Managing Muzzle Velocity

[DocUSMCRetired]

Hey everyone,

I just wanted to give you all a couple things to think about. MV is often thought about as a simpler task than it really is. Because of this it is often managed or measured incorrectly. So here are a couple pointers to help you manage it better:

1) Chronographs do not measure Muzzle Velocity. They measure velocity at their location. Even a MagnetoSpeed measures the velocity about 1/2 to 1 foot away from the Muzzle. In order for the velocity you have to actually be a Muzzle Velocity you need to back calculate the true number. There is one device on the market that I know of which does this calculation for you. The Lab Radar. The V0 displayed on the Lab Radar is an algorithm that does this math for you. Here is the math on this one: http://www.appliedballisticsllc.com/Articles/ABDOC121_VelocityDecay.pdf

2) The quality of your chronograph. This one is critical. If you are using anything other than a MagnetoSpeed, Lab Radar, or Oehler 88 on an 8 to 12 foot rail odds are you have an unreliable device. Here is a free article about that: http://www.appliedballisticsllc.com/Articles/ChronographChapter.pdf (This was performed before the Lab Radar Existed).

3) The MV on the bullet box is not a reliable source of information. Well that is unless they provide you with the test conditions, exact rifle information etc... at the time of testing. Please do not use this as a reference point, research point, and especially in a ballistic calculator for trajectory prediction. Here is a short article on that: http://appliedballisticsllc.com/Articles/Why you cannot trust the MV on the Box.pdf

4) Last but not least, MV Variation for Temp Variation. All gun powders have different variations of temperature stability. What this means is that your Muzzle Velocity will change anywhere from 0.2 to 3 fps per degree of temperature change. Powders with very poor stability could change 30 FPS over just 10 degrees of temperature change. Powders with solid stability might only change 3 fps over 10 degrees. But they will ALL change. Not to get in to the chemistry of it all, but you need to test your favorite load at a minimum of 3 different temperatures at least 20 degrees Fahrenheit apart.

It is important if you are a long range shooter to understand these principles and manage them. Managing them is pretty easy with the right equipment and good notes.

 

[hdwhit]

Thanks for that. And while it is probably relevant to the "five shots, one hole" shooters, for the vast majority of shooters using rifles inside of 200 meters and handguns inside of 25 meters, the difference between MV measured at the muzzle or six feet away from it is insignificant. And the "accuracy" of my chronograph is of less interest to me than whether or not it is showing results with a consistent error. I use my chronograph to ensure that my loads are consistent enough to have the same point of impact from batch to batch and so far my Shooting Chrony has consistently delivered those results. Shooters should understand what it is they are asking their equipment to do and spend their money accordingly. Not everyone needs a Lab Radar. Given the type of shooting I do, I would prefer to have a $130 chronograph, a new rifle, and set of reloading dies for the same money I would spend on something like a Lab Radar.

 

[Offfhand]

I just wanted to give you all a couple things to think about.

Is all this something you just heard about and checking out to see if it's really true? (Sorry, couldn't resist.)

 

[Sunray]

Muzzle velocity, like a recipe, is a guide line.
"...about 1/2 to 1 foot away from the muzzle..." There will be a big, blast of gases and air moving out then back in really fast. Chronographs are usually 10 feet or more from the muzzle for that reason. Chronographs don't really tell you much that's useful anyway.

 

[jmr40]

All technically true, but also basically irrelevant.

The difference between velocity at 10' where it is measured with most chronographs and the true MV will be in single digits. Maybe even in fractions of 1 fps.

For most people a chronograph with an accuracy of +/- 50 fps is close enough, and I've found most $100 units to be far more accurate than that. They have been tested side by side with the high end units and the accuracy is very close, within 10-15 fps most of the time. The difference is that the cheaper units often need ideal conditions to work. At times you simply get no reading, or one that doesn't make sense. When they work, which is most of the time, they are quite accurate. When they don't work you'll know it. It isn't like they will give you a false reading that looks like it could be reasonable, but ends up dangerous.

ALL of my hand loads are right in line with the numbers published in load manuals. Most of the factory loads I've tested are right on the money. There are exceptions and some are off quite a bit. Nothing wrong with that, but having a chronograph lets me know which are correct and which are not. The main purpose of my chronograph is to let me know when my hand loads are approaching max pressure. If the speed I'm getting is within 50 fps of what is expected from a max load in my manual then I know it is time to proceed with caution, or stop altogether.

