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

[dtrkyman]

Cool test and a lot of work, I do not even hunt with or own a larger caliber rifle, only rimfire and .556.

But was still interested, however not surprised with the results, in my limited rifle shooting they hit where the crosshairs sit!

 

[Diced]

7 of the 10 rifles are factory rifles.

They obviously have good barrels. Tikka and sako rifles generally do. The same cannot be said for most brands, which was my point.

 

[justin davis]

Awesome test. Thanks guys

 

[SBR Sarge]

Form, Ryan and Jake,

Thanks! This is a fabulous piece of work.

Did you do any cleaning before or during?

 

[ScreamingPotato]

Impressive and valuable testing, much appreciated.

 

[RS_Non-Res]

Pretty sure you all wouldn’t own one, but what about the non-stress-relieved cheap factory barrels? You know, like drop testing a gold-ring scope.

 

[Formidilosus]

I guess the only thing this shows me is that you have 10 rifles with good barrels. From what I've seen a lot factory rifles(especially cheaper ones from common brands) do have some crazy stringing when they get hot. I think a lot of people have always shot those rifles and that's why so many are afraid of heat.

There’s no doubt. Garbage barrels are garbage barrels. Barrels that walk, shift or move based on temperature are garbage.

It’s like having a vehicle that only starts at 55°, but won’t start when it’s 70° out, then trying to convince people “it’s a good vehicle”. No, it’s broken and needs to be fixed.

 

[Formidilosus]

Pretty sure you all wouldn’t own one, but what about the non-stress-relieved cheap factory barrels? You know, like drop testing a gold-ring scope.

They’re garbage barrels. There is no legitimate reason to suffer a barrel that isn’t properly stress relieved. It’s a coping mechanism that people tell themselves when they really believe they made a good choice on a purchase and that purchase sucks.

It’s a tool. They’re are sub $600 rifles that do not have any issue in functionality or use/ choosing a rifle that does have issues because it “looks” better and then justifying its failures is ridiculous.

 

[woods89]

@Formidilosus

Did Jake have to buy you lunch?

 

[Huntr]

Incredible information!

 

[Reburn]

There’s no doubt. Garbage barrels are garbage barrels. Barrels that walk, shift or move based on temperature are garbage.

It’s like having a vehicle that only starts at 55°, but won’t start when it’s 70° out, then trying to convince people “it’s a good vehicle”. No, it’s broken and needs to be fixed.

Point in fact. The car starts but veers itself off he road when it gets into operating tempature.

 

[Dust Rider]

Thanks for the reporting.

 

[MT_Wyatt]

I really like this “test it” idea to prove or disprove ideas and publish it. Good resource. Thanks for the effort @Unknown Munitions @Ryan Avery @Formidilosus .

 

[ElPollo]

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 cutoff point where more rounds are being shot without really increasing resolution in the results.

Mainly we were discussing whether 10, 20, or 30 round groups should be utilized.
For best data (95% probability) 30 shot groups are required. So that would be 30 cold bore shots, and then 30 hot bore shots from each rifle. The benefit with 30 round groups is the mean point of impact (MPOI) would be very solid- there would be very little deviation between groups and any deviation beyond about .1 inch would confidently be attributed to a real, observable shift due to heat. The issue with 30 round group sizes is time required and the amount of ammunition required for the rifle being shot.
10 rounds was the minimum required to get usable data. The time and ammo expenditure would be significantly less, but the resolution would be less as well. If a rifle averaged 1 MOA for ten round groups, the center of any group could vary by up to +/- 1/3rd MOA. That is, with nothing changing from 10 round group to 10 round group, you can and will see the apparent center shift around by up to .2-.4 MOA due to ten rounds not showing the true cone.
20 rounds would split the difference with being a bit closer to 30 round accuracy than 10 round accuracy.

