Brent 2 shot testing method

[flatsguide]

I have just read where this method for evaluating accuracy was mentioned. Can someone please enlighten me on how this test is performed.
Thanks, Richard

[Lead pot]

Richard it's sort of a ladder load that starts with zero compression and increased by a grain or two every two shots fired.
The tightest two shots can be verified by 5-10 shots to get a better average.
I use a three shot ladder.
Maybe Brent will chime in. I don't see him post to often anymore.
Kurt

[Don McDowell]

The 2 shot method is a good way to find good loads without loading 10 or more of any one load and finding out later that you got a lot of trigger time in, but could of used the powder and bullets for better purpose.

[flatsguide]

Richard it's sort of a ladder load that starts with zero compression and increased by a grain or two every two shots fired.
Kurt
OK! I’m all for saving powder and lead. Question. All this relates to PP bullet. Say I want to use a bullet seating depth of .125. For the first two loads I drop tube a charge that gives me a seating depth, with OP wad of .125 uncompressed. Would I load the next two loads with an increase of say, one grain and compress the load to maintain the .125 seating depth? It seems like accepted wisdom is to have as little bullet in the case that is practical short of breech seating.
Kurt, Don...thank you

[Der Gebirgsjager]

Yes indeed! Great systems, 2 or 3. Can't tell you how many times I loaded 50 of something and came home with 35 of them, and there they sit. :roll:

[Don McDowell]

Don't get wrapped up in the seating depth thing. Go at it just like you would any other bullet, the target will tell you how much compression ,seating depth etc the rifle wants.
I seat my bullets quite a bit deeper than what some would suggest, I got started doing that after close examination of a bullet pulled from an original Sharps Creedmoor round...
Wad stack under the bullet is important too. The less junk you stuff into the case between the powder and the bullet the better.
Fouling control with a paper patch bullet is vitally important to accuracy and maybe more so than seating depth.

[flatsguide]

OK, just need to get out and do it.
Thanks again, Richard

[Lead pot]

Richard the seating depth is your choice. And this ladder load works with PP or a GG. I personally like my bullet in the case 1/8" like you use so I don't have to worry about it falling out when time is running tight.
Start your ladder with all the wads you use at your 1/8" over uncompressed powder and set your compression accordingly. I use a OJ carton wad over the powder then the 1/8" lube wad and a single .040" plastic or I might use two as well as a .060" depending which caliber I'm using. But compress the powder with what ever wad you like to the depth of all wads you use so the bullet seats your .125". Then just add a grain or two for each 2 or 3 rounds you use for your ladder load till you get the maximum compression. With Swiss you will find a close load with .060 to maybe .150" compression and Olde Eynsford 2F around .250" I use the three load ladder and usually 21 rounds fired I see what will need a little tweaking for a match load. Then I will have fun shooting 20 rounds for trigger time and see how the two bank shots will hold an average.
I don't have a long range past 200 yards here so the final load development test is at a match usually :)
Kurt

[rfd]

stacked wad loads *can* work, but typically might require more testing time, tweaking, and evaluation at specific distances ... which is as one would expect. almost all of this stuff is subjective, particularly cartridge loads, and the final analysis of what does and doesn't work will get born from personal testing.

[country gent]

I start with a set depth into the case and find the sweet spot for the powder then adjust depth a little each way to see if it improves the best charges groups any. I chronograph while testing these loads also and have found Standard deviation and extreme spreads tend to drop ( lower) as the load gets close then level at optimum compression then start to rise again shortly after.

[flatsguide]

Thanks country gent. I will be setting up my chronograph when I start shooting and working up a load. Interesting observation about the SD.
Best Richard

[BrentD]

Whoa, the 2-shot method is definitely not anything to do with a ladder load. That is entirely different and appropriate for different situations.

The 2-shot method is one of the few ways you can confidently find small differences in precision between two different loads. It is an actual statistical test, not simply a statistic (which is quite different). You can read about it here
http://www.public.iastate.edu/~jessie/PPB/Stats/Testing%20loads.htm

[Lead pot]

:) With all do respect Brent I'm not scientific enough to use your 2 shot method. I think I will keep using my 3 shot ladder loads to find the tightest down range group :)

[BrentD]

I'm not a ballistics engineer, but I can use a software program to get sight estimates. Using that method is much the same. Just depends on what you want to do. Finding really small improvements require something like this, or just blind luck.

