Reasons To Chronograph Your Loads

[otisrush]

As a data geek I figure I'll be getting a chronograph at some point. It seems like yet another toy that would make things fun.

Nevada Ed in the Barrel Length thread made an interesting comment: "and as mention in a lot of post, maximum FPS is not always the most accurate out of a weapon." I thought I'd start a new thread rather than hijack the other.

I've wondered why people recommend using a chronograph.
* I've gotten the impression there is a belief that the fastest speed gives the greatest accuracy. Intuitively I didn't think that was the case but don't know for sure. And Ed's comment brings up that point specifically.
* I think I've read that muzzle velocity is an objective way of telling if pressures are getting too high. Is that the case? (I think I've concluded that things like primer flow and such are not necessarily good indicators of high pressure.)

Any comments/education I'd very much appreciate.

OR

 

[old&slow]

A Chrono can be a very useful tool.
I use mine to figure 'Power Factor'. USPSA power factor is bullet weight times velocity ,, 165,000 for major & 125,000 for minor.

I use the velocity , bullet BC, etc. to figure bullet drop / trajectory for long range rifle shooting.

Figure velocity with different barrel lengths, e.g. a load in my 3" .357 revolver is 1240 fps. ,, same load in my 16" rifle is 1675 fps.

My 9mm load, in my auto runs about 970 fps. but only about 853 fps. out of my S&W 929 revolver..

Interesting piece of equipment ,, worth having..

 

[AzShooter]

I use the chrono to test loads for velocity and use Standard Deviation as a test of accuracy although it doesn't tell the whole story. I chrono and then I test for groups.

Shooting in ICORE (Intenational Confederation of Revolver Enthusiats) where the minimum power factor is 120 I try to maintain a 130 pf with all my different loads.

I just chronoed 10 different loads with 6 different bullets and now I know what my gun likes and what groups best.

If you change components it's good to look back on your data to come up with a proper load.

 

[OKFC05]

I think I've read that muzzle velocity is an objective way of telling if pressures are getting too high. Is that the case?

Well, yes and no. I can put in a faster powder by mistake and blow it up with excessive pressure before reaching the MV I was expecting.
There is not a one-to-one correlation.

However, if you use the chrono to check the actual MV against the MV you expected, you will find some guns faster than others due to tolerances. If the MV is much higher, that is a caution that something is amiss with the pressures.

If you use the chrono readings as an excuse to exceed recommended limits, you first irrefutable pressure sign may be flying parts.

 

[rwsmith]

It's one of the very few variables..

It's one of the very few variables that we can pin down with relatively inexpensive equipment. Now if we could just get PRESSURE equipment.....

I proposed a ways back wondering if a pressure test could be manufactured inexpensively enough for some of our more enthusiastic enthusiasts to buy and use. It doesn't seem unreasonable.

The firing mechanism and the barrel shouldn't be much more expensive than a gun. Make them interchangeable, like a Thompson Center gun.

A barrel/chamber with a breech lock and firing mechanism on a base hooked up with pressure transducers going to an electronic readout. I'll have to look at the SAAMI test protocol and see if there's a big deal about it.

 

[fredj338]

I've been using a chrono so long I can remember foil screens. They are very useful when reloading to chart where you are & where you want to be.
All things being equal in a given load, vel = pressure. So swapping a single component out will show up in a vel change. This can indicate a change in pressures. Useful info when swapping say primers or diff bullet shapes of the same weight.
Also knowing the vel can be helpful in determining drop & wind deflection for rifles. It's a must if you gun game & need a specific min power factor. The only real downside to a chrono is finding out that factory ammo rarely gives vel advertised, or that your fav wiz bang stick has a slow bbl compared to data in a manual. Just don't get too hung up the numbers. Std dev is nice when it's low, but never garauntees accuracy.

 

[Twoboxer]

Those shooting under Power Factor (mass, vel, bullet diameter) rules obviously want to know the speed of their loads before they are tested at a match.

During load development:

Its useful to have velocities not only to determine how consistent your load is (SD) but also to help explain an odd shot.

MV is useful to determine your own external ballistics. It's also useful in determining the effect of a component swap and may help determine what other adjustments (if any) need be made to compensate.

In many cases velocity is a surrogate for (or at least an indication of) pressure.

