View Single Post
Old April 22, 2013, 05:19 AM   #10
Hummer70
Senior Member
 
Join Date: June 22, 2009
Location: South Carolina
Posts: 121
Ballistic Progams are fun to play with but they won't be on the money unless it is confirmed. Per the guys at the Ballistic Research Lab at Aberdeen Proving Ground down range performance duplicates computer projections 5% of the time


John Unertl had the contract for the first USMC Sniper Scope back in late 70s and he asked me if I could get him a "good ballistic program for M118 Match". He went on to say that he had been provided five ballistic programs and that he had made elevation mechanisms for all five programs. He also said, "none of the programs matched and none of them were the same".


In those days I was working for the Army Small Cal Lab at Picatinny and had been sent to Perry as the Tech Rep for the lab as I was the only active smallbore and highpower shooter at the lab. Thusly when John told me he had data from multiple places and none was correct I was intrigued. When I returned to the lab I immediately went to see the Chief who previously had been at Frankford Arsenal and told him John Unertl's problem and he sent me to Bob Udell who was Chief of Ammo Branch and had spent his entire career in ammunition production. Bob told me to come back the following day as he had a conference that day he was leaving for shortly and another in the morning and to come back right after lunch and he would dig it out for me.
The following day I walked into his area and he saw me coming and headed for his office and retrieved a thick manila envelope and said,”Here it is and there are two additional ones for + and – 50FPS for hot and cold.” On the way back to my area I stopped by the copy office and ran myself a copy I still have somewhere. I was digging through stuff about five years back and ran across it.


I dropped it in the mail to John and heard nothing from it and the following year I went to John’s “shop” on Commercial Row and asked him if it was good and he said, “Absolutely perfect at all ranges.” In those days I was a shooter but had just got into the weapons field and I had no idea of what went into ammo testing and weapons testing.


A couple years later I was offered a job at Aberdeen as Small Arms and Ammunition Test Director when I was sent down to pick up “dust” for a test we were going to run at Picatinny and I took it and thusly my area of small arms knowledge was enhanced even further. It is extremely rare to find someone that has worked both ends (product engineering, development and test and evaluation) and I only know one other still alive. There was a third named W.C. “Bill” Davis and you can see him on the History Channel being interviewed about the M16. He is the guy with the white hair flat top hair cut and he was considered the “Dean of gov’t small arms program” and he was THE authority that was hired by the industry to figure out answers to problems the industry could not. His firm was known as Tioga Engineering in PA.


After arriving at Aberdeen I had a trajectory question and was directed to a guy in the Ballistic Research Lab whose entire career had been in that field and he is the one that told me the “5%” figure and went on to say that computer projections might be right on at two ranges, say 300 and 700 yards but off everywhere else. That floored me but within 18 months I found out exactly why the M118 data was spot on and how it was developed.
I ran the testing to develope the range tables for the M855 round fired from the new 7” twist heavy barrels and the following was how it was done.
All the M16A1E1 candidates were tested for dispersion at 100 yards and the three rifles were selected.


This was the best shooting rifle, a second rifle from the middle of the acceptance range and the worst shooting rifle that met acceptance standards which was 4.5” or less at 100 yards.


Each rifle is also subjected to chronograph records and the velocity differences are recorded for each rifle as the same lot of ammunition is used for all firing.


Next the rifles were zeroed to hit point of aim at 100 meters referred to as POA/POI (point of aim/ point of impact). Once this was accomplished the sights were never touched again as the range increased.


The requirement was for two NRA Master Class shooters to conduct this series but I was the only one on the Proving Ground thusly the Marine Corps had to send Master shooters up on two week TDY status to be the other shooter and a total of three came up. The data crunchers said they could work the numbers as long as there was one shooter that fired all the series and which they would call the control shooter.


The problem with rotating shooters is even though all may be Master Class shooters it is rare for two shooters to have the same point of impact utilizing the same zero and this became apparent as the ranges increased as the rifles are “held” differently and the point of aim is different due to difference in visual ability. A “line of white” is different for different shooters when using post sights thusly the data would be affected unless there is a control factor.
The series is fired as such. Each shooter would fire each of the three rifles three ten shot groups with each rifle (good, mediocre and worst shooting). After each 3 runs of ten rounds we went down and the fun started. From the aiming point we had to measure the distance from a horizontal line and a vertical line that to the middle of each shot hole with a certified calibration meter tape tape down to the closest MM to the center of the shot hole. The location was entered on a data sheet for each rifle and each shooter and sent to a computer center where the data is entered. The computer program (I would love to have this program in my computer) would calculate the extreme spread, the extreme height, width and the mathematical center of all thirty shots and poop out a target indicating all shots and a little triangle figures for group centers for each rifle and each shooter. It had the average of each and for all three rifles and the average of all three rifles for each range increment.

That took about three months to shoot as we could only fire on the days of wind less than 10 MPH so there were times when we were “down” for one to maybe three days” and if we were firing and the wind got up we got a call from the weather boys to advise us and we shut down.


This testing was duplicated at 200, 300,400, 500, 600, 700 and 800 meters. OK if the sights are not allowed to be adjusted how is this done? We had a target that was 32 feet tall and 32 feet wide and we covered the entire board with target cloth. Every time I see a drive in movie screen I think of this testing. When the range increased and the drops got near the bottom we raised the target thusly by the time we finished at 800 meters the aim point was approximately 26 feet from the bottom of the target.


To get the measurements a gun crew member was in a cherry picker bucket holding the tape at the aim point. At the longer ranges this required two bucket trucks. One to hold the tape on the line and the other to read the MMs and a third to record the reading on the data sheet.


The data was very interesting to see the differences of each rifle and each shooter and the averages at each range increment.


Bottom line here is if you want “spot on” values you are going to have to construct your own target and shoot each yard line all the way to 1000 and measure the drops of all shots and determine your average.(Better make your target about 36 feet tall for heavier bullets).


I have a 900 yard range and for all practical purposes for hunting rifles I have a 4X8 foot target that I have will take me to 500-700 yards depending on the caliber/velocity etc. I get a quick and dirty setting by firing 3 shots at each yard line then I measure all shots and get the average drop for each yard line for that barrel and load. If you do the full 30 shots series you are going to have about 400 rounds on your barrel to get the data.


Oh by the way you need to chronograph as well about every 100 shots to see how your average is holding up as when barrels start to wear you will get a change in average velocity especially if you have a barrel burner like a 6.5X284 or a magnum etc. My way of three shots at each yard line will not be nearly as accurate for group center but you will have much more useable barrel life left in your barrel.


If you run 400 rounds on your magnum your barrel is about at the end of its useful life and if you think you can just use that data on your next barrel, chances are very high the data won’t duplicate as barrel internal dimensions won’t duplicate and you are back to square one.


Occasionally you get a guy at Camp Perry and you see them with a green/white line computer data sheet all laid out and calculating the drift after taking the wind speed etc etc etc and they lay down and shoot. I watched this one guy do all his meticulous gyrations and he laid down, the targets came up at 1000 yards and he fired five shots and never made paper, got up, packed up and walked off the line.

There is a saying that fits nicely here: “Just when you think you have all the answers they change all the questions.”
__________________
Distinguished Rifleman High Power & Smallbore Prone
President's Hundred (Rifle) US Palma Teams(2)
US Dewar Team (2),4 Man Natl.Champ Team SB Prone
Cert Test Dir. Sm Arms and Ammo,Aberdeen Pr Ground, Firefighter I, AC4HT
Hummer70 is offline  
 
Page generated in 0.05014 seconds with 7 queries