Velocity Extreme Spread and Standard Deviation
- Thread starter chkunz
- Start date
Just 20 ? That is not enough. Larry
Edited for clarity:
I think that's a great idea. I've heard that brass on it's first firing will give you the lowest ES/SDev but not by much.
I've also heard others claim that over more firings the ES gets lower as the brass more perfectly fire forms to your chamber. This I'm a little more skeptical of. I have a theory that after the initial firing the brass does in fact expand but during the spring back phase may not do so consistently, thus introducing variation. This is just a theory.
I plan on running a few tests myself in the next few days to weeks.
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La
Larry, take another look at the numbers from the one twenty shot string that I referred to and the calculation of the percent change between 5, 10 and 20 shots and think about the calculations. I will copy what I wrote above since some of it may have been missed due to the way that I replayed and sorta messed up the visibility of the complete reply. I agree that most people make decisions on insufficient data especially three and five shot groups but I believe the numbers in this one case for ES and SD say that ten was enough.
Copied from above "I ran a 20 shot velocity string with the MS chronograph and looked at the ES and SD numbers using the first five shots vs. the first 10 shots and then all 20. there was a 2.5% difference in ES between the five and the ten shot strings and a 0.07% difference between the ten shot average and the twenty shot average. So for this one data point the ten shot string is ok.
I did a similar calculation with the SD for this same twenty shot string and got a 11% difference between five shots and ten shots a 0.6% difference between ten and twenty shots. Again ten shots is good.
I did this sort of calculation many years ago with group sizes and since then I always shoot ten shot groups for testing. Also, I also learned to use mean radius for evaluating groups rather than extreme spread."
With respect to your opinion, Larry.
How can you be skeptical of brass in the chamber of you gun being it exposed to internal pressure of 50,000 PSI not being good. Larry
My post was edited for clarity. It's not the brass I'm skeptical of. I'm not sure if brass becomes MORE consistent over MORE firings. A few respected shooters have reported lower ES with new brass.
Many of things can be done to lower ES but without the internal volume off the case being the same you will never get low ES. I have found I can check the internal volume of the cases . With very good repeatedly . It ends up being a one time job. Larry
Warren Dean
Team Savage F-TR
This is a hoot..... 
One quick note on new brass shooting better, then I have a question relative the thread. I watch/scored for my old shooting partner clean the 800 yd. line during the Palma matches at the Nationals at C-P using virgin brass that needed fire formed. X count was 11-12 I think. He didn't have enough formed rounds to complete the match, so he fire formed at 800!
Several of you have referred to consistent neck tension and I for years played with what is the proper amount of neck tension? I know of one world class shooter that on this sight said that he seats his bullets long with very little tension so that regardless of your ogive length or amount of throat erosion the seating depth is the same. (He shoots three rifles in the same caliber). By everyone's definition on here, he is using identical neck tension. I for one am going to test this theory out this spring as I now have the equipment to do it. What do the rest of you think?
Lloyd
Several of you have referred to consistent neck tension and I for years played with what is the proper amount of neck tension? I know of one world class shooter that on this sight said that he seats his bullets long with very little tension so that regardless of your ogive length or amount of throat erosion the seating depth is the same. (He shoots three rifles in the same caliber). By everyone's definition on here, he is using identical neck tension. I for one am going to test this theory out this spring as I now have the equipment to do it. What do the rest of you think?
Lloyd
You certainly can, but I should clarify that the differences you see with brand new brass versus new brass that has been loaded several times should not be as much as what I saw. This is because the brass I had was older and had air hardened as well as work hardened. I didn't start out with brand new brass and anneal it five load cycles later to see these results...what I had was so hardened that I could feel it on the press.
I believe that it may also be affected by the brass alloy. It doesn't seem like all brass cases {different brands} are made out of the same stuff. Some cases seem to work harden more or faster than others. Military brass is thicker so neck tension is affected more if it is not annealed and/or turned. Based on my experience I believe that, regardless of the alloy, brass cases all anneal easily enough and the same procedure works fine.
We used to think that certain powders did better and that certain times of the year {ambient temperature} could have a lot to do with it.
I always had brass sized to headspace, used the same primers, had a Wolf spring in the rifle as well as a Tubb speedlock kit. honed the inside of the bolt, checked and deburred the flash holes, verified pin protrusion and tried to seat the primers all the same. I think I covered it all as to ignition...not saying primer ignition is not important, but with all that done I didn't see it. Don't know if there is anything else I could have altered, yet in spite of all that...annealing the hardened brass still was all I changed to see the numbers drop way down.