There are times you will increase powder charge and your chrono will not show a velocity increase. This is useful to know in load development and may be an indication that you are approaching or have reached the point of over-pressure.

 

[Nevada Ed]

I did well loading for 45 years without a chrony.................

However the chrony does let you know what your loads are doing in the fps department.......
that also lets you know the energy and the drop of your bullet if you have the BC that is usually listed........
but not always accurate, if you look at Sierra, Speer and..... you get my point.... ( mine is better than yours )

As a starter a 55gr SP flat base in my 22-250 will hit 2750 with SR4759 and 3,000 with 4895 and max out at 3600 fps with w748 with lee way for Nevada's summer heat.

A 100 degree Antelope load for the .270 with a 130gr BT does 2700 fps with IMR4831 with minimal pressures and little meat destruction. A factory 3130 fps can be achieved with IMR 4350 if needed.

In my 1903 bolt action I can get the 150 ball to 2590 with 4895 and max it out to 2880 with 4350 for a standard loading. With the 180 gr all purpose bullet, a nice light "Krag" loading at 2430 fps or 2660 fps load is possible with IMR 4350, just depends on the recoil that you want that rifle to beat you with.

A 2" J frame snub nose with a 158gr LRN can shoot a "Mouse phart" load at only 572 fps with Trail Boos or you can move up to a 6" and push this bullet at 1024 fps with Blue Dot in the 38 special case.

Don't forget the little 3.5" C9 that I have......
A 115gr plated can get down to 984 with Red Dot or max it out to 1263 fps with Unique.
A 115gr G Dot at 1208 or a 124 G Dot at 1192 all with Unique in the little short barrel, with data listed, approved, loads.

I would not know all this wonderful stuff, without a chrony........
Did I need to know all this info..................... ?

That's another story.

 

[rsrocket1]

It's one of the very few variables that we can pin down with relatively inexpensive equipment. Now if we could just get PRESSURE equipment.....

I proposed a ways back wondering if a pressure test could be manufactured inexpensively enough for some of our more enthusiastic enthusiasts to buy and use. It doesn't seem unreasonable.

The firing mechanism and the barrel shouldn't be much more expensive than a gun. Make them interchangeable, like a Thompson Center gun.

A barrel/chamber with a breech lock and firing mechanism on a base hooked up with pressure transducers going to an electronic readout. I'll have to look at the SAAMI test protocol and see if there's a big deal about it.

You can get Pressure Trace for about $760 or the wireless version for $500 and attach strain gauges on your gun or pistol. The problem is that you need to calibrate it with a known load, then compare the trace readings based on the known load. Of course the "known load" can be different if your chamber or barrel is significantly different from the industry standard but it might be close enough so that as long as you give for instance a 10% cushion, you'd be safe.

 

[Forrest r]

Chronographs will also tell you if your cast bullets are the correct size. They will also tell you if your using the correct alloy for your cast bullets.

They will also tell you when a powder/load is maxed out. It's not uncommon to work up loads using the ladder method and have a diminished return when the loads are maxed out.

Diminished return example:
A load for a 6" bbl'd 357 using a 158gr cast swc.
A 7.5gr load produced 1150fps
A 8.0gr load produced 1210fps
A 8.5gr load produced 1250fps
A max load of 9.0gr produced 1260fps

A chronorgaph will also aid in figuring out the bullets rpm.
A chronograph will also pick up on ignition issues with a firearm.
Chronographs aid in figuring out when a bullet goes transonic.



Was playing around with the setup pictured above (22lr) shooting standing silhouettes. Every time I went out the turkeys were wipping my behind. Finely a lightbulb lit up & I broke out the chronograph. Turned out the ammo I was using to practice with was going transonic between the 70yd and 80yd line.

 

[swamprabbit]

I use my chrono to give me and idea of how well my loading process is progressing. Coupled with accuracy it helps me find the sweet spot for a load. If I reach a spot where the load is not moving up in velocity much with an increase in powder charge weight I know there is probably not much benefit to increasing charge weight from that point. That's one example of many.

