heat and accuracy question

[supercorndogs]

i have a remington 700 308 with a 26" varmint barrel. my groups seem to open up as the barrel gets hot[10-15] rounds with little time to cool. i expected a heavy barrel to hold groups better than this. it goes from .75 to 1.5 moa. will a better barrel do the same thing or is the only way to stop this by going to a heavier profile barrel

 

[canezach]

Yes, and yes. A better barrel than stock may not necessarily take longer to heat up, but they seem to maintain their accuracy better. A heavier barrel will simply take longer to heat up, but at the cost of weight.

ETA: I'm assuming your rifle is still in its original Remington plastic stock as well? A better made barrel, from what I understand (and will be corrected if I'm not) will heat pretty evenly or uniformly, as opposed to a stock barrel, which might get hotter in certain spots of the barrel. A better stock that allows the barrel to float freely will help, but a better barrel SHOULD maintain its accuracy, even when its relatively hot. You might experience a POI shift, but should maintain its accuracy, though you don't really want to keep throwing rounds down the tube as quickly as possible if you want the barrel to last. Some people are in the "shoot a round a minute and you're good" camp, others are in the "shoot a five round group and let it coll a bit" camp (assuming you're not a competitive shooter, where time is of the essence, but you'd probably be using a better barrel to begin with).

 

[supercorndogs]

i tried it in my bell and carlson with bedding block and my manners t4 with the same results. that is when i realized it was the barrel heating up dispersing my groups. but i was mostly looking for practical experience with stock and better than stock barrels to find out how many rounds it takes for the groups to start to open up from heat. or if this is an abnormally small amount of rounds before this happens in a heavy barrel. if it is i might re-barrel this one instead of re-barreling my 22-250 into a 243.

we are in a great praire dog state and rate of fire is often determined by willingness of targets to come above ground.

 

[Morgan321]

My 700 does the same thing in a Tupperware stock and a nice hs precision. I'm going with a new barrel and hoping it gets more accurate and less heat sensitive.

 

[Struggles]

My sps-v 26" does the same thing. Does you guys poi shift to the right like mine?

 

[supercorndogs]

it shoots kind of like a gun with a bedding problem as it heats up. a couple here a couple there they stay on the 1.5 moa square but no longer all touch each other

 

[Struggles]

With the factory crap stock mine would wander high and right, put it in a bell&carlson and it was a little better. I bedded it with JB weld steel epoxy and it's way better now, it has a slight shift straight to the right now.

 

[GongShow]

Yes...a quality barrel will hold tighter groups from cold to hot with longer strings of fire. Profile being the same. This is what we pay for!

 

[SWRichmond]

Quality barrel makers produce barrels which are, or are nearly, stress-free. When they heat from firing, they do not deform (as much).

 

[whitebread]

<snip> A heavier barrel will simply take longer to heat up, but at the cost of weight.<snip>

They also take longer to cool down.

 

[XTR]

Shooting long range (1000 yard) F-TR over the course of a 20 shot string over 15 to 30 minutes it is very common to have to adjust ¼ MOA of elevation or so in the second string even with the best barrels and bullets that you can buy or make.

Do you cook your rounds? Most F class shooters keep the bolt open until just before they take the shot, though at 100 yards it's pretty inconsequential, MV isn't that big a deal. However it can make differences other places. Have you had the lugs lapped? I had a custom action that for some reason came from the factory not bearing evenly. I figured it out in testing before the nationals. I was running tests to see where my POI shifted if I let the barrel cool as if I was waiting out a wind condition. If I cooked a round for 2 minutes I found that got an impact about 3/4 MOA right. Only explanation I have is that the bolt was heating up and the lugs were bearing differently when it was left closed and allowed to heat up.

The first thing is probably to let someone else who can "shoot small" shoot it and see what happens and make sure you are not inducing the movement with position changes over the long string of fire. If you still get the drift it's probably the rifle.

 

[caldwcj]

Accuracy International did a pretty interesting test of POI shift for flutted vs non-flutted barrels. They proved the non-flutted barrels has less POI shift vs. barrel temp.

This is from the 2013 Sniper Magazine. Article by Tom Beckstrand

“ ….. One design change that resulted from AI’s exhaustive accuracy testing and development for the PSR is the removal of flutes from the barrel. Engineers at AI decided to isolate the barrel flutes to see what impact they had on accuracy. The Engineers attached a laser to the rifle’s receiver, another to the barrel, and a third laser to the scope. All three dots were zeroed to the same point, then they started shooting the rifle. They discovered that, no matter which fluted barrel they used the dots would diverge as the barrel heated. The dots from the lasers mounted to the scope and receiver would stay in place, but the barrels laser would manifest a POI shift. The POI shift from the warming barrel greatly diminished when they used barrels without flutes. Engineers determined that the flutes never heated evenly causing the POI shift. I hope that the results of this test gain wide circulation through the Sniper and Long Range Shooting Communities to help eliminate some of the ignorance that surrounds the perceived advantages of barrel flutes. …..”

 

[supercorndogs]

did they compare fluted vs unfluted of the same weight or diameter. anyone notice less accuracy degeneration with stainless vs chromoly. i think i might re barrel the 22-250 to 308 and compare