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  #31  
Old 10-09-2021, 11:54 PM
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Nope, still not seeing it 2many.
MV spread is caused mostly by variations in the primer and powder.
The peak velocity for each shot determines the amount of spread.
Coefficient of friction of the barrel determines rate of velocity loss.
It will apply to all bullets fired through that barrel.
Standard Deviation is a mathmatical formula based on the velocity of each shot relative to the average of all.
Only way to achieve what I think you're describing, is if the coefficient of the barrel
was different for every shot fired. Only way to do that would be to use a different barrel for each shot
predicting the coefficient required for each shot so as to compensate for the varying peak velocities.
I think....

Last edited by jaia; 10-09-2021 at 11:58 PM.
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  #32  
Old 10-10-2021, 12:00 AM
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Take 2 bricks from the same lot. Shoot one out of 16 inch barrel
Take the othe and shoot out a 24 inch barrel.

Same std deviation?
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  #33  
Old 10-10-2021, 12:06 AM
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Nope. Why? I can't obtain the same ES/SD from two different boxes of 50
from the same brick using the same barrel. That chronograph out front documents the results.
Try it for y'erself. Watch those numbers change with every shot. It's rimfire...no two cartridges exactly alike.
Welcome to the random results of the rimfire assembly line lottery.


The only way I can see to prove this is to measure the bullet velocities
inside the barrel and plot the velocity of each bullet vs it's location in the barrel.
See if those curves remain constant, flatten out or intersect.

Landy had some thoughts on the topic last year...

Quote:
HuskerP7M8
Peak pressure occurs when the bullet is barely out of the case and from approximately 6" on, friction in the barrel is increasingly the dominant force on the bullet. At approximately 16" to 18", velocity starts decreasing due to friction.
From a physics standpoint, friction robs the bullet of a given amount of energy per unit length traveled down the barrel. Because the energy of the bullet goes as the velocity squared, slower bullets will slow down quicker than faster bullets and this leads to an increased velocity standard deviation in longer barrels. The testing I've done in my ballistic tunnel using barrels from 6" to 26" in length with nearly 2000 rds of ammo, indicates the sweet spot for minimum velocity standard deviation and velocity ES is in the 8" to 10" range. This testing was done many years ago, but I may be revisiting it in the near future because I currently have a Shilen Octagon barrel that I believe I've shot out after some 25,000 to 30,000 rds. It'll be the perfect candidate for shooting 100 rd samples for every inch I cut off down to 8" or less. There goes another 2000+ rds and a week of work just to satisfy my curiosity! LOL With "TRUE" match ammo (Eley Match/10X, Midas+, R-50) having velocity SD's on average of 6fps to 8fps and shot at 50 yds/meters, an increase in precision has a weak statistical correlation. However, I suspect precision at 100 yds/meters and beyond should provide for a much stronger correlation to precision. Landy

Last edited by jaia; 10-10-2021 at 12:26 AM.
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  #34  
Old 10-10-2021, 12:45 AM
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Barrel used to be longer for a couple of reasons, sight radius with iron sights and barrel weight to help steady offhand holding. Unless you go back further, it was needed for black powder burn time.

Two things are speculated about long barrels, which may not be fact: number one, that the weight of the longer barrel helps to resist whatever muzzle flip there is from the small recoil of a rimfire round, and number two, by reducing the remaining gas pressures at the muzzle, thereby reducing any steering of the bullet by the gases acting upon flaws of the bullet base. A 28" barrel could be more accurate IF this theory holds water. I haven't really researched it much, there might be lots of information around that I haven't read. It has also been said that idea number one isn't so as a shorter barrel is stiffer, and stiffer is more important than weight.

Certain ammunition is loaded with slower burning powders to get more velocity, for example CCI Velocitors, so shorter barrels will cut velocity from typical sporter length barrels of 22'' to 24''. Probably not enough to care about in the field. I've not seen test data of Velocitors comparing 16-1/2" vs 24" barrels, much less something like a 28" barrel.
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  #35  
Old 10-10-2021, 08:31 AM
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One negative (I guess) with a longer barrel:

Going from 18in to 27in means that post primer strike you must hold rifle "still" 50% longer
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  #36  
Old 10-10-2021, 08:47 AM
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I've always found it curious that manufacturers of different length barrels don't provide any information on why you should select one over another.

Perhaps some do, and I've just never seen it.
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  #37  
Old 10-10-2021, 08:58 AM
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Quote:
Originally Posted by eflyguy View Post
I've always found it curious that manufacturers of different length barrels don't provide any information on why you should select one over another.

Perhaps some do, and I've just never seen it.
To CZs credit they do with the 457 Jaguar

"for those who love Iron Sights. The 28.6 inch barrel provides a long sight radius"
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  #38  
Old 10-10-2021, 10:15 AM
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Quote:
Originally Posted by DrGunner View Post
Quote:
Originally Posted by carbineone View Post
Kinda on the same subject..I want to get a good chronograph..But good bet expensive<img src="https://www.rimfirecentral.com/forums/images/smilies/smile.gif" border="0" alt="" title="Smilie" class="inlineimg" />

I would like to know what the 17HM2 bullet is doing out of my 28 Inch barrel..
Quote:
Originally Posted by StephenBachiler View Post
Your testing in 50 at 200 should have told me that...was not thinking...Is the 100 buck caldwell crony worth it? Or should I look the another way?