 

[AveragEd]

I've never done much chronographing of handgun ammunition. The targets usually are close enough that I don't need anything but the group on the paper to tell me if a load is going to deliver the level of accuracy I desire and I no longer shoot in competition so power factors and such are not a concern. To me, it's all about accuracy and cleanliness. But with rifles, it is an all different story as the shooter can have a lot of unintended influence on group sizes so you need something to help you determine what may have caused a bad group.

Enter the chronograph's velocity deviation readings. Generally speaking, a recipe that yields low shot-to-shot velocity deviation numbers has the potential to be accurate so when I test a load and the group isn't what I hoped for but the numbers are good, I will certainly try it again as I may have caused that inaccuracy. On the other hand, if the deviation is high, I write that recipe off.

Having said that, I do have two rifles that shoot near one-hole or true one-hole groups with slightly ugly deviation numbers and one that consistently shoots a particular load poorly in spite of single-digit deviation so nothing's set in stone in this game. In that second instance, bullet stabilization is likely the problem as they sure are leaving the muzzle at a consistent speed. But it's fun to see what your ammo is doing.

You don't need a more costly chronograph for our purposes. I've made that mistake twice - once with a Pact and again with a CED M2 - and now only reply on my $99 ProChrono digital. They even have a remote communication link you plug into the chronograph that sends the data for each shot and string of shots, including ambient temperature and barometric pressure, to your smart phone via an app. It's all any of us "hobby ballistics guys" need.

Ed

 

[125JHP]

If your trying to duplicate a factory load (velocity wise), the chrony will help there too.

 

[chief38]

Originally I purchased a Chronograph for reloading information but shortly thereafter started chronographing Factory SD & CCW ammo. You will be amazed how most of the specs quoted for Factory ammo is quite misleading. The ONLY Company that I have NEVER found misleading or inaccurate is Buffalo Bore - their posted numbers are 100% accurate! Speer's Gold Dots are at least in the truthful ball park. Buy a Chronograph and you will see for yourself. A very useful shooting tool!

 

[Gamecock]

Assumptions about pressure derived from a machine that gives velocity are all in the mind of the observer.

 

[BB57]

I've used a chronograph for about the last 20 years.

Getting consistent results requires you to understand how it works and to set it up properly - far enough in front of the muzzle, and on a stable enough tripod or support to prevent it from getting moved around by muzzle blast, and properly aligned so that the bullet goes across the center of each sensor, rather than angling across them (which increases distance and results in a low velocity error).

A properly set up chronograph will allow you to determine average velocity as well as the extreme spread in velocity and the standard deviation in velocity. Roughly speaking the extreme spread will be covered by +/- 3 SD in velocity, so a load with an SD of 10 fps will have an extreme spread of about 60 fps, while a load with an SD of 30 fps will have an extreme spread of about 180 fps.

The increased consistency of a low SD load is an asset to longer range accuracy, as the trajectories of each bullet will be more consistent at longer range. Those differences however won't often show up on a 100 yard target however, so having the velocity data is a great qualitative measure. In effect, if I have two loads of similar velocity that both give me a total of three five shot 3/4 MOA groups at 100 yards, but one load has an SD of 12 fps for the 15 shot total and the other has an SD of 26 fps, I'll take the 12 fps load. In fact, I'd take the 12 fps load even if it was slightly less accurate and tweak the powder charge slightly to see if I can find a slightly more accurate velocity.

That's another area where a chronograph can help. Most rifles will have a sweet spot in velocity for a particular bullet weight and style due to the harmonics of the barrel as it vibrates during firing. Doing a ladder test across a wide range in velocity will help you identify more accurate loads, but with a chronograph you can see the velocities where those accuracy nodes occur. Once you know that, finding that sweet spot (or sweet spots) with another powder is much more straight forward.

A chronograph will also highlight differences in primers. for example, in general I've noted that a WSR primer will yield a slightly higher velocity and a much larger SD in an accurate load in a small cartridge than a CCI 400 primer.

It will allow you to quantify the effects of different head stamps in brass. The .22 Hornet for example has a wide range of internal volume based on brand with Hornady being on the low end of the range, and Remington being on the high end, with higher and lower velocities respectively. Having a chronograph will allow you to tailor the loads to give the same velocity across different head stamps.

If you are a long range precision rifle shooter, knowing the mean velocity and the SD are critical to increasing the probability of a first round hit, as well as "truing up" your ballistic calculator results. Even if you are a casual hunter, you need good velocity data to get meaningful results out of a ballistic table, calculator or app.

