Barrel overheating question.

[kritos666]

I have a hart 22" bull barrel that shoots great when cold/cool. However after about 7 rnds it really heats up and accuracy seriously drops off.

.4" groups @ 200yrds (cold)
1.5" groups @ 200yrds (hot)

.308 Win BTW

My question is would fluting my barrel really make a difference? If I send it off, its going to take a minimum of 12 weeks. Not to mention it will cost me a bit.

What do you guys think?

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[OregonJohn]

I think no. I would never mess with a barrel that shot sub 1/4 inch. There is much debate on barrel fluting. My take on fluting is that it is mostly cosmetic (Looks cool) and will lighten up the rifle, but very little. It will increase the overall surface area of the barrel for cooling a little faster, but I don't think to the degree that it would be worth the price. And if done wrong, could effect the harmonics of your sub 1/4 inch barrel. It is not going to cause your barrel to heat up slower. With less metal in the flutes, it may heat up faster. I would ask if the groups fired hot were showing a stringing, up/down/right/left, or just got larger. If they are stringing, you have a bedding issue. If they are just getting larger, you will need to shoot slower and let it cool more often. We all wish we could own a 1/4 inch rifle of any caliber.

John

 

[madcratebuilder]

Fluting would be the last thing on my list. What rifle is this on. Sounds like some external force is being applied to the barrel when heated.

 

[Mark W.]

I would venture that a fluted barrel might be able to fire one more round then the same barrel not fluted before reaching a given temp that effects accuracy.

After spending 3 weekends at the Club helping the public sight in their rifles std weight hunting rifle caliber barrels will start to be effected around 4-5 rounds if fired slowly. 3-4 rounds of fired quickly. The heavy barreled hunting caliber rifles would go 5-7 before things started to spread out. My own Savage Model 12 VLP DBM which is a Stainless heavy fluted barrel will hold to .750 MOA for 10 rounds of .243 factory 100gr. But will start going away right after that.

I agree with the guys above that fluting a currently accurate barrel could be a problem and would not be something I would do.

 

[kritos666]

As for grouping ... there is a little bit of horizontal stringing (1 in 5) targets. Mostly the groups are spreading. The stock is a bedded McMillan A1. The barrel does not touch, in fact I can tap the end of it and you can see the gap. It may however be too close and "slap" when fired. As for clearance.. I can slide 3 dollar bills back to the edge of the bedding without any contact (sorry for the pix .. they were the best I could do). I attached pics of the barrel / stock spacing to hopefully clarify.

I am using a rest (Caldwell Rock Front Shooting Rest and rear bag)


As for powder I have tried 3 types .. Hodgton BLC-2, H335 and Varget. All spread as barrel heats H335 is most consistent as far as groups spreading, however the the group sizing is crap 1.5" @ 200.

PS. this was a gun show score of the decade

 

[JLR]

As others have said, fluting really won't gain you much if anything. I'm actually pretty surprised that you're getting that much heat in that few shots with a .308. The gun obviously shoots well so the bedding probably isn't an issue. Are you noticing any mirage off the barrel when it gets hot? That could be what's causing the groups to open up. Not sure what bullet you're running, but we run 10 round strings shooting 175smk's over a fairly stout charge of Varget in the test rifle we built and it manages to stay pretty cool even with a Sendero/Varmint-ish contour barrel.

 

[eldbillbo]

If you flute it it will heat up faster less metal to warm up but cool off faster more surface for heat to escape , but the amount of difference is not much and probably not worth the cost . I found the best method to keep a barrel cool is shoot in the rain.

 

[Gunner3456]

however the the group sizing is crap 1.5" @ 200.

I am really confused. I'd be delighted with that if I'm seeing it right. One and one-half inches at 200 yards? Is that what you're saying is crap???

 

[eldbillbo]

I am really confused. I'd be delighted with that if I'm seeing it right. One and one-half inches at 200 yards? Is that what you're saying is crap???

+1
No kidding

 

[kritos666]

I am really confused. I'd be delighted with that if I'm seeing it right. One and one-half inches at 200 yards? Is that what you're saying is crap???

.. well when I'm getting .395" groups at 200yrs .. yes 1.5" is crap. -- for me

 

[kritos666]

I'm running Nosler 168 custom competion /w Varget powder. 175's just didn't shoot as well for me. I do notice a bit of mirage.

