Thread: 1 shot groups (cold bore challenge)

The MPOI of my "cold shots" group vs "hot bore" is 2.6mm different for windage and 0.1mm different for elevation at this stage. (0.026 and 0.001 mrad - .25 and .01 of a click). That's as close to "the same" as you can get, of course it could change wildly with 3 more shots if they were miles out of the group but at this stage there is no evidence that it's different at all.


the mean radius hot was 0.05mrad, cold it is 0.06mrad. Again currently functionally identical. The usual concern is that barrel heating will cause a group to "open up" and precision to degrade. At this stage the precision cold cannot get meaningfully better than hot. Even if I put 3 rounds through a single hole directly over the MPOI it could not improve the measured precision beyond the "hot" group. If you felt like measuring group size instead, cold is 19.4mm and hot is 20mm. The cold bore group isn't going to get any smaller.

So there isn't a functional difference identifiable between hot and cold for me here - including shooter inconsistency - so I can be very efficient with my zeroing and characterising precision - a 10 round group all at once tells me practically all I need to know.

Others should test this for themselves before drawing any conclusions for their systems.

Originally Posted by Ground Control

I don’t know anything about first shot velocity difference because I’ve never recorded it .
But I would like to comment in regards to any first shot POI shift .
I was listening to podcast a while ago where the very experienced shooter mentioned that he believes that any cold bore POI shift is more to do with a “ Cold shooter “ rather than a “ Cold bore “ .
He suggested that the shooter should “ dry fire “ a few times before sending that first round down range.
I’ve done this ever since , and it’s surprising how many times I’ve adjusted my natural point of aim / position before shooting that first shot .
I can honestly say that since doing this I’ve noticed very little to no POI shift from my first shot to the subsequent following shots of the group .
When I have a shot fall outside of the group no matter which shot it was in the group, the first thing I question is myself and not the load .
Sure there are times when that flyer is unexplained, but the majority of the time it had something to do with my shooting form / setup.

There's a bit to unpick on shooter error I think.

It's a consistent part of the system and contributes to the overall precision capability of the system. If the shooter has significant errors that create significant "fliers", then a large enough sample of shots at a constant skill level will include these as part of the overall "cone of fire".

This is also the case when shooter error is much smaller but it's less of a significant cause of error. I don't think I'm anything other than a mediocre shooter in any way, especially off a flat range - but on a flat range prone with a bipod my results indicate that my shooter error must be at most less than .5moa or so over a 10 round group.

The trick is knowing the difference.

Ascribing performance that is actually simply poor precision of the rifle to shooter error (or other causes) with insufficient data is chronic, and can really damage confidence - the classic 3-shot group with 2 touching and 1 some distance away. Or 5-shot group with 4 & 1. It leads to no end of concern about "maybe I just can't shoot", however when a larger number of shots is plotted, the "flier" is just part of the precision of the system. It's more confidence inspiring, in my opinion, to have a truer idea of the precision capability of the system and be comfortable with that.

Of course, knowing if you have really poor shooter error requires actually shooting and analysing a good number of shots through a genuinely precise rifle, and those are quite hard to find.

Originally Posted by Tentman

Another thing. Breaking position. If you're hunting your position is always going to vary a lot, down low on bipod to shoot over a ridge of rock, up high to get over a tussock, sitting, etc etc.

It would be interesting to test a rifle of "known accuracy" across several positions to see how much it altered. Very difficult to eliminate the shooter variable I guess. I did once read about a US shooting team guy in some sort of military style match shooting who had to make specific sight adjustments according to his position. I can't recall if it was due to the rifle ( a grarand I think) or other factors.

From any position other than flat prone, my shooter error becomes much larger, making it difficult to measure any changes in MPOI - however for example barricade shooting at 500m off a bag from a standing position I can achieve sufficient accuracy that I can't identify any difference in POI vs flat prone - I feel that I can still have a similar % of hits on a target vs prone. I should really go and get some data on this rather than rely on subjective impression.


May be different for other shooters, systems, particularly with higher recoil I'd expect a more pronounced difference, if the shooter isn't consistent at getting behind the rifle from different positions.

My effort today & shot 1 the cold shot, made a liar out of me, oh well load sorted, shooting well.

I had an old BSA that seemed to throw the first cold/cleanish shot a couple of inches away from the group, but my T3 doesn't vary as far as I can tell. The BSA did suffer from copper build up. Is it possibly that the worse a barrel is either due to copper/carbon buildup, the worse the first shot will be relative to the mean?

Did the cold shot separate, different aim point, on purpose, if you transpose it to the main target there really was no difference.

Originally Posted by flock

My effort today & shot 1 the cold shot, made a liar out of me, oh well load sorted, shooting well.

Attachment 256564

that's a long time between shots

Yep pretty laid back on a wednesday, chatting to other shooters in the bay. Is a standard Sako 85, 308 so don't rush it.

We’ve got some interesting velocity data here.

This is a couple more pictures, not quite on the exact topic of cold bore vs subsequent groups but related:

First group after taking off stock and reassembling. Screws at 40 in.lb

The first shot was the one at 5 oclock.
This was prone with no rest at 100m.

A bit of light relief, some gun prn:



I came up 3 clicks and tightened them to 45 in.lb.
20 shots later (dont look at the kneeling and standing …) and here is the sitting , again no rest or sling:


Possibly not as scientific as Gimp’s Quality Assurance but supports previous experience that its OK to take the stock off and put back on for this sort of shooting.

This is an interesting concept for a Hunting Ethics competition.
Shame that they all seem to be using 20 pound Rifles and get to watch previous shooters to get an idea of wind/conditions .

https://m.youtube.com/watch?v=6yq4u9INw94

https://m.youtube.com/watch?v=W87BhujiqeI

It's nice that there seems to be a wider focus on the practical application of precision, and understanding hit probability.

How's everyone going with their 1 shot groups? I'm away from home and haven't shot since making this thread so I have not added to mine.

and this one, at 100 yards few even got their first shot into the 1 inch aiming point

https://youtu.be/I8jXisOSOns?si=pib0Py2Ujig7kCnj

A few remarks fwiw.
Cold clean bore may not show much deviation at 100m but I've definately seen variance at 500m.
Holding a rifle tight, which may occur at first shot, can actually increae velocity and send shot high.
Tighter or looser pressure on forend hold or rear position support will affect poi, again, more noticable at longer ranges.
Wet cartridge will increase pressure and increase group size.
A 2mm rise in muzzle of a 24" barrel will cause 15" high shot at 500m.
Etc.
So there are a heap of potential variables, some of which will not be very obvious at a short 100m.
Then there is the issue of bbl and load harmonics vs ambient temperature effects varying by day and time of day, light conditions, mirage, wind et al..
In short, consistent cold bore shot ( in the field ) precision is unlikely to ever be as good as a range zero or group.