barrel length

[Tony K Harper]

Hi Tony

Do you see any correlation between the amount of velocity drop and the initial velocity?

Regards
Graham

I’m not sure exactly what you are asking. But let me just say this . If you have two lots of ammo that after shooting 50 rounds the average velocity is say 1075fps. Many times one lot will show a greater average drop in velocity. Most of the time it will be small but enough that you can run the test three times and one will always have more loss of velocity than the other. You don’t often get two lot numbers to test that the average velocity is the same. That is why I have to average averages to determine the differences.
TKH

 

[jpx2rk]

Landy,

Thanks for your reply. It really explains why ammo lot numbers can shoot so differently.

Here is another thing I believe, but can't prove.

Many times when I test ammo, I test by shooting through two chronographs. One at the muzzle, and one just in front of the target.

After narrowing down the lot numbers to the point I can't tell which is better I use the numbers from the two chronographs as a determiner. I do a little math (poor mans math) when I average averages. ( I know, my math teacher told me to never do this.)

But I want to see which ammo looses the most velocity between the two points. I figure the one that looses the less is flying truer. It is only slight but it makes me feel better before I write the check for cases of ammo.

Yea, I've bought a lot of crap ammo, but I've bought some good stuff too!!

BTW: When I can I still prefer to shoot slower ammo on winder days, and faster on less windy days.

You are absolutely right. We need to discuss tuners.

Another subject I suspect a lot about, but know very little.

I think it was Marty that coined the phrase " that is not tuning, that is just getting the rifle to shoot"

TKH

Tony;

Could you expand on your preference to shoot slower ammo on winder days and faster on less windy days?? It seems like just the opposite would be better.

 

[Tony K Harper]

jpx2rk,

This is one of many things about rimfire and slow moving lead bullets that is different from centerfire jacketed fast movers. We shoot match .22lr rimfires below the speed of sound. Hunting rounds that actually break the sound barrier never shoot as accurate. The worse condition is a bullet that goes through the speed of sound leaving the barrel and then slows below the speed of sound before reaching the target.

But getting to your question: a 10 mph wind blowing at 90 degrees across the range will move a .22lr round 1 inch. ( you will also get lift or fall depending on the side the wind is coming from but that is another whole subject).

Take my above statement as a given and remember the wind rarely blows exactly 90 degrees across the range so you are always going to have a fudge factor.

A round traveling faster will blow off POA more than a slower round shot in the same condition. The slower round is more predictable. You often get ammo lots (speeds) that seem to buck wind to a point and then just a little more wind gives you a lot more push than you expected. Those are the shots that kill you.

I can't back up what I'm saying with controlled experiments, you may have a different experience.

But this is my belief and I'm sticking to it.

Supersonic spire pointed rounds buck the wind much better, centerfire shooters prefer faster moving rounds in those same wind conditions.

It can be fun watching really good centerfire shooters start shooting rimfire. Most of their knowledge and skills transfer but not all of them.
TKH

 

[VLNBYR]

jpx2rk,

This is one of many things about rimfire and slow moving lead bullets that is different from centerfire jacketed fast movers. We shoot match .22lr rimfires below the speed of sound. Hunting rounds that actually break the sound barrier never shoot as accurate. The worse condition is a bullet that goes through the speed of sound leaving the barrel and then slows below the speed of sound before reaching the target.

But getting to your question: a 10 mph wind blowing at 90 degrees across the range will move a .22lr round 1 inch. ( you will also get lift or fall depending on the side the wind is coming from but that is another whole subject).

Take my above statement as a given and remember the wind rarely blows exactly 90 degrees across the range so you are always going to have a fudge factor.

A round traveling faster will blow off POA more than a slower round shot in the same condition. The slower round is more predictable. You often get ammo lots (speeds) that seem to buck wind to a point and then just a little more wind gives you a lot more push than you expected. Those are the shots that kill you.

I can't back up what I'm saying with controlled experiments, you may have a different experience.

But this is my belief and I'm sticking to it.

Supersonic spire pointed rounds buck the wind much better, centerfire shooters prefer faster moving rounds in those same wind conditions.

It can be fun watching really good centerfire shooters start shooting rimfire. Most of their knowledge and skills transfer but not all of them.
TKH

Tony...You can back this up. Numerous studies and experiments over many years all show a slower bullet is less affected by wind. Somewhere around 980 f/s is optimal if I remember correctly.

