Cold Bore Remedy

[Kren]

Hey Guys,
I have a question for some of you out there that are way smarter than me when it comes to reloading/firearms.

I have a 300prc that I have been shooting and it is shooting extremely well, except for the cold bore shot. My first shot is consistently .75-1" low at 100 yards with this rifle. This has been true with a handful of different load recipes. I have 2 questions for you fellas.

1.) Is there a remedy for this?

2.) I bought this/set this up to be a long range hunting rifle. Right now, the cold bore shot equates to roughly .25mil low at a 100, so will this always be .25 mils low? So, if i am taking a shot at 500 on an elk is my cold bore shot gonna hit roughly 4" low, or would it likely come in the same 3/4" low as it does at a 100yds? I will be testing some more here this summer but was curious what you all think/know.

Lastly what causes cold bore issues? This gun has been impressive after "warming up" and i have many other rifles that have no difference at all on there cold bore shot. Just curious.

As always appreciate the advice.

 

[Rich M]

For a hunting rifle, the first shot is the one that counts. Take it from there.

I have a 357 mag carbine that shoots 1900 fps first shot an 2000 fps on 2nd+ shot - this is my hunting load. It is tailored around the 1900 fps speed. Your rifle could be similar - that could explain why it is a lil low.

Cold bore hasn't heated up and expanded slightly. Might be oil in there. Stuff like that.

 

[ResearchinStuff]

you probably just need to shoot more rounds in your groups to see their true size. next most likely outcome is that you are flinching. third in line is your scope internals shifting a bit. There's outside chance that you have a barrel with high residual stress. pics of your groups and more details on the set up would be hlepful.

Thread 'Cold bore zero versus (very) Hot bore zero “test”'

Sep 9, 2023

Discussions around “cold bore shifts” and “cold bore zeroes” versus “warm or hot barrel zeroes” are constant. So is the belief that barrels “walk” when they heat up or that groups open when they heat up.

After having multiple discussions, @Ryan Avery and Jake @Unknown Munitions and I set up a day to shoot and measure what happens. Quite a bit of discussion happened with getting everyone on the same page, and explaining the limitations and resolution that would be able to be measured. Basically- the more data, the mare accurate the results will be. However, there is a...

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• Replies: 306
• Forum: Firearms

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[hereinaz]

Cold shooter is a bigger thing than cold bore.

Try dry fire for 5 minutes. Get up and drown a couple times. Settle into shooting and the gear.

How low? How many times? Is it within the cone of fire?

Cold bore shift from a fouled bore is a more rare thing than most believe.

 

[WSMHNTR]

Ultimately if this is a hunting rifle the cold bore shot is the only one that matters. When I zero my hunting rifles I also allow a 10 minute plus cool down between shots. A true 1/2" moa gun in much rarer than people would have you believe and most shooters are not capable of replicating that every single time. If you're getting sub 1" groups including a fouled cold bore shot I wouldn't worry about changing anything with the rifle or load. Spend time shooting at distance, reading wind, perfecting your form and field positions. I'v gone down the rabbit hole reloading trying to replicate those one hole groups I got one time with a particular load and all I did was burn up components and barrel life.

 

[Kren]

I am not sure what a cone of fire is? So not sure there. Also this is a newish rifle probably 10 trips to the range, literally 10 out of 10 cold bore shots have all been low. Never right, never left, never high, always low. I am not be the smartest fella, but I’d say that’sa fairly consistent result? Some bullets/loads have been better or worse, but always low.

Here’s two groups last night fired 15 - 20 minutes apart with gun sitting in shade in between to. I know they’re only a 3 & 5 shot group. But it’s what I have pictures of.

 

[Kren]

Oops both pictures are sideways...rotate 1/4 counter clockwise

 

[ResearchinStuff]

 

[Kren]

@WSMHNTR

I agree with you, was more just curious if there's anything that can be done. I will do some practice at longer ranges with a cold bore and see where they come in. Was more just curious about this.

Appreciate the replies.

 

[hereinaz]

Is your cold bore a clean bore shot?

Cone of fire is what a 30 round group would look like. 10 may seem significant, but show all your groups and shots.

