Using chronograph data to determine the best load????

[RDM416]

Eaglet

I'll second that notion of being pretty ignorant, myself that is /ubbthreads/images/graemlins/wink.gif I have not been a practicing engineer for almost 10 years now, and oh how quickly you lose it!

As I said on my last post, I am not trying to be an authority on this subject. I could be wrong (probably am) but it is an interesting topic to discuss and apply some of that dusty unused physics grey matter to.

As far as "for every action there is an equal and opposite reaction" That is true and is an established law of physics. However, the larger the mass the more slowly it is put into motion. I'm sure you have noticed the recoil of a heavy rifle seems more like a hard push compared to the sharp "kick" of a very lightweight rifle of the same caliber. The foot pounds of "kick" are the same. The weight of the heavier rifle spreads that kick out over a longer time interval and the acceleration of the rifle is not as fast, so we get the perception that the heavier rifle kicks less. In reality the kick is the same (in energy). We therefore establish a practical example of how the larger the mass the more slowly it is put into motion by a given amount of energy. When a cartridge is fired, energy is transferred to the 200 grain bullet and the 10 pound rifle equally and in the same instant. However, it takes a longer time interval for the energy to over come the resting inertia of the 10 pound weight of the rifle than the 200 grain weight of the bullet. Therefore the acceleration of the bullet is much greater than the acceleration of the rifle. This gives the bullet time to exit the bore before any significant acceleration of the rifle has occured.

I will not argue that the recoil starts at the instant of ignition. What I do believe is that due to the mass of the rifle, the recoil is slow to build up. This gives the bullet time to exit the barrel before there is any significant movement. Notice I said significant in my original post as well, because yes the recoil starts instantaneously.

There are many other factors which can come into play regarding how we "hold" our rifle from shot to shot. Different pressure points or amounts of pressure can change the harmonics of barrel vibration etc. Vibration travels up and down the barrel (and action, and stock for that matter)much faster than the bullet. I would be inclined to believe that how firm we hold the rifle changes the effect of the vibrations, therefore the accuracy or POI could be effected.

Bart B, In response to your question on the double rifles. All I can say is I don't have a clue /ubbthreads/images/graemlins/confused.gif

For that matter I may be clueless on this whole discussion and just not realize it. It would not be the first time /ubbthreads/images/graemlins/crazy.gif

 

[Buffalobob]

Someone asked for a Physicist?

O.K. Here I am. You will be sorry!

The answer is over in SS7MM 's reply in the Ramshot thread. BJ verbally got most of it right. As a side note it is interesting how much incorrect information is posted on the internet concerning work and energy in what passes for reference material.


First and foremost for all of the engineers - this is not a mechanical system. It is a chemical system just like a car. Energy comes from the combustion process. How much energy is in the powder and how much is released and converted into mechanical energy depends on barrel length powder burn rate, bullet weight, barrel diameter etc. Being an engineer also, I failed in my first attempt to analyze the problem because I assumed it was a mechanical system.

OK us lets us proceed to answer the question of free recoil versus shoulder recoil versus a brick wall.

Without resorting to any specific powder and bullet combination we will just use some typical numbers.

A primer is struck and ignites the powder which burns and expands at a rate sufficient to occupy the barrel and push a bullet out of the barrel at 3000 fps. In doing this the expanding gas applies pressure (force = mass times acceleration) in all directions. Some is applied to the bullet which moves down the axis of the barrel and a mechanical reaction occurs in the opposite direction if the gun is free to move (free recoil). The gas expands at a velocity that is controlled by the resistance of the bullet to moving down the barrel. This is the central point everyone is overlooking. The rate of powder burn and gas production in the barrel and the velocity of its expansion is the same no matter if the gun is attached to an F4 fighter jet going Mach 2 or is in a vise on a brick wall or in the extreme situation it could be mounted firing backward on a rocket sled which is a very funny situation of bullet falling on the ground. In physics we use different frames of reference called inertial frames to analyze this type of problem. This involves an observer involved with the situation and an independent observer standing off to one side.

The amount of time it takes to get the bullet out of the barrel by the expanding gases is the nearly the same (I said nearly) in all cases because the powder burns at the same rate no matter if it is moving or still. So the velocity of the bullet as it exits the barrel is 3000 fps if a person was sitting on the end of the barrel.