 

[HuskerP7M8]

I'd like to make a few more comments but a bunch of stuff came up this morning that'll take the rest of my day to sort through.
Landy

 

[jpx2rk]

Tony;

Thanks for the reply. I'll have to get some slower speed "stuff" and see what happens for me. Is there a particular wind speed (or approximate speed) that seems to make the most difference and warrants a change in ammo speed for that day/conditions?? TIA

 

[Tony K Harper]

No, at least that I know of.

Wind is never constant. Sometimes you can get a steady blow that will give you a predictable push on the bullet but it normally doesn't last long. You have to be flexible and move your point of aim constantly.
I can't remember the last time I held the same point of aim on a complete target.
Shooting a rimfire at 50 yards without wind flags is like shooting blind.

The art of shooting rimfire at 50 yards is just that, an art.

Shooting at 100 yards plus is a whole different thing. There is so much going on over the longer distances you are nearly always shooting your last shot, meaning where ever the last one got blown, you aim accordingly, and hope the next one gets blown the same.

There may be places and times where there is little to no wind, but not where I do most of my shooting.

TKH

 

[gkgeiger]

When I first started reading this thread I thought, not another barrel length thread. I think every shooting forum has one, but this one has turned into a very informative read. Thanks especially to Tony and Landy.

 

[dellet]

The anomaly of less drift at slower speeds is pretty well documented with black powder and cast bullet shooters. Drift increases from 1300 fps up to about 1700 fps, then stabilizes or decreases. You can see this in most ballistic calculators. JBM has 22 rimfire bullets listed in their library. A 40 grain bullet will have about 1.5-2” less drift at 1000 fps 100 yards than at 1200 fps. in a 10 mph cross wind, depending on zero.

The reasoning has to do with wind effect on the shock wave produced.

So called subsonic ammo is actually trans sonic, so that same shock wave is developing in flight as is turbulence. Bullet shape is key. Just as in early jets that shook to pieces crossing the tran sonic speeds.

For the most part precision air guns shoot below the trans sonic window at less than 1000 fps to avoid this.

Bullets traveling right at the point of breaking that sound barrier 1075-1125 are in the worst possible speed.

A lot of this will show up on target with subsonic centerfire since you can predictably load for certain speed and verify on target what is predicted on paper. It’s very interesting to play with.

 

[HuskerP7M8]

Well I appreciate your input......actually there a a lot of variables in the conversation, I can only speak to my experience testing them, Lot of 52. 40x. Anschutz with 26" plus barrels that perform quite well, I think the pressure curve is equalized better in longer barrels.

Oh Yeah, lots of variables. Another one we could add to what you stated would be reduced muzzle pressure that might be beneficial regarding transitional ballistics, as opposed to internal and external ballistics.

Landy

 

[HuskerP7M8]

Landy,

Thanks for your reply. It really explains why ammo lot numbers can shoot so differently.

Here is another thing I believe, but can't prove.

Many times when I test ammo, I test by shooting through two chronographs. One at the muzzle, and one just in front of the target.

After narrowing down the lot numbers to the point I can't tell which is better I use the numbers from the two chronographs as a determiner. I do a little math (poor mans math) when I average averages. ( I know, my math teacher told me to never do this.)

But I want to see which ammo looses the most velocity between the two points. I figure the one that looses the less is flying truer. It is only slight but it makes me feel better before I write the check for cases of ammo.

Yea, I've bought a lot of crap ammo, but I've bought some good stuff too!!

BTW: When I can I still prefer to shoot slower ammo on winder days, and faster on less windy days.

You are absolutely right. We need to discuss tuners.

Another subject I suspect a lot about, but know very little.

I think it was Marty that coined the phrase " that is not tuning, that is just getting the rifle to shoot"

TKH

Hey Tony,

I'm not sure I've really explained why lot numbers shoot differently, just given maybe one of many possible causes.

I've visited with Ivan Wells a lot over the last few years and he's gone to incredible lengths to identify some possible reasons for the differences in lots, but you can't test it reliably because in most cases you destroy the cartridge while measuring what may be the most important differences. It's a conundrum I've yet to find a solution for yet.

