Group consistency-advice-thoughts

[Dog Breath]

This is a reoccurring consistency issue I'm having. Groups 11 thru 13 look promising so I continue, seeing if the load holds out. Groups 14 and 15 go to hell and I call it a day. It was cold 5c (40f), raining, no wind. 100 yards. Barrel heating shouldn't be an issue as I was loading at the range so there was around 10 minutes between each 3 round group.

This is a low charge weight of 41 grains of IMR 4064 at 2450 fps as I was wandering around the outer ranges of previous test loads looking for node patterns but this is not a usable fps range for me. Regardless this displays the reoccurring issue.

General background info - Tikka varmint 308, 24", bedded into MDT chassis, Lapua brass, Hornady Match 155gn, IMR 4064, CCI BR2.

Any thoughts or advice is appreciated. Thanks

 

[Bc'z]

The bottom 2 shots of targets 14&15 would be in group if all targets were overlaying.

 

[justinp61]

This is a reoccurring consistency issue I'm having. Groups 11 thru 13 look promising so I continue, seeing if the load holds out. Groups 14 and 15 go to hell and I call it a day. It was cold 5c (40f), raining, no wind. 100 yards. Barrel heating shouldn't be an issue as I was loading at the range so there was around 10 minutes between each 3 round group.

This is a low charge weight of 41 grains of IMR 4064 at 4450 fps as I was wandering around the outer ranges of previous test loads looking for node patterns but this is not a usable fps range for me. Regardless this displays the reoccurring issue.

General background info - Tikka varmint 308, 24", bedded into MDT chassis, Lapua brass, Hornady Match 155gn, IMR 4064, CCI BR2.

Any thoughts or advice is appreciated. Thanks

2450?

 

[Dog Breath]

2450?

Yes! fixed

 

[jpx2rk]

Do you think the weather conditions had anything to do with the shooter???

 

[Dusty Stevens]

Lets see your rest setup and which wind flags did you use?

 

[Jager]

Hard to say without knowing a bit more about the rifle's history (what's the best it's ever shot, and with what?).

But two quick thoughts...

First, that's a very low-pressure load. 42K vs SAAMI max of 62K. Low pressure loads are often a little bit erratic.

Second, what is your bench setup?

Edit: I see Dusty beat me to the second one...

 

[chkunz]

It is possible that you are just seeing the normal statical variance in the population of data you are working with. You are dealing with a small sample of data. Do you have any experience with statistical analysis of data?

 

[LHSmith]

2 more possible causes : 1/Parallax issues 2/ slow mirage - the sight picture changed in the 10 minute intervals between groups. I prefer to get shots downrange quickly to avoid this phenomenon. High moisture levels exasperates this condition. To witness what I am talking about, set your scoped rifle ( requires a high magnification ) in a sturdy benchrest setup and precisely align your sight on a target bull, then without touching the rifle return at intervals several minutes apart and if the target is no longer aligned with the reticle you have optical dispersion caused by mirage.

 

[Dog Breath]

Do you think the weather conditions had anything to do with the shooter???

I don't think so. Was reloading indoors and then stepping out to take the 3 shots from under a roof. I was inside most of the time.

Lets see your rest setup and which wind flags did you use?

Concrete bench, Mystic MPOD bipod on carpet, Protektor Bumble Bee rear bag, dead calm no flag movement but flags were wet.

Hard to say without knowing a bit more about the rifle's history (what's the best it's ever shot, and with what?).

But two quick thoughts...

First, that's a very low-pressure load. 42K vs SAAMI max of 62K. Low pressure loads are often a little bit erratic.

Second, what is your bench setup?

Edit: I see Dusty beat me to the second one...

The best it's done is about what you see in the pic 11-13 with Hornady 155s. Around 1/2 moa. With 175 tmks, 185 juggs 3/4 moa-ish.
Yes it is a very low-pressure load but I seem to have this lack of consistency up to the the 2800s.
Even if this rifle shot 1 moa consistently I would be fine with it. it is what it is. But it will shoot longish 1/2 moa strings an then pop out a couple 1- 1 1/4 moa groups. It seems to be capable but then...
i

 

[Dog Breath]

It is possible that you are just seeing the normal statical variance in the population of data you are working with. You are dealing with a small sample of data. Do you have any experience with statistical analysis of data?

