Which has higher velocity? Rifled or Smooth bore...

[roundball]

Chronograph tested PRB velocities between two new GM .62cal barrels:
One a GM Flint smoothbore.
One a GM Flint smoothbore that had been rifled.
With everything being as identical as possible, same day at the range, etc...the rifled bore gave a higher average velocity of 28 fps.

GM .62cal/.20ga Flint ”˜Rifled’ barrel
100grns Goex 2F
.020" Oxyoke prelubed pillow ticking
.600"/325grn cast lead balls
Wiped the bore after every shot
Pact Pro Chronograph at 15 feet
Average velocity = 1270 fps
Standard Deviation = 25 fps

GM .62cal/.20ga Flint smoothbore barrel
100grns Goex 2F
.018" Oxyoke prelubed pillow ticking
.600"/325grn cast lead balls
Wiped the bore after every shot
Pact Pro Chronograph at 15 feet
Average velocity = 1242 fps
Standard Deviation = 30 fps

Chronographs take out all the guesswork...an excellent tool for shooting hobbies.

 

[Rifleman1776]

Not enough diff. to be significant, IMHO.
If asked, I will just say 'no difference'.

 

[BrownBear]

Not enough diff. to be significant, IMHO.
If asked, I will just say 'no difference'.

But that runs right up the back of keyboard ballisticians and internet experts.

Heck, one of them is at this moment composing page after page about an ancient formula passed on to him by a mysterious old man, one who deserves all our respect because he was a nice guy and loved his kids. By this "rediscovered" formula, I bet we'll learn that if roundball had only flipped his wads over, there would have been 32fps difference, rather than only 28. :shake:

 

[Va.Manuf.06]

Not enough diff. to be significant, IMHO.
If asked, I will just say 'no difference'.

But that runs right up the back of keyboard ballisticians and internet experts.

Heck, one of them is at this moment composing page after page about an ancient formula passed on to him by a mysterious old man, one who deserves all our respect because he was a nice guy and loved his kids. By this "rediscovered" formula, I bet we'll learn that if roundball had only flipped his wads over, there would have been 32fps difference, rather than only 28. :shake:

Or not. "Troll" baiting doesn't always work after all....... :rotf:

 

[roundball]

There has always been a couple schools of thought on this:
1) A smoothbore would be faster from no rifling resistance slowing down the payload;
2) A rifled bore would be faster because indeed the rifling tends to hold back the projectile allowing gas pressure to build higher;

My chronograph test were only with my two .62cal barrels, 5 shots each, and as such really do not represent any real statistically valid sample.

Never-the-less, at least 5 shots in the rifled bore were all higher than 5 shots in the smoothbore...certainly not less...so in that regard I could see the argument being made for a "rifled bore" to have a higher velocity.

But the difference is so slight...at least in my tesst...that from a practical point of view it's of no consequence, essentially the same

 

[George]

2) A rifled bore would be faster because indeed the rifling tends to hold back the projectile allowing gas pressure to build higher;

The same thing was and is said about leaving the bore rough to increase resistance and thus pressure. It has always seemed to me that line of reasoning fails to recognize that the increase in pressure is only enough to overcome the increase in resistance, nothing more. The pressure will not continue to rise above that level, so the extra resistance and extra pressure cancel each other out. Once the extra resistance is overcome, you are back at baseline, and the ball will then move at the same speed as with a polished bore.

Spence

 

[roundball]

2) A rifled bore would be faster because indeed the rifling tends to hold back the projectile allowing gas pressure to build higher;

The same thing was and is said about leaving the bore rough to increase resistance and thus pressure. It has always seemed to me that line of reasoning fails to recognize that the increase in pressure is only enough to overcome the increase in resistance, nothing more. The pressure will not continue to rise above that level, so the extra resistance and extra pressure cancel each other out. Once the extra resistance is overcome, you are back at baseline, and the ball will then move at the same speed as with a polished bore.
Spence

I personally don't know...I've watched threads on other forums almost turn into fights over one belief or the other.
At the time, I had a matching pair of GM drop-in barrels for the T/C Hawken, and it would be a simple matter of taking an extra barrel to the range for swap-out that day.
So since I could, I decided to at least run those tests to see if they might show anything dramatically different...but they didn't.

