How Do You Use a Chronograph to Develop a Load?
- Thread starter skeeljc
- Start date
Dusty Stevens
Shiner
Find the load that shoots best the chronograph it. Then as the temp changes keep it shooting that speed
Fast14riot
Gold $$ Contributor
The target develops your load, the chronograph tells you how fast its it's going. I'm not a fan of the popular 10 shot load development with a chronograph method. My 260AI had nearly a linear velocity increase, but the node was easy to find based on a round robin OCW test on paper.
I don't always use one because small groups have little to do with speed.
But...there's lots to learn from them. I like to know speed but I also like to know how the load will react to temps. So, I look for speed at different temps and I want to know the value of a tenth of a grain at different temps. IOW,I want to know the speed at shoots best, and the speeds at .3 increments and how temp affects it at those increments...ofyen, powders that are very predictable at normal temps become volatile at temp extremes.
Knowing where plateaus are and if they hold up at higher pressures and in extreme temps helps prevent surprises.
Powders contain x amount of energy at y temps. Sometimes the relationship is somewhat linear and sometimes not. Avoiding surprises is a big deal from both an accuracy and a safety standpoint.
Bottom line, they mean very little to shooting a small group but provide good info to keeping it tuned.
Beyond all of that, particularly if I'm dealing with a cartridge I'm not very familiar with, I start by tuning to a general velocity.
But...there's lots to learn from them. I like to know speed but I also like to know how the load will react to temps. So, I look for speed at different temps and I want to know the value of a tenth of a grain at different temps. IOW,I want to know the speed at shoots best, and the speeds at .3 increments and how temp affects it at those increments...ofyen, powders that are very predictable at normal temps become volatile at temp extremes.
Knowing where plateaus are and if they hold up at higher pressures and in extreme temps helps prevent surprises.
Powders contain x amount of energy at y temps. Sometimes the relationship is somewhat linear and sometimes not. Avoiding surprises is a big deal from both an accuracy and a safety standpoint.
Bottom line, they mean very little to shooting a small group but provide good info to keeping it tuned.
Beyond all of that, particularly if I'm dealing with a cartridge I'm not very familiar with, I start by tuning to a general velocity.
Last edited:
Sending rounds down range without running them through a chronograph is a waste of powder and bullets, in my opinion. I shoot far longer ranges than 100 yd groups. If you don’t know the speed and extreme spread you can’t come up with reliable ballistic tables! If you are going to shoot, you might as well know how fast it’s going, even if you don’t really care.
BP
BP
Sounds a lot like wind flags. Never shoot without them. Its a waste of bullets and powder. If you're gonna miss, ya might as well know why you did!
When developing a load, the only thing the chrono really helps with is in telling you how consistent you're loading the cartridges. That consistency involves things like accurate powder measuring, neck tension, seating depth or even some other cartridge tuning elements. If you find your reloading is getting low SD's and ES's, then the rest is about finding the load for getting into your barrel's accuracy node and that's best measured on paper.
Once you've found a load that's giving you accuracy and precision, the numbers from your chronograph provides for loads will help when shooting at various distances by feeding that data into a ballistic calculator for correct elevation and windage.
PS: OH, there is one other way I use my chrono along the lines of load development and that's like when I might use a different powder, I'll take the chrono data and see what the app QuickLoad suggests for a load to get a similar velocity. That's puts me in the ballpark and saves a little time and expense for the development process.
Last edited:
I like to look at ES (extreme spread) and SD (standard deviation). When I get low numbers I feel that indicates a greater consistency in my load.
From what I understand, when a barrel is broken in, velocity of a given load may increase.
From what I understand, when a barrel is broken in, velocity of a given load may increase.
Personally, I develope the load first....then chronograph. As far as the chrono telling you when the barrel is BROKE IN, I believe a barrel takes few shots to brake in, speeding up is another story. Some barrels will speed up what may appear to do it twice. It's either that or they hadn't completely finished picking up speed, and where chronographed to soon.
Last edited:
Ned Ludd
Silver $$ Contributor
Velocity data is simply more information you can measure and obtain about the properties of a load. Nothing more, nothing less. Its value depends, to some extent, on the specific discipline. For example, you can have some pretty wide velocity variance at 100 yd and never have an issue. But at 1000 yd, the same velocity variance will kill you.
Sure, it is absolutely possible to develop a good load without any velocity data, simply by looking at the groups on the target. Nonetheless, velocity data can be useful information, particularly with regard to the consistency/repeatability of your reloading techniques/practices. For that reason, it can often be a good troubleshooting tool. The bottom line for me is that I own a chronograph, why not use it? I may not ever need to look at the velocity data, but if I don't actually record it, I can't ever look at it. It takes very little extra effort, so I do it.
Sure, it is absolutely possible to develop a good load without any velocity data, simply by looking at the groups on the target. Nonetheless, velocity data can be useful information, particularly with regard to the consistency/repeatability of your reloading techniques/practices. For that reason, it can often be a good troubleshooting tool. The bottom line for me is that I own a chronograph, why not use it? I may not ever need to look at the velocity data, but if I don't actually record it, I can't ever look at it. It takes very little extra effort, so I do it.
