In Bore Bullet Yaw/Hummer Barrels and Jim Boatright

[ecomeat]

I have stumbled onto the website belonging to Jim Boatright, who is both a retired aerospace engineer and a retired custom rifle maker, and want to share it with anyone interested in some fascinating reading on "accuracy subjects". I think this guy might be the USA's version of our own "Williada" .......and I would actually not be at all surprised if they aren't great mates !!
Have a look at
http://www.thewellguidedbullet.com/index.html
His papers on interior Ballistics have answered my questions on "bullets going to sleep" that Willada refers to (130 yds + for a 308) but which I was embarrassed to ask for more information on.
Hummer barrels, bullet yaw etc etc.......lots of excellent reading. His article on differential thermal expansion ..ie aluminium scope tubes mated solidly to stainless steel actions has really got my mind going . Maybe we need to reconsider that big, tough scope mount theory.
Just a bloody great website....... now i wont be able to sleep! wondering what the Leade Angle will be on the new 284 Win reamer with a 313 nk and .220 freebore that is hopefully on its way to me !
I would honestly rate this as one of the best website I have ever found .....behind ozfclass , of course

[BATattack]

Sometimes knowledge is power . . . . .. sometimes the well rested win.

I was having a conversation with a ballistic professor who was having a few issues with some equipment. I said that there is generally two types of people in our sport. One type spends their time researching and studying everything they can find on how and why then tuning their rifle watching the chronograph and mapping trends against results but often miss the little things.

The other is one that is more mechanically minded and views their loading and rifle as an art more than an exact science where one rule doesn't apply for all and spends the majority of their time looking at their results (groups or scores) and practicing at the range rather than spending time trying to find out how they achieved those results.

He replied "you look for cause and effect, you come home and open the fridge and the beer is cold and everything is good, you don't care how the fridge works . . . . . you just care that the beer is cold because at the end of the day that is your desired result"

After feeling slightly insulted for a bit I realized this is a guy that makes his living from decades of ballistic research and has knowledge in areas that most of us would struggle to keep up with BUT was calling me because he couldn't achieve his desired result due to a fairly simple issue.

All I'm saying is if your already getting good accuracy . . . . Sleep is good . . . . Practice is better!

[ecomeat]

Adam,
You are wise beyond your years
I am definitely, and unashamedly, in that first category. Hell I even compete occasionally with a MagnetoSpeed on my barrel, to get real world feedback eg testing different primers.
And it would seem to be true that I often miss the little things (killing barrels)
But I also know that quite a few of "us F Classers" simply enjoy reading these technical articles, especially when they are put into a laymans language that most can easily follow, and I honestly believe that sharing the links to this sort of thing is the right thing to do.
I think that the greatest strength of this website is its sharing of knowledge, and so for a broken down old cow cocky like me that will never have the technical knowledge or background of some of our amazing contributors, my only input is to ask silly questions and ask for help, and then to share links like the one referenced in this thread. It's actually possible to thoroughly enjoy these sort of articles/papers without letting it ruin your shooting or give you into a bad case of OCD !
My wife keeps asking me why I am always practising..........wait till she hears that I need to do more.

[aaronraad]

Interesting site Tony.

4 deg leade angle for nominal 6.5mm projectiles instead of 1.5 deg...Ay caramba!

With BATattack's comments in mind, proving a long range improvement over current achievable accuracy from a 1.5 deg leade angle (maybe Matt Paroz can comment?) is really tough.

How do we define long range accuracy, if I can propose such a simple question even if limited to F-Open at 1000y (that has probably been argued before on here)? Do we say my rifle produces an average vertical of 0.3MOA with an USL of 0.5MOA at 6 standard deviations for a 10-shot string?

A 50% improvement overall would be great (0.15MOA to USL(6*SD) 0.25MOA), but I don't see any products or processing designs/techniques allowing this to happen in my generation? Crunching the USL would be more achievable with maybe a slight reduction in the average to say 0.25MOA to USL(6*SD)0.4MOA.

Just trying to think about the practical. It's the thought that counts isn't it BATattack?

[BATattack]

Defiantly Tony! If the technical stuff is what blows your hair back that's go for it! It's nearly a hobby in itself

There wouldn't be too many serious open shooters at a queens that don't have a rifle that shoots .5moa or under during testing and i do wonder (maybe someone with those fandangled stats prediction computers can work it out! Haha) how much higher scores people are actually achieving by spending practice time and barrel life getting their guns to shoot in the .2s or .3s?