[Lead pot]

Brent we all have our way to get the best out of out loads for match accuracy. I don't believe in luck. When I make a good score or a bad one it's not luck it's either screw up or I shot well.
I'm one of the anal shooters that will start with a two or three shot group that ends up in 10 to 30 shot groups simulating a silhouette match less the chicken line. If that ending 30 shot group has a 2MOA group out of the total 30 shots my load is a failure and I try to improve on it.

Granted I just cant shoot as well as I have in the past, age is catching up on me so I need all the help with a good load to carry me through and a larger then a 2 MOA just don't get the job done.
For the long range matches anything more then a 2 MOA and your out in the 9 ring barring the wind call.
But again when all this testing is done at 200 yards chances are beyond midrange all might be lost at the 800 to the 1000 yard line.

Brent you are one of the shooters I put in the class as being a hard holder. You do well with the handicap of only testing at less then 200 yards. Would you improve if you had the use of a longer range to work out your loads? I would think the guys that have the use of say 600 to 1000 yards would be at the top of the leader board at a higher percentage then what they are.

[BrentD]

Well, I'm pretty much done with arguing about the validity of statistics as applied to shooting. I wrote up that method to be helpful to those trying to wring the last drop of precision out of their loads. I've gotten a lot more grief than thanks for it. Use'em or don't; that's not my call.

[rfd]

i think it makes sense that a total of five of the "two shot method" (or basically, two consecutive shot "groups"), where the base average of each two consecutive shots is more indicative of consistent accuracy then measuring the outer most target face holes of ten consecutive shots. and, besides testing sans wind, off as stable a platform as possible, such as a led sled. naturally this works with one load only, and changing one parameter (ladder loading, etc) means doing it all over again. randy wright's ppb book describes this type of "statistical two shot group". instead of have one data point for the outer most holes in a ten shot group, five groups of two shots yields five data points, and statistically that makes lots more sense and is a truer picture of how a particular load functions, given both the shooter and the environment of the testing. a simple statistical 200 yard load test example would be ...

two shot group 1 = 7.50"
two shot group 2 = 4.50"
two shot group 3 = 2.50"
two shot group 4 = 3.50"
two shot group 5 = 3.00"
total for all shots = 21.0"

average for ten shots = 21.0" divided by 5 groupings = 4.20", or just over a 2MOA for that particular load, under those conditions, for that shooter. noticing that the first group could have been a flyer could mean this might have been a sub 2MOA load. if the distance between the furthest holes was used, which could be lots more than 7.5", that would be even less indicative of how the load actually worked. just simple statistics. right on brent.

[flatsguide]

As the OP and a total novice at BP cartridge shooting, for this statistical method to be a valid, wouldn’t one have to collect the data at the actual range you’ll be shooting at for score and then how is wind effect on individual group size accounted for? I’m not trying to be argumentative just really interested.
Thanks, Richard

[Lead pot]

Brent I'm not arguing with you on your way of doing this and I haven't seen any of these posts at this point doing it. Your article is a good explanation for getting a average so I will just say relax...…..Kurt

[rfd]

As the OP and a total novice at BP cartridge shooting, for this statistical method to be a valid, wouldn’t one have to collect the data at the actual range you’ll be shooting at for score and then how is wind effect on individual group size accounted for? I’m not trying to be argumentative just really interested.
Thanks, Richard

NO, not at all. yer evaluating a specific load in as controlled an environment as possible, wind and weather and shooter be as they may, if you only have a 100 yard range, so be it. the bigger factors will be you, the shooter, how you bench the gun, then comes the wind and overall environment. consistency be thy name, which also includes how consistently well you've built yer cartridges.

[BrentD]

As the OP and a total novice at BP cartridge shooting, for this statistical method to be a valid, wouldn’t one have to collect the data at the actual range you’ll be shooting at for score and then how is wind effect on individual group size accounted for? I’m not trying to be argumentative just really interested.
Thanks, Richard

Richard,
By "range" I assume you mean distance, and not location (as in my particular rifle range). In some ways, it would be best to test at the distance of the match. However, there are at least two reasons not to. 1st, we don't often have those distances available to us. My longest shooting distance is only 300 yds, and most of my shooting begins beyond that distance (turkeys at 385 meters out to 1000 yds).