If a person is on the ground watching the gun being fired from a jet plane then the velocity of the bullet is 3000fps PLUS the speed of the plane. The pilot sees the bullet depart at 3000fps.
If a person watches a gun mounted backwards on a rocket sled and the sled is traveling at 3000 fps when the gun is fired the bullet will simply falls straight to the ground. The person on the rocket sled see the bullet depart at 3000 fps.

For all of you unbelievers, the next time you go deer hunting and are riding around in the back of your buddie's pickup truck try throwing your beer bottle backwards and see if the bottle actually flies backward or if it actually flies in the same direction the truck is moving. Which occurs depends on how fast the truck is going and how drunk you are.


At this point in time those of you who are too bored to read anything else and are still with me, will probably understand that the movement of the gun during the time the bullet is in the barrel affects the velocity that a third party observer will see. So now lets get to free recoil versus shoulder vs brick wall.

Brick wall. Gun cannot move so bullet velocity is controlled solely by powder combustion process and exits at exactly 3000fps as seen by both observers.

Free recoil. Bullet in relation to barrel exits at 3000fps but barrel is moving to the rear at 4 fps (Bart B's number). Independent observer sees bullet at 2996 fps. How fast the barrel moves to the rear can be calculated with any of the recoil calculators available on line. The one I have bookmarked is

http://www.travellercentral.com/rules/ke.html


Chuck hawks has these number for pistols

http://www.chuckhawks.com/handgun_recoil_table.htm

Shoulder recoil. The shoulder is simply addition of weight to the weight of the gun so there is more mass to move backwards. How much weight depends on how many Christmas cookies you have been eating. The shoulder slows the rearward motion of the gun down from the free recoil speed of 4 fps to let us say 1 fps (Monkey Blaster excepted – no shoulders big enough to slow it down). Bullet leaves the barrel at 3000 fps in relationship to the barrel but an independent observer standing to one side sees the bullet come out at 3000 – 1 = 2999fps.


Hope y'all have some accurate chronographs. /ubbthreads/images/graemlins/grin.gif

 

[MT4XFore]

Gonhuntin: Now see what you started!!! /ubbthreads/images/graemlins/shocked.gif

Gentlemen: I thought that after 40+ years of shooting and reloading I knew a little about those subjects. But I am beginning to realize that like a couple of others here have said, "I dont have a clue!" /ubbthreads/images/graemlins/confused.gif I must say however that this has been one of the most enjoyable discussions I have ever read. Frankly, it doesn't matter to me who is right , wrong , or indifferent for that matter, I am fasinated! I must also note that all of you gentlemen have conducted yourselves in an exemplary manner and I find that with this level and depth of discussion that is quite refreshing. Now, for my purposes, I find that the OCW method combined with a chronograph works just fine (I like to LOOK like I know what I'm doing whether I do or not /ubbthreads/images/graemlins/blush.gif)
So please, carry on and continue with the theories and discussions, I am learning more with each post.
Happy New Year and Good Shooting!
Jim

 

[Bart B]

RDM416, your comment: "A bullet traveling at 3000fps will take .000722 seconds to exit a 26" barrel." is interesting. A 3000 fps bullet moves 1 foot in .000333 seconds, 2 feet in .000667 seconds. And bullets accelerate from 0 to X fps out the barrel in a nonlinear way. My guess is your number is very close to exact (kudos to you!!). So, where'd you get this number from?

 

[Eaglet]

Buffulobob,
I'll buy your explanation!!!!!!!!!!!
I gotta question for you. When you typed this:
[ QUOTE ]
For all of you unbelievers, the next time you go deer hunting and are riding around in the back of your buddie's pickup truck try throwing your beer bottle backwards and see if the bottle actually flies backward or if it actually flies in the same direction the truck is moving. Which occurs depends on how fast the truck is going and how drunk you are.

