How Warm is too Warm for good groups??


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Bull Nutria
December 14, 2011, 11:41 AM
I have a TC Venture in 7mm08, it gets warm after about 3 shots, i generally shoot another gun or piddle for about 5-10 minutes between 3 shot groups and do good with my groups.

is there some rule of thumb for barrel cooling between groups in a sporter contour rifle barrel??

i realize ambient temperature is critical ,but what say you rifle gurus??

Bull

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243winxb
December 14, 2011, 03:19 PM
To warm when you can not keep your hand on the barrel. Some factory barrels walk/change point of impact as they heat up.

BigN
December 14, 2011, 06:23 PM
In the summer I let the barrel cool down between each round, not each group, never have the walking problem. If you don't, the poi will creep up on you.

35 Whelen
December 15, 2011, 12:03 AM
Every barrel is different. Some (Mini-14) begin to scatter bullets after only 2 or 3 shots. Others can go 10 shots fired on rapid succession and still shoot nice groups. (Seen this over and over at High Power matches)

If your 7-08 is a hunting, then 3 shot groups will probably tell you all you need to know anyhow. I mean, in what situation would you fire over three shots in a relatively short period of time?

35W

Grumulkin
December 15, 2011, 02:16 AM
http://www.orchardphoto.com/h5uz260.jpg

Just curious; what would this 3 shot group tell you?

35 Whelen
December 15, 2011, 02:56 AM
Just curious; what would this 3 shot group tell you?

I'm assuming that's a rhetorical question. But, what the heck....

What will that 3 shot group tell me? The same thing these will...
http://i60.photobucket.com/albums/h6/308Scout/Targets/Ruger77308target-1.jpg
http://i60.photobucket.com/albums/h6/308Scout/Targets/35Ww225grTSX-1.jpg

....that I got lucky. Make no mistake, both the rifles that fired these groups are quite accurate, but one-hole groups like these from run of the mill rifles like mine are the exception.
I've been using this same load in my Whelen for about 6-7 years and typically it groups between 5/8" and 3/4". NEVER more if I do my part.
The .308 belongs to my Dad and it's just silly how accurate an old un-modified, '70's vintage Ruger 77 can be, but one hole groups are the exception, not the rule.

So, your picutre tells me that you have an accurate rifle, but got REAL lucky, like I do from time to time. Show me five or six 3 shot groups like and you have my undivided attention!

35W

BigN
December 15, 2011, 05:39 AM
those shots would tell me that I can load up some identical and head to the woods :D

FROGO207
December 15, 2011, 07:16 AM
I have to agree that every rifle is different with respect to barrel heat changing POI. I have some that will wander after a single shot and some that will shoot 10 or more without moving. The .22's with heavy barrels tend to be the most stable after multiple shots so there is definitely need to try your rifle both ways if you want to know what it acts like. Most large caliber hunting rifles especially need to be zeroed in as they will be shot, that way you stand the best chances of accuracy IMHO.

quartermaster
December 15, 2011, 08:00 AM
If your point of impact is changing as the barrel heats up, check to see if it is free floated away from the forend. Slide a dollar bill under it all the way to the reciever to tell. There may be a point near the forend where manufacturers leave a bit of forend pressure. Somtimes this is good and sometimes it isn't. Personally, I like the barrel completely floated.

As the barrel heats up it expands which may make stock contact putting pressure on it which is not there when it is cool. The resulotion is bedding or removal of material from the forend. Before you do anything, make sure your action screws are torked properly

Grumulkin
December 15, 2011, 10:30 AM
The above 3 shot group is the best I've ever done and was made using a rifle that would not consistently do any better than 1 to 1.5 inch groups at 100 yards. The group is a lot better than the rifle is really capable of doing and is better that I can do. I do wish I could take the credit but I can't.

I guess the point I'm making is that 3 shots is a low enough sampling that you can be deluded into thinking things are better than they are. You need to either shoot multiple groups or put more shots into the group to know how a gun or load does.

It's true that some guns "walk" when they heat up. Personally, I think that's a serious defect and I wouldn't tolerate it in a gun. If a gun does that, it means something is wrong with the bedding or the barrel. Though I'll probably need no more than 2 or 3 shots in a row while hunting, I expect a gun to keep shooting where it's supposed to even after 10 or 15 shots.

Seedtick
December 15, 2011, 05:21 PM
what would this 3 shot group tell you?

That group would tell me,

1) that someone besides me shot it
2) that I completely missed the paper with the other two shots
3) that instead of wasting time shooting I should have been playing Lotto

Seedtick

:)

Jasper1573
December 16, 2011, 12:53 AM
It's true that some guns "walk" when they heat up. Personally, I think that's a serious defect and I wouldn't tolerate it in a gun. If a gun does that, it means something is wrong with the bedding or the barrel.

I believe that part of the reason that a rifle may shoot a bit higher after several rounds, say after 5 to 10 rounds have been put through it, is because not only does the barrel heat up, but also the chamber, and where does your newly chambered round lie but in the chamber. So if that round stays in the chamber, it heats up quite a lot in say 10 seconds while you re-adjust and then fire. As my chamber warms, I find the rounds tend to climb a bit, then stabilize on a point slightly above the original POI.

In F-Class matches, I often use my sighter rounds to warm my barrel, then adjust down a 1/4 MOA or 1/2 MOA to compensate for the chamber warming, and the POI remains in the same place once a stable temperature has been achieved. Not sure this indicates a defect, but rather a physical phenomenon that is even more noticeable in the heat of the Alabama summer.

Just my 2 cents.

41 Mag
December 16, 2011, 05:27 AM
If your 7-08 is a hunting, then 3 shot groups will probably tell you all you need to know anyhow. I mean, in what situation would you fire over three shots in a relatively short period of time?

MANY times I have dumped all five rounds as quick as I could acquire the target, on those darned hogs of course.....shoot them till your empty, then reload, and go find some more. :D

To the OP, I generally use the inside of my wrist, right behind my palm, laid on the barrel just ahead of the chamber to check the temp when testing out loads. I had an old fellow who shot BR show me that years ago. If you can hold your wrist there for a 15 count, then your usually good to go. Once it gets to hot to do so let it cool down. I have a few rifles that I can shoot up close to 10 rounds with a minute or so wait between shots, and another few that it only takes two shots to get there. Many different factors involved, as these are all different barrels and different calibers. The powder choice is most often the culprit, but not always.

Also as mentioned the temp of your chamber can effect the next round shot, if it is pretty warm. Interesting test is to take one, or a couple, of small cheap styrofoam coolers. Use one of the gel type ice packs, for a cool weather test, and one of the large chemical type hand warmers for a warm weather test. Lay a hand towel over the ice packs and the hand warmers then a couple of rounds on top of the rag. Let them get either cool or warm and shoot them against your ambient temp ammo. Be very careful if your loads are on the top end, as this has bumped a few of my loads up into the sticky extraction area.

It will however show you real quick if you have a load that will vary much depending on the temp. You also need to be sure you chamber is at ambient temp to test as well. I usually do my development in the early spring, while it is still fairly cool. The above test is cheap and easy to repeat, so I use it if I work up a load that might be questionable. It only takes one of the bigger sized hand warmers to get the temp up to a good summer time heat index of around 100 degrees, and any cheap thermometer, will work as a indicator letting you know how long to let your bullets lay on the rag.

It might sound a bit overboard, but I have had great grouping loads, go to sorry grouping loads with only a 20 degree temp change. It has had me starting to wonder about the rifle when it was the load all along.

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