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

[illuveatar]

I would have guessed that the rifled barrel would fire balls at a slightly lower velocity. The difference would be in proportion to the amount of rotational velocity imparted to the ball.

I just did the math to derive the angular momentum of a .495cal prb spinning at one turn in 60 inches. The resulting momentum only accounts for a .04 ft/s difference; unless I've overlooked something from my classical mechanics studies. This difference in velocity would be obscured by the greater normal random variations in muzzle velocity.

 

[Ron_T.]

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.

***************************************

This answer surprised me because I thought the lack of friction in the smooth-bore would allow the rifle ball to achieve a higher velocity.

Obviously, that wasn't the case.

Now that the rifled barrel shows a definite velocity advantage, I have to assume that the patched rifle ball doesn't allow any of the powder gasses to escape 'past the ball as it may in a smooth-bore when the ball is traveling up and out the barrel. As a result, the rifled barrel is "sealed" by the tight fitting patched rifle ball which yields the highest velocity by a very small margin which is, for all intents and purposes, the SAME velocity in both the smooth-bore and the rifled barrels.

However, I would not have believed this was so had not this test been performed on both smooth-bore and rifled barrels with all factors as equal as possible which provided PROOF as to what the outcome actually is.

I never cease to be surprised by these black powder, muzzle loading rifles. :idunno:

Always make GOOD smoke...


Strength & Honor...

Ron T.

 

[PGTMG]

Thank you for posting.

 

[Dphar]

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.

***************************************

This answer surprised me because I thought the lack of friction in the smooth-bore would allow the rifle ball to achieve a higher velocity.


Strength & Honor...

Ron T.

Actually, as someone else pointed out, slick barrels are invariably slower. Or should be.
As I think I posted in another discussion, somewhere, the British makers used to roughen the breech end of shotgun bores to increase velocity. They know this by testing penetration of the shot.
Increased friction retards initial acceleration and increases pressure which increases velocity. It will also reduce the standard deviation in most cases. But a rougher bore is also a fouling trap.
28 fps really is not a great amount and the sample is small.
However, Roundball, by initiating the discussion brought about more information being posted and more understanding gained.
Back in the day--1840s-50s, Forsythe, a vocal advocate of slower twists, thought that less friction increased velocity. But he, and almost everyone at the time, had a poor understanding of INTERNAL ballistics. The only advantage to his advocacy of 96+" twists was that the slower twists allowed more powder to be used without blowing the patch in the 14 bore (69 caliber) rifles he mentions most often. Forsythe KNEW that the idea that the barrel had to have a faster twist as the diameter increased or that they needed on turn in the barrel, often giving twists less the 30", was wrong in that it prevented the charges needed for flat trajectory and penetration on heavy game. Had he had the capability and tested a 72" twist against the 10-12 ft twist I think he would have seen no significant velocity gain with the slower twists and that the 72 might have shot BETTER at all ranges with the 5 drams he used as a heavy load in his 14 bore.
Forsythe's EXTERNAL ballistics and effects on game are correct and repeatable today (well shooting Indian Elephants and Tigers is frowned upon). His INTERNAL ballistics were 19th c. level science and supposition, by modern standards it was pretty poor.
It would be interesting to see how the Schoultz method compares, in standard deviation to a slick lube like tallow. But I did enough chrono work back when shooting BPCR a lot that it does not appeal to me and now mine only gets out every few years when I am really curious about something.

Dan

 

[tg]

"However, I would not have believed this was so had not this test been performed on both smooth-bore and rifled barrels with all factors as equal as possible which provided PROOF as to what the outcome actually is"

I wonder if the larger patch was used in the smoothbore and pouned down if needed if they velocites would have been closer, as I stated before how does one really get an apples to apples test here? If the test was done with a smaller patch in the smoothbore why could one not use a larger patch than the rifle test to increase the velocity? Again not certain we have the apples to apples needed for a true comparison, someone else may use a super tight combo in the smoothy and a moderate thumb start in the rifle which would be as comparatively valid as the test shown and might show a reversal of results as to which is faster????

 

[MSW]

Roundball, thanks for the post.

As near as I can tell, it doesn't seem to make a substantial difference - Bambi won't care about the extra 28 feet per second.

 

[roundball]

Roundball, thanks for the post.

As near as I can tell, it doesn't seem to make a substantial difference - Bambi won't care about the extra 28 feet per second.

