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Posted: 1/2/2004 7:42:09 AM EDT
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I just got a new used RRA flattop with 20" bull stainless barrel - in excellent condition. It came with a mount and a scope - nothing special at all. In fact, what appeared to be locking screws on the elevation knobs appeared loose. I tightened everything up before shooting. I chose this particular gun because with it's 1:8 twist rate, it should shoot heavier loads best. That's what I wanted. Shooting it the first time a couple of days ago, I wasn't expecting great accuracy until I got the barrel properly broken in. Good thing I didn't have any expectations. I didn't get very good accuracy at all AND I noticed after some shooting that I was getting vertical stringing. What can cause that? I can work on finding the right load for accuracy, but what could be the cause of the vertical stringing... it was extreme. I went from 1" - 1 1/2" groups to 4" vertical groups. I shot Federal & Winchester 69g match loads and Black Hills 60 & 69g loads. Nothing was great - which was surprising. Any ideas on what to look at? |
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Bullet resistances down the bore (rough bore), Build(ing) up of fouling at the end of chamber cut causing the rounds to be higher in pressure over the course of fire, loose barrel, a bolt/chamber working in, or just a cheap ass scope (read leaper) that is not holding a Zero. If installing a correctly working/holding zero scope does not resolve the problem, my solution would be to just pull the barrel, hand lap the bore and polish the throat/crown engagement (non-chrome lined), check the barrel extension for burs, lap the bolt into the lugs, then reinstall the barrel per spec and be done with it. Granted all of this may not be needed, but this is what I do to a barrel before it’s ever mounted onto one of my rigs. |
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Were you shooting the rifle off a rest or bipod? What point on the front of the rifle was being supported by the rest/bipod? Is the barrel free-floated? If the barrel is free-floated, check to make sure the FF handguards and barrel are tight. Generally, the FF handguards are what hold the barrel on the upper receiver, so if there is any play in the handguards, it may mean that the barrel is not properly attached to the receiver. A loose barrel will have some rotational play to it, it may be very minor though, a properly tightened barrel will have no rotational play whatsoever. If the barrel is not FF, then there is a good chance that pressure on the barrel from the rest/bipod, along with the barrel heating up, is causing your problem. If the above doesn't solve the problem, then start looking at the scope and mounts. If that still doesn't solve the problem, then it probably is the barrel and Dano's advice would be applicable. I assumed you gave the barrel a good cleaning, using a good copper solvent like Sweets 7.62 or Barnes CR-10. If not, copper fouling could also be the culprit. Might not hurt to use some JB bore compound on the bore as well, to smooth things up and clean out any remaining fouling. If the vertical stringing didn't start until the barrel got hot, and doesn't happen if you keep the barrel cool, then your scope and mounts are fine, it's the barrel or way the barrel is being supported that is causing your problems. |
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Thanks for the advice guys. This was a new rifle and the first thing I did was give it a good cleaning. I cleaned between every 5 shots too. I am 110% sure that is not the issue. The forearm is the cyndrilical free-floating type, but I have not taken it apart to inspect the barrel and forearm. I can do that next. I was shooting from sandbag rests fore and aft with the forearm only on the front bag. No exact point of contact, but probably on the front third of the forearm. I can play with that on the next trip, trying it closer to the barrel. I have replaced the scope with one of known quality that I have used on several rifles and have turned the base around so I could better position it. That is my first alteration. Hopefully, the last! Thanks again Mark |
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Check to see if your gas tube is binding a bit in the gas key. It should "swish" through dead center, and you should not be able to feel any drag as the tube enters the key. Pull the upper off the lower, and move the carrier back and forth about 3/4" from closing and you should not be able to feel the tube scraping inside of the gas key. If it is, you'll need to bend the gas tube until it swishes through the center of the key. I am not sure this problem could be severe enough to cause a 4" string, but you certainly won't be shooting 1/4" groups if the tube is binding up inside the key. |
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