What affects .22LR match ammo bullet trajectroy?

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grauhanen

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Muzzle velocity variation for .22LR ammo is considered a very important component of the eventual POI downrange because faster and slower rounds will have vertical spread.

To illustrate, a ballistics calculator shows that for every 10fps difference between two rounds results in a vertical spread of about .25" at 100 yards and a full inch at 200. As a result, a 40 fps difference in MV between two rounds gives an inch of vertical at 100 yards and four at 200.

If wind is completely excluded as a factor, and considering only the ammo itself, what other factors, if any, can influence the flight of a .22LR bullet?
 
There is heat rise over the longer distances. It’s the varying up\down air currents with the air changes over greater distances. Kind of why there is a heat haze when looking through the scope
 
Weight differences between each bullet.
I also wondered if the lube being shed in flight had an effect.
 
How many have tried wiping the lube off Eley match grades and checked the differences?

I tried it with nothing more than poorer results.

Shedding the lube in flight would be similar to the claims that centerfire bullets with lead tips are less accurate as the lead melts away in flight.

While testing veloities in CCI MiniMags, with consistent velocity, three shots in about 1/2" at 100 yards. A drop of about 30 fps on #4 was about 3/4" low and #5 dropped event more fore a 1.75" group.
 
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As far as tips melting in flight, well thats a fact and not a myth. Proven with dopler and high speed photography. I could post the link but not required as its old news. But we are talking centerfire rounds and not rimfire, The cleaning off of lube resulted in drastic accuracy loss with both cotton cloth wiping and isopropyl alcohol wiping. Hint, leave well enough alone . Eley,Lapua and RWS know way more than we do,PERIOD. How would the bullet lube be shed in flight with a rimfire going at rimfire speed? Just curious.
 
A rimfire bullet is spinning at something like 50 000 rpm. One might wonder if that would fling off a lot of lube but recovered bullets usually have quite a bit left. Differences in lube from one round to the next could influence interior ballistics.
I'd agree that it's pretty difficult for the average shooter to come up with anything the manufacturer hasn't investigated but you never know.

Humidity and temperature affect air density and has an effect on the trajectory.
 
I agree:
"Humidity and temperature affect air density and has an effect on the trajectory." to quote VV.
Then throw in wind which is the one thing where most concentration is required.
 
One thing I will add that I feel shooting a 22 LR beyond 50 yards all bets are off. At 50 yards with 3 wind flags and a rifle that is honest you have the chance of hitting the X ring every time. The limiting factors are a flyer from the pack, a quick switch in condition that you miss or bad gun handling. Honest rifles are just that honest. I do not care what anyone says, a winning rimfire is built by a builder who understands rimfire. I will make a lot of unhappy people here but if I were to have a BR capable rimfire built it would not be Canadian made. No one shoots full blown hardcore BR matches in Canada. Attend a hardcore 50 yard match and your eyes may be opened up. JMO
 
cycbb486 said:
One thing I will add that I feel shooting a 22 LR beyond 50 yards all bets are off. At 50 yards with 3 wind flags and a rifle that is honest you have the chance of hitting the X ring every time. The limiting factors are a flyer from the pack, a quick switch in condition that you miss or bad gun handling. Honest rifles are just that honest. I do not care what anyone says, a winning rimfire is built by a builder who understands rimfire. I will make a lot of unhappy people here but if I were to have a BR capable rimfire built it would not be Canadian made. No one shoots full blown hardcore BR matches in Canada. Attend a hardcore 50 yard match and your eyes may be opened up. JMO
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you know that, and I know that.....and a few other guys know that....but we also know that they shoot a match with 4 or 5 lots of ammo on their bench and they watch the temperature and humidity and change lot numbers to match the conditions, 90% of canadians don't understand, and or wish not to believe the lot to lot variances and what they can do to your accuracy.....we have fewer purchasing options, and canadian retailers don't sell enough volume to care to understand what we know, so you get what they have, and they don't bend over to check lot numbers or secure enough of a lot number of series of to cater to our expensive needs........you can move your tuner a click or two and try to adjust the gun to the condition, but it's no where near the same as changing lot numbers
 
Yes, we are at a massive disadvantage compared to our American counterparts. Trying to order a small quantity of multiple lots of ammo is like pulling teeth with some vendors. Fortunately there are a couple that will happily do it.

In the last 4 years I’ve tested 15 to 20 different lots/brands and have managed to get 1 lot to stand out from all the others. To show up at a match with multiple lots to compete with would be a dream. The fall off from my match lot to the others is quite steep.
 
If wind is completely excluded as a factor, and considering only the ammo itself, what other factors, if any, can influence the flight of a .22LR bullet?

If it's accepted that .22LR match bullets may have unpredictable trajectories, the question is: why do some.22LR match bullets have unpredictable trajectories while others don't?

