nvshooter
member
So tell me, why should I buy a chronograph? What will knowing how fast my reloads are traveling at 15 feet from the muzzle really tell me? I have no idea what extreme spread and standard deviation is...
Looking at buying a chronograph...
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Grumulkin
Member
A chronograph satisfies curiosity. I do not use a chronograph to work up loads since I load for accuracy with acceptable pressure and not for velocity. When I get a load all worked up and only if I'm especially energetic, I get the chronograph out to see how fast my bullets are going.
For shots at up to 200 yards with a rifle, I don't think a chronograph helps much. For shots above that and especially in the 300 to 500 yard range, it's nice to know the velocity so one can consult a ballistics table to get an idea of how much holdover/windage adjustment to use on a long range target.
For shots at up to 200 yards with a rifle, I don't think a chronograph helps much. For shots above that and especially in the 300 to 500 yard range, it's nice to know the velocity so one can consult a ballistics table to get an idea of how much holdover/windage adjustment to use on a long range target.
Dr. Dickie
Member
The standard deviation is a measure of the precision of your speeds. That is, about 100% of the speeds of your shots will lie within + - 3 standard deviations of the mean speed.
If you are doing some bench rest shooting, getting that value down would be important, if not, not so much.
The extreem spread is simply the range from highest to lowest speed.
If you are doing some bench rest shooting, getting that value down would be important, if not, not so much.
The extreem spread is simply the range from highest to lowest speed.
ChristopherG
Member
They're a necessary tool if you reload for some kinds of competition--i.e., where you have to meet a certain power factor. I've always been able to borrow one for this purpose.
Some folks use them to test the results of increasing pressure in handloads. The way I understand it, you continue to increase your charge (in the absence of other pressure signs) until velocity stops increasing--then you know you're getting into hairy territory. I trust to loadbooks and general caution, and don't worry about getting the very last 25 fps out of a given load combination, so have never used one this way.
Some folks use them to test the results of increasing pressure in handloads. The way I understand it, you continue to increase your charge (in the absence of other pressure signs) until velocity stops increasing--then you know you're getting into hairy territory. I trust to loadbooks and general caution, and don't worry about getting the very last 25 fps out of a given load combination, so have never used one this way.
MCgunner
Member
I don't know how I ever lived without my chronograph. I'm wanting an Ohler with a strain gauge. 
They are hugely helpful tools. You first of all can verify your velocities from which you can calculate energies. This is a good thing for pistols and revolvers for self defense or whatever. But, with the help of a good ballistics program (available for free on the net, google PCB1.8 or "ballistics program"), you can, with your calculated mean velocity, work out trajectory drop tables, energy at range, wind drift, etc, and calculate point blank range sight in. In fact, you can calculate your 3" point blank range, then if all you have is a 100 yard range, just zero to whatever the drop table says you are at 100 yards with that point blank range sight in. Over the years and from experience, most calibers are about 2-2.5" high at 100 for their 3" point blank range.
Now, if you know nothin' about this stuff, point blank range is the range at which the bullet will neither be above or below 3" (for a 3" point blank range, used for a deer sized kill zone). IOW, if you zero the gun for its optimum point blank range, you can just hold on the deer all the way out to that range and you don't have to worry about drop or hold over, just aim and shoot. If you zero the gun at 100 yards like a lot of hunters do, fine in the woods where you're not likely to get a longer shot, and you DO get a longer shot, you're going to have to worry about hold over. Hope that makes sense.
Standard Deviation, without writing out the formula, is the square of the square root of the average deviation divided by N-1 (degrees of freedom), or something like that. Been a while since I took statistics, like 35 years. IOW, it's a measurement of variance, the accuracy of the load. The smaller the number, the less variance of velocity from the mean (average) and the less elevation error you're going to have. A high standard deviation will mean you're going to string your shots vertically. For rifles or handguns, I've found really GREAT SDs are under 20. Anything over 30 is not good. With, say, an SD of 35, you’re going to start to see some shot stringing in elevation.
Now, then, lets say you are loading a marginal caliber for deer hunting, say a 7.62x39, and want to find out what range it falls below the magic 1000 ft lbs. You can do that if you know the mean velocity at the muzzle (or 15 feet in front of it) and run it through an exterior ballistics program, another good use for such info. Heck, I wrote my own exterior ballistics program 25 years ago before computers were common using a Timex Sinclair computer and the BASIC compiler built in to it. That program is quite accurate and does the statistical analysis that PCB1.8 (the free program) doesn't. If I'm serious about the load, I'll go plug in my old Tandy Color 3 computer and run it through my program. I guess I could break down and buy a better program, but actually, I can calculate standard deviation long hand, the math hasn't left my senile old brain yet.