The 2nd reason is that there are so many different things that can go wrong at longer distances during the flight of an individual bullet. Even if you can see every single wind current and eddy out to the 1000 yard line and you can accurately adjust for all of them, the reality is that the bullet doesn't arrive at the target until about 4 seconds after you decide to pull the trigger -so lots of things can happen with respect to conditions while the bullet is in the air. Things you could not predict unless you are clairvoyant. So, by restricting one's testing to shorter distances, I like 200 yds usually, you can remove some of the environmental variance - and that increases your statistical power to detect differences in load accuracy.

Maybe I should add a 3rd reason as well. By whatever method you attempt to discover the most accurate load, you will face exactly the same problems. The use of a proper, formal statistical procedure only minimizes these problems to the best extent possible. Shooting a 10=shot group or a 3-shot group with each load and going picking the winner has exactly the same problems only much MORE so, not less.

There are, of course, a few precision issues that really must be tested at the range of your matches. The most important of which is bullet stability. The reason being that instability increases exponentially with distance, not linearly. So, imagine you have two bullets, one of which is very stable all the way to 1000 yds, and one that is not. But you don't know which is the stable one. At 200 yds, the differences in precision might be extremely small, so small that you cannot determine the winner, even after shooting 20 2-shot groups of each one. In such a case, you wouldn't be able to determine the winner with a couple of traditional 10-shot groups either. But at 1000 yds, that unstable bullet may reveal itself pretty easily, yet you can imagine if conditions are a bit breezy, it will be harder to assess instability than if it is dead calm (oh so rare at a 1000 yds, but it happens sometimes).


On to wind effect. Wind effects on any testing method are a problem. If they weren't we could shoot just two bullets of each load, measure and go home (assuming we are perfect aimers and trigger breakers). But that's not the case. So, we try for ideal and consistent conditions but we also recognize that there will be differences in group size caused by stochastic factors beyond our ability to control or even detect. And that is why we shoot more than one group. So, the 5 or 10 or 20 2-shot groups you shoot with each load, you hope will all experience about the same range of conditions over the course of the testing event. In that way, the variation in conditions is controlled for by replication and the average group sizes of the two loads can be compared to each other statistically.

I don't always use a formal statistical approach when I begin to work up a load. For gross changes in load precision, the tradition, informal statistical methods that shooters apply will suffice. But once you get down to the nitty gritty - Federal 210s vs CCI-BR2s or LDPE wads vs fiber wads, now you are talking small improvements, if any, and formal statistical testing is really the only way (besides getting lucky) of determining the best selection.

There are few sports where statistical testing makes so much sense as it does in competitive shooting, but there seems to be no sport where statistics are more cavalierly dismissed.

[Gunlaker]

Brent is 100% correct about the application of statistical analysis to shooting. You don't need to do it, but it's a certainty that if you don't you'll be deceiving yourself regarding improvements from small changes. Nearly every shooter I've met forms opinions that are incorrect because they don't understand how they should really design their "experiment" so that the results are meaningful.

The majority of people don't do this stuff and can be quite successful, but it is enlightening to go through the process once or twice.

Basically every decision you make when tuning a load leads to a decision. The idea is to maximize good decisions and minimize bad ones. Your intuition can guide you on whether a change was positive, but will generally fail you on things that make small differences. Statistical analysis is how you can determine the likelihood that a change was actually positive.

Chris.

[rfd]

a 2 shot group, fired 5 times (10 shots), type of load statistical test evaluation, given a good venue and setup, just makes worlds better sense than a 5 shot or 10 shot aggregate poke 'n' hope group evaluation. it does at least require a spotting scope, in order to mark relative hit locations and their number while at the bench in order for later target hole measurements. not a big deal at all and a more realistic load evaluation.

[flatsguide]

Brent,
Thank you for taking time to clarify this method. It takes a certain mindset to do a more rigorous test such as this. I believe it was a fellow from Wyoming by the name Deming that used these methods to greatly improve the manufacturing process. Without a doubt, math works. Your last three paragraphs really sums it up for me. Thanks!

Chris,
I agree !

Thanks guys,
Richard