Cold Bore Shot usually higher?

[DoubleGobble00]

Since metal expands with heat and shrinks with cold.. Is the cold bore shot usually higher? My thinking is that the barrel was tighter with first shot making a slight difference in pressure and velocity. Then the last two shots were about the same temperature... Or maybe I just pulled the first shot...

I shot 3 shots at 325 yards with my 308 today. The first shot was about 3 inch high and the last two shots were not... Wish I would have shot one more round just to find out. Thoughts? If cold bore shot is going to be higher, this might need to be taken into account when hunting long range.



DoubleG

 

[Hatchet_Jack]

Most of my guns shoot low on the first shot or 2. I always figured it was because of less pressure considering there is no fouling and possibly some oil residue from cleaning. I assumed this created a bore with less resistance and lower pressure. Seems practical but I'm no metalurgist.

 

[DoubleGobble00]

Well the gun was not clean. It had 20 shots through it from earlier this week.... before I shot these 3 shots.

Maybe I just pulled it. Wish I would have shot a few more but it started raining and those bullets are $$$$

 

[armaster]

Yes, your first cold bore shot will be out of the group vertically. In a hunting rifle you need to figure out where the first shot goes so you can aim accordingly on game in the field. Coated bullets will not do this.

 

[armaster]

You will have a different POI for a clean/cold bore and fouled/cold bore. You will have to spend some time at the range to figure this out for yourself.

 

[DoubleGobble00]

Got ya.. Just wanted to double check my theory of why the first one was high. I guess if I truly wanted to develop a drop chart, I need to shoot and wait till the barrel is fully cold before I shoot my next round. Then my vertical might truly be cold bore based. It is hard to wait around.. I wonder how long it takes to get the barrel back cold?

I plan to leave the barrel dirty for now since I know cleaning it will drop my POI vertically until it is dirty again.

 

[armaster]

For best results your probably better off just waiting until the next day.

 

[JamesnTN]

Typically I've found mine shoot low 1-2 shots then back on POI now in saying that I just acquired an Accuracy international that cold bore shot or the 25th shot all have same POI I've never seen this from any rifle until now. I now don't have worry about putting a couple fouler down range before load development I can go straight into my load work which is great.

 

[Texas Solo]

My 308 findings are the same as the OP. First shot from a cold/clean bore is always 2" high at 100yds. It only takes one fouling shot, then all the rest will group. That's from a cold/clean bore. I've never tried a cold/fouled bore.

 

[DoubleGobble00]

I probably just pushed it. Hope to shoot more soon to confirm. It did get me thinking!

 

[jhn]

My .308 CZ 750, shoots the first shot 0.5MOA higher.
Second shot, on target, thats every time.

I did some pillar and glasbedding with devcon on the rifle.
So it might be more repetable.

My 22lr cz452, just coldbore no cleaning, first shot 1MOA up.
Anchutz 1813 supermatch, hardly differance, except after cleaning.

 

[stool]

i would say all guns are different.
some of mine shoot left..none shoot right.
the real test is to shoot from a cold clean bore.....three shots maybe enough.
likely one will be off from what you thought was your zero, sucks if the second one is also.

hunters really need to know where each of the first three shots go.

 

[fdshuster]

The reason why everyone has the choice at our match's, to fire one shot into the dirt before firing for score. It does make a difference. I've had the first clean, cold shot go high or low, although most of the times low.