.222 Remington Grouping vs. Jump Question

[222Jim]

I was going over some shooting results recently and noticed an (to me at least) interesting pattern. I am curious if any of you have seen similar trends and/or have any thoughts on why this trend appears to exist.

The "interesting pattern" is with respect to group precision versus jump. For reference, I'm shooting a .222 Remington, Berger 52 FBV, 19.40 gr of IMR4198, Lapua cases, and Federal GM205 primers. FYI, I judge precision in terms of CEP 90% which is roughly 1.75 times the Mean Radius (CEP 90 = Probability that 90% of shots will land within a given radius measured in MOA).

Looking at the chart below, what I'm seeing is the repeatability of my group precision results goes "wonky" as jump gets smaller. FYI:
(a) Each "dot" below is the average of an individual 20 shot group determined using the OnTarget TDS program.
- I shoot four 5-shot groups and then combine them using OnTarget TDS
(b) Standard Deviation of each jump measurement is +/- 0.0005".
(c) Results are based on 100 meter range.

In my opinion these results are good, i.e., a 0.50 CEP 90% is roughly equivalent to an average group diameter of 0.6" (mean radius 0.3"). But the trend has me scratching my head.

I have my own pet theory on why I'm seeing this trend. That theory is that at smaller jumps, the bullet lacks sufficient velocity as it enters the throat to smoothy overcome any load-to-load inconsistencies (i.e., bullet alignment/concentricity?). That results in a feedback loop in which bullets may slow/stall their forward motion for factions of a millisecond, thus creating different levels of back pressure needed to push the bullet forward. That then manifests itself as precision inconsistencies.

And, for reference, I've also included the velocity measurements (velocity error bars equal 2 times the Standard Deviation).

Anybody have any thoughts on this?

 

[Coyotefurharvester]

Possibly your rifle likes/needs more bullet surface inside the case neck?

 

[ELR LVR]

I was going over some shooting results recently and noticed an (to me at least) interesting pattern. I am curious if any of you have seen similar trends and/or have any thoughts on why this trend appears to exist.

The "interesting pattern" is with respect to group precision versus jump. For reference, I'm shooting a .222 Remington, Berger 52 FBV, 19.40 gr of IMR4198, Lapua cases, and Federal GM205 primers. FYI, I judge precision in terms of CEP 90% which is roughly 1.75 times the Mean Radius (CEP 90 = Probability that 90% of shots will land within a given radius measured in MOA).

Looking at the chart below, what I'm seeing is the repeatability of my group precision results goes "wonky" as jump gets smaller. FYI:
(a) Each "dot" below is the average of an individual 20 shot group determined using the OnTarget TDS program.
- I shoot four 5-shot groups and then combine them using OnTarget TDS
(b) Standard Deviation of each jump measurement is +/- 0.0005".
(c) Results are based on 100 meter range.

In my opinion these results are good, i.e., a 0.50 CEP 90% is roughly equivalent to an average group diameter of 0.6" (mean radius 0.3"). But the trend has me scratching my head.

I have my own pet theory on why I'm seeing this trend. That theory is that at smaller jumps, the bullet lacks sufficient velocity as it enters the throat to smoothy overcome any load-to-load inconsistencies (i.e., bullet alignment/concentricity?). That results in a feedback loop in which bullets may slow/stall their forward motion for factions of a millisecond, thus creating different levels of back pressure needed to push the bullet forward. That then manifests itself as precision inconsistencies.

And, for reference, I've also included the velocity measurements (velocity error bars equal 2 times the Standard Deviation).

Anybody have any thoughts on this?

View attachment 1668070

Is it possible, what you're seeing is more that the bullet is coming away from optimum seating depth?
Tune
In "your Particular" rifle

 

[Doom]

Your primary assumption is that closer to the lands will decrease your CEP 90%. While that may be a widely held assumption it may not apply to every bullet design. it can also be specific to specific chambers.

Also, and I'll get kickback on this, I often see bench rest shooters make decisions on small sample sizes and small changes in group size. I don't know whether or not they are right but when using scientific analysis tools their results don't pass the threshold of being different.

