with a clean barrel.

The causes include asymmetrical barrel stress, in which case stress relief would be needed, and that's a nuisance because it normally involves removing the barrel and soaking it at about 1100°F. Cryo treating may stress relieve it a little, and I think one of the cryo-treating outfits offered a kind of magnetic hammering for stress relief, but I don't know whether it is still available or not? A more common problem is the stock touching the barrel with an asymmetrical pressure that changes as heat transfers from the barrel to the wood. That can be relieved by normal barrel floating and bedding methods.

You got the lead sled precisely to help you sight in a heavy recoiling gun, so the idea it could damage the gun kind of neutralizes its purpose. I expect, however, you can largely mitigate the problem by putting one or two Past recoil pads between the gun butt and the sled, same as a human does to protect his shoulder. Even two or three layers of carpet scrap would afford some significant protection.
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