New brass always shoots good. It is soft and even from factory annealing and this gives you good bullet releases. As far as Tubb Speedlock goes, that is bad for accuracy. When shooting from benchrest, many rifles have shot worse. You need firing pin energy to set primers off evenly. Most short-range BR guys get there pins weighted for more accuracy. They send brand new actions to Dwight Scott or Dave Bruno and have the pins weighted. Sometimes certain brands of primers can improve numbers.
I agree that certain powders will change things also. Some burn better at certain temperatures. I believe to be accurate, they have to burn clean. If you look at match or benchrest shooters you see certain powders used in certain cartridges. There is a reason for that. They just plain work. There is also certain cartridges that do better then others. Matt
I agree that certain powders will change things also. Some burn better at certain temperatures. I believe to be accurate, they have to burn clean. If you look at match or benchrest shooters you see certain powders used in certain cartridges. There is a reason for that. They just plain work. There is also certain cartridges that do better then others. Matt
Works like a champ with VLD bullets.
Jay Christopherson
Not An Admin
Truer words have never been spoken in the realm of reported chrono numbers.
Pay attention here - I wish someone had let me know this early on in my reloading career. Once I was twigged to it, it made a huge difference and saved a lot of agonizing. I never develop a load now without testing at least 3 different brands of (known good) primers AND without keeping track of the number of rounds on my firing pin spring.
I'm not familiar with "air hardening". Can you explain please?
Not a metallurgist, so I may not be explaining this correctly, but...brass will harden just from sitting. Unlike most metals brass gets harder just over time. There is probably some "molecular level" change or better explainable reason for it, but I never got quite that far into it other than to know that it seems like time alone will make brass hard. I am not sure why it is referred to as "air" hardening, other than it is just sitting in air??? I believe if I remember right that air hardened brass to a point can be annealed back to being as soft as the alloy can be or will allow. There is also a point over time that it cannot be recovered by annealing.
If you ever find a box of old ammo, like from the 50's or 60's there is a very high probability that it has gotten so hard that the case necks will be split.
Different metals get hard or soft by different actions or processes...I know from restoring old doubles and lever guns with case colored receivers that to anneal them the receiver is put in a stainless or cast iron vessel filled with wood charcoal and heated to what I always heard called "critical temperature"...the point where steel loses any magnetism. Like 1500-1600 degrees and then is shut down and allowed to cool in the wood charcoal. When cool you have a dead soft piece of steel that can now be polished or engraved with ease. Add bone charcoal to the mix and heat again and you get the colors back...but you have to quench it in water this time. Metal is strange stuff to say the least.
Interesting...first time I ever heard it claimed that increasing lock time enhanced accuracy...not saying yes or no, just that this is the first I have heard of it. My question is...if you have a given firing pin and a given striker spring traveling a set distance and none of these three things change.....what gives you the difference in primer strike??? Where does that difference come from, it doesn't seem like the factors affecting it are any too awful much variable to me...the given weight of the striker assembly is not changing, the spring is not getting wound up any more, it is moving the exact same distance to strike, where or what exactly is the "variable"???? Even if in fact the heavier pin causes the primer to ignite "better", how is it more consistent for purposes of es/sd. If the primer doesn't go quite as "bang" because it got hit softer...isn't it still getting hit softer the exact same every time.
First off you are only talking milliseconds difference in time between a regular pin and a speedlock. The speed may help slightly in offhand shooting. Search Tubb speedlock on the internet on here and there will be lots of info. Make a thread on here about Tubbs speedlock and you will get lots of replies. If the primer isn't hit hard enough the ignition gets inconsistent. I have even heard a firing pin fall and then the boom, like a flintlock. A lighter pin will not have the Kinetic energy of a heavier one. This inconsistency sets different vibrations into the barrel, thus changing the harmonics and nodes. With the lighter and faster pin, it will tend to bounce more when it hits the primer, setting off vibrations. Maybe somebody like Donovan, Dusty or zfast will step in and explain it better then me. Matt
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You did a very good job of explaining it. News to me, that's all. Not saying I don't believe you...just that I have never heard such a thing. I get that it's milliseconds, I always heard that the bullet was "three feet out from the muzzle in a Speedlock 700 before the primer got hit in a stock gun." Sounds good, but admittedly could be a sales point, and if it is then it worked for a right good while!!! But it also seems measurable or a simple matter of mechanics...how do you measure or confirm that a primer getting hit lighter is "erratic"???? Bad groups plus "must be the primer" equals "sounds good"????? I guess to confirm it someone could change weighted firing pins and check velocity of given ammo??? Anybody done that??? My primers appear to be struck and dented just as much as they were before, it also has a heavier Wolf spring. Cant tell if they are bouncing, but there is definitely no "flintlocking" going on either.
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