There’s a lot of talk about ‘cold bore’ shots in the precision rifle community. Hollywood has made the term popular and so many a new shooter finds themselves overly concerned with their cold bore shot. They want to know how the cold bore shot is different than other shots, and how to account for the difference to increase chances of a hit. The goals are all well and good but some of the information is a bit misleading. Having been involved with long range shooting for several years now we can discuss this and hopefully put some of the rumors and voodoo to rest!
The Cold Bore Shot Myth
That’s right, we’re calling it a myth. When I got started in precision shooting I thought this was something to be concerned about. After some training, many rounds of experience, and reviewing training material from knowledgeable folks at Sniper’s Hide and Rifles Only, we can pretty much call it what it is. This is a myth. As the story goes a cold barrel, unfired for the day or whatever, will exhibit a shift in point of impact from the zero. This point of impact is different from where the bullets land after the barrel has warmed up, so the myth goes.
Personally, I like Frank Galli’s take on this. He said something to the effect of, “If your barrel shoots to a different point of impact cold than it does warm there is something wrong with the gun.” That’s pretty blunt and pretty true in my experience. There is often a difference that you can see on paper with regard to where rounds impact on the first shot versus shots fired later in the day. However, as the folks at Rifles Only have termed it, what you really have to deal with is ‘cold shooter.’ The point here is that the gun is a mechanical device. There are things that will cause shifts but the barrel being warm or cold isn’t one of them.
Frank Galli even did a video to disprove it, burning through 20 rounds or so quickly after leaving the gun in the sun and dialing back down to zero. He put the final round right next to the initial round of the day. If this video doesn’t convince you this is a myth I’m not sure what will!
Clean Bore Shots?
There is such a thing as a clean bore shot. This is where some of the myth comes from. A barrel that has been scrubbed clean with solvents and patches and has a bore that is unfouled by bullets and powder likely will exhibit a shift in the point of impact initially. A barrel that has been ‘fouled’ by several rounds will usually have some copper, powder, and miscellaneous grit that works its way into some of the small pores and imperfections of the barrel. Having those pores filled will guide the bullet in a different way than a completely clean barrel. A clean bore may exhibit a shift in point of impact the first few rounds. After which it will settle in and stabilize.
This is also why the common recommendation is to avoid cleaning your barrel constantly! Every time you give it a good scrub you need to fire a few fouling rounds afterwards or you risk taking a shot that will be affected by the clean bore shift. We talked about rifle cleaning practices in our article on Cleaning a Precision Rifle. Generally I suggest you clean your rifle every 300-350 rounds or sooner if you notice accuracy degrading. Certainly don’t clean it after every shooting session when you get home or you set yourself up for a few rounds that aren’t going to go where they should, even with a good zero on the rifle.
Testing the Cold Bore Myth
This is another suggestion I have to give Rifles Only credit for, and it’s a good one. If you are one of these people that refuses to believe that cold bore shots are a myth give this a whirl. If you have a rifle you are convinced has a cold bore shift, bring it to your next range session. Set it aside. Shoot the first half of your day with another rifle, or a buddy’s gun, whatever. Come back to the problem rifle after you have had some shooting time logged and you feel pretty loose and warmed up and see how the problem gun shoots. Chances are it will shoot the way it always does. If it doesn’t, try having a buddy shoot your gun using the same process to test it. There shouldn’t be a temperature induced shift, if there is, you may need a new barrel because a properly assembled gun shouldn’t have this issue.
Another thing that may give you a shift in point of impact is shooting with a suppressor. This has nothing to do with the temperature of the barrel and everything to do with muzzle velocity and barrel harmonics. Shooting with a suppressor will often times give the rifle a small boost in muzzle velocity. Obviously, given enough distance, the difference in muzzle velocity between suppressed and unsuppressed fire will produce a shift in the point of impact. Additionally, you are affecting the harmonics of the barrel by hanging a suppressor on the muzzle. This happens by adding weight to the front of the gun. This shift should be consistent and repeatable but since we are talking about shifts in point of impact, we thought we’d mention this. We’ll talk more about suppressors and shifts in future articles!
The whole cold bore thing is a lot of myth and superstition. Don’t buy into the hype. If its too late and you’re already convinced this is true, try testing it and see if you can disprove it! At the end of the day, assuming you fired a few fouling rounds after the last cleaning session, your rifle should shoot the same on the first round as it does on the 200th round. If it isn’t, chances are that it’s the shooter that is introducing the difference. Try focusing more on the Fundamentals of Marksmanship! Videotape yourself at the range and see if you can see a flinch or slap of the trigger that isn’t there after you have warmed up. Like many things in the shooting world this really boils down to a training issue. If you train properly you can mitigate and eliminate the effect completely.