Is There Something I'm Missing?

[lloyd-ss]

............Rate of twist and number of grooves have always been one of those bones of contention but I have seen all kinds of rifling make good accuracy. I think accuracy has more to do with the reaming and the rifling and now the Taper lapping. I think high end barrel making is an art form and most everyone knows little and the barrel makers who know are not sharing all that much......................... Benchmark/Mac1 2 grooves are .22 only.

Tim, your posts always serve to remind me of all that I don't know that I don't know.   So I always try and listen and learn.  Do you have an opinion on the possible use of a Marlin Micro Groove type of rifling for big bore when shooting lead bullets instead of pellets?  It just seems like the lead would displace easier and seal the bore more efficiently.  But I really don't have a clue.
Thanks very much,
Lloyd

[BigBoreJack]

Lloyd wrote:  " Do you have an opinion on the possible use of a Marlin Micro Groove type of rifling for big bore when shooting lead bullets instead of pellets?  It just seems like the lead would displace easier and seal the bore more efficiently.  But I really don't have a clue.
Thanks very much,"
_____________________________________

I am convinced that the "perfect" rifling for a big bore air rifle, would do all your are mentioning, and more, while not leading up, would be the early day English Lancaster smooth oval bore rifling, but good luck in finding someone to do such rifling today.

[longhunter]

In my feeble mind, I can picture the velocity maxing out before max spin. But I picture it as the spin COULD increase after leaving the barrel. Then it would be true that max velocity reached at a different point than max spin. Like I said, I'm no physics major, just looking at it in my feeble minds eye.
 

agree with your assumption. it would stand to reason that spin rate could increase AFTER the pellet left the barrel, due to the lessening of drag, induced by the barrel. however, I would think that the difference would be minimal, at best. ok, now I've got a headache.

[longhunter]

the lenght of the barrel... longer barrel gives the pellet or bullet more time to stabilize in flight . powder burners or pellet guns. i discussed this with my gunsmith . a carbine and a rifle side by side same gun but diffrent barrel lenghts shoot them at a target at a oh say 30 yards and see which gun is easier to keep on target . thats why its harder to hit with a pistol. i got 2 identical rifles out and tried it and well it was that way for me .so im going to go with what my gunsmith said and he has been working on guns and building them for over 40 years . he keeps busy out in the coountyr without advertisements so that says he knows

the longer barrel is easier to keep on target, because of the longer sight radius.
bullet design, ballistic coefficient, velocity and spin rate determine projectile stability. not barrel length.

[WECSOG]

Perhaps what he means is that the peak rotational stability occurs a few inches after peak velocity. Not the peak rpm. That would make sense to me.

[TimmyMac1]

............Rate of twist and number of grooves have always been one of those bones of contention but I have seen all kinds of rifling make good accuracy. I think accuracy has more to do with the reaming and the rifling and now the Taper lapping. I think high end barrel making is an art form and most everyone knows little and the barrel makers who know are not sharing all that much......................... Benchmark/Mac1 2 grooves are .22 only.

Tim, your posts always serve to remind me of all that I don't know that I don't know.   So I always try and listen and learn.  Do you have an opinion on the possible use of a Marlin Micro Groove type of rifling for big bore when shooting lead bullets instead of pellets?  It just seems like the lead would displace easier and seal the bore more efficiently.  But I really don't have a clue.
Thanks very much,
Lloyd

I don't have any experience with bullets or The grooving you mention. I'm a pellet guy and I think I probably always will be unless they start shooting slugs in BR guns. Not likely.

TimmyMac1

[Slavia]

I'm with you, Bob.  Angular and linear velocity should be tied together by the twist rate.  You would think any "lag" between them would result in barrel leading or evidence of shearing on the pellet.  The barrel would in effect become a file.

My daughter just told me something that surprised the heck out of me.  She says things on the internet aren't always true, and people aren't always what they say they are.  Who'd have thunk it?

[rsterne]

REALLY?.... I'd never have guessed that!....

Bob

[Doug Wall]

I'm with Bob. The pellet/bullet is locked into the rifling in the barrel, and as such, it would be impossible for the peak rotational speed to be at a different point in the barrel from the maximum velocity without stripping lead. Also, the rotational speed of the projectile can't increase outside the barrel. Increase in the rotational velocity would constitute an acceleration, which can't occur without energy input.

[rsterne]

Old post, guys.... subject was settled over 2 years ago.... or at least thrashed to death....

Bob

[Methuselah]

I'm no expert by any stretch of the imagination, however, it has been my experience that "industry insiders" bearing insight are sometimes more knowledgeable about effects and corrective measure than fundamental understanding of actual cause.  Maybe there are other factors at play?

Some things that rattled around my noggin after reading all the responses including the linked websites; 1) a round may encounter inconsistent rifling width making grooves which may be wider than the rifling at some points in the barrel, 2) the air pushing/accelerating the round may cease to provide sufficient force to perpetuate said acceleration before the round leaves the barrel, 3) if acceleration ceases or wanes, drag may result in an unpredictable combination of forces such as shifting of pellet groove side now riding the rifling, stored kinetic energy (possibly manifesting as a torsion or distortion in the pellet), a generated harmonic in the pellet, and 4) interactions in pellet dynamics and barrel harmonics (at any critical point in the barrel?!) may create a set of circumstances that result in an inaccuracy which may be subject to "cure" when the factory changes the barrel length (even if more consistent rifling or change in anything effecting barrel harmonics would have also been an effective cure).