Figuring out bullet drops using chronograph data is secondary. But even if the numbers I get are off by 50 fps or even more I'll be close enough to be on paper at any range I'll shoot. My current 308 load shooting 178 ELDX bullets shows just over 2600 fps on my chronograph. Even if it is 50 fps optimistic the drop at 500 yards is only 2 1/2" more. I can't see 2 1/2" at 500 yards. So far I've only shot that load to 300 yards, but my drops are right on the money with what the charts say. I certainly wouldn't expect to start shooting at 1000 yards and have the drops perfectly in line with the computed ballistics calculations. But they should be pretty close and only need minor adjustment.

Temperature CAN make a difference depending on the powder chosen. I tend to prefer temp resistant powders for this reason and will never see more than about 30-50 fps difference from 110 down to -20. Even with non temp resistant powders you won't see enough difference to matter except in truly extreme conditions.

Most of the stuff in the links provided deal more with user error in setting up their chronograph wrong than with any issues with the equipment.

 

[MistWolf]

There will be a big, blast of gases and air moving out then back in really fast

Source?

 

[taliv]

Even if it is 50 fps optimistic the drop at 500 yards is only 2 1/2" more. I can't see 2 1/2" at 500 yards.

it matters when you're shooting targets that are 3" wide at 500 yards. it matters for larger targets too because it decreases your probability of hitting

"for most people" who never shoot past 25 yards, it doesn't matter at all. i think it's pretty clear doc knows where the handloading forum is and didn't accidentally post that in rifle country. serious precision rifle shooters whoexpects first round hits at unknown distance, use a chronograph to calculate drop.

 

[Casefull]

it matters when you're shooting targets that are 3" wide at 500 yards. it matters for larger targets too because it decreases your probability of hitting "for most people" who never shoot past 25 yards, it doesn't matter at all. i think it's pretty clear doc knows where the handloading forum is and didn't accidentally post that in rifle country. serious precision rifle shooters whoexpects first round hits at unknown distance, use a chronograph to calculate drop.

 

[MEHavey]

Chronographs don't really tell you much that's useful anyway.

Other than a particular listed load for my 98Krag was producing velocities 300fps over spec (and over QL)... and should be dropped immediately after 1st round.

Naaaaaa, not much useful there.

 

[DocUSMCRetired]

It is true it can be said, that some of this may not be "necessary" for some shooters. Especially those who rarely shoot benchrest or past 100 yards. I don't really need a chronograph for my 30-30 with irons on it. 100 yard deer are a chip shot in that aspect.

However, it is good to know. It is also good to always practice the highest level of your sport if you can. Maybe one day a shooter wants to excel to the next level. To start competing, and to start shooting at a much higher level. Having the right knowledge in the back of your head is always good. Or at least having that "answer on the tip of your tongue" so you go back and look for it again when the time is right.

I placed this here for a reason, so that others can learn. It is always best to have the right information, even if you don't plan on taking things to the highest level of accuracy. But for those who are just starting to stretch their legs, it can certainly help to get started on the right foot.

 

[MachIVshooter]

All technically true, but also basically irrelevant.

My thoughts as well. The variables you can't control or account for at extreme range have orders of magnitude more effect than 10 or 15 FPS fluctuation in MV. Yes, the long range shooter should control for all that he can, but this group often makes a storm in a teacup about some of the minutiae. And if you're going to go into such pedantic detail about minute changes in velocity, you should not fail to mention how altitude will affect; at 7,000 ft, bullets hold velocity better, and you get another 100 FPS before the bullet goes transonic compared to shooting at sea level. That matters a lot more than calculating velocity loss in the 10-15' from muzzle to chronograph or changes due to ambient temp.

 

[DocUSMCRetired]

My thoughts as well. The variables you can't control or account for at extreme range have orders of magnitude more effect than 10 or 15 FPS fluctuation in MV. Yes, the long range shooter should control for all that he can, but this group often makes a storm in a teacup about some of the minutiae. And if you're going to go into such pedantic detail about minute changes in velocity, you should not fail to mention how altitude will affect; at 7,000 ft, bullets hold velocity better, and you get another 100 FPS before the bullet goes transonic compared to shooting at sea level. That matters a lot more than calculating velocity loss in the 10-15' from muzzle to chronograph or changes due to ambient temp.

The effects of Drag in flight, and Muzzle Velocity are easily two separate topics. however if you have a SD above 10fps and plan on being competitive at LR or ELR you might have some trouble. An SD of more than 10 will give you a larger than 1 MOA spread at 1000 yards.

 

[MachIVshooter]

The effects of Drag in flight, and Muzzle Velocity are easily two separate topics. however if you have a SD above 10fps and plan on being competitive at LR or ELR you might have some trouble. An SD of more than 10 will give you a larger than 1 MOA spread at 1000 yards.