Short answer no Other than say a string of 4-6 nice groups and then 2 or 3 double in size over a total of 8-10 groups.

 

[Dog Breath]

2 more possible causes : 1/Parallax issues 2/ slow mirage - the sight picture changed in the 10 minute intervals between groups. I prefer to get shots downrange quickly to avoid this phenomenon. High moisture levels exasperates this condition. To witness what I am talking about, set your scoped rifle ( requires a high magnification ) in a sturdy benchrest setup and precisely align your sight on a target bull, then without touching the rifle return at intervals several minutes apart and if the target is no longer aligned with the reticle you have optical dispersion caused by mirage.

Interesting. If I understand this correctly and there was a parallax shift in the 10 minute interval, lets say a 1/4 moa shift to the right, shouldn't the the group shift 1/4 moa but stay relatively the same size?

Is it possible that the very high humidity was affecting the unbottled exposed powder?

 

[jelenko]

Short answer no Other than say a string of 4-6 nice groups and then 2 or 3 double in size over a total of 8-10 groups.

What's causing you to think that's not statistical variation?

 

[Dusty Stevens]

Until you get consistent repeatable groups you gotta find out whats doing it. Itll be something with your gun (bedding, scope, bipod hopping, etc) or you. Most likely it isnt your loading technique but your gun may want a different component like a bullet or powder or even another barrel.

 

[LHSmith]

Interesting. If I understand this correctly and there was a parallax shift in the 10 minute interval, lets say a 1/4 moa shift to the right, shouldn't the the group shift 1/4 moa but stay relatively the same size?

Is it possible that the very high humidity was affecting the unbottled exposed powder?

No parallax is independent of mirage. Slow moving mirage actually has your target changing position over time due to changes in light refraction from atmospheric changes . This movement is usually very subtle- unlike fast mirage boil seen coming off the ground on a hot sunny day. Between match relays I can observe on active days the target bull circling around the 1/16" target dot (45x scope) by as much as 1/4" ( 1/2" total travel) over just a few minutes. Reticle stays stationary while target moves.
The powder exposure to moisture was short term so I don't believe it had any effect.

 

[Dusty Stevens]

No parallax is independent of mirage. Slow moving mirage actually has your target changing position over time due to changes in light refraction from atmospheric changes . This movement is usually very subtle- unlike fast mirage boil seen coming off the ground on a hot sunny day. Between match relays I can observe on active days the target bull circling around the 1/16" target dot (45x scope) by as much as 1/4" ( 1/2" total travel) over just a few minutes. Recticle stays stationary while target moves.
The powder exposure to moisture was short term so I don't believe it had any effect.

This is why the long wait between shots or shooting that round robin thing doesnt work very well

 

[HandgunHTR]

Are you loading up your bipod before each shot?

 

[chkunz]

Until you get consistent repeatable groups you gotta find out whats doing it. Itll be something with your gun (bedding, scope, bipod hopping, etc) or you. Most likely it isnt your loading technique but your gun may want a different component like a bullet or powder or even another barrel.

I agree completely. but.....what if the load is not consistent and repeatable?

One technique I use during load development is to mix in groups from an accurate load that I have a lot of experience with and use that as a statical "control".

If there is a statistician in the house he will probably tell us that there is a better than 50% probability that there is no difference in these groups. When variances are small it takes a lot of data to define probability limits.

 

[Dusty Stevens]

I agree completely. but.....what if the load is not consistent and repeatable?

One technique I use during load development is to mix in groups from an accurate load that I have a lot of experience with and use that as a statical "control".

If there is a statistician in the house he will probably tell us that there is a better than 50% probability that there is no difference in these groups. When variances are small it takes a lot of data to define probability limits.

Thats a good point but when you use care in loading, like he has, the groups will be similar but big if the load is off. Just say your load is off and shoots 1” if you shoot 5 of them they will look the same if your setup is sound

 

[Ccrider]

How often are you cleaning your barrel?