Could be the rifle/scope gets jostled and the first shot is low. Cold bore invites a lot of speculation because it is hard to pin down.

 

[TaperPin]

Hey Guys,
I have a question for some of you out there that are way smarter than me when it comes to reloading/firearms.

I have a 300prc that I have been shooting and it is shooting extremely well, except for the cold bore shot. My first shot is consistently .75-1" low at 100 yards with this rifle. This has been true with a handful of different load recipes. I have 2 questions for you fellas.

1.) Is there a remedy for this?

2.) I bought this/set this up to be a long range hunting rifle. Right now, the cold bore shot equates to roughly .25mil low at a 100, so will this always be .25 mils low? So, if i am taking a shot at 500 on an elk is my cold bore shot gonna hit roughly 4" low, or would it likely come in the same 3/4" low as it does at a 100yds? I will be testing some more here this summer but was curious what you all think/know.

Lastly what causes cold bore issues? This gun has been impressive after "warming up" and i have many other rifles that have no difference at all on there cold bore shot. Just curious.

As always appreciate the advice.

As others have said, sometimes it’s not the rifle. Getting settled into a position can change things, how a tripod is loaded, what the tripod is on, or even if the forend is held or not, and your hand pressure or pressure into your shoulder can change the shot, but 1” is a lot. A 300 mag is more susceptible to this than smaller cartridges because recoil causes it to move more before the bullet leaves the barrel. I get 5/8”ish of shift when taking my hand off the forend in a similar rifle.

Double check the action and scope mount screws.

I’ve personally had a scope begin to fail and the first shots were in one place then the group would open up an additional 3/4”. Turned out it was a loose lens inside that would settle in one position, but recoil would cause it to shift. The rifle was very consistent for a number of years, like a decade, until one day the lens fell over sideways. Instantly the rifle went from 1-3/4 MOA to MOA. Ever since then I’ve wondered how many other rifles folks think change of impact is from barrel heat and it’s actually the scope.

 

[NSI]

It continually fascinates me that folks are willing to burn diesel driving multiple times to the range, burn time posting on forums, and burn ammo shooting multiple small groups, but are simply unwilling to lie down on the ground to shoot a 10 round group ONCE and slip turrets ONCE, arriving at a definitive answer and a usable system within a box of ammo. This is bare minimum (and in my view STILL short of sufficient).

Don't clean the rifle. Don't mainline caffeine. Go back to the range. Double up your ear pro. Get low, get stable. Check your parallax. Then get more stable. Dry fire 20 times. Fire 10 rounds at whatever cadence you personally believe makes sense. If that's 10 minutes between shots so be it. Pretend you're shooting your bow - build pressure on the trigger slowly and do not allow bad shots.

I think a field rifle ought to be able to go 10 rounds without wandering, but my opinion doesn't matter here - just yours. Note the position of your first shot. Draw a circle around the whole group. Post it here. Then we can actually help you diagnose an issue, if there is one.

Love,
-J

 

[wind gypsy]

Do you chrono your shots? If your first round is consistently in line with average velocity and continues to print low, I'd assume your first round is likely to impact with that "cold bore" offset at all ranges. I.E. if it continues to exhibit this behavior and averages .75-1 MOA low of POA, I'd expect it to remain .75-1 MOA from POA at all distances if the velocity isn't also off from the avg velocity of all your non-cold bore shots.

Hell if I know what would cause it. A poor barrel stress relief or scope issue would be my first guesses.

 

[mxgsfmdpx]

@Kren take the advice from folks here and go shoot minimum 10 shots at a 1” target at 100 yards. 20 or 30 would be better. Chronoing while you do it is a good opportunity to take advantage of the time and can provide some information.

Particularly with a big bob barker like 300 PRC in lightweight hunting guns, you will start to begin to see the capabilities of your shooting and the guns true accuracy. I have a hint for you and you’re not gonna like it, 2 MOA or maybe slightly better is where your 30 round group is going to end up.

I have seen anomalies like @wind gypsy mentioned with barrels that aren’t properly stress relieved. And of course, something in the scope/mounting system shifting under recoil is always an option, particularly with very popular used scopes in hunting guns like variable power Leupold and Vortexes unfortunately.