Separate discussions in theory perhaps, but inseparable in practice. Point being, you decided to post (without prefacing a reason one might care at all) about an aspect of precision shooting that has far less impact on precision than all of that which you didn't mention one bit. It would make more sense if you were doing a series of such posts pertaining to LR shooting of which this were one, but it comes across more as a random musing, and one that is of dubious value to the extreme majority of this board. I shoot varmints at long range, and a few degrees change in shot angle or a couple MPH in down range crosswind make a lot more difference than my MV SD. Yeah, I neck size, weigh bullets & cases, trickle the powder charge and all that jazz for the most consistent loads possible, but all of that makes no difference if you don't/can't account for down range conditions. We don't get wind flags out there.

 

[DocUSMCRetired]

Separate discussions in theory perhaps, but inseparable in practice. Point being, you decided to post (without prefacing a reason one might care at all) about an aspect of precision shooting that has far less impact on precision than all of that which you didn't mention one bit. It would make more sense if you were doing a series of such posts pertaining to LR shooting of which this were one, but it comes across more as a random musing, and one that is of dubious value to the extreme majority of this board. I shoot varmints at long range, and a few degrees change in shot angle or a couple MPH in down range crosswind make a lot more difference than my MV SD. Yeah, I neck size, weigh bullets & cases, trickle the powder charge and all that jazz for the most consistent loads possible, but all of that makes no difference if you don't/can't account for down range conditions. We don't get wind flags out there.

You assume this is the last post that I will make with the idea of helping to pass along knowledge to the shooter by saying "if you were doing a series of posts". Who is to say that I am not going to share more information down the line? This is actually one of many posts I have made on here sharing variants of information.

This is simply one aspect of shooting, one that is good to understand.

The idea is to help share knowledge, and help users better understand or replace bad information that has been shared on the forums and through other outlets. Its simply knowledge, there to have if you want it and to ignore if you don't. It never hurts to learn. This topic is not about other down range variables, those will be covered in other topics. I like that you find this has no value to this board, I would say let those who want to learn decide if it has value to them or not.

 

[horsey300]

Separate discussions in theory perhaps, but inseparable in practice. Point being, you decided to post (without prefacing a reason one might care at all) about an aspect of precision shooting that has far less impact on precision than all of that which you didn't mention one bit. It would make more sense if you were doing a series of such posts pertaining to LR shooting of which this were one, but it comes across more as a random musing, and one that is of dubious value to the extreme majority of this board. I shoot varmints at long range, and a few degrees change in shot angle or a couple MPH in down range crosswind...........We don't get wind flags out there.

Yes we do, if their hair is fully ruffled we're talking 15+mph, and after the first shot, the dissipation rate of the dust cloud provides the rest of your info!

 

[Demi-human]

I have always appreciated your posting, here and elsewhere. I must admit some of it goes over my head. (Or maybe straight though.) None the less it gives me more to think about, which is not a terrible thing. I have placed my savage F/TR on the back burner since acquiring some choice pistols, but as you can see I am reading here now. Thank you very kindly for the information.

 

[MachIVshooter]

You assume this is the last post that I will make with the idea of helping to pass along knowledge to the shooter by saying "if you were doing a series of posts". Who is to say that I am not going to share more information down the line? This is actually one of many posts I have made on here sharing variants of information.

This is simply one aspect of shooting, one that is good to understand.

The idea is to help share knowledge, and help users better understand or replace bad information that has been shared on the forums and through other outlets. Its simply knowledge, there to have if you want it and to ignore if you don't. It never hurts to learn. This topic is not about other down range variables, those will be covered in other topics. I like that you find this has no value to this board, I would say let those who want to learn decide if it has value to them or not.

Why not say so? "Hey guys, this is another thread in a series I'm doing to help folks with long range shooting". If you had prefaced with that, you wouldn't be dealing with those of us who don't see much value in this information as a stand alone. That's my point. It's not that it isn't good information, but rather that it's scope of utility is pretty limited, and for those not especially interested in the intricacies of LR/ELR shooting, it feels like we've had our time wasted in reading something that we thought might be important but come to realize isn't for our purposes, ergo the dismissive attitude.

 

[taliv]

MachIV, I'm struggling to understand your beef. The title of the thread is muzzle velocity. it's not about wind or position or bullet construction or anything else. Bickering about that seems pointless.

 

[MtnCreek]

Thanks for posting DocUSMC. This is likely one of the small variables that have frustrated me. Enter all the "knowns" and still be a little off at distance.