Agree...it was just one of those things that I'd seen debated on forums on and off for a few years, and one day the thought occurred to me that I was as close to being able to run tests as I'd ever be, having just rifled one of two identical GM .62cal smoothbore barrels.

And I repeat, even though there was a slightly higher velocity from the rifled barrel, my tests certainly weren't anything that could be pointed to as some "industry wide statistically valid test"...LOL.

But still...it was interesting and to an extent, did reveal a consistent pattern of results as it relates to the theoretical discussions of velocity differences in a rifled bore vs. a smoothbore. Not aware of anyone else ever posting such test results so I was simply sharing that with the membership

 

[Dr5x]

I, for some time, felt that slicker patch lube was the best.
During my experimentation on achieving the exact same amount of slickness in each and every patch in order to eliminate vertical strings of hits, I had quite a surprise when I found I was getting tighter groups each time I used slightly dryer (less Lubed) patching strips.

My only explanation was that as black powder burns progressively the pressure builds up over a very brief period of time. With the slick patch lube the patch/ball combination begins to move as soon as the powder begins to burn.
With the dryer, less slick, lube there is a bit of resistance a small hesitation before the Patch/ball begins to move. The very small delay allows the BP to produce a bit more pressure behind the ball, you get more out of your powder.
What I do not understand is why this dryer lube causes the groups to tighten.

I have always wondered about the value of chronographs. They tell you how fast the ball is traveling. And that helps How?I am not being critical or smartass. I really don't know and want to learn.

My only test of a patch ball combination or powder charge or the stability of the ball is
What happens on target.

The object of shooting is to place a bullet or ball as exactly as possible on a predesignated spot. How well the rifle and/or the rifleman achieves that is the best way to judge the effect of your loading practices.

I do tend to run on and on”¦

Dutch

 

[hanshi]

A chronograph tells you how uniform your ballistics are. Normally a fine load will show a small extreme spread and standard deviation. This might not show up at close range but will certainly show vertical dispersion at longer range. It's an indispensable tool for the serious experimenter/tinkerer/accuracy buff.

 

[Dr5x]

Wouldn't varying speeds show up on target as a vertical string of hits?

Dutchj

 

[gizamo]

Perhaps,...

At least off a bench.

Offhand, increased recoil will shift body mechanics. Up, down, right, left.... Depends on the shooting stance, height, weight, foot position....etc.

Why Benchrest shots off a rest differ so much from handheld standing shots, for some...

 

[Mort Scott]

Perhaps,...

At least off a bench.

Offhand, increased recoil will shift body mechanics. Up, down, right, left.... Depends on the shooting stance, height, weight, foot position....etc.

Why Benchrest shots off a rest differ so much from handheld standing shots, for some...

 

[Dphar]

My only explanation was that as black powder burns progressively the pressure builds up over a very brief period of time. With the slick patch lube the patch/ball combination begins to move as soon as the powder begins to burn.
With the dryer, less slick, lube there is a bit of resistance a small hesitation before the Patch/ball begins to move. The very small delay allows the BP to produce a bit more pressure behind the ball, you get more out of your powder.
What I do not understand is why this dryer lube causes the groups to tighten.

I have always wondered about the value of chronographs. They tell you how fast the ball is traveling. And that helps How?I am not being critical or smartass. I really don't know and want to learn.




Dutch

In BPCR the slowing the initial movement of the projectile is referred to as "load inertia". It can have a considerable effect on the shot to shot velocity spread.
In BPCR it is necessary to get the standard velocity variation down to the accuracy level of the chrono to allow hitting a target at distances past 200 yards or so. Where the velocity induced vertical dispersion can be in feet at 300 yards with a standard velocity deviation of 40fps.
This applies to MLs in that a more consistent shot to shot velocity will produce more consistent shooting even at shorter ranges. I too think the less slick patch lubes increase "load inertia". Slicker patch lubes may require more powder to shoot as well.
While its less important in ML load development its an important tool in BPCR and I used to use one a lot when I was shooting competition with them. It was standard for range sessions.
They are less important with a ML and I seldom use one other that to satisfy some curiosity.

If trying to find something out. Like SB vs Rifle velocity then its a must.
But mine mostly stays in the shop these days.

Dan

 

[pab1]

Roundball, do you notice any difference in accuracy past 50 yards with the rifled barrel?

 

[roundball]

Roundball, do you notice any difference in accuracy past 50 yards with the rifled barrel?

I never got around to running those kinds of comparison tests on that pair of barrels, and now they've both sold...