I'm glad you elaborated in a later post regarding how you're using the chronograph because if I hadn't been busy I would have posted that's there's always nearly a perfect correlation to MV vs downrange V and you've accomplished nothing. The correlation is nearly perfect for the two in that the higher MV always results in more V lost downrange. When you reported you did it only when the avg MV's matched each other, it confirmed you hadn't made that mistake.

You and Graham may find this interesting.

It entails an incredible amount of work for me to set-up in my tunnel for calculating drag coefficients and converting them to BC (Ballistic Coefficients) and the last time I did it was in November of 2015.

I did a search for that data and then made the following Excel chart based on 15 lots of mixed pedigree ammo and varying avg V's, with each lot consisting of 20 test shots.

Landy

 

[HuskerP7M8]

Time and again shooting subsonic centerfire, you see one hole 50 yards groups, turn into 6” vertical strings 1” wide at 200 yards. Looking at ballistic calculators you often see 10 fps ES accounting for at least half of that vertical.

As bullet quality drops from match grade to bulk cast, horizontal and vertical dispersion always seems to grow with little tangible explanation other than bullet quality.

Applying precision rimfire and air rifle thinking to centerfire subsonic shooting was a big help in shrinking groups. Being able to use quality bullets at subsonic speeds I think adds substance to many of the things you mention.

Some of the best centerfire subsonic bullets seem to also be ones known to be very stable passing through the trans-sonic speeds at distance. Example being bullets designed for Palma class.

These are just observations on thousands of rounds.

I tend to think we shouldn't experience as much dispersion as you reported unless the bulk jacketed have very poor quality control which is certainly possible. Bulk cast bullets however would likely be a different matter, but I'm stumped concerning why the groups you reported would have so little horizontal dispersion vs vertical, and there's little or no technical literature on the subject, nor have I ever tested beyond 100M.

Based on your comments I'm guessing you're aware of the horror stories associated with the SMK that was originally designed for Olympic 300M competition, and the calamities that occurred when gobs of shooters tried them in Palma and long range CFBR. Even though gyroscopic or rotational stability was adequate, lousy shot distributions and keyholing were the results due to very poor "Dynamic" stability.

So, it may be possible a combination of Cg Offset combined with the "Dynamic", as opposed to the "Gyroscopic" stability, could cause the dispersion you're seeing.

A little more info from previous comments I made:
The non-linear growth in group ES for the 158 samples at the distances of 50M and 100M resulted in a ratio of 2.81. In other words the average growth for a group of 1" at 50M grew to 2.81" at 100M. But, there were actually 14 of the 158 groups where the angular measurements or MOA decreased at 100M. I also saw examples of horizontal strings at 50 turn into vertical strings at 100, but on average, vertical at 50 was much more pronounced at 100.

I'm afraid there's no way to put a cap on a discussion of this nature unless someone is able to build the instrumentation to "statically" or "dynamically" calculate Cg Offsets as Harold Vaughn did and test. Unfortunately, to the best of my knowledge, I'm not aware of anyone who has been successful at that endeavor.

It wouldn't be all that hard with jacketed projectiles, but with RF or cast it not only would be very difficult, it would only be of limited usefulness because the act of obteration of the bullet at ignition as well as it travelling the length of the bore will likely change any characteristics we measured.

This would be a good time to make my usual disclaimers when attempting to discuss subjects that are so much more complex than most realize. I'm self-taught in everything I do regarding ballistics/statistics, and that means I'm more susceptible to making mistakes than the professionals are.

I don't believe anything I read on internet forums and I'm not sure anyone else should either. Unless you have a great deal of experience combined with at least some technical expertise, it's literally impossible to separate the BS from the good stuff.

Landy

 

[Tony K Harper]

Landy,

It is a dull and depressing day here in Pa. Rained nearly all day, then I looked at the charts you put up, they make my head hurt, and I realize there are so many factors that can prevent a bullet from going where it is intended.

Instead of feeling great despair I fall back to one simple and true fact.

Wait for it!

Here it is:

There is always, always, a place somewhere you can point the rifle that will send the bullet to the exact spot you intend it to go. You just have to find that spot for each target you shoot.

This is where you are suppose to laugh!!

TKH

 

[HuskerP7M8]

Landy,

It is a dull and depressing day here in Pa. Rained nearly all day, then I looked at the charts you put up, they make my head hurt, and I realize there are so many factors that can prevent a bullet from going where it is intended.

Instead of feeling great despair I fall back to one simple and true fact.