[/ QUOTE ]
Were you smiling, laughing or just busting up? Please respond! /ubbthreads/images/graemlins/laugh.gif I was laughing so hard my family thought i had lost it! /ubbthreads/images/graemlins/smile.gif

MT4XFore,
I did enjoy your post! It is fascinating indeed! /ubbthreads/images/graemlins/smile.gif

 

[Guest]

[ QUOTE ]
Gonhuntin: Now see what you started!!! /ubbthreads/images/graemlins/shocked.gif



[/ QUOTE ]

You're welcome!!

Does anyone know where I can get a rocket sled??? I know a guy that I think could be talked into sitting on the back and firing a rifle so we can see proof of that bullet falling to the ground theory! Even if it doesn't work out, he won't screw up any more of my hunts!! /ubbthreads/images/graemlins/grin.gif

 

[Eaglet]

GonHuntin,
That's hilarious!
This guy you know has to be your hunting buddy! /ubbthreads/images/graemlins/smile.gif
Poor Guy!

 

[green 788]

Okay, back from the range, muddy boots and all... /ubbthreads/images/graemlins/frown.gif /ubbthreads/images/graemlins/laugh.gif

Folks, I can't tell any difference. That doesn't mean that there isn't some difference--just that with the handloads and factory loads I was shooting, the ES would appear to eclipse any actual difference in free recoil velocity versus firmly held velocity.

Now. There's an additional surprise which we can chew up another gross of pencils over which I'll save for the end of this post... /ubbthreads/images/graemlins/smile.gif

I first shot a little Model 34 Smith & Wesson .22LR (revolver), with a 4" barrel. Checked six shots (CCI Stingers), three with firm hold, three with as loose a hold as I could manage and still pull the trigger.

FH = Firm Hold, and FR = Free Recoil:

Average velocities...
FH...1258
FR...1251

Then I shot a 1911A1 45 ACP, using 230 grain surplus ball ammo. For the FR shots, I just put the butt of the pistol on a sandbag and used my thumb to compress the grip safety and my index finger to squeeze the trigger (yeah, don't try this at home!)... ES's were bad, but here are the averages of ten shots firm, ten loose...

FH...769
FR...770.5

For the record, one shot of the FH went 801 fps, and one shot of the FR dropped to 693. These two numbers pulled the averages pretty close. If I count those two odd shots out, it looks like:

FH...765
FR...787 /ubbthreads/images/graemlins/smile.gif

On to the rifles. These were shot off a bench, and for free recoil I just used my thumb behind the trigger guard and my index finger pulled the trigger.

On my pre64 Model 70 Winchester in .270 win. Load was 60.0 grains of Accurate Magpro with Sierra 150 grain Gameking:

FH...2758
FR...2772 /ubbthreads/images/graemlins/smile.gif

6.5 x 55 Swedish Mauser, M38 Oberndorf. Load was 46.3 grains RL22 and Sierra 142 grain Matchking.

FH...2526
FR...2537 /ubbthreads/images/graemlins/smile.gif

Please consider that this info is probably worth about what I charged you for it. But from what I saw today, when I was actually trying to figure out the effect of loose or firm hold on velocity, I have to recant my previous assertion that velocity can change all that much based on how firmly the gun is held. In fact, the crude little test I did today would seem to indicate that free recoil increases velocity as often as it decreases it--but I'm sure that's just a fluke...

I would still like to see some numbers from some other members who may take time to try this little experiment out next time they go to the range. There may be particular scenarios (certain gun, certain cartridge) where there is a more noticeable difference. I'm not at all familiar with the double rifles Bart mentions, so I can't really offer anything there...

Okay. For the surprise I mentioned earlier...

Why doesn't the POI on target change noticeably between FH and FR? It's supposed to. Everybody always says it will. /ubbthreads/images/graemlins/confused.gif Granted, none of the rifles I tested today were shooting BR sized groups, but both were printing about 1.5 MOA with the loads I brought along. Holding at the same bullseye during free recoil seems to land the shots right in the group--even though the rifles were thrusting backward a good three feet (into my cousin's hands, who was standing behind the bench to catch the rifles during FR firing). I would have thought that POI would have been significantly different with FH versus FR. I would have to assume that with bug-holing BR rifles, the POI shift is more noticeable at 100 yards... But I'm glad no one asked me how that would have turned out before I did my little test today.

I would have been wrong twice! /ubbthreads/images/graemlins/blush.gif /ubbthreads/images/graemlins/laugh.gif

In any event, it appears that I was wrong once, so here I go...

