Your Groups Are Too Small

[solarshooter]

It's worth quantifying how much deflection at the end of the barrel is needed to produce significant dispersion. 1moa is 1/60th of a degree which is 1/360th of a circle. You would be hard pressed to draw me a 1deg slice on a piece of paper, let alone 1/60th of that slice. On a 24" barrel, 1moa of rotation is (1/60)*(pi/180)*24 = 0.007". For a 1 moa group, the barrel deflects half that to either side of center, so 0.0035". On that same 30" 1.25" straight contour barrel I referenced earlier, it takes 1.4lbs of lateral force at the muzzle to deflect it 0.0035". Put another way, on a barrel like that that weighs ~10lbs, 0.1-0.2G of acceleration is enough to deflect it 1/2moa. You could do this by hand just shaking the gun. So it really doesn't take much to produce the dispersions we're concerned with.

 

[ResearchinStuff]

completely agree that the most important thing is consistency.

looking at your numbers, 1.4# of radial force at the muzzle is still quite a bit,. Consider that the the moment arm of ~2' from the muzzle to the rifle's cg that number means basically any rifle fired without significant lateral support is going to spin itself off of the bench due simply to the unbalanced moment from the barrel deflecting due to the 1.4# of lateral force you surmise is present. Yet, when rifles are actually shot, even unsupported, they tend not to spin laterally off the rest, but rather tend to just react straight back and rotating up - exactly as you'd expect if the dominant forces were in the axial direction rather than the radial and the stock design promoted pivoting because the normal force from the rear is applied below the cg. This occurs despite the moment arm from the muzzle to the cg being significantly greater for any transverse force compared to any longitudinal force, and despite the forces being of similar magnitude (many guns that shoot groups larger than .5 moa have recoil less than 10#).

magnetospeeds are not rigidly connected, and similar to a loose brake or a loose suppressor will mess things up because they are free to behave erratically from shot to shot, regardless of the direction of motion the barrel wants to take their inertia is going to just oppose it, and oppose it differently from shot to shot. Obviously, that's a highly erratic situation and dispersion is going to suffer dramatically.

However when stuff screwed on the end is tight/rigid (and thus actually change the natural vibration characteristics of the barrel by changing the effective length, cg, and moments of inertia for the beam), that erratic behavior goes away. My personal rifles have zero difference in their group size with identical loads whether bare muzzle or with a 9", 16 oz suppressor mounted. POI does shift, as expected because the static load does cause cantilever beam bending.

Reaching a conlcusion that you're actually finding and remaining in a long-axis cantilever vibrational node despite the above facts, and despite all the known errors in powder charge weight and ES/barrel travel time requires ignoring more information than you actually include, and certainly involves ingoring the largest force exerted on the barrel, which is the swelling in the radial direction. Combined with the fact that "nodes" tend to disappear when tested to statistically valid group sizes, it seems very unlikely to me that the longitudinal vibration node theory is correct for explaining why rifles produce groups the way they do.

 

[solarshooter]

The major force is definitely in the axial direction, 60000psi on the face of a 0.5" bolt produces 12000lbs of force. Some of that load is reacted through the barrel on the face of the bullet, ~4500lbs in the case of a 30cal bullet. The remainder pushes on the stock, if only for a moment. This accelerates the gun backwards, and due to CG offset of the gun from the bore centerline, can produce a rotational acceleration too. This excites longitudinal bending modes.

So maybe what we should be doing is balancing the rifle CG to be on the bore centerline to get it to recoil straight back? Rokstok 2.0? Wheel weights up on the scope?

 

[solarshooter]

due cimply to the unbalanced moment from the barrel deflecting due to the 1.4# of lateral force you surmise is present

To be clear, I'm not saying there's a 1.4lb force that generates the deflection. I was just trying to come up with a simple physical equivalent load case. I think most of the excitation is shock and inertial (acceleration, F=ma) in nature.

 

[ResearchinStuff]

don't add stuff into quotes you're attributing to me.

here's a pretty interesting thesis for you to check out. Figure 42 will be particularly insightful.

https://scholarworks.uvm.edu/cgi/viewcontent.cgi?article=2609&context=graddis

 

[solarshooter]

?

 

[ResearchinStuff]

well crap, typo's on me.

 

[solarshooter]

well crap, typo's on me.

All good. Thanks for linking this paper, I am about halfway through. I think so far everything I've said here is consistent with his analysis and findings.

Barrel deflections due to modal excitation from the shot are real and the main driver of rifle precision. Now, is "tuning" against these deflections possible? I think the consensus so far is yes by changing components, maybe/maybe not by changing only powder charge.