Another thought on your post. You state that the SD of your jump is 0.0005". In perspective that is roughly 0.001" for 95% of the rounds. At 0.080" that is 0.001/0.08x100 or 1.25% variation, while at 0.020" it's 0.001/0.02x100 or 5%. So there is a much greater variation in seating depth (or jump) shot to shot. So if bullet jump and variations in it are important your smaller jumps would be more likely to give larger variations in precision.

 

[gunsandgunsmithing]

So you seem to be adjusting jump in .020 increments. Why such large increments. Also, have you tested varying amounts of jam? As a sr br shooter I can tell you that most of my loads are jammed by some amount and that as little as .002-.003 can make a significant difference in tune.

Your report is in great detail but my opinion only is that your incremental inputs are massive. So, GIGO. I'd suggest starting at square marks on the bullet and working out of the lands in .003 increments and then post the same result format.

 

[WV Hitman]

I seat my .223 Contender handgun and .22-250 handgun bullets 0.03" off the lands. Both shoot 3/8" at 100. Kill groundhogs out to 400. Good enough for me.

 

[ELR LVR]

I seat my .223 Contender handgun and .22-250 handgun bullets 0.03" off the lands. Both shoot 3/8" at 100. Kill groundhogs out to 400. Good enough for me.

somewhere between -.010 - .030 off is very often good medicine

 

[SeabeeKen]

My 22 & 6 ppcs didnt like jam. Preferred .010 off for the 22 and .020 off for the 6.

 

[Webster]

I was going over some shooting results recently and noticed an (to me at least) interesting pattern. I am curious if any of you have seen similar trends and/or have any thoughts on why this trend appears to exist.

The "interesting pattern" is with respect to group precision versus jump. For reference, I'm shooting a .222 Remington, Berger 52 FBV, 19.40 gr of IMR4198, Lapua cases, and Federal GM205 primers. FYI, I judge precision in terms of CEP 90% which is roughly 1.75 times the Mean Radius (CEP 90 = Probability that 90% of shots will land within a given radius measured in MOA).

Looking at the chart below, what I'm seeing is the repeatability of my group precision results goes "wonky" as jump gets smaller. FYI:
(a) Each "dot" below is the average of an individual 20 shot group determined using the OnTarget TDS program.
- I shoot four 5-shot groups and then combine them using OnTarget TDS
(b) Standard Deviation of each jump measurement is +/- 0.0005".
(c) Results are based on 100 meter range.

In my opinion these results are good, i.e., a 0.50 CEP 90% is roughly equivalent to an average group diameter of 0.6" (mean radius 0.3"). But the trend has me scratching my head.

I have my own pet theory on why I'm seeing this trend. That theory is that at smaller jumps, the bullet lacks sufficient velocity as it enters the throat to smoothy overcome any load-to-load inconsistencies (i.e., bullet alignment/concentricity?). That results in a feedback loop in which bullets may slow/stall their forward motion for factions of a millisecond, thus creating different levels of back pressure needed to push the bullet forward. That then manifests itself as precision inconsistencies.

And, for reference, I've also included the velocity measurements (velocity error bars equal 2 times the Standard Deviation).

Anybody have any thoughts on this?

View attachment 1668070

Don't want to understand what your doing, but an R sq. under .9800 is getting pretty bad. I go by group size only and the group being round. If it's round it should be repeatable. No math involved. I load for an accurate GH hunting rifle.

R-squared (R2) is defined as a number that tells you how well the independent variable(s) in a statistical model explains the variation in the dependent variable. It ranges from 0 to 1, where 1 indicates a perfect fit of the model to the data.

 

[222Jim]

Don't want to understand what your doing, but an R sq. under .9800 is getting pretty bad. I go by group size only and the group being round. If it's round it should be repeatable. No math involved. I load for an accurate GH hunting rifle.

R-squared (R2) is defined as a number that tells you how well the independent variable(s) in a statistical model explains the variation in the dependent variable. It ranges from 0 to 1, where 1 indicates a perfect fit of the model to the data.

