Do soft lead PRBs obturate?

[Canuck Bob]

I'm asking in regards my Parker Hale P61 carbine.  It has the historically correct progressive depth rifling.  Muzzle grooves are very thin but breech end is much deeper.  I'm just trying to understand if a soft lead ball will obturate to fill the breech grooves.

Someday I might acquire a Pritchet bullet mold but not possible now.

[Daryl]

.003 at the muzzle. .008 deeper at the breech. I had a similar rifle and it shot just fine with denim patched round balls of pure lead. I used a .562" Lee mould with that rifle as it had an undersize bore of .574", not .577 nor .578.
Did they obturate? I don't know, but the recovered patches were reusable and the rifle shot very well with 85gr. 2F GOEX. I assume they did obdurate, or there should have been scorch marks
or burns from the flame getting past them in the grooves. There was no such damage.

[45-110]

I recovered a bunch of .58 round balls this spring that where shot into a snow bank. They where absolutely perfect and still round, showing the cloth imprint on the lands. 110 gr. loads showed no obturation into the grooves.
kw

[Daryl]

I patch a little tighter than that, I guess.
Mine, recovered from any of my rifles, look just like the suggested Lyman's patch 'engraved' balls, however are not perfectly spherical, but ever so slightly elongated
and usually with a ring around the upper surface from the cupped, starter.
If they are put into the muzzle with a strip of patching, then pulled out, they looks just like these
engraved by the patching from the lands and the grooves. I double there is any more slugging up, but there could be.

[Canuck Bob]

Thanks to bad health and covid 19 this has turned into a research topic for me.

1.  We are advised to obturate a lead slug by trapping a bar in the barrel and using it to tap the slug into the grooves.  I've only slugged cartridge chambers but it doesn't take much tapping to swell a soft slug.  Edit: I've got this wrong I think.  One need only tap an oversize slug into the muzzle.  The trapped bar is for removal afterwards.

2.  Many feel tapping or "whanging" the loaded ball with the ramrod slugs up the ball in the breech area, many don't agree.

3.  The youtube vids of captured expanded balls from gel sure show a pliable projectile.  Of course the energy involved is tremendous.

It is interesting that searching PH Enfield and Springfields with progressive depth rifling doesn't answer the questions.  I found lots of anecdotes praising and complaining of PB performance.  I didn't keep track but the 48" twist Enfields fared better than most.

I'm assuming the rifling involved was the outcome of complex military manufacturing.  Did progressive depth rifling ever turn up in civilian english or american long rifles?

Has anyone ever retrieved a R.E.A.L. slug and seen evidence of engraving on the bore sized bottom bands?

[Canuck Bob]

Thanks Daryl, your experience is my initial method.  I sure hope this carbine is a shooter as recoil from a .560 ball has got to be less than a 500 gr. Minie style ball.  This short rifle suits me and it is the closest I'll get to a HC muzzleloader. The stock fits but it does have a high comb.  The lock hits like a hammer!

[Daryl]

I think the progressive depth rifling was only done on military rifles and I think around the world this was true - or almost. I'm quite sure the Austrians as well as French and English did it as well as the US rifles and all for the hollow based Minnie-style "balls".
The Italian and other replicas of the US rifle muskets and rifled muskets, Zouaves, etc, just had .003" to .004" rifling, one end to the other - no progressive depth & 72" rate of twist.
They all shot really well with a .575" ball and .022" denim patching. I never shot slugs in them.  The Zouave I had, shot best with 120gr. 2F- groups of 2" to 2 1/2" at 100 yards were the norm.
For some odd reason, I rarely shot closer in those days , sometimes, 50yards.
With the Parker Hale Enfields, the original bar was reset - progressive depth rifling.
Back in the mid 70's I worked in a gun shop and sold a lot of the Parker Hale rifles. Seems to me the long one, the 3-band rifle had 3 groove rifling and a 78" twist. It shot amazingly well with patched round balls, my typical load was a .022" denim patch and a .575" ball. Some guys used .562" ball and the same patch with equally (maybe) but good results non-the-less.
My favourite at that time was the 2 band rifle with 32" bl. and 48" twist. These shot amazingly well with 85gr. 2F and either the .562" or .575" round balls & the denim patching.
I had not tried the Musketoon, 1861 model until just a couple years ago. Mine was the Italian (Southern) Copy, with brass hardware(bl. bands). It also had progressive depth rifling, .003" at the muzzle and .011" at the breech. I initially started with 75gr. 2F and a .575" ball and of course, my 10oz. .022" denim patching. These were quite snug as the bore of this rifle was .574". When my .562" mould came in, I used that one exclusively, same patching, of course. loading was not difficult. Another member of our club has the Parker Hale model of the Musketoon and he shoots it well indeed, with 50gr. 3F and a .562" ball, patched in denim (I think).
So- I have not heard of the progressive depth rifling giving any trouble at all. I will also note, that the sights usually have to be changed, height or windage, or both.
With the fairly large boss of the PH & other rifles, slotting and soldering in a higher front sight is not a problem. For windage, soldering a "V" plate on the rear sight elevator is also NP for necessary windage.
Hope "this" helps.
ps- I have never shot slugs in any of the military .59's I've owned, only in the .58 Hawken. The hooked butt plate was murder.
Seems to me, the stamped 'service' load on the barrel of my Musketoon was 3 1/4 drams, which is 88.73gr. The service bullet was 560gr.  Even with the wide butt plate, I don't think that would
be fun after a few shots.

