Engraving / obturation needed for PRB accuracy ?

[roundball]

My recent testing of brass balls as possible non-toxic PRB substitutes, using stout 120grn Goex powder charges, caused these brass balls to drive through almost 2 feet of tightly packed shredded rubber mulch.
The balls were recovered, inspected, measured again with dial calipers and found to be in perfect original condition, sustaining no damage whatsoever or undergoing any changes in their dimensions...and saved for reuse.
Accuracy results were excellent small groups at 50yds as good as or better than lead balls produce.

For what it's worth, the obvious conclusion I draw is that top notch accuracy does not depend on PRB obturation as these hard solid brass balls did not obturate at all. In addition, top notch accuracy also does not depend on a PRB being 'engraved' with patch weave marks or rifling marks as there were no such marks on these solid brass PRBs.

IMO, like a train rides the rails, a PRB simply rides the lands through the bore with patch material jammed into the grooves providing twist, with no additional requirement on 'engraving' or 'obturation' for excellent accuracy whatsoever.
I've never had patch weave / rifling marks engraved on my lead PRBs, and now two completely separate tests using two completely different material smooth solid non-toxic PRBs substitutes have proven to me that accuracy has no dependency on engraving / obturation at all.

 

[BrownBear]

I'm convinced it's not necessary, but some dogs won't die.

 

[Rifleman1776]

I know this is a much cussed and discussed issue. I don't know of obduration occurs with soft lead prb.

I've never had patch weave / rifling marks engraved on my lead PRBs

I hate to criticize someone who goes to so much work testing and reporting. (for which I thank you) But, I'll betcha you just haven't see the patch/rifling engraving.
I have seen it plenty on balls pulled and the occasional shot out with light charges for a dry ball and with CO2 dischargers. Not just on my rifles but when helping others.
And easy test, and way to get a good notion of what ball/patch combo works best in a rifle, is to lube some patch material ( a big piece), seat the ball and drive down bore only about 1" to 2". Then pull back out and inspect. A good fit is not too hard to drive down but snug and with the appearance of both rifling and patch weave on the ball.
It is a great way to start without shooting, or even leaving the house.
BTW, thanks for the brass ball tests. Very interesting.

 

[Robby]

I have seen rifling and fabric imprints on some P/B, not all combinations that I use. Do I think it is necessary for good accuracy? No. I think of the patch much the same as a sabot in modern inlines and shotgun slugs. Wonder where they got that idea? :hmm:
Robby

 

[roundball]

"...I'll betcha you just haven't see the patch/rifling engraving..."

Yeah...that's it...I've just over looked it on almost 21,000 shots in the past 20 years ???


It really doesn't matter...the point of the thread is that patch weave engraving, obturation, rifling engraving are obviously not necessary for excellent accuracy...because the solid glass and solid brass balls don't allow any of those things.

 

[roundball]

I'm convinced it's not necessary, but some dogs won't die.

You said a mouthful there for sure...LOL.
My two separate tests...first, several hundred glass marbles a few years ago...and now this brass ball test.
Neither material could be engraved and they were not.

 

[Vaino]

What do the patches look like?. For maximum efficiency, obturation has to be maintained to achieve a seal between the projectile and bore. Patches do this w/ a RB, slightly oversized dia. for a conical plus the compression of the lead and the skirt on a Minie. A RB itself doesn't obturate the bore...the patch does. Accuracy and maximum efficiency are 2 different results and don't necessarily coincide. It would be interesting to measure the patched brass ball and the PRB efficency w/ a chronographed velocity using the same powder charge. Of course the difference in weight between the two, might skew the results.

By the way....I do get weave imprints on the lead balls .

Very interesting "experiment" which somehow defies logic....at least mine. I would have thought the brass ball would have not followed the rifling, but instead just run down the bore w/o rotation, because nothing is "grabbing" the brass ball....similar to a smoothbore. There is an inertia affecting the brass ball...it doesn't want to rotate.

Thanks for the "experiment"...very thought provoking.....Fred

 

[roundball]

We all pick up every imaginable item every day of our daily lives without leaving engraving marks on them...from smooth glass to rough stones...as long as we grip them tight enough with the texture of our skin, they won't slip when we raise a glass, throw a baseball, etc.
Grip is obviously important in the PRB...and is why I tried to study / think this through, bought the size balls & patch material that I did...but have never seen any reason that anything should be engraved into a ball.
As long as the fit is snug, and it's going to be under heavy acceleration, the tight gripping patch will transfer the rotation of the rifling.
Also, posters are often commenting how they use PRB combos so loose they can just thumb start them...as I believe it's commonly accepted that our ancestors did...not conducive to engraving patch weave.