Ultimately it was decided that we would use 10 round groups- one 10 round group of cold bore shots, and one 10 round group of hot bore shots as a baseline, with the understanding that there can be a shift of apparent center by up to .3 MOA or so with no change. If you shoot 10 cold bore rounds into a group, and another 10 cold bore rounds into a second group- the centers of each group will vary slightly in respect to the point of aim because 10 rounds isn’t enough to show you the true center for most rifle systems.
Due to that statistical and group reality, it was agreed that only significant and functional shifts would be noted and that was agreed to be .1 mil (.36 inches at 100 yards) or one click of the scope. Again due to limitations of ten round groups, any rifle that showed a shift of more than .36 inches from cold to hot would have another ten rounds fired to see if it was consistent.

This process would be done with ten (10) different rifles. A starting temperature was measured inside the chamber and at the end of the barrel for each rifle before starting. The rifles would be shot one round at a time round robin style, and then the rifles would be cooled to ambient temp before shooting the next cold bore shot, repeating this until 10 rounds was fired from each. The hot barrel shots would be taken as quickly as possible and the ending temp recorded.

No group reduction techniques would be allowed- every round fired counted. Mean Point Of Impact would be the center of all rounds fired in a group no matter what shape or how ugly. Group size would be noted, but has no bearing for this test. Only the difference in mean point of impact or “zero” would. So too, whether the round hit point of aim or not is immaterial, as all groups would be measured using Hornady’s Grouo Analysis tool which gives deviation from aimpoint.

The scopes would be set on the highest magnification or max 20x if they went higher. Fixed scopes were what they were.


The rifles were as follows-

1). Unknown Munituons Competition 7PRC braked, in XLR chassis with NF NX8 4-32x scope. UM ammo.

2). Tikka Varmint T3x 6.5cm suppressed, in a Mesa Altitude stock, with NF NX8 4-32x scope. UM ammo.

3). Unknown Munitions 6.5 SUAM Imp, suppressed, in a Manners LRH stock, with NF NX8 4-32x scope. UM. ammo.

4). Factory T3 lite 308 in Stocky’s VG stock, suppressesd, with SWFA 10x scope. Hornady Black 155gr AMAX ammo.

5). Gunwerks Nexus 6.5 PRC, suppressed, with NF NX8 4-32x. Hornady 143gr ELD-X ammo.

6). Factory Tikka T3 223, suppressed, with SWFA fixed 6x scope. UM Ammo.

7). Tikka Tac 308win in KRG Bravo chassis, braked, with Bushnell Match Pro scope. Hornady Black 155gr AMAX ammo.

8). Tikka T3 Lite 223, suppressed, with SWFA fixed 6x scope. UM ammo.

9). Sako S20 6.5 CM, suppressed, with Trijicon Tenmile 3-18x44mm scope. UM ammo.

10). Tikka M595 Master Sporter 6XC, suppressed, with Minox ZP5 5-25x56mm scope. 115gr DTAC ammo.


Results:

Each target has the 10x cold bore shots on the left, and 10x hot barrel shots on the right.



Gun #1 no shift cold to hot.
View attachment 599436


Deviation between cold and hot was .21” elevation, and .16” windage. Well inside statistical variation.



Gun #2 no shift cold to hot:
View attachment 599437

Deviation between cold and hot centers was .28” elevation, and .07” windage. Well inside statistical variation.


Gun #3 no shift cold to hot:
View attachment 599438

Deviation between cold and hot was 0.0” elevation, and .13” windage. Well inside statistical variation.


Gun #4 shifted .52” in elevation, .13” windage with an asterisk.

View attachment 599439

Somewhere around shot 5 or 7 of the hot barrel group a loud “ting” was heard, and the gun recoiled noticeably more than usual. Firing stopped, the rifle was unloaded and was checked for a baffle strike. Suppressor was fine and nothing could be found. Firing resumed with a noticeable shift down in the group following the event, and the same noticeable difference in recoil.
The next day after further shooting and checking it, it was found that the action screws had loosened substantially. Once retorqued the rifle performed as normal. No shifts could be noticed.



Gun #5 no shift cold to hot.
View attachment 599440

Cold and initial hot group were different enough that a third group was fired to confirm. The rifle just doesn’t particularly like the ammo. The third 10 round group landed smack in the middle of the first two, filling in the cone.


Gun #6 no shift cold to hot:
View attachment 599441


Deviation from cold to hot was .03” elevation and .29” windage. Well inside statistical variation.