/ubbthreads/images/graemlins/laugh.gif

Dan

 

[ss7mm]

Re: Using chronograph data to determine the best load????GonHuntin

Guys:

This is all very interesting but I think the original post has been forgotten, even though the results have been very interesting.

Remember that if you look at what buffalobob said you will easily see that free recoil would have only the weight of the rifle to resist rearward movement. Adding the shooters body, no matter how firm the hold, adds the weight of the body to that of the gun to resist rearward movement. The result would be that the rearward movement of the gun would be less with the body in the way but the velocity at which the gun moves to the rear is very minute compared to the speed at which the bullet travels forward.

Simply put, the bullet accelerates so fast that it is out the end of the barrel before the gun has moved very far at all. This is proven by the fact that muzzle brakes work. The bullet, and the gas that is moving the bullet, get to the muzzle and the gasses and pressure interact with the brake before the mass of the gun has moved much, if any. This allows the brake to work.

This is probably why Dan didn't see the changes in POI that he expected to. Yes the free recoil guns moved a long ways back but I would think that the bullet was out of the barrel before much, if any, of the rearward movement of the gun had occurred.

What does all of this have to do with GonHuntin's original post? Nothing but it's interesting.

GonHuntin, I use a chronograph for every round I fire during load development and testing. This doesn't make it right or wrong, it's just that I want all available data I can get my hands on to make my decisions. I do not develop loads based solely on the chronograph data, my main goal is to develop the most accurate load I can. Drops are easy to figure, but it's really hard to hit anything at extended ranges with a fast, but inaccurate load.

Most of the time you are not going into load development blind. By that I mean that you are probably loading a cartridge/bullet/powder/primer combination that someone else already has used. You probably have data for that load. You are simply starting at a safe level and working up to an area that is known to be maximum under certain conditions, looking for the most accurate combo in your gun.

I use the ladder method and find it works best for me. I start low and work up. I hope to find one or more "nodes" somewhere in the test that indicates to me that the gun "likes" that combination. Every round I fire is documented and goes into my notes. I also make notes of all pertinent field conditions every time I shoot. This is invaluable later on when you go from cold to hot conditions etc.

I also check for pressure indicators with every round fired. This is very important and combined with the other data you collect helps with what you are trying to accomplish. Just remember that with a custom action and quality brass, like Lapua, pressure signs may occur later than what you are used to seeing. Some primers will indicate different than others, some brass handles pressure better than others. Don't just keep increasing the loads and dropping the hammer. Be careful and analyze everything you know and everything you are being presented with.

I would expect to see the velocities climb as I increase the loads, but remember it's normal to see a round with an increased charge produce a lower velocity than the previous round fired in a ladder test. This is due to the ES that the different loads would produce. One load might show a velocity at the upper range of it's normal group ES and the other might show a velocity at the lower range of it's normal group ES.

I look for any velocity changes out of the normal. I don't expect to see the velocities start to drop and I don't expect to see a drastic jump in velocity that doesn't follow what has been occurring with the load increases so far. Remember you are probably working with a combo that has already produced a known velocity. You are just being careful and working up to an accurate, safe load in your gun.

At this point you can't be concerned with ES or SD because you are only firing one round per charge. You are simply trying to find the place where your gun seems to group 2 or 3 loads very closely. Later I take the loads in the nodes I have detected and load up several groups of each, in smaller increments, to try and find one that runs in the center of that node and is the most accurate in my gun. I am still concerned mostly with accuracy and am not looking for the best ES or SD.

When you get to this point and start testing, say at 100 yards and find a load that produces the best accuracy, you may find that it isn't the one with the best ES or SD. This quite often is the case as it's not written in stone that the lowest ES and SD will always produce the most accurate loads.

You then need to test your most accurate load at extended ranges. If I find a load that seems to be the most accurate at 100 yards and also have another that's not the most accurate but has a much lower ES and SD, I will then go to extended ranges and shoot not only the most accurate load at 100 yards but also the ones with the lower ES and SD. I want to find out what combination gives me the most accurate load at extended ranges, not at very close ranges. Sometimes you will be surprised to see what the most accurate load is, in your gun, at extended ranges. Some load combos will tighten up at extended ranges and some will get worse, some will track as expected at extended ranges. You won't know without shooting them all.