I have spent some time going through other threads as people recommended, like the '10 shot group' thread. I'm not so sure Form's assertion that most any gun is shooting 1.2moa 20shot groups with factory ammo and barrels is true. Especially not at higher muzzle energies. Again, this is consistent with what I've experienced.

However boiling this way down to Form's other big point, does the hit rate improve significantly with increasing accuracy, I can also see how pure accuracy quickly goes to a point of diminishing returns. I messed around with the hit probability calculator on Bison Ballistics, which looks to be a much dumber version of WEZ, and determined the following. For my rifle with a 1.5moa group, shooting at a 2moa target at 600yds in a 10mph +/- 2mphSD wind, I have a 67.6% hit rate. If I drop that group to 1moa, I get a 78.4% hit rate. If I drop that group to 0.5moa, I get 85.6%. So yes the delta is half as much for the last 0.5moa, but it's still a ~10% improvement. And it's a 16% improvement just going from 1.5 to 1moa. Those seem like large improvements and probably the cheapest/easiest upgrade in hit rate available. Why not pursue it?

 

[Macintosh]

I like and appreciate everything that engineers do. Sometimes I wish I was an engineer. Trying to read the above couple posts makes me feel like I dumb.

Also, my factory tikka ctr in the factory plastic stock, off a $30 caldwell bipod and an athlon cronus btr scope, shooting the $50/50 rounds hornady American Gunner practice ammo, consistently shoots 10 round groups right around 1moa, sometimes a little less. Am I correct in thinking thats not so different than the performance achieved with this full load workup, or am I missing something?

2 groups below from 195 yards on 2 diff days, both more or less as fast as I could work the action and get steady again. This'll grow a bit at 20 and 30 rounds of course, but is it significantly different than 1.5-1.75moa 20 and 30 round groups that come from the "full meal deal"?

 

[Formidilosus]

All good. Thanks for linking this paper, I am about halfway through. I think so far everything I've said here is consistent with his analysis and findings.

Barrel deflections due to modal excitation from the shot are real and the main driver of rifle precision. Now, is "tuning" against these deflections possible? I think the consensus so far is yes by changing components, maybe/maybe not by changing only powder charge.

I have spent some time going through other threads as people recommended, like the '10 shot group' thread. I'm not so sure Form's assertion that most any gun is shooting 1.2moa 20shot groups with factory ammo and barrels is true.

270wim, 7mm RM, etc- probably not. Any modern cartridge or cartridge that has well known loads for- absolutely. 1.1-1.4 MOA for 20 rounds is not uncommon at all.

However boiling this way down to Form's other big point, does the hit rate improve significantly with increasing accuracy, I can also see how pure accuracy quickly goes to a point of diminishing returns. I messed around with the hit probability calculator on Bison Ballistics, which looks to be a much dumber version of WEZ, and determined the following. For my rifle with a 1.5moa group, shooting at a 2moa target at 600yds in a 10mph +/- 2mphSD wind, I have a 67.6% hit rate. If I drop that group to 1moa, I get a 78.4% hit rate. If I drop that group to 0.5moa, I get 85.6%. So yes the delta is half as much for the last 0.5moa, but it's still a ~10% improvement. And it's a 16% improvement just going from 1.5 to 1moa. Those seem like large improvements and probably the cheapest/easiest upgrade in hit rate available. Why not pursue it?

Because +/- 2mph wing calling in broken , mountainous terrain is about world class level. Legit shooters practicing regularly are capable of around +/- 4mph. Furthermore, the precision levels are not attainable in the field- you are not shooting 30 round groups of .5 MOA in the field hunting.

 

[sierracharlie338]

This thread makes my head hurt over the last few pages lol. I understand the theory of what is talked about in the OP and will be trying this on a couple of rifles I am about to have up and running.

 

[solarshooter]

Because +/- 2mph wing calling

I had interpreted that as SD, meaning up to 6mph wind error on 250 simulated shots. But like I said the Bison tool is pretty dumbed down so I'm not sure. Running it again with 5mph SD on a 10mph wind, it throws an error saying that some values are negative, so I think it's assessing 2+SD.

 

[Formidilosus]

I had interpreted that as SD, meaning up to 6mph wind error on 250 simulated shots. But like I said the Bison tool is pretty dumbed down so I'm not sure. Running it again with 5mph SD on a 10mph wind, it throws an error saying that some values are negative, so I think it's assessing 2+SD.

What bullet and MV are you using?

 

[Shortschaf]

I had interpreted that as SD

Yes. It is labeled SD, info tag says "standard deviation of the wind speed".

 

[solarshooter]

What bullet and MV are you using?

Berger 175 Elite hunter, MV 2830fps with an SD of 8fps.