It's known that unpredictable trajectories happen even in testing tunnels, where wind or air movement is as irrelevant as is possible.
The unpredictableness occurs in different humidity levels and different temperatures and is not related to "heat haze".
It is not related to some rounds shedding lube more or less than others. (The lube is shed inside the barrel.) It is not related to any melting of .22LR bullets in flight.

As flyr suggests, it can be related to different bullet diameters, because individual bullets can vary in that regard. But that's not the only or main cause.
 
I take it that we're talking about shooting from a competition quality rifle that 'likes' the ammo being used and the barrel is warm and hasn't been cleaned between shots. In that case, what seriously affects the bullet trajectory out of my rifles is the loose nut behind the trigger, which is to say me.
 
rim to driving band and rim thickness attribute all sorts of variables to where the bullet will land on a target, these are 2 sorting techniques that few if any put into place. I have a target on the wall with 3 groups that are under .24 inches, however they are in different locations of the target and when overlaid they create a group of just over 1/2 inch, the only difference in the ammo in the 3 groups is rim thickness, 39,40, and 41 thou rim thickness had a significant impact on where the bullet landed on the target. all 3 groups were shot in a custom rifle in a make shift indoor range made of 3 discarded 53 foot reefer trailers. spending a lot of time to sort SK Rifle match and figuring out what parameters of +/- tolerances of the ammo and how to match those to my chamber/rifle actually had it shooting better then the best unsorted lt number of Eley Match ammo, the biggest variable is where a bullet lands on target all starts with how the cartridge fits in the chamber
 
yodave said:
rim to driving band and rim thickness attribute all sorts of variables to where the bullet will land on a target, these are 2 sorting techniques that few if any put into place. I have a target on the wall with 3 groups that are under .24 inches, however they are in different locations of the target and when overlaid they create a group of just over 1/2 inch, the only difference in the ammo in the 3 groups is rim thickness, 39,40, and 41 thou rim thickness had a significant impact on where the bullet landed on the target. all 3 groups were shot in a custom rifle in a make shift indoor range made of 3 discarded 53 foot reefer trailers. spending a lot of time to sort SK Rifle match and figuring out what parameters of +/- tolerances of the ammo and how to match those to my chamber/rifle actually had it shooting better then the best unsorted lt number of Eley Match ammo, the biggest variable is where a bullet lands on target all starts with how the cartridge fits in the chamber
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In my experience that's all true once you have a good-enough rifle, and don't forget the crimp on the brass or lack thereof.
 
grauhanen said:
If wind is completely excluded as a factor, and considering only the ammo itself, what other factors, if any, can influence the flight of a .22LR bullet?

IMO there are several issues at play. The priming compound serves a dual purpose as ignitor and propellant due to the small amount of powder charge. So, consistency of amount and uniform placement of priming compound is important assuming the rifle has a strong and consistent firing pin strike. Then, bullet heels. Bullet heels need to be uniformly perfect. Crimp needs to be uniform and consistent as well.
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Many shooters who have tracked MV and POI have noted that there isn't always a relationship between a round's MV and where it strikes the target relative to other rounds. I observed this first hand when I first tried out a chronograph while shooting .22LR at 57 yards last summer. (See https://www.canadiangunnutz.com/forum/showthread.php/2174793-More-to-ammo-behaviour-than-MV)

I also observed this behaviour when chronographing shots at 100 yards in October during a period when several hours each morning were as calm as can be imagined.

Depending on the ammo lot used, sometimes MV and POI were in harmony. The same lot of ammo, with two different rifles, usually produced targets such as these. The MV information is included on each and the results are as might be expected.

In general, no rounds in the examples below (but a few over the course of many other ten shot groups) were significant "outliers". The ammo was the best performing lot of Lapua Center X I've had the pleasure of using. This lot of ammo had most rounds performing as expected.

 
flyr said:
Weight differences between each bullet.
I also wondered if the lube being shed in flight had an effect.
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Bullet weight has nothing to do with the trajectory unless the bullet weight changes also changes the BC. A 150gr .308 bullet with the same BC as a 75gr .224 bullet and fired at the same velocity have identical trajectories when all other parameters are the same.
 
But not all lots of CX ammo perform well.

In the examples below, some had rounds with POI matching MV. But there were slower rounds with higher POI than expected; and some faster rounds had a lower POI than others of similar MV.

Group size appears not to suffer (based on limited data), but bullets don't always go where expected.



Even a the one lot of X-Act, Lapua's top tier ammo, produced results where MV and POI matched.



When I shot a poor lot of CX or SK Rifle Match ammo, the difference between MV and POI was more stark. Not only did more rounds not strike where their MV might have predicted but group sizes were much larger. In other words, more unpredictability of POI meant larger groups.

 
muzzle velocity doesn't effect trajectory near as much as people think, I've played with centerfires that have a 10 shot spread of 3 FPS but print over a 2 inch group at 100 yards, bullet shape and length has more effect then speed
 
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