Hot Barrel Accuracy

[Stein]

Another option would be to send the scope back and have it looked at.  You have time until fall and it would be good to at least have that checked off the list.  Sounds like you have a Vortex?  They turn those around pretty quickly in my experience.

[Fidelk]

I shoot a Browning A-bolt (predecessor) and have always noticed the same thing.  My barrel heats up and the groupings get all wonky.  A few years ago I bought this plastic barrel fan you put the nose in your chamber and turn on the mini fan and it cools the thing down in a hurry.  Had much better luck getting groupings since.   I see amazon has something resembling mine called a "chamber chiller" but mine just uses a AA batery and cost like $15.  Can't recall exactly where i got it.

This is good to know. I’ll get a fan. As I mentioned before, the barrel got HOT by that last round, even though I was waiting several minutes between shots. Hot enough to be uncomfortable to touch.

My main question here is if the floated barrel should mitigate hot barrel inaccuracy, but maybe it only partially does. It’s a 300prc, and the barrel isn’t particularly heavy. Perhaps a floated barrel only does so much..

Not ruling out recoil flinch, but this thing doesn’t kick much with the muzzle break. It’s a real pleasure to shoot, except that you have to get a second mortgage to buy ammo. .

Will try some cold groups and report back.

If you had stopped after the first three sub-MOA groups, you wouldn't be thinking that you have a problem. You posted that the barrel got "HOT" (which you spelled in capital letters).......I believe you. I'm still guessing that it is heat caused. Try with the fan, etc......but wait 5 minutes between shots (or as long as it takes until you feel that heat diminish) and go past the first three groups of three. Last time the first 9 shots were tight......then they opened up with shots 10 through 15. To truly compare and determine if there is a difference, repeat the 5 groups of 3 and wait the 5 or more minutes between shots.

Don't be distracted with the fluted/free floated barrel......that's what you have and you are trying to work with what you have.

[Karl Blanchard]

If I were you, this is what I would do....

1. Thoroughly clean out all carbon and copper. A virgin barrel fouls fast as it strips out all the chamber imperfections. After that initial scrubbing I never clean a rifle until accuracy degrades. That could be a few hundred or never, depending on the caliber/powder/etc.


2. Go back through your rings and bases and make sure everything is properly torqued.

3. Shoot a slow min 5 shot group. 10 is even better. 3 shot groups are basically pointless. I've shot a lot of really small 3 shot groups but when you stack them all together you realize your quarter minute rifle is more like an moa rifle. Don't touch your dials until you've printed at least 10, then zero off that group.

Where heat can get you is that powder heating heating up in a hot chamber. Some powders are temp sensitive. Like north of 1fps per degree of temp. So if that chamber is hot you're gonna get wild velocity spreads.

[buckfvr]

Put another shooter behind the scope.

[Fidelk]

Put another shooter behind the scope.

That would be a useful verification/comparison. I would still recommend repeating the original session (5 x 3 shots) WITH added wait times to possibly rule out heat as the main factor. Then follow with another shooter doing the same thing......to expand the test, if desired.

If the added wait times result in five 3 shot tight groups.......for WoolSocks and/or the other shooter......it would be logical to assume that HEAT was the issue, especially since the OP has mentioned that the barrel was HOT to the touch.

[okie john]

There was a “mirage” effect, with the heat radiating up from the ground. Still had a clear view of the bullseye though.

I grew up in the long range target-shooting (Palma, F-Class, NRA Service Rifle, etc.) world. I'd bet this is your issue. Mirage will definitely open up groups in any rifle. That's why long-range target shooters use a mirage shield, which looks like this:

https://bulletin.accurateshooter.com/tag/mirage-shield/

There's no need to put one on a hunting rifle. But as others have said, once you fire a group, let the barrel cool down until you can touch it without discomfort. Mirage will seem to disappear before this, but it's still there--you just can't see it.

I do most of my load development work in cool weather because barrels cool down more quickly. A sporter-weight 308 like the Remington 700 will usually make two or three 3-shot groups before mirage becomes a factor. A similar 30-06 will make one or two groups unless I use a hot-burning powder like N560, in which case I need to let it cool after each 3-shot group.

There are lots of ways to cool a barrel: blow air through the bore with a scuba tank or compressor, use ice packs, or build one of the field-expedient chillers you can find online and on YouTube. Shooters in Arizona and other desert states are experts at this.

I use this one: https://magnetospeed.com/products-riflekuhl The only thing I don't like is that it eats batteries like a fat kid eats cake.

Without a cooler, take the bolt out of your rifle and let it sit on the bench with the muzzle up at about a 30-45 degree angle. It will cool faster than if you leave it horizontal or vertical, or if you leave the bolt in place.


