Chronograph Question

[deadon]

I keep hearing chrony, chrony, chrony. What will a chronograph tell me other than bullet speed? Thank you all in advance!

[rossman40]

It will show you consistency of the load. When you have high SDs or ES your not consistent in the barrel. It could be anything from a firing pin to barrel fouling and everything in between. Big MV swings will give you serious vertical stringing.

[deadon]

Ross, you are talking to a dummy. What is sd and es?

[rossman40]

If you shoot a number of shots that is called a string. What the chrono will do (at least better ones) is not only tell you the velocity for each shot but will give you a average for the string and ES and SD. It is not hard to calculate if you just have the velocities but some of us country boys are a little slow. Now the Standard Deviation (SD) is the measure of how close each shot’s velocity in the shot string will be to the “average.” For benchrest guys they would want it like 9 or 10 fps. The Extreme Spread (ES) is the fastest shot minus the slowest shot. Now great would be 20fps for a benchrest guy, three digits is bad. Just getting the ES and SD low as possible all the time shows your consistent. If you look at some of Richards data you can see the numbers he is getting

[deadon]

Thank you but I am a slow learner. If I find a load that shoots MOA,Then shoot at 50,100, 159 and 200 yds,and know the poi at those ranges,why do I care how fast the bullet is traveling. Personally, I have shot enough to know that if this load drops 20" at 150 and 60" at 200 I want a hotter load.

[rossman40]

Computer generated drop tables are a guesstimate and have to be verified. The chrony is just another tool to help with load development.

[Richard]

Deadon.............Your are missing the point! Rossman gave a good explanation.
A load that shoots MOA...........say at 100 yards, might not do so at 159 or 200. Lets just say you fire a three shot group at 100 yards and it is MOA. Shot #1 is maybe 2300 fps, #2 is maybe 2350 and #3 is 2250 fps. Lets say that this load is shooting flat enough at 100 yards that the three shot group in one inch (moa or close to it) Now, lets go out to 200 yards and see what it will do. You now have a 100 fps ES (extreme spread) Run your ballistic program and see what the drop is for each of the velocities? You will find a big difference and no longer have MOA accuracy at 200. Because the BC (ballistic coefficient) is so low on the typical ML bullet, your drop will be significant with the longer yardages. Also, as your bullets slow down (and remember you have three different velocities), each will be effected differently by the same.............say 10 mph, wind.
With my .45 and bullets traveling at 2900 + fps, I can have variations of 50 to 100 fps at 100 yards and still shoot small groups.............Take the same load at 300 and it will look like a shotgun pattern! ;D Unless you can get your ES down low enough, your long range accuracy will suffer...........Hence the need for a chronograph. It will tell you something is irregular with your load. Then its up to you to figure out what the problem is.
To give you a better example (Rossman mentioned 20 fps for a benchrest shooter)(and that would be a long range benchrest shooter - which is what I do) With my 6.5 x .284 improved shooting a 140 gr. VLD bullet at 2900 fps, a 25 fps ES at the muzzle.......................translates to 4" of vertical at 1,000 yards. So, if that is the best I can manufacture my loads, I am starting out with a minimum of a 4" group. Now take into consideration my holding ability, the wind over two valleys with a mountain to my left and wide open spaces to my right AND, wind currents that swirl and dip and who knows what all, and you have the makings for a big, big group! Under ideal conditions, you have to shoot at least 6" five and ten shot groups to make it to the "shoot-off"

A chronograph is essential if you want to obtain target type accuracy. Sure, you can get away with an eight or ten inch 200 yard group and still kill a deer at that distance. Provided you, under cold hunting conditions with less than ideal rests etc. can actually produce that group. But generally, you have to just get lucky! Now if you can reliably shoot 3" two hundred yard groups, your chances get much better of making that 200 yard kill.
Richard

[Jon]

Richard very well put

[deadon]

Hey Guys I think I finally got it. Richard, The examples for a dummy WORKS ;D I have a chrony, somewhere, I just have to find it. Thanks again

[boarhog]

I am convinced that it is virtually impossible to develop, and test, loads without a chronograph. In addition to the pluses itemized above, there are other benefits. Knowing the speed will help you be certain that the bullet you plan to use will do the job you need it to do. For instance, many on this board have experienced less than satisfactory bullet performance on game. Manufacturers usually publish a velocity range for optimum performance. If a 250 grain bullet is designed to perform well at 1000 to 1800 fps impact velocity, you should probably select a tougher model if you're getting 2800 fps MV. At the other end of the spectrum, if the bullet you wish to use is designed for 2000-3000 fps, and your load is averaging 2300 fps, you can use free online ballistics programs to learn at what yardage your load drops below the speed necessary for good expansion.

Another important asset is that a chronograph can also help you know when a maximum charge has been reached in your particular rifle with your load. This is especially true with metallic cartridges, but can also apply to muzzleloading. For instance, if you look at some of the pressure traces, posted by Edge and others, you may observe that a certain load produces a speed, and a pressure curve that rises above 40K. If you start with a lesser charge, and work up, you can be safe to assume that you are getting very close to the same pressure when your chrono shows the same speed. This can be true even if your load is a few grains less powder than the one that was pressure tested. The same is true when using data from a loading manual. When your load reaches the speed listed for the MAX load shown, you should assume that you are getting the MAX pressure also. Even if your load is several grains less powder.

Guess I've rambled on more than enough.
Boarhog