Accuracy, is it due to heat????

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gaetoune

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HI, my buddy has a 280 rem custom gun built on Mauser action. The barrel is a really light contour. We've been developping loads for it and can get it to group 3-4 bullets group rapid fire. The loads Are 165gr btsp sierra, IMR 4350 from 49 to 53.5 gr. If he shoots slowly, letting the barrell cool between each shot it's allright.

My concern is, when he shoots lighter loads, 140gr Factory loads the gun shoots goods, about 1,5-2 MOA.

Can the hotter loads and heavier bullets make that much of a difference in heat? Should we reload lighter loads?

We've been playong with OAL as well with no real luck.

Thanks for answer

Gaetoune
 
Rapid firing with a light contour barrel can definitely affect accuracy. 1.5-2 inches for a custom rifle isn't very accurate, did the guy just have it built or has it been around a while?
 
He bought it like that, it could make sub moa, but now it's getting really finnecky. Nothing we tried so far worked.

When it get hot it shoot so bad, 4 MOA approx. Seriously, even trying, I could not reload that bad (Hopefully!!!!!). So We're starting to think the barrel heats up too fast with hot loads/heavy bullets combination
 
Rapid fire! sure that could have an effect because of the heat. Beyond a certain point you need a water jacket, or multiple barrels, etc... Also rapid fire and shooting for groups could cause some difficulaties, certainly logical enough to want to check that performance out, but one would have to be a very accomplished shooter to get meaningful results.
 
"...rapid fire..." Whatever for? Light barreled hunting rifles aren't made for any kind of rapid firing. They're made for cold barrel accuracy, not repelling boarders. The rifling twist will determine if the rifle is more suited to heavy bullets.
"...about 1.5-2 MOA..." Tell him to try a different brand. Find a factory load that shoots a bit better(1.5 to 2 inches is ok for hunting though), then start working on a load using whatever factory bullet weight shoots best. And no more rapid fire.
 
Thanks Guys. That's what we figured out too. He does not know the rifling twist but i'm pretty sure it is better for lighter bullets as it shows better accuracy with light stuff.

The rapid fire I meant was more of follow up shots on an animal. 2-4 bullets one after the other. The accuracy gets bad in that particular situation.

We shot 3 bullets in a minute then cool down the barrel in the truck under A/C the shot 3 bullets again. Amazingly same results, first at 1/2 MOA of the other first and the other 2 same thing as well in an upward pattern. Second and third bullets going up about 1 to 1"1/2". It was a really hot day though.

Thanks again
Gaetoune
 
If this is a hunting rifle, my advice is to shoot all groups similar to how you would when you hunt. Who cares what it does with a series of cold bore shots?

If you know that the rifle is zeroed for cold bore, and that your rifle will hit an X MOA circle low left on the next one, this is more valuable to me then how it groups cold bore.

Certainly, it is unlikely that you will get more then 2 shots at anything, but practice at the pace that you'd shoot the first 2. This way, you will know where the follow ups will be in relation to the cold bore, and at the same time load what is acceptably accurate. 4MOA is still a heart shot in many situations.
 
If the barrel temp is different from shot to shot, you can create problems such as a "stringing group". Most target shooters will therefore let the barrel cool between shots. It can take a long time for the barrel to cool to ambient temp, so I tend to let the barrel cool to "first shot" or "second shot" temp - usually 2-3 minutes. If you hold the rifle vertically with the bolt open, you create a natural stack effect and air circulates up through the barrel quickly, accelerating the cooling.
Other than that, you may find that flat based bullets may group better than boat tails. I have my best luck with Hornady Spire points.
Twist rate being respected,your rifle will naturally tune to a particular bullet weight due to barrel harmonics. This is a fundamantal consideration for all rifles.
 
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+2 on what cosmic said. Barrel harmonics play an important part in pin point accuracy. Your buddy may want to free float the barrel. This may require some relief in the barrel channel and a bedding job. Takes some work but is pretty easy to do.
 
280

The .280 Remington should be 1 turn in 9 & 1/2, so any weight should work if the rifle likes that particular bullet.
Every .280 I have had liked 160 grain bullets like the Nosler Partiton or TSX from Barnes.
Find another bullet that groups better and let it cool between shots....:cool:
 
Thanks guys. We'll head out to the range again in the next couple of week and try to cool enough between shot.

We'll also try some lighter loads in the 140gr range.

Thanks again

Gaetoune
 
it's actually my gun... i've been gone for a while so i missed this thread.
this gun used to shoot amazing... 3 shots in sucession would group in 1/2 inch at 100 yrds. but now they climb up and right.

Turf said:
+2 on what cosmic said. Barrel harmonics play an important part in pin point accuracy. Your buddy may want to free float the barrel. This may require some relief in the barrel channel and a bedding job. Takes some work but is pretty easy to do.
Click to expand...

that's exactly what i'm thinking... bedding. but something else has me a little concerned too. the bullet jump on this thing is in the range of 180 thou. this seems really high. (now this was a very rough measurement using a dowl down the barrel. once with a proper AOL bullet chambered and once with just a bullet seated to the lands). since i want the gun looked over by a pro i took it to bashaw. (i heard he was the best aroun here) i told them to go over it thououghly. bedding, bullet jump specs, check the barrel etc. i also told them if the barrel has to come off to fix the bullet jump to AI it.
hope they can figure it out. oh yeah it has a shillen barrel on it.
thanks for the input
 
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