Cold Bore Shot?

[LR1955]

What up with this?

A buddy and I were out fine tuning our Grendels, getting ready for the deer gun hunting season.

With my 18" Liberty/Saturn Grendel barrel I'm getting a cold bore shot about an 1.5" low which I have noticed before. After that it groups fine.

With my buddies 16" AA Grendel this does not happen. By the way I sold him the 16" barrel and kinda regretting it.

Any thoughts?

1.5" low at what range?

Here is something you can do if you have about twenty rounds to shoot.

Get a small indoor / outdoor thermometer that has a sensor attached to a wire.

Let your barrel cool down to the ambient temperature. Shoot one round, blow out the smoke from the chamber, and measure the increase in temperature of the barrel at the chamber. I bet it doesn't even go up five degrees F. You will find that you have to shoot a decent sustained fire string of ten to see a decent increase in temperature of maybe fifty degrees.

So, ask yourself if one shot that may raise the chamber temp two or three degrees will throw that first shot that far from a group.

Shoot a sustained string of ten in about a minute and measure again. Keep doing this until you get the chamber temp up about 100 or more degrees F. Then take a round of ammo and measure its temp as best as you can. Put it in the chamber and let it sit for five minutes. That ought to be enough time for the powder to heat up. Remove it and see how much hotter it got. Generally speaking, the hotter the powder temp, the more energetic will be its burn and so your velocity ought to be higher. You will find, though, that you really need to get the powder very, very, hot to see a difference of fifty fps. 60 or maybe 70 fps generally equates to about a minute.

I have watched thousands and thousands of 'cold bore' shots made at 600 yards from many guys. I have never seen a pattern set with any single rifle or even any single shooter.

I believe mirage coming off the barrel and downrange has more to do with shots not going to a zero than whether the rifle is clean or not and or the bore is cold or not. That said, I do believe a clean barrel will probably show the first shot or three to be slightly out of zero. Hard to tell, though.

I wouldn't get wrapped around the axle over it.

LR55