 

[Formidilosus]

Berger 175 Elite hunter, MV 2830fps with an SD of 8fps.

600 yards, 12” square, wind +/- 4mph (I.E., you can call it within 4 mph 95% of the time)

1.5 MOA= 58.6% 1st round hit probability-




1 MOA= 61.4% 1st round hit probability-




For a difference of less than 3%. You will not see this in the field. 5% takes a lot of shooting and logging (hundreds, to thousands of novel, 1st round of the day shooting in novel conditions). 10% is about where you can observe a difference with a day of shooting.



Let’s say you are shooting in novel mountain conditions, and winds weekly, and are a near world class wind caller.

600 yards, 12” square, wind +/- 2mph (I.E., you can call it within 2 mph 95% of the time)


1.5 MOA= 84.2% 1st round hit probability-



1 MOA= 89.4% first round hit probability-




A difference of 5.2%. There are very few people that are skilled enough, practiced enough, and shoot enough to see 5% difference in mountainous conditions with wind, on terrain they’ve never shot before.



Now let’s look at reality here. The way the program runs this is not an aggregate of x amount of 3 or 5 shot groups. It is based on a perfect zero, and 95% probability of group size- I.E., 30 shot extreme spread at 100 yards. To clarify- for “1 MOA”, it’s saying that you setup, shoot one round at 1” target at 100 yards, and you hit it- 30 times in a row on demand. How many people do that? But, let’s say you and your rifle system does do that on demand, you aren’t doing it on animals, in the field.
The best field shooters are about 1.5 MOA on demand with solid non competition rifles. Really skilled ones are about 2 MOA.

 

[solarshooter]

This is super insightful, thank you for taking the time to run the numbers. I totally understand what you mean about how unimportant rifle precision is relative to other sources of error. And this is really just wind, I see you have pretty tight SDs on the other parameters there, probably much better than I can get under time pressure out of cell reception in the field. So the rifle precision will matter even less. I relent! Though I will still go and shoot that test of my worst powder charge from my initial ladder to answer that lingering question.

I feel like I should pony up and buy a copy of WEZ!

 

[ResearchinStuff]

I like and appreciate everything that engineers do. Sometimes I wish I was an engineer. Trying to read the above couple posts makes me feel like I dumb.

Also, my factory tikka ctr in the factory plastic stock, off a $30 caldwell bipod and an athlon cronus btr scope, shooting the $50/50 rounds hornady American Gunner practice ammo, consistently shoots 10 round groups right around 1moa, sometimes a little less. Am I correct in thinking thats not so different than the performance achieved with this full load workup, or am I missing something?

2 groups below from 195 yards on 2 diff days, both more or less as fast as I could work the action and get steady again. This'll grow a bit at 20 and 30 rounds of course, but is it significantly different than 1.5-1.75moa 20 and 30 round groups that come from the "full meal deal"?
View attachment 659506View attachment 659507

I would not spend the time to load development in that situation.

 

[Formidilosus]

This is super insightful, thank you for taking the time to run the numbers. I totally understand what you mean about how unimportant rifle precision is relative to other sources of error. And this is really just wind, I see you have pretty tight SDs on the other parameters there, probably much better than I can get under time pressure out of cell reception in the field. So the rifle precision will matter even less. I relent!

I don’t want it to seem that my goal was to “win”- it isn’t and wasn’t. It’s that I view everything through as much of a data based approach as possible, but always with the end result in mind- hitting animals in the field. People that know me personally, know that I was as psychotic about all the things as anyone. But the more I shot, experimented, and started testing “known things”, the more it was obvious most of it is BS.

Though I will still go and shoot that test of my worst powder charge from my initial ladder to answer that lingering question.

I will be interested in seeing the results. Thank you.

I feel like I should pony up and buy a copy of WEZ!

If you put realistic inputs in and not best case inputs, it is one of the best/most enlightening tools available. What’s really neat is taking it into the field with a group of people where you have all of their data, then seeing how the 1st round live fire hit rates match up to what the WEZ predicts. Do it enough with the correct data in it, and you see it is spot on.

 

[stan_wa]

600 yards, 12” square, wind +/- 4mph (I.E., you can call it within 4 mph 95% of the time)

If the input in the WEZ for wind is the SD (standard deviation) on wind error, and you say you can call it within +/-4 mph 95% of the time. I think thats like saying 2*sd= 4mph. and would expect that "

(I.E., you can call it within 4 mph 95% of the time)

gives a SD of 4mph/2=2 mph.
Because 2 SD captures 95% of occurrences? If the WEZ has specific documentation that says the SD input should be what you expect to see 95% of the time and its not standard deviation ignore me.