ALL the above is pure conjecture and an overcomplicated way of suggesting the original presentation of insider facts/findings may have been an oversimplification of what may have been 99% effort to fix an issue accompanied by a 1% understanding of the true cause of their problem.

To put it more bluntly, maybe their explanation fits only SOME of the facts.  Aww, you guys know what I'm trying to say.  Now my head hurts too...

On another forum I got into a discussion about barrel length and accuracy.... A chap who used to work for BSA stated that if the barrel is too short the pellet spin rate would be too low for stability.... I ran the numbers, and of course if you shorten a barrel to the extreme the velocity is so low that the pellet RPM is too low for stability.... that makes sense.... He stated that was NOT the mechanism, however, and that the "velocity peak and the pellet spin peak" occurred at different barrel lengths.... He stated that the velocity peak occurred as much as 8" before the pellet spin rate peak....

I can't see how that is possible.... Surely the pellet, once engaged into the rifling, accelerates both rotationally and horizontally at the same rates.... double the velocity, double the RPM.... To do otherwise would smear the rifling marks on the pellet.... Am I missing something?.... Is there some mechanism that would cause (allow) the pellet to "spin up" at a slower rate than the rifling says that it should?.... We're not talking progressive twist or smooth twist barrels here, BTW.... a standard, constant, helical rifling twist....

Bob

[rsterne]

Two important facts....

1. For the pellet not to travel in lock-step with the twist rate, it would have to strip.... RPM is proportional to velocity, for a given twist rate, period....
2. There is no force available to speed up the rotation of the pellet after it leaves the muzzle.... it can only slow down in both velocity and RPM....

That leaves this statement impossible....

the velocity peak occurred as much as 8" before the pellet spin rate peak....

If the peak velocity occurs at the muzzle, so does the peak spin rate.... If the peak velocity occurs 8" (or some other distance) before the muzzle, and the pellet slows in the barrel before it leaves the muzzle, then so does the pellet spin rate.... I think the gentleman in question came to the wrong conclusion about spin rate vs. velocity, and I see nothing in this thread to change my mind....

Bob

[Allen Rice]

 Bob, You're not missing anything.  I agree with You, Tom, Loyd and the gang of others who know that the velocity and spin rate are "in lock-step" as stated here in.  I do not agree with the guy Bob encountered whose "... posts are hard to understand.... just unsubstantiated claims from "his days at BSA"....

I think he might have retained a little too much of the "BS" when he left BSA.

[William]

Here is the answer to the puzzle...
The faster you push the handle with the spiral shaft, the faster it spins lol

Hmmmm could be something here 



William

[MicErs]

On another forum I got into a discussion about barrel length and accuracy.... A chap who used to work for BSA stated that if the barrel is too short the pellet spin rate would be too low for stability.... I ran the numbers, and of course if you shorten a barrel to the extreme the velocity is so low that the pellet RPM is too low for stability.... that makes sense.... He stated that was NOT the mechanism, however, and that the "velocity peak and the pellet spin peak" occurred at different barrel lengths.... He stated that the velocity peak occurred as much as 8" before the pellet spin rate peak....

I can't see how that is possible.... Surely the pellet, once engaged into the rifling, accelerates both rotationally and horizontally at the same rates.... double the velocity, double the RPM.... To do otherwise would smear the rifling marks on the pellet.... Am I missing something?.... Is there some mechanism that would cause (allow) the pellet to "spin up" at a slower rate than the rifling says that it should?.... We're not talking progressive twist or smooth twist barrels here, BTW.... a standard, constant, helical rifling twist....

Bob

You could teach me for sure, but there is something that happens with BP rifles shooting patched balls.

You can push the ball so fast that it strips the rifleing by slipping the patch.  I don't know.  Is this what he might be describing, a pellet slipping the rifleing because it is accelerated so quickly that it can not grip?

Obviously this would be a function of depth of rifleing, rate, and breech pressure...

No clue here to be honest.

[tweedking]

i would imagine that the pellet's lack of ability to get up to speed, is what is leaving lead in the barrel as it shears off.

we all know that too long of a barrel, will create too much friction, slowing the pellet down.

at what point does the pellet spin up to speed and then slow back down (fps)? would slowing back down (fps) start to affect the RPM?

if you could run a vid-scope into the bore on a super-long barrel, would you see leading from the bolt to max rpm/velocity and then from there out the barrel?

i suspect the lead-free portion would be inches long, and the max velocity would be found at or during the beginning of this portion.

is this even a viable course thought?

thanks,
rob

[K.O.]

me I do think on a 1:36 .177 barrel an 8" barrel has only turned the pellet about 1/4 of a revolution...and I feel at least a 12 inch barrel is needed...

Just a gut feeling...

[William]

 

[rsterne]

If someone can come up with a logical, workable mechanism whereby the pellet can be made to spin faster than the twist rate of the barrel.... or to be spinning slower than the twist rate of the barrel when 8" from the muzzle and then magically catch up.... please post it.... Otherwise, just let this thread die, as it should have 3 years ago.... The answer should be obvious.... If it doesn't make sense, it isn't true.... I regret posting a rhetorical question....

Bob