 

[MCMXI]

I find Doc's posts interesting, helpful and depressing all at the same time! But then I see what taliv is doing on a regular basis and it gives me hope again that those of us who don't have access to the tools and individuals that the AB team does can still utilize a sound methodical approach to obtain a fairly high first round hit rate on sub moa targets out to 1,500 yards. Knowledge is power and we should be soaking this stuff up and thinking about what we're doing. Keep it up Doc!

 

[Varminterror]

A guy brings doughnuts to work one morning then gets called an ******* for not bringing Danishes and milk too...

I personally don't devalue the process of trying my MV's, as it indeed does have a substantial impact upon performance - it's far from irrelevant or insignificant. I shoot in matches and hunt in multiple states, spanning sometimes 100•F and 5,000+ feet in elevation from one shot taken with a rifle to another shot within the season. The density altitude difference makes a huge difference, but the MV differential between late season coyotes in Minnesota vs. early season in Kansas or late season hogs in TX isn't without consequence. Even at a paltry 400-600yrds I can have a swing of 6" in POI shift - which is unacceptable when you're talking about placement on prairie dogs or coyote vitals, or even hogs for that matter.

MV and BC truing, including thermal effects upon internal ballistics, are critical components of LR and ELR shooting, in my experience - important spokes in the wagon wheel of a ballistic solution. Aerodynamics aren't solely dependent upon environment, the substrate, but are also such upon the projectile and the position. Reading accurate wind, density altitude, and range - especially angle compensated range - is easier today than ever before, as is truing your BC and MV with some of the improved equipment on the market, but ALL OF IT has to come together to reliably deliver hits on target.

 

[taliv]

Scott's ELR PRS match in Wyoming was this past weekend. According to him, there were 163 rounds in the match that added up to 166,175 yards or 94.4 miles of bullet flight. Average shot distance was 1019 yards. And "many shooters were above 70% and a whole boatload were 60-70%" in 25-35mph winds.

That doesn't translate to first round hits cause I'm sure there were several targets that you'd shoot 3 times at or something. But it's still indicative of how shooters are getting a LOT better.

my personal thoughts on the OP's stuff are

1. half a foot away doesn't matter for me. it's good enough well past the effective range of any caliber i own.
2. agree, except I don't like the lab radar either. it's super cool, but everyone i know who has one misses shots all the time.
3. agree, but this shouldn't be news to anyone at all
4. agree. not sure what powder is 3 fps difference per degree. that would suck for sure. R17 is widely regarded as extremely temp sensitive and is about 1.7 fps in my 260AI. As long as you put that into your calculator, no big deal. hard to imagine what powder is worse.

what is missing from OP's post are the following:

5. MV changes with barrel life and it's different per caliber. over MANY barrels, the curve on my 260AI looks nothing like my 6.5x47L. So you probably need to track it
6. It also changes based on how many rounds it's been since you cleaned
7. and it can change in field conditions in ways that are unpredictable to me if you get water or sand or dust etc in your chamber

 

[Danoobie]

I've always understood it's just a general approximation of actual MV,
and barrel length and a few other factors are going to have an influence
on this ballpark figure.

 

[DocUSMCRetired]

Scott's ELR PRS match in Wyoming was this past weekend. According to him, there were 163 rounds in the match that added up to 166,175 yards or 94.4 miles of bullet flight. Average shot distance was 1019 yards. And "many shooters were above 70% and a whole boatload were 60-70%" in 25-35mph winds.

That doesn't translate to first round hits cause I'm sure there were several targets that you'd shoot 3 times at or something. But it's still indicative of how shooters are getting a LOT better.

my personal thoughts on the OP's stuff are

1. half a foot away doesn't matter for me. it's good enough well past the effective range of any caliber i own.
2. agree, except I don't like the lab radar either. it's super cool, but everyone i know who has one misses shots all the time.
3. agree, but this shouldn't be news to anyone at all
4. agree. not sure what powder is 3 fps difference per degree. that would suck for sure. R17 is widely regarded as extremely temp sensitive and is about 1.7 fps in my 260AI. As long as you put that into your calculator, no big deal. hard to imagine what powder is worse.

what is missing from OP's post are the following:

5. MV changes with barrel life and it's different per caliber. over MANY barrels, the curve on my 260AI looks nothing like my 6.5x47L. So you probably need to track it
6. It also changes based on how many rounds it's been since you cleaned
7. and it can change in field conditions in ways that are unpredictable to me if you get water or sand or dust etc in your chamber

We have 5, 6, and 7 in the works. We actually have some good data on one particular cartridge + powder as to how many fps per shot it speeds up. Kind of an interesting set of data.