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Old June 9, 2013, 08:08 AM   #1
garyalarson
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Help! Inconsistent/random shot group

Hope you guys can help me understand what's going wrong here. I shoot a Remington 700 SPS Varmint, 26" heavy barrel. I have created a couple loads that shoot great (sub-moa) at 100 yards for the first several shots then start spreading out. The spread is mostly vertical going up about 2 min and down about the same.

I bore snaked the rifle at the range and cleaned it out. Then fired a tight group of 6 shots. Several shots later the spread started again.

Wonder if its something I'm doing in my reloads as I haven't seen this in factory loads. Could it be my barrel is getting too hot (pretty hot to the touch after 10 rounds). Could it be some goo that builds up in the barrel? How many rounds is too many through a barrel in one sitting.

One person said I should get my barrel free floated and glass bedded.

Open to all thoughts.

(Today's load was 168 Sierra Matchking BTHP, 39.2gr of IMR 3031, Remington Large Rifle primers, PPU Brass, OAL 2.800, est. velocity 2,600)
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Old June 9, 2013, 09:15 AM   #2
KillThe9Ball
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My first thought would be to look for variances in the bullet's weight.

For me, heavier bullets will shoot higher, lighter ones shoot lower. This could be a reason why you see differences on the Y axis.

I assume you're not seeing any key-holing on paper targets?
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Old June 9, 2013, 03:47 PM   #3
HShack
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Some thoughts.............

I have the same gun. Have done a lot of work to get sub 1/2" groups.

Make absolutely sure scope bases and rings are installled correctly and Loktited [blue].

Free float the barrel- more than just a dollar bill's thickness.

Glass bed the action and about 2" of the barrel. Torque action screws and Loktite.

Sierra 168 Match Kings are good. They will probably group best if seated close to the lands. Mine are well into the lands. You would have to single load at this length.

Adjust the amount of powder. Start low, shoot 3 shot groups, adjust up .5 grains at a time until you get the best group. Of course, always watch for pressure signs. Varget powder may do better.

Allow more time between shots; hot barrel not good. This, by itself may solve your problem.

I clean my barrel after every 10 shots or so. Thorough, not just one pass with a bore snake. [But I am a benchrest shooter].

If sub MOA is OK with you, glass bed and free float is best bet to fix problem.

Let us know .
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Old June 9, 2013, 03:58 PM   #4
cryogenic419
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A few things come to mind.

Your first few shots group great, but after that start to spread. Sounds like the barrel is heating up and POI is shifting. Try taking more time between shots. After firing, open the bolt and eject the brass and let some air get through the action and barrel to help cool it down. See if after letting the barrel cool some if you are still getting the same issue.

I've got the same rifle, put a HS Precision stock which has an aluminum bedding block and free floats the barrel. Overall the groups tightened up a little bit, but it is not going to change the POI shift from the barrel heating up.

Barrel cleaning and the million and one ways everybody says to do it properly....oh man...that is a can of worms you do NOT want to open. Some folks clean meticulously, some folks only do it as often as they renew their drivers license. I'm somewhere in between and haven't had issues with accuracy. Get yourself a good copper solvent and do it as often as you feel it necessary.
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Old June 9, 2013, 04:59 PM   #5
steve4102
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Remington rifles have a pressure point built into the forend of the stock. Does your SPS have this? If so, remove it to free float the barrel and see if that helps.

A hot barrel and a pressure point can change POI.
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Old June 9, 2013, 09:53 PM   #6
Colorado Redneck
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My SPS in 204 Ruger is just the opposite. When the barrel is cleaned thoroughly it takes about 15-20 rounds to get settled in and shoot really good. Some of the more experienced shooters here advised that maybe the barrel on this gun is fine if not scrubbed with vigor. Seems to be thataway.

How clean do you normally try to get the barrel? And one other thing, how many rounds does the gun have through it? I have a 222 Rem that I bought new a year or so back. Accuracy would suffer after 10-15 rounds. Clean and let it cool a bit, accuracy was good. Same deal---10 -15 rounds was about all that would group good. But lately it has been going lots longer without needing a cleaning. Maybe it had some imperfections that have improved with use. Maybe has 300-400 rounds down the tube. Just a thought.
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Old June 9, 2013, 10:05 PM   #7
WWWJD
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Based on my experience with the 20" SPS, I can say that the heavy barrel contour doesn't really suffer POI shifts based on barrel temperature. I've tested several loads... slow fire, rapid fire, cool barrel, barrel too hot to touch. Once I found my 'real' accuracy load, none of that matters. Freshly cleaned or fouled by 200 rounds doesn't really seem to effect my SPS either.

Your load is on the bottom end of the scale according to hodgdon and middle of the road according to lyman's 49th. How does the rifle shoot at 39 gr and 39.4 gr of 3031? Load might be a little soft, and.. could be that the load you think is so good isn't very temperature tolerant, and the chamber temperature is sending your pressures up into a region that kills your accuracy.

You ever try an OCW test? I'm pretty much convinced its the only way I want to do load development; it works quite well. 3-5 shots each in .2-.3gr increments between the min and max charge weight. Should be two or three groups that have close to the same POI and group size. That's where the money's at.

Of course this is all just conjecture on my part; assuming all of the other things mentioned by other posters has been ruled out. Don't over-clean.. a fouled barrel is a happy barrel IMO.
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Last edited by WWWJD; June 9, 2013 at 10:16 PM.
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Old June 10, 2013, 09:01 AM   #8
Bart B.
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There's two things that typically cause shots to string vertically range when shooting from a bench with the rifle's fore end resting atop something.

One is the shooter puts different amounts of downward pressure on the stock as he holds it. If there's any pressure point in the fore end tip to the barrel, that force will change with varying down pressure on the stock. It'll cause the rifle to whip different amounts vertically as the bullet goes down the barrel. And shots start stringing vertically.

The other is the barrel's not fit to the receiver properly; there's a high point between the receiver face and barrel tenon that's at the top or bottom of the barrel. As the metal parts (barrel and receiver) heat up, there's more force applied to the barrel at that point and the stress changes the amount of barrel whip in the vertical axis.

As far as it taking several shots after cleaning a barrel to get good accuracy, the most common cause is poor rifling finish, There's enough rough spots that they need to wipe off a lot of bullet jacket to fill them; those bullets are unbalanced too much and will never shoot accurate. After a few (several?) shots, no more jacket material's wiped off the bullets, they are well balanced now and shoot where they're aimed. Two solutions; get a new, better barrel or don't clean that one too much. Good barrels shoot at their best accuracy level starting with the first shot and for dozens of shots later.
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Old June 10, 2013, 09:11 AM   #9
603Country
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If I had a rifle that was doing like the OP's Remington, I'd freefloat the barrel. Hot barrel contact with the stock would be my guess as to the problem. But if the OP is letting a round sit for a while in the hot chamber and heat up prior to shooting, that could also cause the problem.

As for dirty barrels, I can't agree with WWWJD's point about fouled barrels being happy barrels. That isn't necessarily wrong, but is an overgeneralization. Some rifles shoot great when fouled and some don't. My 220 Swift fouls enough at 15 to 20 rounds to cause accuracy to worsen. My 223 seems like it'll shoot all day dirty and shoot just fine.
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