 

[HandgunHTR]

I agree with Wind Gypsy on getting velocity readings on those shots. 99% of the time if the issue really is heating or "cold bore" that first shot will be outside the velocity range of the others. If the velocity is inline with the other shots then the most likely culprit is the shooter. Especially with a rifle that is chambered in a "larger" cartridge (i.e. has a bit more recoil).
For the first shot there is no recent frame of reference, so unless you shoot all the time and actually have the good muscle memory and discipline to be consistent on the rifle. So, most of the time for that first shot, people do one of two things. The first option is you "get into the gun more" because you expect the recoil to be more than it actually is. Your grip is a bit tighter and you are making sure it is good and tight against your shoulder and your body is tense, which all leads to a different follow-through. The other option is that you are a bit too loose on the gun, allowing for more muzzle rise during your follow-through.
In this particular situation, due to the fact that the first shot is consistently low, I would guess it is the former. Once that first shot happens, your brain goes, "Oh, it isn't that bad." and you loosen up a bit, which allows for a tiny bit more muzzle rise during recoil, thereby your rounds are impacting just a bit higher.

Just one more thing. You stated that 10 out of 10 cold bore shots are low, how many rounds are you firing during each range trip? If it is only 5-10, and you are only in the 50-100 rounds fired stage with this gun, then that barrel may not even be "settled in" yet and it may go away once you get 200 rounds on it and your velocities even out.

 

[Harvey_NW]

I agree with everyone else that your samples are too small. I will add that the advice to record velocity with an accurate chronograph will help diagnose any outliers, but that also requires a large sample to prove as well. The low round count on your rifle also has to be taken into account during this diagnosis, as velocity may migrate as it "breaks in". You also need to use the same lot of ammo during this test if you shoot factory loadings.

Don't clean the rifle. Don't mainline caffeine. Go back to the range. Double up your ear pro. Get low, get stable. Check your parallax. Then get more stable. Dry fire 20 times. Fire 10 rounds at whatever cadence you personally believe makes sense. If that's 10 minutes between shots so be it. Pretend you're shooting your bow - build pressure on the trigger slowly and do not allow bad shots.

This is exactly the way I would go about it, I prefer to do 5 shot strings and then let the rifle cool for 10 min or so. I find when trying to shoot tiny groups mirage will start to get noticeable by shot 5. I would also shoot at least a 10, if not 20 shot group as precise as possible. Then, I would shoot a 10 shot cold bore group. One shot, in the truck in the a/c for 5 min, on the bench for 10 min, another shot. Factoring in variability if the POI deviates measurably from the 20 shot group produced, you might have proof of an issue.

 

[mxgsfmdpx]

I agree with Wind Gypsy on getting velocity readings on those shots. 99% of the time if the issue really is heating or "cold bore" that first shot will be outside the velocity range of the others.

Let’s say his first shot is 150 FPS slower than his 3rd shot. What is your estimate on what that group looks like when a robot shoots the gun at 100 yards?

 

[TaperPin]

There’s no advantage to shooting a single 10 shot group vs three three-shot groups or two two-five shot groups stacked on top of each other. It should be common sense, but gets repeated so often that 10 shots all at once is somehow giving better information.

There are most definitely guns, even custom guns, that put the first shots in a different spot than those once it’s warmed up. A year ago there was a fellow with a Shilen barrel that was really bad, and even with repeatable results with big group sizes Shilen didn’t want to even look at it. He shipped the barrel and said look at it or don’t look at it if that’s your level of customer service, but this POS isn’t worth shooting so I don’t want it back. What do you know, right in the chamber area was a slag pocket easy to see with a borescope. Had it been just under the surface Shilen would probably still be thinking the guy was full of it.

 

[TaperPin]

100 yard velocity shot with powder measured sloppily with a Lee dipper wouldn’t be enough to make a MOA change in the point of impact.

 

[Harvey_NW]

There’s no advantage to shooting a single 10 shot group vs three three-shot groups or two two-five shot groups stacked on top of each other. It should be common sense, but gets repeated so often that 10 shots all at once is somehow giving better information.

No one ever said it was, it's the sample size of at least 10 that's important.