Before chronographs were common, ammo companies would exaggerate claims of performance and there was on way to verify velocities of the load much less work out a drop table. The dedicated reloader/rifleman would just have to take the velocity claims in the manuals on leap of faith. When sighting in, if you wanted to shoot to a 3" point blank range, you needed a 300 yard range and you just burned a lot of powder experimenting. With chronograph info and a decent exterior ballistics program, press a few buttons and BOOM, there's your answer. Think of it as computer modeling the path of the bullet.
They are hugely helpful tools. You first of all can verify your velocities from which you can calculate energies. This is a good thing for pistols and revolvers for self defense or whatever. But, with the help of a good ballistics program (available for free on the net, google PCB1.8 or "ballistics program"), you can, with your calculated mean velocity, work out trajectory drop tables, energy at range, wind drift, etc, and calculate point blank range sight in. In fact, you can calculate your 3" point blank range, then if all you have is a 100 yard range, just zero to whatever the drop table says you are at 100 yards with that point blank range sight in. Over the years and from experience, most calibers are about 2-2.5" high at 100 for their 3" point blank range.Now, if you know nothin' about this stuff, point blank range is the range at which the bullet will neither be above or below 3" (for a 3" point blank range, used for a deer sized kill zone). IOW, if you zero the gun for its optimum point blank range, you can just hold on the deer all the way out to that range and you don't have to worry about drop or hold over, just aim and shoot. If you zero the gun at 100 yards like a lot of hunters do, fine in the woods where you're not likely to get a longer shot, and you DO get a longer shot, you're going to have to worry about hold over. Hope that makes sense.
Standard Deviation, without writing out the formula, is the square of the square root of the average deviation divided by N-1 (degrees of freedom), or something like that. Been a while since I took statistics, like 35 years. IOW, it's a measurement of variance, the accuracy of the load. The smaller the number, the less variance of velocity from the mean (average) and the less elevation error you're going to have. A high standard deviation will mean you're going to string your shots vertically. For rifles or handguns, I've found really GREAT SDs are under 20. Anything over 30 is not good. With, say, an SD of 35, you’re going to start to see some shot stringing in elevation.
Now, then, lets say you are loading a marginal caliber for deer hunting, say a 7.62x39, and want to find out what range it falls below the magic 1000 ft lbs. You can do that if you know the mean velocity at the muzzle (or 15 feet in front of it) and run it through an exterior ballistics program, another good use for such info. Heck, I wrote my own exterior ballistics program 25 years ago before computers were common using a Timex Sinclair computer and the BASIC compiler built in to it. That program is quite accurate and does the statistical analysis that PCB1.8 (the free program) doesn't. If I'm serious about the load, I'll go plug in my old Tandy Color 3 computer and run it through my program. I guess I could break down and buy a better program, but actually, I can calculate standard deviation long hand, the math hasn't left my senile old brain yet.
Before chronographs were common, ammo companies would exaggerate claims of performance and there was on way to verify velocities of the load much less work out a drop table. The dedicated reloader/rifleman would just have to take the velocity claims in the manuals on leap of faith. When sighting in, if you wanted to shoot to a 3" point blank range, you needed a 300 yard range and you just burned a lot of powder experimenting. With chronograph info and a decent exterior ballistics program, press a few buttons and BOOM, there's your answer. Think of it as computer modeling the path of the bullet.
A chronograph will tell you the speed of the load and you can infer that you are at safe pressures in Your Rifle (based on published info). If your speeds are consistent you are on the right track… if not you need to work on something…
There are several load programs which will work out the mussel Vel based the mussel – chronograph distance
There are several load programs which will work out the mussel Vel based the mussel – chronograph distance
nvshooter
member
Thanks to all who answered. I live in the desert east of Reno-- I have thousands upon thousands of empty acres on which to shoot, so I can indeed sight for 300 yards and more. I got the answer I wanted: about how to calculate for drop over various distances. I want to shoot 1000 yards; the answer has been provided.
45crittergitter
Member
It's pretty much the ONLY way to stay in the safe pressure range with handloads, short of a pressure gun or strain gage. Forget all about flattened primers, sticky bolt lift, etc.
.38 Special
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I've never used my chronograph to calculate trajectories, as I believe there are too many variables: if you want to know trajectory, you have to fire at those ranges to get valid info.
Having said that, I would be pretty unhappy without a chrono; if for nothing else than to know for a fact exactly how fast my handloads are going. Just 'cause the manual says 1300 FPS with XX grains of H110, doesn't mean you're within 200 FPS of that figure...
