I have an Browning xbolt in .270 and its really accurate. The one thing i've noticed, however, is after about 15 shots or so, my POI drops about an inch. I noticed the barrel is really hot. Normally, I shoot 8 rounds in a 15 minute period, stop shooting for 5 minutes, then shoot 8 again. Is the barrel getting hot responsible for this?
Hot Barrel???
- Thread starter fsfty
- Start date
Some rifles are bad about stringing shots vertically as they heat. I have one Savage 10 in .243 that will string shots up the page about four inches from a cold barrel to a hot barrel. My rifle has a pencil-thin sporting barrel and the stringing is very pronounced. I'll normally only shoot three shots through it at a time, wait for the barrel to cool, shoot three more shots.
Marquezj16
New member
I have an X-bolt in 270 also. And mine is very accurate as well. Less than 1" groups at 100 yards. I have never noticed a shift while I'm shooting. However, I only shoot 3 shots at any given time while sighting in. I wait just enough to be able to touch the barrel with my bare hands. I don't time it. I guess if the barrel gets really hot the POI could shift. But hey one inch low is not bad. 
FrankenMauser
New member
Test it, and find out.
Anything else is just a WAG. Every rifle is different.
http://www.youtube.com/watch?v=3UZ-mApuUoM
Some say differently but i believe thin sporter barrels are subject to change in POI due to heat.
Some say differently but i believe thin sporter barrels are subject to change in POI due to heat.
All barrels are subject to change in impact due to heat, but some are particularly affected. Barrels lengthen with heat, but don't change diameter much. Change in length can make a bit of a difference, due to harmonics, but internal stress caused by either cold-working, or barrel straightening can cause more wandering.
I never shoot more than 3 shots at a time with a sporter deer hunting rifle and often clean, then cool the barrel and shoot a last shot to verify cold barrel, first-shot condition.
Protectant like Break-Free in the bore can affect POI even more than firing 5 shots fairly quickly in a deer rifle barrel, but it doesn't noticeably affect my .270 Win. Maybe that's because .270 Win rifles are known to be generally quite tolerant of different loads. For instance, in my free-floated barrel, both 90 Grain Sierra HP light target handloads and 130 grain hot handloads POIs hit within a quarter-inch at 100 yards! That may have something to do with the small variation in clean/dirty POI with hunting loads.
For some reason, my 1960's-old Savage 110 30-06 was not tolerant of ammo changes, printing 125 grain loads about 2" from 150s at 100 yds. Neither my .22-250 Rem or Tikka .223 are as load tolerant as my .270. (Your results may vary.)
I never shoot more than 3 shots at a time with a sporter deer hunting rifle and often clean, then cool the barrel and shoot a last shot to verify cold barrel, first-shot condition.
Protectant like Break-Free in the bore can affect POI even more than firing 5 shots fairly quickly in a deer rifle barrel, but it doesn't noticeably affect my .270 Win. Maybe that's because .270 Win rifles are known to be generally quite tolerant of different loads. For instance, in my free-floated barrel, both 90 Grain Sierra HP light target handloads and 130 grain hot handloads POIs hit within a quarter-inch at 100 yards! That may have something to do with the small variation in clean/dirty POI with hunting loads.
For some reason, my 1960's-old Savage 110 30-06 was not tolerant of ammo changes, printing 125 grain loads about 2" from 150s at 100 yds. Neither my .22-250 Rem or Tikka .223 are as load tolerant as my .270. (Your results may vary.)
"Protectant like Break-Free in the bore can affect POI even more than firing 5 shots fairly quickly in a deer rifle barrel, but it doesn't noticeably affect my .270 Win."
This is interesting. I just switched to CLP Break Free a few months ago when I noticed the POI changing. Why would CLP affect POI?
This is interesting. I just switched to CLP Break Free a few months ago when I noticed the POI changing. Why would CLP affect POI?
BPowderkeg
Moderator
has anyone heard of "barrel whip" ?? it is not too noticable with a cold barrel, but as they heat up the whip is more pronounced, it can only be seen in high speed video, i have seen it, maybe on "Time Warp", check out the URL below.
here is a very good explanation of rifle barrel whip:
http://www.shootingsoftware.com/barrel.htm
here is a very good explanation of rifle barrel whip:
http://www.shootingsoftware.com/barrel.htm
Yes, I've heard of barrel whip. They all do. Stiffer barrels whip less than flimsier ones. Barrel whip's the reason the British SMLE and its .303 cartridge shot so darned accurate at long range. Bullets leaving at higher velocities exited when the muzzle axis was a bit lower on the upswing than lower speed ones that exited when it was higher. Which ended up with ammo with large spreads in muzzle velocity shot long range groups with not much elevation shot stringing.
Any metalurgist will tell you that as rifle barrels heat up, they don't whip any different than when they're cold. They don't heat up enoug to change their rigidity. There's lots of matches where center fire rifles are shot very rapid with shots anywhere from 5 to 20 seconds apart and their accuracy doesn't get worse as the barrel heats up. And rifle barrels typically whip at a very low frequency; 50 to 80 Hz or thereabouts.
A friend shot 40 shots through a Hart barrel at a 600 yard target starting with a cold barrel. They all went inside 2 inches. I've shot a 30-shot string at 1000 yards that was well under 6 inches. Lake City Arsenal would shoot 150 to 200 rounds testing lots of 7.62 NATO match ammo with each shot about 20 to 30 seconds apart. Good lots would shoot under 7 inches. All of these barrels got really, really hot when the last few shots were fired.
Two things cause barrels to shoot to a different point of aim as they heat up. One is the receiver face ain'g square with the chamber axis; its harder against the barrel tenon shoulder at one place. As the barrel heats up and expands a tiny bit, that hard contact point puts stress in the barrel and it whips more in one direction. This is validated by shots stringing in one direction as the barrel heats up.
Factory rifles and their barrels do this most often. A receiver whose face is squared up won't do it.
Any metalurgist will tell you that as rifle barrels heat up, they don't whip any different than when they're cold. They don't heat up enoug to change their rigidity. There's lots of matches where center fire rifles are shot very rapid with shots anywhere from 5 to 20 seconds apart and their accuracy doesn't get worse as the barrel heats up. And rifle barrels typically whip at a very low frequency; 50 to 80 Hz or thereabouts.
A friend shot 40 shots through a Hart barrel at a 600 yard target starting with a cold barrel. They all went inside 2 inches. I've shot a 30-shot string at 1000 yards that was well under 6 inches. Lake City Arsenal would shoot 150 to 200 rounds testing lots of 7.62 NATO match ammo with each shot about 20 to 30 seconds apart. Good lots would shoot under 7 inches. All of these barrels got really, really hot when the last few shots were fired.
Two things cause barrels to shoot to a different point of aim as they heat up. One is the receiver face ain'g square with the chamber axis; its harder against the barrel tenon shoulder at one place. As the barrel heats up and expands a tiny bit, that hard contact point puts stress in the barrel and it whips more in one direction. This is validated by shots stringing in one direction as the barrel heats up.
Factory rifles and their barrels do this most often. A receiver whose face is squared up won't do it.