At any rate, here are some recovered balls & patches

 

[Trench]

I have noticed weave patterns on some of my my balls after I've had to pull a load, but that was always with using a VERY tight patch/ball combo.

I wouldn't say that these markings are an indication of a super-accurate load. I did some load work-up with my .58 with a combo that always left those marking and certain charges will still throw the balls pretty wide at 50yards. It still required me to find a sweet-spot. There is a different sweet spot with thinner patches in the same rifle that don't imprint the fabric weave.

 

[David W.]

Obturation isn't necessary by any means. The only reason it may happen is because pure lead is so soft and when a heavy enough charge is used, it can/should change the shape of the ball. Otherwise, it means absolutely nothing and will not affect the accuracy of harder objects like brass balls because they don't obturate.
What roundball says about gripping the ball seems like sound advise, though.

 

[dbutch]

Soft lead is the cause..
Tight patches help keep the fowling down too!
No swabbing.

 

[DOUBLEDEUCE 1]

Very interesting information. I liked your marble test also.

 

[necchi]

Bill, Thank you for the testing and all the work.

Your style of shooting is bench shooting with this experiment and your work here has been specific to the brass ball your working with.
The application of this thead and experiment isn't designed to prove or disprove a lead ball being engraved or not for accuracy.
I have no reason to doubt you have seen no engraving on lead let alone the much harder Brass.

Yet even beloved Thompson Center directly states that a lead ball used for Target Shooting should be engraved, example here in their manual on page 24 of the manual/page 26 of the PDF; http://www.tcarms.com/assets/manuals/noncurrent/Shooting_TC_Side_Lock_Black_Powder_Guns.pdf

While I'm sure these ball are accurate, and I'm sure you'll harvest deer with them, there are many ways to obtain accuracy, and several different levels of accuracy as defined by different people with different goals.
Yours is one way to obtain the accuracy you want and I'm happy that it works out for you.
Fact is many others find the accuracy they need also,, and many of them have actually seen this engraving on lead ball from the patch and lands.
The use of False Muzzles is another single example of a need to engrave a PRB.

With your many postings of your best accuracy, I'm suprised the load wasn't the same as all other best groups and 90grns of 3F, :idunno:

I'm simply presenting that there are different observations and documents of this observation.

I actually have alot of lead at hand, and my use of lead isn't specific to ML's, I'll probably become an outlaw if lead is ever banned.
But I don't expect to see that in my lifetime, again a very interesting experiment and Thank You for your time, work, observation and summary.

 

[hanshi]

FWIW, I checked the few balls I've managed to recover from deer and couldn't see anything I'd say looks like weave patterns. Of course I could see only a little of the ball as they were pretty flattened.

 

[roundball]

T/C consolidated a lot of what was thought to be conventional wisdom over 40 years ago and it hasn't been updated since.
Their manual also states to plug the vent with powder to "lay a fuse" to the main charge...LOL.

And it looks like you're confused based on your remarks about 90grns of powder.
As my text states, my normal load in this .58cal was a mid-range charge of 100grns Goex 2F.
(I use 90grns in the smaller calibers)

 

[Vaino]

Obturation refers to "sealing the bore" so that gases aren't allowed to escape past the projectile and this can be accomplished by different means. W/ a PRB, it's the patch that obturates the bore...not the RB. A conical obturates the bore by being slightly oversize and by the force of the gases compressing the length thereby increasing the dia. A Minie ball's skirt obturates the bore. Obturation is necessary for maximum efficiency or maximum velocity.

Round Ball's patch thickness and brass ball dia. certainly do obturate the bore, but again, I'm not sure that the brass ball is rotating or that it might be rotating but not at the twist rate {slippage} when it leaves the muzzle. His patches show a "smearing" of the rifling, but don't exactly know what causes this.

A very interesting topic....Fred

 

[roundball]

"...recover from deer and couldn't see anything I'd say looks like weave patterns..."

Yes, it's a puzzler...I've blown them out with compressed air and reused them;
I've pulled them with ball pullers and reused them;
I've recovered them from deer and posted photos of them;
Nada...

 

[roundball]

"...I'm not sure that the brass ball is rotating or that it might be rotating but not at the twist rate {slippage} when it leaves the muzzle..."

So Fred, now you're a mystic? Just too funny...LOL

 

[cynthialee]

it has already been shown that it just takes a small amount of spin to keep a round ball stable, so it realy doesn't matter if the ball is geting the full effect of the twist on his barrel, so long as that brass ball starts to spin to some degree

the ball had enough stabelization to dead center at 50 yards

 

[wulf]

Well sir, I have to compliment you on your re-search and the work you put into your expariments.
I would like to caution you to always remember to
put in that 120 grs first because it would be
pretty difficult to pull the brass ball...other
than that, you must be a genius.
Wulf