[DaveMc]

I wrote something to do that exact simulation once Adam - perhaps Alan can dig up the revised version again.

[AlanF]

http://ozfclass.com/phpbb/viewtopic.php?f=35&t=4169&hilit=excel+simulator

[BATattack]

Doesn't look like I have the authorization (

[aaronraad]

Doesn't look like I have the authorization (

Neither do I BATattack, and here I was thinking I was in Tony's camp, now I don't what to think.

It's not easy being this annoying and going off topic all the time.

[AlanF]

Sorry, the link was to one of the hidden team forums used prior to Raton.

Here's a link to Dave's Excel file : http://ozfclass.com/forums/xls/twintargetmodel.xls

Here is some of Dave's commentary :

It is a target plotter that generates a set of random conditions and hence a hypothetical 10 shot relay. It is far from perfect (so please don't pull it to pieces - I am aware of most of the issues with it.) but still very useful in demonstrating some things even in rough form.

Hit F9 to generate a new set of random numbers (new shoot).

The targets are done in a "paired" test. This allows the user to put in slightly different variables (red figures) in one graph to the other. These two "twin" rifles are then hit by same vertical and horizontal random variables so you can see the effect on the score under different scenarios.

VERY useful for comparing bullets (e.g. in the example and relevant to this team the 180 hybrids in my rifle vs 180 VLD's. The 180 hybrids are exhibiting slightly more vertical SD than the VLD's but have slightly better wind bucking ability.

Have a play then I will come back later to talk more about it.

1) Try looking at one target for a while and look at the range of scores you can get from what is essentially the same rifle and shooter in same conditions. Do this for mild conditions (lower wind and vertical SD) and then for rough. This happens simply by the random fall of the numbers and is "normal" (why we call them normal distributions.)
2) Start comparing bullet types as in the example. Increase SD of wind and vertical and see the patterns.

OK I have updated the file which now gives it much more power to resolve differences. Alan has kindly reloaded it but due to the size of the file can you please upload and save it to a folder on your computer (rather than upload several times from the page here).

1) There is a 1000 replicated shoots page now which gives the average score for 1000 paired shots. This gives real power in understanding the differences between setups

I have uploaded 2 hypothetical scenarios. 1) an accurate 284 with VLD at 2850 fps (about 5.5 minutes wind drift at 1000 yards according to JBM) but low vertical sd of 0.15 minutes. this generally means holding around the x ring in elevation with perhaps one high or low every 20 shots or so. 2) a not so accurate 7mm magnum with pointed hybrids doing 3100 fps. I have given this one a vertical SD of 0.25 which is basically holding the 6 ring for most shots but the odd one may venture outside.

It is really interesting to change the wind sd (this is a combination of wind variability and wind reading capability) - try 0.5mph sd and 1.0mph sd. Basically at the first the accurate 284 has the higher scores and at 1mph the magnum takes over.

What does this mean in the real world?? Basically no matter who you are - an excellent wind reader or novice it shows that with average scores around 57-60 (very calm for novice to "tricky" for expert) then the accurate 284 has the edge. Once the wind howls or your scores start dropping to 55 and below the less accurate magnum takes over. This will be different wind levels for different shooters but nonetheless interesting!

Of course if you are a perfect wind reader and can get 58+ in all conditions then the accurate 284 is the choice all the time. Alternatively if you can get your magnum to vertical sd of under 0.15 minutes (basically holding x ring) then it is magnum all the way - but it is a tall ask for 20 shot strings!

[williada]

Dave, that post is a real eye-opener. You guys are working at a very sophisticated level producing practical outcomes.

Tony, thanks for the compliment, but the likes of Jim Boatright are miles in front of me although I can follow what he says. I still mix up my terminology these days at times, and trying to make the difficult simple, it sometimes doesn't work. The beauty of this site, is that an idea can be really sorted by our shared experiences and our education can be re-visited and that includes me.

[Norm]

Very interesting program.
I would be interested to see a comparison that includes a horizontal component of accuracy as well as the vertical component.
Maybe it already does??
This would then be handy for working out what distance to switch from say a 6mm Dasher to a .284 when the wind gets stronger.