Now that you have found the most accurate load for you and your conditions you can now play with seating depth, primers etc. and it goes on and on and on if you want to. Just remember to only change one component at a time and do your testing with just that one item changed. Normally, if I'm happy with the results at this point, I will only change seating depth and try some different settings. I don't really like to seat bullets to engage into the lands unless I have to. I try to find a load that lets me start with the bullet just at the lands and then I will try seating in small increments off of the lands since most of what I load for is a hunting setup. Remember, if you do your testing at the lands and then decide you want to go into the lands, you must remember that this is going to increase pressures and you must make changes accordingly. You may find that certain types of bullets like to be seated into, at, or off the lands to a certain point. How much testing you do depends on how anal and picky you are at the time.

Just remember that you should be looking for the most accurate, safe load combo for your gun under your conditions. Velocity is not the determining factor and is actually way down the list for me, but it is another valuable tool and indicator that I'm glad I have every time I put a round through the chronograph.

 

[Buffalobob]

Eaglet

Most science comes from observation. We have all ridden around in the back of pickup trucks as kids and thrown rocks at mailboxes, road signs, any cow close to the road or anything else that struck our teenage interest. I was trying to get people to associate what they personally knew as a fact with what I was saying. And in the process keep the discussion interesting enough to read.

The reference to deer hunters in trucks is because I was so disgusted with what happened to me yesterday. Many of the back roads are frozen sheet ice and I was blackpowder hunting in a new area and decided to park my truck at the bottom of the mountain and walk up the icy road to the saddle and then hunt the sunny side of the mountain. I did not see another hunter in the woods but was constantly having to step off the dead end forest road to avoid the road hunters sliding their trucks into me as I walked along. It was a two mile walk and I got to the top and sure enough all the deer had bedded down on the sunny side of the nountain. I didn't kill any deer but it was good to get out into the woods and explore a new place.

Glad you enjoyed the discussion.

PS. 786 or who ever -- That is the greatest picture of eating crow. I have saved it so I can use it sometime.

 

[Eaglet]

green 788,
I for my self do appreciate your efforts, your actitude and willingess to find answers. Thank you! Bless You!

 

[bailey1474]

Thanks buffalobob. I really thought this was correct but either I am just to lazy or not smart enough to put it the way you did!!!

788 and BartB,

This has been a very good discussion. I, as well as others, gained alot of respect for you and everyone invlolved. We actually behaved like adults and not 2 year olds!!

It's been fun. Great job everyone!!

 

[RDM416]

Bart B.

The way I got the .00072 number is as follows. 3000fps X 12(inches in a foot)=36000 inches per second. 26 inches divided by 36000 = .00072 seconds.

Actually that number is technically incorrect, but I felt it was close enough for our discussion. You are correct that the bullet is accelerating as it travels the 26" length of the barrel. Starting at 0fps and exiting at 3000fps. So, the actual time would be more than .00072 seconds..........but not much!

Buffalobob,
Thanks for weighing in on the subject. This is what I really like about this site /ubbthreads/images/graemlins/smile.gif This has been a fascinating discussion with several opinions expressed but no one started name calling. Everyone just seemed to enjoy the discussion and try to learn something. And as usual on this site someone who really knows what he is talking about steps in provides the answer.....Thanks!

I know we all got a little off topic on this one, but it sure was fun /ubbthreads/images/graemlins/grin.gif

 

[green 788]

Definitely off topic, in more than one direction! But this has been very enlightening. The lack of a significant POI shift issue was a serendipitous discovery that I'll not forget. /ubbthreads/images/graemlins/laugh.gif Amazing...

But on the velocity thing... The only thing to do was to test the idea before we took this thread to a dozen pages mulling it over. It appears that the effect is negligible--but no one seemed willing to bet the farm on that /ubbthreads/images/graemlins/wink.gif until we had some actual data (crude as it may be) to pour over...

A friend of mine from Sweden has a saying, which translates to English something like "Trust your own observations rather than relying on what others tell you." That's good advice, and seemingly pertinent here.

Dan