 

[illuveatar]

Your logic is sound. I've heard the idea of increased resistance providing higher pressures and thus greater velocities before and it has always bothered me. Unless there's some additional factor that has been left out the idea violates the laws of physics.

Is there any reason you used two different patch thicknesses in your field test RB ?

Another variable you might want to consider and do a few tests on is how tight the powder is packed. Do you have any technique to achieve consistent ramrod pressures ? If you wanted to do a truly good experiment you would have to be sure to eliminate that variable as well.

 

[Rat Trapper]

Roundball,
While you were out playing with the crony, you should have gotten some readings on the 40 cal REAL bullet! :wink: :grin:

 

[roundball]

Roundball,
While you were out playing with the crony, you should have gotten some readings on the 40 cal REAL bullet! :wink: :grin:

Except I ran all these tests back in 2008...LOL

 

[longcruise]

The same thing was and is said about leaving the bore rough to increase resistance and thus pressure. It has always seemed to me that line of reasoning fails to recognize that the increase in pressure is only enough to overcome the increase in resistance, nothing more. The pressure will not continue to rise above that level, so the extra resistance and extra pressure cancel each other out. Once the extra resistance is overcome, you are back at baseline, and the ball will then move at the same speed as with a polished bore.

Without trying to analyze the whys of my own results, I'll say that of the ML guns that I have firelapped, they all shot a bit slower once they were smoothed out. Especially the spanish and italian barrels. Two TC barrels showed no significant change.

Roundball's 28 fps diff between smooth and rifled is much less difference than I've found with identical rifled barrels. One comparison showed 120 fps diff with heavy loads in a pair of .54 rifled guns.

This leaves me thinking that it would be very difficult to set up a valid velocity comparison of smooth to rifled.

 

[hanshi]

It would come down to simply a test and results for the shooter's own rifle(s) with little relevance to other similar guns.

 

[longcruise]

It would come down to simply a test and results for the shooter's own rifle(s) with little relevance to other similar guns.

Yup, which is what we see with Roundball's test. In order to be answer the question of which is faster, smooth or rifled, one would probably need about two hundred identical guns with half smooth and half rifled. Then, ten shots from each averaged for each gun and then those averages averaged for the results of smooth vs rifled.

Why do I get the feeling this experiment will never happen? :haha: :haha:

 

[roundball]

Just so we're clear, you did see my statement, correct?

"...My chronograph test were only with my two .62cal barrels, 5 shots each, and as such really do not represent any real statistically valid sample..."

I was only freely sharing some FWIW data on some tests I ran, about a subject that comes up from time to time
:wink:

 

[longcruise]

I saw that and understand the spirit ofyour test. My comments were more directed at the inevitable discussion that arose. Namely, which is faster, smooth or rifled?

What I took away from your stats was; probably no diff. Until the 200 gun 2000 shot testing is completed, I plan to cling desperately to that opinion. :haha: :stir:

 

[tg]

"2) A rifled bore would be faster because indeed the rifling tends to hold back the projectile allowing gas pressure to build higher'

Could one use a tighter patch and get the same or more resistance ? also the ballpatch would be touching the entire circumfrance of the ball at the bore. seems one would really have a hard time getting apples and oranges with the "tightness" of the load thing here? Maybe one cannot really get a true "equall" condition comparison situation due to the different area available for contact

 

[roundball]

:wink:

 

[hanshi]

With lots of luck maybe one day I'll own a couple hundred guns and conduct that "scientific" test. :rotf:

 

[rafterob]

You must have never taken statistics then :surrender:

 

[illuveatar]

The difference in average velocity falls within one standard deviation which Roundball noted. Thus the velocity differences aren't considered statistically significant. We can't distinguish normal random variation from a causal variation due to barrel differences.

Also as RB stated, with a sample of only 5 shots each it isn't appropriate to treat this as a statistically valid experiment.

Until more data comes out I'm inclined to believe there's no measurable difference.