[macguru]

This would then be handy for working out what distance to switch from say a 6mm Dasher to a .284 when the wind gets stronger.
•••••••••••••••••••••

and , say , then switch to a 300 WSM + 230 berger hybrids when its a bit stronger again ...

[DaveMc]

Just a couple of quick comments (and I apologise for replicating above but just in case some gloss over the fine print) as I don't have much time to contribute at the moment unfortunately.

1) Please save the program when you download it to save Alans loading on the system.

2) Norm - we have had several versions since but this one encompasses two normal distributions. vertical and horizontal. The horizontal is governed by the "wind reading ability" standard deviation multiplied by wind drift. In reality this combines all possible horizontal components in one figure. You are correct a persons horizontal shot placement as well as rifle accuracy should be considered separately to wind drift but generally can be absorbed by the major component (wind) for demonstration purposes. The result of what you speak is a very slight skewing of outcomes towards the larger wind drift (as all horizontal components are increased proportionally with this figure) Increase and decrease this figure (currently set to 1mph) for various conditions or wind reading abilities.

At the default conditions - comparing an accurate 284 VLD doing 2840 odd fps to a less accurate SAUM pointed hybrid in the 3000+ bracket it was obvious there were very little difference when the conditions were good (or obviously the wind reading ability is up there) set the horizontal wind reading ability to say 0.5 mph sd and hit f9 a few times. you will see similar score s- if not leaning slightly towards the accurate side. What is obvious from this outcome is when conditions are good (and winning scores are up there in the 59-60 bracket then there is far less difference between these to scenarios. When conditions are exceptional - accuracy wins every time. When it gets hard however - and average scores fall down to the mid 50's or below the pendulum swings the other way.

But get an accurate SAUM/300WSM - then the outcome is obvious - once again not much difference in perfect conditions or run by experts but when the going gets tough (or less experienced shooters) and the scores become markedly different.


And sorry there is a typo above - 1000 shoots (*10 shots) but 10,000 shots for each rifle - Hit F9 and it is another 10,000 - hard to replicate this sort of power in testing at the range Adam - Our approach was to try and combine the science and modeling with getting out there in the field and proving it. This one gave us clarity on direction as a team for FCWC and Rod and Linda decided we needed a few bigger rifles in case it got tough - even if they weren't holding the same vertical they can be handy in severe conditions. In the end we ended up with a few accurate SAUMs that were indeed handy but the humble 284 and milder SAUM loads held together better in the heat and altitude than the big magnums - but we had both cases well covered. (Mark actually brought along 2* SAUMS and 2 WSMS, plus I had 2 SAUMS going and Rods 7WSM as well - we had the team covered if it proved necessary (luckily it didn't so we could use all our very accurate 284's and their equally outstanding team of pilots)

We went on a mad few year mission of investigating many of the common accuracy myths with respect to 1000 yard accuracy and heavy wind training for coaches. As such much of it was put down once we had a "field" outcome and remains as unfinished work - hopefully next year will prove a little easier and Peter and I can finish some articles. I wish I had more time to contribute whilst the likes of Williada and others are contributing amazing volumes of very interesting stuff. - The links to Jim Boatright included.

Aaron - yes this thread was hijacked a bit sorry - I was responding to Adams comments.- considering this is the first time we have posted this spreadsheet to the general public perhaps it might be best to go to its own thread and leave Jims work for the attention it deserves.

[Norm]

Dave, thanks for the clarification and excellent information.
Quite an interesting program.
I have been studying the scenario of high accuracy/lower BC rifle, verses lower accuracy/higher BC rifle recently. So this has been a very handy piece of additional information.

I have been coming at it from a more simplistic perspective. Including the angle of wind reading error by the shooter plus the average accuracy of the rifle/load combination at short range. Then looking for the point where shots start to land outside the 6 ring with a centre X hold.

I came up with this chart for a high accuracy 6mm verses a less accurate .284 under two different wind reading error conditions.
As I say its is simplistic and all points were manually calculated which is time consuming. I think I much prefer your program!



Bottom axis is distance. side axis is % of 1/2 the 6 ring. i.e. 100% equals the edge of the 6 ring and the point where you start to loose points.

Tony, sorry for the thread hijack. Sometimes these things seem to happen on this site...LOL.
That link on bullet yaw/hummer barrels etc, was also interesting and to add a little bit of bait to the subject. Why do you think that a chamber reamer that is slightly worn, will quite often produce a more accurate outcome than a brand new reamer?