Re R-squared.....yes, I know. Supports my case that the results are "wonky", i.e. no or very little correlation.

 

[222Jim]

So you seem to be adjusting jump in .020 increments. Why such large increments. Also, have you tested varying amounts of jam? As a sr br shooter I can tell you that most of my loads are jammed by some amount and that as little as .002-.003 can make a significant difference in tune.

Your report is in great detail but my opinion only is that your incremental inputs are massive. So, GIGO. I'd suggest starting at square marks on the bullet and working out of the lands in .003 increments and then post the same result format.

I've done smaller jumps, i.e. 0.003" and/or 0.005". But I do this as a "rough first pass" to, among other things, get a better idea what's typical, and also to tune QuickLoad (mainly Ba and Shot Start Initiation Pressure).

 

[Straightshooter1]

I've done smaller jumps, i.e. 0.003" and/or 0.005". But I do this as a "rough first pass" to, among other things, get a better idea what's typical, and also to tune QuickLoad (mainly Ba and Shot Start Initiation Pressure).

I don't know if you've seen when I've posted this a couple times before, but maybe the graph below might give you some ideas??? This comes from a study done long long ago and was kinda an eye opener for me to better understand the effects of blowby that fills the chamber before the bullet is fully engraved as it relates to seating depth and its effects on powder burn from changes in the case volume.

 

[222Jim]

I don't know if you've seen when I've posted this a couple times before, but maybe the graph below might give you some ideas??? This comes from a study done long long ago and was kinda an eye opener for me to better understand the effects of blowby that fills the chamber before the bullet is fully engraved as it relates to seating depth and its effects on powder burn from changes in the case volume.
View attachment 1668269

This is exactly the type of material/study I'm looking for! Do you have the full report? I'd love to read it if you can forward it to me.

 

[Straightshooter1]

This is exactly the type of material/study I'm looking for! Do you have the full report? I'd love to read it if you can forward it to me.

Here you go (attached PDF file)

 

[358WCF]

Here you go (attached PDF file)

I believe this is the same Dr. Brownell who penned a number of articles in a few early issues of Handloader magazine which were later incorporated into Wolfe Publishing's long out of print Firearms Pressure Factors. ISBN: 0-935632-85-9.

 

[222Jim]

This is exactly the type of material/study I'm looking for! Do you have the full report? I'd love to read it if you can forward it to me.

Thanks for that report. Interesting read. I've gone through it quickly this morning and will read it in depth later this week.

In addition to that graph you originally sent, I found the graphs plotting charge vs. pressure very interesting (see below). In part because the (a) range of pressures at a given charge, and (b) large swings in pressure at lower charge now referred to as "flash-over", but in particular because:
(1) "Shot start initiation pressure", which includes the force (pressure) needed to engrave the rifling into the bullet, is commonly said to be in the range of ~3,625 psi ("lots" of jump) to ~7,500 psi (when jammed), while
(2) Their data showed the bullet wouldn't consistently eject at ~10,000 psi.

The difference between those two (10,000 vs. 3,625 - 7,500 psi) is reasonable to account for dynamic engraving forces!

Jim

 

[222Jim]

I don't know if you've seen when I've posted this a couple times before, but maybe the graph below might give you some ideas??? This comes from a study done long long ago and was kinda an eye opener for me to better understand the effects of blowby that fills the chamber before the bullet is fully engraved as it relates to seating depth and its effects on powder burn from changes in the case volume.
View attachment 1668269

I believe this is the same Dr. Brownell who penned a number of articles in a few early issues of Handloader magazine which were later incorporated into Wolfe Publishing's long out of print Firearms Pressure Factors. ISBN: 0-935632-85-9.

I'd love to get my hands on a copy of that book. Sadly, it's as scarce as those proverbial hen's teeth, and when I find it there's always a warning the accompanying access codes for the CD Rom "are not guaranteed to work".

FYI, I have attached a short piece of recent research on performance vs seating depth done in Poland (in English) using .30-06.