Okie John

[WoolSocks]

[/quote]

I grew up in the long range target-shooting (Palma, F-Class, NRA Service Rifle, etc.) world. I'd bet this is your issue. Mirage will definitely open up groups in any rifle. That's why long-range target shooters use a mirage shield, which looks like this:

https://bulletin.accurateshooter.com/tag/mirage-shield/

There's no need to put one on a hunting rifle. But as others have said, once you fire a group, let the barrel cool down until you can touch it without discomfort. Mirage will seem to disappear before this, but it's still there--you just can't see it.
[/quote]

Fascinating. So is the optical effect of the mirage the problem, or is the mirage just an indication of a too-hot barrel?

[jaymark6655]

I would say just the mirage itself. It bends the light, so the target could look clear or be just a little bit blurry, but the position of the actual target and the image of the target could be in different spots.

While mirage is an indicator that the barrel is getting hot, usually if you can hold onto, it isn't too hot. Also, other conditions can cause mirage, like the sun heating the ground between you and the target, especially if there are different surface that absorb sunlight at different rates. Example: Shooting across a paved road that might be used to travel to target location on larger/longer shooting ranges.

Example: Light hits target, it is reflected toward the scope. As the light passes through the air above the barrel, the heat causes difference in air refractive index, this difference refracts light just before enter scope. Just like fish in water being in a different location than we observe, just on a smaller scale because the air transition is more similar than the water to air transition.

[okie john]

Fascinating. So is the optical effect of the mirage the problem, or is the mirage just an indication of a too-hot barrel?

Both.

The optical effect will definitely open up your groups. A hot barrel can shift point of impact, but the heavier your barrel and the more precisely your rifle is built the less of an issue it is. Palma shooters fire unlimited sighters and 15 rounds for record in 22 minutes. They start at 800 yards, move to 900 yards, and finish at 1,000 yards. POI on those guns either doesn't shift or they've graphed it so that it's predictable.

But they all use mirage shields...


Okie John

[buckfvr]

Being able to "hold on to" the barrel to sense the temperature is NOT an indication of the temperature at the throat of the chamber where damage will occur first.

[Bushcraft]

Clean the barrel, chamber, and all aspects of the fire control group.  Use a bore scope for chamber and barrel.  Cleaning a rifle without one is an exercise in fooling yourself and is giant waste of time.

Make certain that the contact areas between action and stock are absolutely clean and dry.  Snug action and all scope related screws/fixtures to torque specs.

Shoot at least 5-10 rounds to "foul" the barrel and stabilize velocities.  Note how the velocities and impact locations of these shots.

Then, shoot 10 consecutive rounds with the exact same point of aim, with a different point of impact (so that you're not blowing a hole or obscuring your POA).

The 300 PRC generates a lot of heat that's absorbed by your barrel.  The thinner the barrel, the faster it's going to heat up.  Heat sometimes does funny things to metallurgy.  You'll need to be doing this early in the cooler part of the day and time.  Make certain you engage your rifle IDENTICALLY every time you shoot.  Do a lot of dry-firing. If you can have a buddy load dummy or live rounds while you shoot to expose a flinching problem...so much the better.  It sounds like you have a lighter weight rifle system, which can be more difficult to shoot to the same POI consistently.

If you run into the same issues, try changing out scopes for one that isn't going to puke its guts out from a heavy recoiling rifle.  Finally...sorry to say it, but outside of their highest end models, most Vortex scopes are entry level garbage that just don't hold up over time.

[jaymark6655]

Being able to "hold on to" the barrel to sense the temperature is NOT an indication of the temperature at the throat of the chamber where damage will occur first.

Agreed, especially if the heat hasn't had time to spread out of those areas. Even if you shoot one shot a day vs 10 rounds a day, the throat is still going to be damaged to almost the same extent per shot, it will just take 10 times as long to see that damage. If you really get the barrel hot, ie can't hold it just in front of the chamber or scope, then the cracking and erosion can occur much faster depending on how hot you get it.

For me a barrel isn't considered hot until it hits 165, which takes quite a few magazines of .300 WM fired roughly every 30 seconds and then I won't shoot until its cooled to about 125 or were I can hold my hand on the barrel without feeling any discomfort. Rifle doesn't really have a target barrel on it, but isn't a lightweight hunting rifle either. I haven't seen any groups really open up due to heat when mirage is mitigated or eliminated by firing from a fixture with shooter completely removed from the loop and no adjustments after initial aiming before a group is fired.

[WoolSocks]

Hot barrel was the culprit. I lapped the rings and cleaned it thoroughly to make sure. Took it to the range and consistently found on the third round with 2 minutes between shots the barrel was hot to the touch and started throwing fliers. Progressively worse with 4th and 5th rounds.

Switched to doing 2 shots at a go and 5 minute rest with a cooling fan. Put 6 shots in a .5MOA group. Looks like a thin-barreled 300prc just gets hot fast.

[Fidelk]

You have a good one.