Gun #7 no shift cold to hot:
View attachment 599442


Deviation between cold and hot was .12” elevation and .11” windage. Well inside statistical variation. The rifle does not shoot this ammo well.



Gun #8 no shift cold to hot:
View attachment 599443


Deviation from cold to hot was .36” elevation and .04” windage. Well inside statistical variation for this rifle. Of note, this was with a fixed 6x scope and these are the two best 10 round groups this rifle has ever produced. It normally is around 1.1 to 1.2 MOA for ten rounds. It also has more than 20k rounds in this barrel without ever being cleaned.



Gun #9 no shift cold to hot:
View attachment 599445

From cold to initial hot group had a deviation of .73” in elevation and .03” in windage. A third 10 round group was fired and it centered in the middle between the first two groups filling in the cone.


Gun #10 no shift from cold to hot:
View attachment 599446

Deviation from cold to hot was .06” in elevation and .07” in windage. Well inside statistical variation.

Cont….

Good info, thanks. And I totally get why you are so fond of #8 and #10.

 

[Tullis94]

What do you think caused the action screw to become loose on #4? What were they torqued to? I've been looking forward to this test since I heard about it on the podcast. Thanks for taking the time and effort! @Ryan Avery @Unknown Munitions @Formidilosus

 

[keystone112]

How about barrel thickness? Would we expect a thin barrel to show a change while a thick barrel would not?

 

[BjornF16]

Nothing like tearing down strongholds

 

[Formidilosus]

What do you think caused the action screw to become loose on #4? What were they torqued to? I've been looking forward to this test since I heard about it on the podcast. Thanks for taking the time and effort! @Ryan Avery @Unknown Munitions @Formidilosus

Basically I didn’t think the stock would be in this rifle more than a couple days and didn’t do the full install process. When I initially mounted the stock, I was supposed to be using it in a 6UM, however the barrel was taking too long and we wanted to start shooting it. So I put it in the 308, but only used a dab of blue loctite and torqued it. That wasn’t and isn’t enough, and it was dumb of me to do it.

How about barrel thickness? Would we expect a thin barrel to show a change while a thick barrel would not?

?

There was zero correlation to barrel diameter and group size- none. Actually if there were, in these ten rifles the smaller the barrel the better the groups.

By far the smallest groups were fired with the smallest diameter barrels used- T3 lite sporters, one of which was fluted. Barrel contour has no functional effect on precision- good barrels are good barrels and will shoot regardless of thickness.

 

[tredell17]

Basically I didn’t think the stock would be in this rifle more than a couple days and didn’t do the full install process. When I initially mounted the stock, I was supposed to be using it in a 6UM, however the barrel was taking too long and we wanted to start shooting it. So I put it in the 308, but only used a dab of blue loctite and torqued it. That wasn’t and isn’t enough, and it was dumb of me to do it.






?

There was zero correlation to barrel diameter and group size- none. Actually if there were, in these ten rifles the smaller the barrel the better the groups.

By far the smallest groups were fired with the smallest diameter barrels used- T3 lite sporters, one of which was fluted. Barrel contour has no functional effect on precision- good barrels are good barrels and will shoot regardless of thickness.

Out-of-curiosity, would you expect a Blaser R8 to perform the same as the rifles in 5hia test? I've seen you talk about their quality/reliability before.

I was also wondering if the results are primarily attributed to barrel quality or is it a combo of the barrel and the action. Asking cause you mentioned the loose screws causing more recoil but no shift due to a hot/cold barrel.

Sent from my Pixel 6 using Tapatalk

 

[id_jon]

Basically I didn’t think the stock would be in this rifle more than a couple days and didn’t do the full install process. When I initially mounted the stock, I was supposed to be using it in a 6UM, however the barrel was taking too long and we wanted to start shooting it. So I put it in the 308, but only used a dab of blue loctite and torqued it. That wasn’t and isn’t enough, and it was dumb of me to do it.

I haven't been loctiting action screws as I tend to move actions between stocks a lot, do you recommend just checking torque more often in that case? I know the ideal situation is to just leave things together, which I hope to get to one day.