Shifting POI; accuracy/groups opening up

"How much does the point of impact (POI) typically wander at say 100 yards?"

7/16 inch.


"How much do the groups open up?"

3/8 inch.

More or less. ??
 
You'll just have to shoot and see. Every gun is different. High quality custom barrels are less prone to this than typical factory barrels. Thicker, heavier barrels as a rule will shoot smaller groups for more shots than thinner barrels. The Ruger has a standard weight sporter barrel. You should be able to shoot 3-5 shots at a normal pace at the range, say once every 30-60 seconds with no problems.

Every thing is a tradeoff. Heavy barrels will shoot more consecutive shots before group size opens up, but they can be a pain to carry around. And in a hunting situation you rarely get more than 2-3 shots anyway.

Based on my rifles, a standard barrel like on your Ruger should be fine for the situation described above. For my standard weight rifles 3 shots is usually in the .5-.75" range. Two more would usually stay in the 1" +/- a bit range. Never tried more than 5.

A truly lightweight barrel could be much different. I used to own a Remington MT Rifle with a very thin barrel. It would always place the 1st 2 shots perfectly to the POA with both holes overlapping. A 3rd shot would typicaly open up to 1" +/- a tiny bit. On the occasions I tried a 4th and 5th shot groups would be in the 3-4" range.

That did not concern me in the least. The first 2-3 shots were plenty good enough and it wasn't meant to be a target rifle.
 
I agree with most of the posters but would add that the caliber and amount of powder being burned will make some difference in the rate of heating.

My .270 hunting barrel with 54 grains of IMR 4350 heats up after 2 shots. The first two are either in the same hole or are touching at 100 yards. The third moves out about 1/4 inch at 2 o'clock and the fourth moves out another 1/4 of an inch. In really cold weather the third shot might move out 1/8 inch.

A .223 with 25 grains of H335 won't heat up as much as a long action.
My .223 takes a few more shots to start to get hot enough to move the POI.
 
The Ruger has a standard weight sporter barrel. You should be able to shoot 3-5 shots at a normal pace at the range, say once every 30-60 seconds with no problems.
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This sounds pretty good for a sporter barrel. I'm curious as to how long a very hot barrel would take to cool down to get back to the accuracy above.


My .270 hunting barrel with 54 grains of IMR 4350 heats up after 2 shots. The first two are either in the same hole or are touching at 100 yards. The third moves out about 1/4 inch at 2 o'clock and the fourth moves out another 1/4 of an inch. In really cold weather the third shot might move out 1/8 inch.
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Interesting information. I guess a person can get to know his rifle and compensate on subsequent shots. Example based on above: On the 10th shot of a string, put the cross-hairs 2 inches 8 o'clock from where you want the impact. On the other hand maybe POI would walk more than 1/4 of an inch for each shot as you get closer to the 10th shot.
 
All barrels heat up at virtually the same rate for a given rate of fire with the ammo for a given cartridge. And those of the same make, shape and cartridge heat up at the same rate. But how much they bend causing a shift of point of impact will vary. Most factory rifles are notorious for doing this.

Most of the cause is the barrel's not fit to receiver whose face ain't squared up with the chamber axis. A few barrels are not stress relieved properly and they'll bend a bit as they heat up regardless of how they're fit to the receiver. Then there's those with a bedding pad under the chamber area; a well known cause of POI shifts as the barrel gets bigger in diameter from heating up and that changes the pressure on it at the bedding contact area.

Fix whatever problem causes POI to change as the barrel heats up to eliminate it.

I've seen no POI shift across all sorts of good barrels well fit to receivers. Shorter, more slender ones shoot to point of aim for a few dozen shots starting out from ambient temperature to skin-burning hot as thicker, stiffer ones. Some thinner ones fired 20 to 30 seconds apart for a couple dozen shots or every 5 seconds apart for 10 shots. Arsenal test barrels do so for a few hundred shots fired at the same rate.
 
I've got a bone stock Savage 10 in .243, a standard tupperware stock and a hunting scope that demonstrates that very problem. If I take my time, wait between shots, it's extremely accurate.

.243sav+01.jpg


However, if I start getting impatient, and fire too quickly, it starts stringing vertically as the barrel heats.

243w03t.jpg


This is a bone stock hunting rifle, and I've never done anything to it, other than mounting the scope. I could probably stop that stringing problem with a better stock and a bedding job, but it's always been low on my list of projects. However, it's a hunting rifle, and I've never fired more than two shots with it on a hunting morning. After the shooting, I'm normally too busy dragging venison.

One of these days, I'll get a better stock, bed it, and probably put a better barrel on it. Until then, I don't let it get hot.
 
i would believe that as your barrel is heating up that the barrel whip is being multiplied and most likely this is why you get a vertical climb when shooting to fast. i have a savage also in 22-250 and if i shoot more then 5 shots without a cool down period i get huge poi changes also in a vertical pattern this is the curse of light sporting barrels i believe. however the same applies if i shoot slow with enough cool off i have sub inch groups at 100 yrds pretty easy and thats with a 3-9 bushnell on it.
 
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