Perhaps most importantly, a chronograph will help you determine that the load is doing what it is supposed to do. If you are getting wildly different than expected results, than you need to suspect and look for the cause.

Monitoring trends in SD can tell you when you've reached an upper or lower limit. For example, pressure spikes can be a problem with some powders in reduced loads, and as you reduce the load you'll see a sharp increase in SD in your chronograph data. In some cases, you'll also see an increase in SD as you increase the load beyond a certain point, due to the effects of decreased efficiency in a given barrel length or issues with the pressure curve.

It will also tell you about individual differences in firearms. For example, a PP series pistol in either .32 ACP or .380 ACP has tighter chamber than the FEG AP and APK series pistols (which are based on the PP series), resulting in a velocity difference of about 50 fps.

 

[jtcarm]

IDK why anyone would think max velocity = max accuracy. Maybe it's the notion that best accuracy is attained when the case is completely filled. That's also not necessarily true. Anyway, I don't recall seeing many people express this idea.

I just started running a chrono for many of the same reasons other folks state, but primarily because the the array of components available today are absolutely dizzying. There is lab-developed data available for only a tiny fraction of the combinations.

 

[fredj338]

I've never done much chronographing of handgun ammunition. The targets usually are close enough that I don't need anything but the group on the paper to tell me if a load is going to deliver the level of accuracy I desire and I no longer shoot in competition so power factors and such are not a concern. To me, it's all about accuracy and cleanliness. But with rifles, it is an all different story as the shooter can have a lot of unintended influence on group sizes so you need something to help you determine what may have caused a bad group.

Enter the chronograph's velocity deviation readings. Generally speaking, a recipe that yields low shot-to-shot velocity deviation numbers has the potential to be accurate so when I test a load and the group isn't what I hoped for but the numbers are good, I will certainly try it again as I may have caused that inaccuracy. On the other hand, if the deviation is high, I write that recipe off.

Having said that, I do have two rifles that shoot near one-hole or true one-hole groups with slightly ugly deviation numbers and one that consistently shoots a particular load poorly in spite of single-digit deviation so nothing's set in stone in this game. In that second instance, bullet stabilization is likely the problem as they sure are leaving the muzzle at a consistent speed. But it's fun to see what your ammo is doing.

You don't need a more costly chronograph for our purposes. I've made that mistake twice - once with a Pact and again with a CED M2 - and now only reply on my $99 ProChrono digital. They even have a remote communication link you plug into the chronograph that sends the data for each shot and string of shots, including ambient temperature and barometric pressure, to your smart phone via an app. It's all any of us "hobby ballistics guys" need.

Ed

Std deviation doesn't tell the entire story on accurate loads, especially at distances under 100yds, especially with handguns. It's about bbl harmonics. So while low SD #s are nice, paper groups are the final word. I shoot for groups over a Chrono. I note the numbers but certainly won't toss a load out that groups well because of mediocre numbers.

 

[fredj338]

IDK why anyone would think max velocity = max accuracy. Maybe it's the notion that best accuracy is attained when the case is completely filled. That's also not necessarily true. Anyway, I don't recall seeing many people express this idea.

I just started running a chrono for many of the same reasons other folks state, but primarily because the the array of components available today are absolutely dizzying. There is lab-developed data available for only a tiny fraction of the combinations.

Depends a lot on caliber. Over bore magnums often group better closer to max Ime. Part of this is 100% load density with slower powders. They want that for better combustion. Could you get better accuracy backing your 7mag down to 7-08 vel, faster powder, maybe, but then why not just get the 7-08 & run that? So it just depends.

 

[Bkreutz]

I chrono my ammo to make major power factor (bullet weight x speed) for USPSA competition. First I aim for around 170PF (165 is minimum) then I'll adjust powder for best accuracy. My current load is a 124gr at 1380fps which gives me a 171 PF. If I go faster the grouping opens up, and I don't want to get any slower because chronos aren't always consistent and I don't want to get caught on a slow chrono at a match (or variation due to altitude or temperature) Failing to make the 165 PF drops my scoring into the minor range for that match. Not what I want after traveling, hotel cost, restaurant bills, and match fees.