LabRadar
In that price range, listen to jaia. CE’s Pro Chrono line, like his PAL offers great utility at an affordable price. Pass on the Caldwell.

If you’re going to get a chrony, BUY ONCE! I did a BUNCH of research into them last year because I needed to pick up a good one for working up the best pellets and slugs to use in my PCP air rifles. Utility and features should be at the top of the list - I bought a Competition Electronics Pro Chrono DLX. It is Bluetooth compatible with my iPhone, and can track data and run average and extreme spread over multiple shot strings. It has a generous shooting area with good sensitivity. You’ll also want to budget for a decent camera tripod to mount it on, as positioning is not as easy as you think... best to set up rifle and rest, then line the chrony up in a way to get good data without shooting the chrony. I’m not joking, it happens all the time.

The Pro Chrono DLX is $129 @ Brownells. I got mine on sale for $99.

https://www.brownells.com/shooting-a...10070301008005

DrGunner
The more I think about cronographs...the more i think I don't need one. With all the work Jiai has done with his crono work on 50 at 200..why do I? He has tested and shown ES spreads for nearly all .22lr rounds. While those ES spreads might vary by lot number...they give you a general idea of where each ammo ranks. If I where doing Centerfire load development I could see the need.
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  #39  
Old 10-10-2021, 10:15 AM
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I did some chrony testing several years ago. Several brands of ammo and rifles.
to sum it up my 28" 40X barrel; was the fastest
Next fastest was the 540XR
Then the 16" chipmunk
Then other brand rifles.
This was with all makes of ammo tested

This is just some of the info from my testing.
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  #40  
Old 10-10-2021, 10:17 AM
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Quote:
Originally Posted by jpickar View Post
I did some chrony testing several years ago. Several brands of ammo and rifles.
to sum it up my 28" 40X barrel; was the fastest
Next fastest was the 540XR
Then the 16" chipmunk
Then other brand rifles.
This was with all makes of ammo tested

This is just some of the info from my testing.
I did not see those results coming!!!? Wow...so you found FASTER fps?

I guess it kinda makes sense...think about it...while the powder might be burned up by 16 inches, the bullet is still in the barrel and the gasses still in a confined area. So while the projectile might be decelerating from its high velocity, at say 18 inches, it is STILL. Accelerating generally from is stand still speed of "zero" in the chamber

Last edited by StephenBachiler; 10-10-2021 at 10:22 AM.
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  #41  
Old 10-10-2021, 11:10 AM
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Quote:
Originally Posted by StephenBachiler View Post
I did not see those results coming!!!? Wow...so you found FASTER fps?

I guess it kinda makes sense...think about it...while the powder might be burned up by 16 inches, the bullet is still in the barrel and the gasses still in a confined area. So while the projectile might be decelerating from its high velocity, at say 18 inches, it is STILL. Accelerating generally from is stand still speed of "zero" in the chamber
Kinda nice when somebody posts hard facts instead of parroting what they read on the internet isn't it.
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  #42  
Old 10-10-2021, 08:02 PM
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Quote:
Originally Posted by StephenBachiler View Post
The more I think about cronographs...the more i think I don't need one. With all the work Jiai has done with his crono work on 50 at 200..why do I? He has tested and shown ES spreads for nearly all .22lr rounds. While those ES spreads might vary by lot number...they give you a general idea of where each ammo ranks. If I where doing Centerfire load development I could see the need.
Iíve found mine to be very useful. Using someone elseís data has its pitfalls, since itís not representative of YOUR rifle and the ammo YOU use.

Mine has been particularly useful in analyzing the lots of GOOD ammo I run across.
Running it through the chrony has helped me to identify the best muzzle velocities and ES in the ammo Iím shooting through MY rifles. When I find a lot that really WORKS, I know what to look for next time.

Itís also a VERY useful tool when tuning PCP air rifles with different pellet and slug weights.

DrGunner
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  #43  
Old 10-10-2021, 08:14 PM
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%%%%, these kinds of posts always make my head hurt.
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  #44  
Old 10-10-2021, 08:19 PM
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When shooting at a fixed distance, it shouldn't matter whether the average MV is a little faster or a little slower. If anything, slower is better as it drifts a bit less in the wind.

In any case, two barrels of the same length may easily have different average MVs with the same lots of ammo. I have two rifles of the same make with barrels that are exactly the length. One always shoots the same lots of ammo a little faster -- about 20 - 30 fps faster -- than the other.
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  #45  
Old 10-10-2021, 09:36 PM
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%%%%, these kinds of posts always make my head hurt.

Mine too!
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