Here is how I do it. I have been using a chronograph for about 30+ years. Before I get a new barrel I gather as much info as possible about the cartridge I have decided on. I will have a pretty good idea of not only the bullet I plan on using, I also know IN ADVANCE approximately the velocity I plan on obtaining. I choose a powder that I THINK will get me there. Then I start loading at what I THINK may be a "starting" load and run 30 rounds down the bore CHRONOGRAPHING that velocity. This gives me a "baseline" velocity to work from. Knowing that most barrels "speed up" about 25-60f.p.s. average, I start "preliminary" load development based on my baseline velocities. If my "target" is say 2875 to 2915, I will slowly work towards that direction. As the barrel speeds up it does not go INSTANTLY from one velocity to another. It goes up gradually and usually has some "speed spikes" along the way. Once I get a load that looks decent, I will shoot a match to put a lot of bullets down the bore. This generally "settles" the barrel down as far as "speed up" goes. Then I will go back out with a chronograph and "tweak" the load with a "seating depth ladder" and finally a primer test. By the time I am finished I will have a load that shoots somewhere from say an average of 0.750 to 1.125 inches at 330 yards. The velocity will be somewhere in my target range with E.S.s somewhere in the single digit to about 12f.p.s. spread over 25 shots. The chronograph will tell you quickly if the powder you have initially chosen is either too fast or too slow. EXAMPLE: My 7mm Sherman Short Mag was to shoot 184 Bergers. Based on previous experience with .284 Shehanes, I THOUGHT H4350 would be a GREAT powder. The chrono told me it was TOO FAST of a powder. My target was about 2885 to 2920 based on experience and research. I could NOT get to 2880 without a "sticky" bolt lift and the groups showed it. The velocity showed around 2860 and accuracy was not very good. I went to H4831sc. That got me the velocity I wanted and the accuracy was good. I shot a match with it BUT during the match I got 2 "where did that come from flyers"! I went to H1000 and life became good. With H1000 I started my development over as at the beginning. I finally was running 2910 with great accuracy and my E.S.s were right at 9-12 f.p.s. spread. This is how I use a chrono for load development.
okie
Gold $$ Contributor
ok. thanks
Forum Boss
Administrator
I consider a load with more than 15 fps ES (Extreme Spread) for five shots to be OK, but needs improvement. If ES is 20+ I consider that unacceptable. With a good barrel and good brass, 5-shot ES approaching 10 fps is possible. If you have a high ES, look at your neck tension, primer selection, bullet seating consistency, brass quality, die fit. I do think it makes sense to use a chrono when load developing, if you are shooting at 400 yards and beyond. One important advantage of the chrono is it tells you if your reloading methods are good or bad.
The first question I ask someone seeking help for loading is "what is your ES"? If I hear "25-30 fps", I know they are doing some key thing wrong, and my suggestions may not be relevant until they get the basics straight.
The first question I ask someone seeking help for loading is "what is your ES"? If I hear "25-30 fps", I know they are doing some key thing wrong, and my suggestions may not be relevant until they get the basics straight.
Would you say all center fire calibers/cartridges are equal in their ability to get low ES's . . . say like 10 fps?
If yes, are some calibers just more difficult to do so?
Last edited:
normmatzen
Banned
Gunsandgunsmith,
There are two prominent resonances in a barrel. There are a bunch of secondary resonances also, but the two primary ones we can easily attack!
The longitudinal resonance is like an organ pipe and is a function of length and speed of sound in the barrel material. The weight of the barrel and the tuner are second order for this resonance. When the load is set right, the explosion causes a slight bulge to propagate down the barrel. When this "bulge" reaches the muzzle, the phase inverts as the end of the barrel is open so a slightly pinched ring propagates back down the barrel. When the load is tuned correctly, any load causing a slightly higher velocity will be slowed down by the "pinch" and any slightly higher Mv will be sped up by the effect of the "bulge". The net result is that the barrel will self correct for slight errors in Mv.
As most of us have found out, there is no first order connection between low ES in velocity with respect to accuracy. But, with a better ES we can do a better job in tuning the barrel.
The other resonance is a vertical cantilever whip motion (but slight). This resonance can be tuned by adding weight to the end of the barrel causing the whip frequency to change slightly. Now, we want to tune the vertical resonance to a frequency that will point the barrel up slightly for bullets that are slightly slow like aiming a little higher for a slower bullet. And, conversely, aiming down a bit for faster bullets to compensate for a slight rise in impact point. At longer ranges, this is commonly called positive compensation.
Of course this compensation affected by the tuner is sensitive to temp. changes as well as air density. Then us crazies can vary the tuner settings slightly as a function of at least temperature and Density Altitude for some of us hard core nuts!
There are two prominent resonances in a barrel. There are a bunch of secondary resonances also, but the two primary ones we can easily attack!
The longitudinal resonance is like an organ pipe and is a function of length and speed of sound in the barrel material. The weight of the barrel and the tuner are second order for this resonance. When the load is set right, the explosion causes a slight bulge to propagate down the barrel. When this "bulge" reaches the muzzle, the phase inverts as the end of the barrel is open so a slightly pinched ring propagates back down the barrel. When the load is tuned correctly, any load causing a slightly higher velocity will be slowed down by the "pinch" and any slightly higher Mv will be sped up by the effect of the "bulge". The net result is that the barrel will self correct for slight errors in Mv.
As most of us have found out, there is no first order connection between low ES in velocity with respect to accuracy. But, with a better ES we can do a better job in tuning the barrel.
The other resonance is a vertical cantilever whip motion (but slight). This resonance can be tuned by adding weight to the end of the barrel causing the whip frequency to change slightly. Now, we want to tune the vertical resonance to a frequency that will point the barrel up slightly for bullets that are slightly slow like aiming a little higher for a slower bullet. And, conversely, aiming down a bit for faster bullets to compensate for a slight rise in impact point. At longer ranges, this is commonly called positive compensation.
Of course this compensation affected by the tuner is sensitive to temp. changes as well as air density. Then us crazies can vary the tuner settings slightly as a function of at least temperature and Density Altitude for some of us hard core nuts!
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.