Having said that, I would be pretty unhappy without a chrono; if for nothing else than to know for a fact exactly how fast my handloads are going. Just 'cause the manual says 1300 FPS with XX grains of H110, doesn't mean you're within 200 FPS of that figure...
MCgunner
Member
double post
MCgunner
Member
TWO variables is too many? Muzzle velocity and ballistic coefficient are the only two you need input. Sure, air density (affected by temperature, altitude, and relative humidity) has some influence, but not enough to through you much off until you get way out there. You might be off a few inches at 1000 yards, but the calculations get you pretty danged close. There are better programs that you can input air density parameters, but I'm happy with PCB1.8, the freebee.
It's amazing how accurate calculated drop tables are, actually. Within hunting ranges, you might as well say they're spot on. Mainly what I use the tables for is to determine such things as effective range, point blank range for hunting purposes for a load.
.38 Special
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My experience has shown that air density can indeed play an important role. Moreover, ballistic coefficient is a misleading number unless you have performed the calculations yourself. Not only are manufacturer's numbers inconsistent with other manufacturer's numbers -- as they are mostly using different methods to derive those numbers, and doing their testing in widely varying conditions -- but also tend to include a bit of blue sky, as they know folks are comparison shopping.
I maintain that the only way to know what your bullets are doing is to shoot them at the ranges you are curious about.
< edit > I will admit that the tables can be pretty accurate at normal hunting ranges. But then, drop with normal cartridges at normal hunting ranges is a few inches. I fail to see the need for a computer to instruct us as to exactly how many inches, considering that our rifles are going to give us this information the first time we take them to the range. I do believe that computed drop tables could be of some use if we are plinking or target shooting at extreme long range, except for the fact that those nasty variables come into play at extreme long range and again, we won't really know until we've actually done the shooting.
Short version: chronographs are fun tools for enthusiasts who like to weigh themselves down with information. And yes, I sort of fit that category, although I'm getting lazier and lazier as I age. But as for importance or true usefulness? Well...
And as always, YMMV!
I maintain that the only way to know what your bullets are doing is to shoot them at the ranges you are curious about.
< edit > I will admit that the tables can be pretty accurate at normal hunting ranges. But then, drop with normal cartridges at normal hunting ranges is a few inches. I fail to see the need for a computer to instruct us as to exactly how many inches, considering that our rifles are going to give us this information the first time we take them to the range. I do believe that computed drop tables could be of some use if we are plinking or target shooting at extreme long range, except for the fact that those nasty variables come into play at extreme long range and again, we won't really know until we've actually done the shooting.
Short version: chronographs are fun tools for enthusiasts who like to weigh themselves down with information. And yes, I sort of fit that category, although I'm getting lazier and lazier as I age. But as for importance or true usefulness? Well...
And as always, YMMV!
MCgunner
Member
I've tested my drop tables out to 500 yards and found no more than an inch or two variance. That works for me. I'm not a 1000 yard shooter and don't have anywhere to try a 1000 yard shot, so they may be a bit more off that far out, I don't know. Bullets are dropping like a rock at that range. Accuracy does indeed depend on the accuracy of the input data and I am at sea level where the tables correlate.
I agree that out to 350 or 400 yards, most good calibers are pretty similar, but I wouldn't know that first hand if I hadn't dabbled in the tables for several calibers. Anymore, I'm more interested in remaining energy at range for some marginal calibers for hunting than getting drop tables, usually, things like 150 grain Sierra Game King in a 12" contender. I am getting 960 ft lbs at 200 yards, makes the gun a 200 yard deer gun for me. Factory flat points ain't even close. Also, 3" above zero at 100 yards gives about 4" below IIRC at 200, so pretty close to a 200 yard PBR. I zero at 3" high at 100 yards with that gun. I wouldn't know all this about that gun if I hadn't run the ballistics program on it.
I agree that out to 350 or 400 yards, most good calibers are pretty similar, but I wouldn't know that first hand if I hadn't dabbled in the tables for several calibers. Anymore, I'm more interested in remaining energy at range for some marginal calibers for hunting than getting drop tables, usually, things like 150 grain Sierra Game King in a 12" contender. I am getting 960 ft lbs at 200 yards, makes the gun a 200 yard deer gun for me. Factory flat points ain't even close. Also, 3" above zero at 100 yards gives about 4" below IIRC at 200, so pretty close to a 200 yard PBR. I zero at 3" high at 100 yards with that gun. I wouldn't know all this about that gun if I hadn't run the ballistics program on it.
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