Barrel "warm-up" before chrono?

N

NINEX19

New member
This may be an amateur question, but I can not seem to really find any information about it out there.

Do you "warm-up" your test barrel before you start testing your loads with the chronograph?

Why do I ask? Well, I have noticed a trend in my own testing that has lead me to the conclusion that I should take 5-6 shots of non test ammo before I start to read velocities. Since I am usually under average predicted velocities by quiet a bit and I usually start testing with a cold barrel, have noticed on my strings that when shooting my test loads (of all the same charge), they seem to climb in velocities the more I shoot. If I remove the first 5 or so velocities from the average, I would usually be hitting, or much closer to the predicted velocities.

So, am I on the correct track or is there something wrong with my chronograph?
 
Yep. As Reloader2 said, it depends on what my load was for that I'm testing.

Hunting load, I'd take my time and see what a cold barrel velocity was.

Match Ammo, when I shoot my workup, the first several charges aren't generally what I'm looking for so they warm the barrel up for me and my barrel gets more to a match status where the barrel is warm/hot when shooting the strings.
 
I do not know. I do not go to the range with one rifle, it takes too long to cool. I have rifles that were not built to cool. I took one to the range, it took me all day to run 120 rounds through it. Not a problem I had 5 other rifles.

If I had a problem with a rifle that shot when cold and or hot I would use a barrel 'cozy', something like a 'tea cozy'. Then there is that other problem, loading in the summer and shooting in the winter. If cold ammo is a problem store your loaded ammo in the freezer and carry the ammo to the range in a cooler.

Do not leave fired cases in the chamber, open the bolt and extract the fired cases.

F. Guffey
 
It's pretty normal in target shooting for barrels to need a few fouling shots before they settle. It's also common for increased barrel temperature to raise pressure and velocity a bit (though you occasionally see the opposite happen). The main thing is to learn if it's the temperature or the fouling that's making the difference. So, if you leave the gun fouled and let is cool, then fire it again, has the velocity gone back down? If not, it's the fouling adding some bore resistance to make it easier for the powder to build pressure. A slightly faster burning powder might give you less difference if that is the cause. If it is actually temperature itself, you might, again, experiment with different powders or even different primers to see if you get better velocity consistency with a different one.

Published velocities are often fired in SAAMI standard test barrels which have tighter chamber and tighter bore tolerances than production guns normally do.
 
When chronographing a large quantity (50 or 60) of an ammo recipe, and starting with a cold gun, I've anecdotally observed that velocities tend to increase with lead slugs as the barrel warms up.

So now, I put three cylinders' worth through the barrel before I begin chronographing.

Plated or jacketed bullets seen to decrease in velocity. I suspect it's due to the lack of lubrication, coupled with copper fouling. But that's a whole 'nuther post.
 
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