How many rounds until heat affects accuracy?

[Bigtanker]

I've got a single shot .243 Rossi. After putting on a scope, I sighted it in. I was able to get it centered at 50 yards in about 4 shots. (Just using a sandbag.) Then moving to 100 yards, the best I could do was about a 4", 3 shot group. Time didn't allow me to stay at the range any longer.

That was last year. Today I brought it back out to see what it could do. At 50 yards, I had 3 shots in a 1" circle with 2 holes touching, about 1" left of the bullseye. I moved to the next target and now I was doing a 3 shot group about 2" left and the group opened up to about 1 1/2". I let the rifle cool down about 20 minutes while I shot my 10/22. I then moved to a 100 yrd target and my 3 shot group was about 2". Moving to a new target right away, my group was about 4 inches.

Is this just the barrel heating up? I'm not a super great rifleman but I can do pretty darn good with my 10/22. Or am I just used to rimfire and my AR (both heavy barrels) that can take dozens of rounds at a time without the effects of heat?

 

[JHB]

The heavier the barrel the longer it takes to heat up. Bullet velocity is also a factor. High velocity bullets and thin barrels heat faster and open up groups. Hot barrels will walk groups around also.

 

[red_zr24x4]

Is the barrel free floated?
If its touching the fore arm, as it heats and expands the fore arm could be pushing the barrel

 

[roscott]

Pencil barrels heat up quick, especially hot rounds like .243. Sounds like you were definitely seeing that.

I’ve seen pencil barreled hunting rifles that could barely stay on paper after 25 rounds.

 

[Bigtanker]

Is the barrel free floated?
If its touching the fore arm, as it heats and expands the fore arm could be pushing the barrel

Probably not since it's a break apart.

 

[cb46184]

I once had a German made MK V .300 Weatherby, pillar bedded that would shoot 1/2 MOA...but only if I waited several minutes between shots. That was fine with me. It was a rather light contour barrel definitely not made for bench rest. It was a hunting rifle and IMHO, the first shot out of a cool barrel is the only one that counts. Besides, the recoil was fierce and it took a few minutes for my teeth to stop rattling anyway. ;-)

 

[NyleRN]

Probably near impossible to quantify that measure. So many different barrel contours, lengths, powders used and charge weights. Try a different load/bullet weight. What the twist rate?

 

[Bigtanker]

Probably near impossible to quantify that measure. So many different barrel contours, lengths, powders used and charge weights. Try a different load/bullet weight. What the twist rate?

It’s a 1/10. 100 gr is the heaviest I’ve used. I also have a few 85 gr left but I didn’t try any today.

 

[NyleRN]

I've never owned a 243 but my shooting buddy is fan of the caliber. I'm pretty sure all the Howa and Savage 243 rifles he's owned never shot the heavy for caliber stuff worth a crap. Even his handloads. I believe all those factory rifles are 1:10 also. He's had the best luck with the 65gr stuff. I know every barrel is different but it seems the trend for him is that the 1:10 only likes the lighter stuff. It's worth a try. Groups shouldn't open up that much after 4-8 shots.

 

[Bigtanker]

I'll see what I can find in a lighter bullet. I found the 100 gr stuff for $11 a box and bought a bunch.

 

[actaeon277]

It could be me, and I've never shot .243, but to me, that seems kinda open for that many shots.

Could it be a scope issue?

 

[Bigtanker]

My first 2 shots are ok. And I can repeat them when the gun is cold. The trigger is not that good which I'm sure doesn't help much.

 

[actaeon277]

My first 2 shots are ok. And I can repeat them when the gun is cold. The trigger is not that good which I'm sure doesn't help much.

then I'm probably wrong.

 

[Hohn]

The heavier the barrel the longer it takes to heat up. Bullet velocity is also a factor. High velocity bullets and thin barrels heat faster and open up groups. Hot barrels will walk groups around also.

All of this, plus the total amount of powder burned and the peak pressure.

You run a fast load that's overbore with a big powder column at high pressure in a thin barrel and heat will become a factor pretty soon.

You run a heavy .308 load at 2500fps with a bull barrel and it will take much longer to get into heat.

 

[Hohn]

It’s a 1/10. 100 gr is the heaviest I’ve used. I also have a few 85 gr left but I didn’t try any today.

If it's a typical hunting bullet (soft point, not super long) then 100gr will stabilize usually in a 1:10 unless it's a super short barrel.

 

[Crandall Crank]

For a truly heat temperature issue, it can be in as little as four rounds. Next time you go to the range and take an infra-red heat gun. Document the air temp, barrel temp, accuracy
and time.

 

[two70]

If it's a typical hunting bullet (soft point, not super long) then 100gr will stabilize usually in a 1:10 unless it's a super short barrel.

Yes, it's the length of the bullet that matters, not the weight. If you intend to hunt with it, then you should stay around 100 grains of bullet weight unless you switch to one of the mono-metal bullets. Some of the mono-metal bullets may be longer than the 100 grain lead tips even if though they are lighter.

 

[Bigtanker]

It's for range fun now. I don't have any private land to hunt on.

 

[nipprdog]

My first 2 shots are ok. And I can repeat them when the gun is cold.

I had a handi rifle in 30.06 that acted the same. First 3 shots were right on target. then they would drop a few inches if I fired more without letting it cool down.

 

[patience0830]

Yes, it's the length of the bullet that matters, not the weight. If you intend to hunt with it, then you should stay around 100 grains of bullet weight unless you switch to one of the mono-metal bullets. Some of the mono-metal bullets may be longer than the 100 grain lead tips even if though they are lighter.

85 grain Gamepoints are sufficient for venison and very hard on coyotes.

If you wanted a range toy, BT, you might have been better off with a Howa bolt action. Looks like that break action single shot is designed to put the "one shot, one kill" sentiment into your range time. If you need three bullets to kill the target, your doing it wrong.