[Hungry Horse]

 I believe the most obturation you’re going to get is just enough to engrave the ball with the pattern of the patch material. And, then only in a dead soft lead ball.

  Hungry Horse

[WadePatton]

I recovered a bunch of .58 round balls this spring that where shot into a snow bank. They where absolutely perfect and still round, showing the cloth imprint on the lands. 110 gr. loads showed no obturation into the grooves.
kw

This assumes any obturation would result in permanent deformation and I'd think that it would not--that the balls would spring back into roundness once outside of the pressurized confinement of the barrel.

Kinda like you have to bend metal past the point you want it bent because of "springback". Or stated otherwise, obturation, in this case, doesn't exceed the plasticity of the ball.  I could be wrong-and that's okay.  Pb is a lot less springy that most other metals and we are dealing with much lower pressures than nitro generates.

[Canuck Bob]

The more I thought about it this discussion begs at least one question.  If obturation was substantial there would be less variability of performance between medium thickness patches and tight ones.  Of course all speculation on my part. 

Researching this sure changed my ideas around black powder.  BP creates a lot of energy at a surprisingly low pressure.  Also increasing the charge from 60-140 gr. in a 58 cal. gun creates a roughly linear pressure curve.  None of the dangerous spikes possible with smokeless powders.  At least according to the Lyman BP Handbook.

[Daryl]

Yeah - that book is a bit out of date, however the "trends" continue with today's powders, I'm sure.
Today's powders develop higher velocities than the ones used in Lyman's book.
 In the book, the 24" bl. developed 1,163fps with 80gr. of GO 2F. My 24" barreled Enfield produced
1,308fps with 75gr. GOEX 2F.  According to the book, they were still only running 1,205fps at 130gr. GO2F
& they actually went up to 190gr. before declaring a maximum load at 9,990LUP (lead units of pressure)
which does not compute either to PSI or CUP. The velocity with that huge load, was 1,809fps.

An interesting 'fact' I was able to glean from the book, was that given the same powder type, ie: 3F or 2F
a relationship between velocity and pressure could be assessed.  By this, I mean that if 2 guns are developing
the same velocity with the same granulation, they are producing the same pressure.
Thus, a 28 bore rifle producing 1,400fps with a round ball, is producing the same pressure as a 24 bore rifle, or
14 or even 12 bore rifles, at the same velocity, even though it takes a huge increase of powder to get that speed
in the larger bores. That stands to reason as well.

[Pukka Bundook]

I'm convinced soft lead balls do obturate on ignition.

Found this to be so when firing a .750" musket ball between two thick felt wads (lubed) in a .76" bore barrel.  (125 grains 2F powder)
10 thou windage, yet the fired balls had definite flats around their circumference on recovery, where they had bumped up to fill the bore.

[Canuck Bob]

Daryll, my 2nd. ed. handbook, 2001, clearly lists the pressure as psi. It also lists the 58 cal. load range from 60-140 grains across the board. Shows sure meddling from lawyers.

In the 24" barrel listing for the .570 PB they list a range of 4900 psi (60 gr.) to 9800 psi (140 gr.)  GO 2F.  The 80 grn. loads listed velocity is 1288 fps..  Of course that is slower than your chronograph readings.

Safety Edit:  For those that don't have the manual or simply don't care much I need to clarify the pressure data for safe interpretation.  a .45 PRB loaded to 120 gr of goex, either 2 or 3F, produces 20,000 psi in a 28" barrel.  I do not want anyone reading my post to think a hot load is only going to generate 10K psi.  Many loads regularly listed can GENERATE SIGNIFICANT PRESSURE. 


Manuals are representative at best but I think they are close enough to make safe decisions based on the data.

PukkaB that is encouraging info. 

[Daryl]

I have a feeling, obturation depends a lot on the mass of the ball. The larger sizes being more readily obturated
than smaller ones.
I would not think .32's or .36's obturate at all, even though they are driven to much higher velocities than the larger bores.
Bob your book out-dates mine by 30 years. I had a second edition in the late 70's, but I don't think it had any load data, mostly
just stories. I had that one, but it's no longer in the rack, for some reason.

