how long to let barrel cool?

[NFN66]

I have recently started working up loads for my new .338 Lapua CZ HET rifle and am getting some inconsistent results so far. This is the largest caliber I've ever worked with as my next biggest gun is a .308win.

What seems to be happening is that my first 2 shots will be through the same hole at 100 yards and then my 3rd shot will be off by about 3/4 inch. This is happening fairly consistently.

A friend suggested that this is caused by my barrel heating up and that I'm not allowing enough time for it to cool between shots. I do allow it to cool, but perhaps I'm not waiting long enough? I'm usually waiting at least a few minutes between firing rounds and then I give it a cool down of about 10 minutes or so after each 5 shots. Should I be waiting longer? I have just sort of been going by feeling the barrel and when it is no longer very warm, I start shooting again.

What sort of wait times are typical when shooting a caliber of this size?

 

[Shynloco]

I don't shoot a .338, but do shoot a .308. And I follow much of the same "cool down" regiment you do, with one exception that you might want to employ. This is something I learned from an older friend and makes good sense in helping cool a barrel when it gets hot or when the ambient temps are up there. And that is, go to your local Pet Shop and find one of those small battery operated air pumps that come with a clear small plastic tube. Put some D sized batteries in the unit and after shooting 5 shots, attach the plastic tube to the unit and stick the other end into the chamber, and turn that baby on. Wait for your 5 minutes abd shoot the next five...repeating the air pump number. That'll help cool of the barrel at little expense. Works for me!

As for the load issues, can't help you with that.

Alex

 

[DOGCAPPER]

I used a 338L for some time...You may need slower powder...180 Nosler shot .2 at 100 (3 shot)with 1__ gr H 870 max 1__( gathered from a mag review on the first AR 30 review)....300SMK liked IMR 7828 __ gr gave heavy bolt lift but shot .660 at 200 yds(3) dont try this load unless you are shooting for the money...__ gr shot almost as good.... easier on the gun and brass..LT

 

[4xforfun]

You need to find the reason for your issue, not slow down your shots in the hopes it will go away.


It's not the heat, per say..it is heat induced stress. Maybe your tube wasn't properly stress relieved. Shoot more than a three shot string. See what happens on shot 4, 5, and six. Warm that baby up once and see what happens. See if the bullets move one way and keep moving in the same direction, or if it forms two groups, or the group simply falls apart.

I have MANY, MANY 1000 yard match tubes that get SMOKIN HOT. My original LG in 300 WBY, for instance. I would shoot at least 10 to twelve sighters, most of which are in the last two min of the sighter period, and then a TEN shot sting in under 30 seconds.......SMOKIN HOT. The impact points do not move when the gun heats up, except for that little bit of velocity gain you get as the bbl swells up as it heats. But that swelling is , or is suppose to be, uniform around the bbl. If you have some unwanted stress in that tube, it will actually bend as it swells (heats up) .

Just my .02.

keep us informed,
Tod

 

[gollygee]

This is a cooler that I built so I could zero to a cold barrel thirty years ago, wore out several motors:





This is available from Grainger:

 

[LCazador]

I have recently started working up loads for my new .338 Lapua CZ HET rifle and am getting some inconsistent results so far. This is the largest caliber I've ever worked with as my next biggest gun is a .308win.

What seems to be happening is that my first 2 shots will be through the same hole at 100 yards and then my 3rd shot will be off by about 3/4 inch. This is happening fairly consistently.

A friend suggested that this is caused by my barrel heating up and that I'm not allowing enough time for it to cool between shots. I do allow it to cool, but perhaps I'm not waiting long enough? I'm usually waiting at least a few minutes between firing rounds and then I give it a cool down of about 10 minutes or so after each 5 shots. Should I be waiting longer? I have just sort of been going by feeling the barrel and when it is no longer very warm, I start shooting again.

What sort of wait times are typical when shooting a caliber of this size?
Have you chronographed the loads ? It would be interesting to note the velocity on that third shot . Sounds like you jumping pressure up on that third shot with the chamber heat from the first two . Try going down a couple of grains with your load or try a different powder or primer .

 

[LCazador]

My reply to your quote (above) did not get separated from your original post . Sounds like one of your components isn't quite right for your load . Verify that with your chrono .

 

[JThorsby]

338 Lapua Magnum?
7 to 10 days.....................

 

[BlackEagle]

Are you fouling the barrel before you shoot the groups?

 

[dragman]

I say somethings wrong. unless the barrel is really thin it doesn't seem right not to be able to get 3 shots down range.

 

[people]

I just looked up what you are shooting and how is the recoil on that rifle? The reason I ask is back when I had a 7mmRM I could not shoot it more than a few times before I would start jerking the trigger.

How is the stock for being stiff? Barrel free floating?

I give my rifle around 10 to 15 min to cool. I usually shoot something else during this time.