 

[JLR]

Well it's possible that you're suffering the effects of mirage shifting the target around a little. It takes a lot of things to go right to consistently shoot sub 1/4moa groups. Does your accuracy come back after you let it cool down?

 

[Gunner3456]

.. well when I'm getting .395" groups at 200yrs .. yes 1.5" is crap. -- for me

Well, that's just about what my .270 does. About 3/4" at 100, and 1 1/2" at 200. I'm delighted, but then I'm not into competition.

I've never owned a rifle that didn't change point of impact a little as it got really warm, so maybe you can solve it. Good luck and post back if you figure it out.

 

[kritos666]

Well, that's just about what my .270 does. About 3/4" at 100, and 1 1/2" at 200. I'm delighted, but then I'm not into competition.

I've never owned a rifle that didn't change point of impact a little as it got really warm, so maybe you can solve it. Good luck and post back if you figure it out.

I didn't mean to sound like a jerk, ...
I've just gotten those groups pretty consistantly until the barrel heats up. And the point of the post was to figure out if there was anything I could to to minimize the impact on grouping.

 

[kritos666]

I did go out today 60-65 degrees vs. 85-90 degrees the other days shooting.. The groups were more consistent. Maybe I should just shoot my AR in the summer and wait till cooler weather and rain

 

[dmancornell]

I didn't mean to sound like a jerk, ...
I've just gotten those groups pretty consistantly until the barrel heats up. And the point of the post was to figure out if there was anything I could to to minimize the impact on grouping.

Sorry but .4" groups at 200 yards means your sample size is too small and therefore your group size isn't indicative of actual performance. Try shooting a 10 shot group then compare hot/cold before spending any money.

 

[civilian75]

If they are just getting larger, you will need to shoot slower and let it cool more often. We all wish we could own a 1/4 inch rifle of any caliber.John

+1 If I owned a 1/4"@200yd rifle like yours, i'd stop at seven rounds and call it quits. . I don't know how what you where expecting but, you are saying your 308Win is 1/8MOA with a cold barrel and 3/4 MOA once it is warm!! Darn!! If you are so unhappy with it, let me take that "lemon" from you.

Gosh! When you are talking pushing the envelop at this level, anything can affect accuracy. Although Varget is known to be temperature insensitive, well, you could be adding another variable that is affecting your accuracy, like loading 168gr bullets. For instance, I find it harder to get under 1/2 MOA with 168gr bullets than with 155gr, 175gr and 180gr. There is a certain mv sweet spot for 168gr that does not exactly reside at the top of the 308Win load/pressure range, like almost always happens to be with other bullets.

It might even be possible you get rid of that issue by adding/dropping 0.1 or 0.2gr of powder to your load. Or it might get worst. Who knows!

Before you try anything permanent, why don't you wait until temps drop a bit more to see what it does to your rig?

Are you chasing the lands or seating at magazine length?

My $.022 (or 2 cents adjusted for inflation)

 

[kritos666]

Sorry but .4" groups at 200 yards means your sample size is too small and therefore your group size isn't indicative of actual performance. Try shooting a 10 shot group then compare hot/cold before spending any money.

I appreciate your sentiments, I have already had long drawn out discussions of accuracy and have found what works for me. I can pull out my spreadsheets and discuss the statistics but that isn't my point of this post.

However, I am very happy with the accuracy of this rifle and my use of it.


The main point of the post, is that when shooting, I notice that my groups get bigger as what appears to be heat induced issues.

I have certainly appreciated getting a lot of help from folks. I am hoping to deduce the cause of the groups blowing out. To have a hart barrel blow out after 7 rounds seems pretty bad. Perhaps I am expecting too much.

Thanks for any and all input.

 

[kritos666]

My barrel seems to like 168's best, I have tried 175's (its a 1-12)

After ladder testing, I have take the sweet spots of the barrel and then adjusted in .1 gr. increments. (That's how I've gotten it as dialed as I have)

I am currently 20 thousands off the lands, I can bring it tighter. I have really just finished my powder work, so seating depth is next.

Don't get me wrong, I love the gunshow deal-of-the-decade

I agree on the temps comment. I certainly did better today that in the previous weeks when it was hot.