[Oil Derek]

Yeah - that book is a bit out of date, however the "trends" continue with today's powders, I'm sure.
Today's powders develop higher velocities than the ones used in Lyman's book.
 In the book, the 24" bl. developed 1,163fps with 80gr. of GO 2F. My 24" barreled Enfield produced
1,308fps with 75gr. GOEX 2F.  According to the book, they were still only running 1,205fps at 130gr. GO2F
& they actually went up to 190gr. before declaring a maximum load at 9,990LUP (lead units of pressure)
which does not compute either to PSI or CUP. The velocity with that huge load, was 1,809fps.

An interesting 'fact' I was able to glean from the book, was that given the same powder type, ie: 3F or 2F
a relationship between velocity and pressure could be assessed.  By this, I mean that if 2 guns are developing
the same velocity with the same granulation, they are producing the same pressure.
Thus, a 28 bore rifle producing 1,400fps with a round ball, is producing the same pressure as a 24 bore rifle, or
14 or even 12 bore rifles, at the same velocity, even though it takes a huge increase of powder to get that speed
in the larger bores. That stands to reason as well.

Hey Dayrl, I have the 1st edition of 1975, I think you quoted the "Ft/lbs" (1205) as listed velocity. In my copy, the 130 gr load is 1446 FPS.

[Pukka Bundook]

Daryl,

You wrote above,  "I have a feeling, obturation depends a lot on the mass of the ball. The larger sizes being more readily obturated
than smaller ones."

When I was writing my reply above, I was thinking Exactly the same thing.  Takes much more work to get a greater mass moving.  (Moment of inertia).
Being in a rush as usual, I didn't go into it, but thankfully You did!

Best,
R.

[Daryl]

Yeah - that book is a bit out of date, however the "trends" continue with today's powders, I'm sure.
Today's powders develop higher velocities than the ones used in Lyman's book.
 In the book, the 24" bl. developed 1,163fps with 80gr. of GO 2F. My 24" barreled Enfield produced
1,308fps with 75gr. GOEX 2F.  According to the book, they were still only running 1,205fps at 130gr. GO2F
& they actually went up to 190gr. before declaring a maximum load at 9,990LUP (lead units of pressure)
which does not compute either to PSI or CUP. The velocity with that huge load, was 1,809fps.

An interesting 'fact' I was able to glean from the book, was that given the same powder type, ie: 3F or 2F
a relationship between velocity and pressure could be assessed.  By this, I mean that if 2 guns are developing
the same velocity with the same granulation, they are producing the same pressure.
Thus, a 28 bore rifle producing 1,400fps with a round ball, is producing the same pressure as a 24 bore rifle, or
14 or even 12 bore rifles, at the same velocity, even though it takes a huge increase of powder to get that speed
in the larger bores. That stands to reason as well.

Hey Dayrl, I have the 1st edition of 1975, I think you quoted the "Ft/lbs" (1205) as listed velocity. In my copy, the 130 gr load is 1446 FPS.

Yeah - you're right. is it 1,446fps for 130gr. That's only 138fps faster than my 75gr. 2F load. Today's powders are better, that's for sure.

[Daryl]

Daryl,

You wrote above,  "I have a feeling, obturation depends a lot on the mass of the ball. The larger sizes being more readily obturated
than smaller ones."

When I was writing my reply above, I was thinking Exactly the same thing.  Takes much more work to get a greater mass moving.  (Moment of inertia).
Being in a rush as usual, I didn't go into it, but thankfully You did!

Best,
R.

Yeah - however,  now that I think about it, I should have said, the AMOUNT of obturation, if any, likely depends upon mass, but as well, perhaps the fit in the bore and grooves themselves.
We now that loose fitting Minnie balls obturated, in part due to the hollow base and thin skirt.  I wonder at which point a patched round ball resists the "moment of inertia" in a similar manner
and how much the spherical ball can actually obturate (shorten & become wider).

[45-110]

The .58 balls that came out of the snow bank showed NO obturation......and where once atop 100 gr. 2f. They where not beat down the clean barrel, nor was the rammer thrown. Balls had the cloth patch impression.
kw

[Daryl]

Interesting occurrence. Some things not easily explained, nor observed.

[WadePatton]

The .58 balls that came out of the snow bank showed NO obturation......and where once atop 100 gr. 2f. They where not beat down the clean barrel, nor was the rammer thrown. Balls had the cloth patch impression.
kw

Wondering how much lead can move and go back into shape, plasticity that is. Other metals one can imagine obturating somewhat under the pressure of internal ballistics but not taking on permanent deformation and returning to original size/shape once it escapes the constriction and pressures of the bore.  Lead doesn't have a lot of spring-back though, as we all know, but do we know it on a thousandths of an inch scale?