Wait for it!

Here it is:

There is always, always, a place somewhere you can point the rifle that will send the bullet to the exact spot you intend it to go. You just have to find that spot for each target you shoot.

This is where you are suppose to laugh!!

TKH

Weather has been crappy here in NE also but improved in the last couple of days and I'll have a window to shoot in the tunnel tomorrow to ease the cabin fever.

I'm laughing and grinning like the Cheshire cat, but I'll always feel some despair knowing I'll never figure out all the answers to what we're most curious about.

Maybe I'll turn over a new leaf in life and just wish my bullets to a location on target. Come to think of it, that may work! There's been quite a few time I've accidentally touched the trigger when my hold off wasn't where it should be and still drilled the dot!!!! LOL

Landy

 

[VLNBYR]

I can find that magic spot 100% of the time......"after" I pull the trigger. It's getting it right before the trigger pull that's the hard part.

 

[dellet]

I tend to think we shouldn't experience as much dispersion as you reported unless the bulk jacketed have very poor quality control which is certainly possible. Bulk cast bullets however would likely be a different matter, but I'm stumped concerning why the groups you reported would have so little horizontal dispersion vs vertical, and there's little or no technical literature on the subject, nor have I ever tested beyond 100M.

Based on your comments I'm guessing you're aware of the horror stories associated with the SMK that was originally designed for Olympic 300M competition, and the calamities that occurred when gobs of shooters tried them in Palma and long range CFBR. Even though gyroscopic or rotational stability was adequate, lousy shot distributions and keyholing were the results due to very poor "Dynamic" stability.

So, it may be possible a combination of Cg Offset combined with the "Dynamic", as opposed to the "Gyroscopic" stability, could cause the dispersion you're seeing.

A little more info from previous comments I made:
The non-linear growth in group ES for the 158 samples at the distances of 50M and 100M resulted in a ratio of 2.81. In other words the average growth for a group of 1" at 50M grew to 2.81" at 100M. But, there were actually 14 of the 158 groups where the angular measurements or MOA decreased at 100M. I also saw examples of horizontal strings at 50 turn into vertical strings at 100, but on average, vertical at 50 was much more pronounced at 100.

I'm afraid there's no way to put a cap on a discussion of this nature unless someone is able to build the instrumentation to "statically" or "dynamically" calculate Cg Offsets as Harold Vaughn did and test. Unfortunately, to the best of my knowledge, I'm not aware of anyone who has been successful at that endeavor.

It wouldn't be all that hard with jacketed projectiles, but with RF or cast it not only would be very difficult, it would only be of limited usefulness because the act of obteration of the bullet at ignition as well as it travelling the length of the bore will likely change any characteristics we measured.

This would be a good time to make my usual disclaimers when attempting to discuss subjects that are so much more complex than most realize. I'm self-taught in everything I do regarding ballistics/statistics, and that means I'm more susceptible to making mistakes than the professionals are.

I don't believe anything I read on internet forums and I'm not sure anyone else should either. Unless you have a great deal of experience combined with at least some technical expertise, it's literally impossible to separate the BS from the good stuff.

Landy

The short answer is probably that short distances hide multiple errors that compound at distance.

If you look at numbers for a reasonable quality bullet like a 208 AMax, put in what ever parameters you like for conditions. Then check velocity for drop at 990/1000 and 1090/1100 interesting patterns start to show that are basically repeatable and can be confirmed reasonably well with live fire, the best of my ability and equipment.

208 Amax with a 50 yard zero to see drop at 200 yards

990 fps 51.2"
1000 fps 50.2"
1090 fps 42.2"
1100 fps 41.5"

So with this particular bullet with 10 fps difference in velocity, drop can be from 3/4-1" depending on the velocity window, but a full 10" at 100 fps. The difference in drift will only be .1" with no cross wind and less than .25" with a 10 mph cross wind.

Different bullets have more or less vertical, but less horizontal than vertical is typical.

Stability forces that may pull it left or right, seem to have a larger effect on velocity/drop than horizontal is my best guess. I have never had a chronograph set at 200 yards to get that info.

I have ran numbers where 10 fps was good for about 1 MOA and confirmed that at distance, so stating that half of a 6" string was due to a 10 fps ES was a stretch. It would need to be closer to 25+ with this bullet.

Again these are my observations.