On a warm day what is the shortest.....

[Pond James Pond]

..... period of time you would allow to pass when doing an accuracy string?

I have the heavy barreled CZ550 Varmint in .308 and tomorrow I hope to see what my OCW charge ladders for two separate bullet types will do, so that is about 60-80 shots in total and if I wait for 3 mins between each I will be home by Tuesday.

So, in this nice spring air of abut 17-20 degrees celsius, how little time can I let pass before loading the next shot, without letting barrel heat affect my results?

 

[Brian Pfleuger]

If the gun is a good one, you will see no POI change as the barrel heats up. If it's not, and most aren't, you will.

What I do is shoot a string of 3 and then wait about 5 minutes. That way, except for the first string, the barrel temp is close to the same for all.

 

[Bart B.]

If your shots start moving off the aiming point as the barrel heats up, shoot several about 30 seconds apart with each round in the chamber 10 seconds before shooting it until they start clustering in one place. Set your sight to that point on target; that's your hot gun zero. The round count to get there's your warm up number.

Before testing a load, shoot your warmup number in 30 second intervals then switch to the test load. Shoot the test load once a minute with a 10 second chamber time for each shot. This should work well for 10 to 15 shot test groups providing the bore doesn't foul too much.

The barrel temperature will be very constant doing this. I've shot commercial 30 caliber match rifles this way. They would have a 1.5 MOA zero change over 5 to 7 shots then keep the same zero for at least a couple dozen shots

 

[jmr40]

Very few factory barrels are good enough to not change POI as they get warm. Almost all do, it is just a matter of how much. Some more expensive aftermarket match grade barrels are better in this regard.

I always take at least 2 and sometimes as many as 4-5 rifles to the range with me. At least 1 will be a 22. I'll shoot each of the centerfires 3-5 shots each, then switch to the 22 for a magazine or 2. Usually shooting at reactive targets placed at different ranges practicing off hand or other field positions.

By the time I shoot all of them 10-15 minutes have passed and the centerfires are cool enough. I'll then start the cycle over again. Sometimes I'll even walk over to the handgun range for a little practice as my rifles cool. Not possible at all ranges, but very easy the way ours is laid out.

But during the summer it can get awful hot here at mid day. Over 100 is common. I'm usually putting up targets in the dark and ready to shoot at 1st light. I'm usually packing up and done by 9-10 AM before it really gets hot. But at times I've had no choice but to shoot mid day. I've been known to leave the truck running with the AC on high and keep the rifles in the cab to cool down faster. At 100 degrees it can take 30 minutes for a barrel to cool enough to touch after a few shots.

The rifle matters too. My 300 mag takes a lot longer to cool off than my 308's or 223's.

 

[Pond James Pond]

The round count to get there's your warm up number.

That sounds like a nice system, and it'll definitely keep me busy loading to stay on track time-wise!!

Previously, I have run a bore-brush and dry patch down the barrel every 6 shots to keep in clean: that might be hard to do in 50 seconds!!

As it happens, other than my sighting rounds (first 3 per OCW workup) and about 16 factory PPU rounds, I have no more .308s.

Would that be enough to get that hot zero?

 

[Bart B.]

A hot barrel zero usually takes about six shots in 3 minutes. You'll need to test your barrel to see how many shots to cluster in a small area.

Get a small, low cost infrared thermometer to measure barrel heat and you'll know when your barrel temperature has stabilized.

Or buy some reversible temperature labels to put on your barrel to see how it changes and stays stable:

http://www.omega.com/pptst/RLC-50.html

I'd get the 30-90C and 90-120C sets to cover 86-248 degrees F.