Thoughts on "load inertia"

[Daryl]

I-too look with excitement on Larry's experiment's.
I modified the post above to remove the 'slam' against a forum member. We here have seen his posts on marble shooting and at close range, he is getting good accuracy with what seems a 'fun' load for plinking, for him. I agree, Roundball, that part of the post was certainly unnecessary.

[Daryl]

I think the gist of the question here is, shooting a normal PRB combination, is there any obturation or fattening of the ball when fired. And if so, how much. And what parts do lead purity, loading compression, powder charge/granulation and fouling play. What provides resistance at the moment of ignition to assist in obturation if any.

 

Our normal loads use a ball .005" under, with a .020" to .025" denim patch - compressed with a mic. A pair of calipers will give measurements .003" to .005" thicker, compressed between the fingers, not just with a thumb on the slider and using the wide part of the tines as the contact surface.

I have some pre-lubed pillow ticking, marked .018", however it's only .012" by my mic., .015" with my calipers.

We don't use mallets, only a starter, sharp smack, or by using the short stud on ball and a smack of the palm on the opposite side. This puts the patched ball down 1/4" to 1/2" depending on the length of the stud. From there it is advanced down the bore with the long shaft of the starter. It may, if you prefer, be loaded as Dphar showed in his video, by just using the rod, but after it is pushed into the bore far enough to make the patched ball, fit the bore.  Just fir fun, I loaded a few as Dan does, using my .40 (.398" bore) with a .0215" (mic'd) denim patch and .396" round ball. The ball is only .002" smaller than the bore, yet using Dan's process, it was loaded with the 3/8 hickory rod. I prefer to use a starter, as it's easier & faster loading.

In using a long strip of cloth seating the ball some 1/2" into the bore, then pulling the ball out by the cloth's tags, it is marked all the way around, lands and grooves - if you use a substantial patch and a large ball.

In the .577 Musketoon (progressive depth rifling), with it's .574" bore and .003" rifling at the muzzle, a .575" ball, even with a thin .013" denim (mic'd) patch, will show heavy cloth impressions all the way around the ball, land and groove. It shoots very accurately, but - since the groves are .008" deeper at the breech,  obturation would seem to be necessary to fill the rifling depth at the breech.  The barrel does not to foul for a day's shooting with no wiping at any time, even though the ball/patch is .008" 'loose' on each side, at the breech - perhaps they do obturate - some?

 

[Dan]

Methinks this is getting some interesting thought.

I think you all realize that there isn't going to be a quick, easily found answer to this.

 
YEP!

On the matter of ball size vs. bore size, I have used .440" balls in a .450" bore quite a bit and they shoot well with a .010" patch.  Perhaps a bit better with .015" patch but it's hard to make that call with offhand shooting from one day to the next. Both are far better than minute of deer heart at 50 yards and that has been my only litmus to date.

There is much to ponder and perhaps most will only be determined on the line rather than here. Some of it, such as the effect of a ball screw might not be so difficult....

[Dphariss]

It may, if you prefer, be loaded as Dphar showed in his video, by just using the rod, but after it is pushed into the bore far enough to make the patched ball, fit the bore.  Just fir fun, I loaded a few as Dan does, using my .40 (.398" bore) with a .0215" (mic'd) denim patch and .396" round ball. The ball is only .002" smaller than the bore, yet using Dan's process, it was loaded with the 3/8 hickory rod. I prefer to use a starter, as it's easier & faster loading.
 

It seemed to load a harder than "normal". Could be this batch of ticking is little thicker than what I had been using, the rifle had not been shot since 2007 so this batch of patching might be a little thick. I hardly ever measure the stuff so this is possible.
I should have loaded a 530 too I guess.

Dan

[Daryl]

Methinks this is getting some interesting thought.
On the matter of ball size vs. bore size, I have used .440" balls in a .450" bore quite a bit and they shoot well with a .010" patch.  Perhaps a bit better with .015" patch but it's hard to make that call with offhand shooting from one day to the next. Both are far better than minute of deer heart at 50 yards and that has been my only litmus to date.

Dan- please note the target shot in this post from the accuracy thread.  It shows both bench and offhand targets shot with tight shooting load and those of lesser accuracy.  It shows a load that groups closely, does so offhand as well, and one that spreads, falls apart when shot offhand - just as expected.
http://americanlongrifles.org/forum/index.php?topic=4307.msg41908#msg41908

[Dphariss]

What often happens in any shooting is what a friend calls "the law of compensating errors.
If the errors compensate. The shooter is off to the left and and the ball off to the right making a center shot.
In limited  testing, one group of a group of 3-5 shots can result in the fliers from the group being well placed and making the load look better than it is. Thus serious accuracy testing requires 20 shots or more to prove the accuracy.
In offhand shooting a shooter might not be aware of  a poor load if he does not have the offhand skill to know when a shot is "off or on".
If the shooter calls the shot low left and is confidant of the call and the shot goes high right the load may be the fault.

So shooting a poor load because offhand "don't matter" is silly as Daryl pointed out.

Dan

[Dan]

Not sure how to interpret that actually, or if it is really pertinent to the point.  I would expect any load to shoot a smaller group from a rest.  My comparison went to the point of a previous comment about ball/bore size and what results, this in context of obturation.  Shooting offhand does not validate the accuracy potential, nor is comparable accuracy with different loads invalidated by offhand shooting...in my opinion.  Until now I have been viewing demonstrated accuracy in my rifle in context of field use, not scientific analysis of accuracy.  I'm not certain the endeavor proposed here on the question of load inertia will assure less dispersion either, but it might answer a few questions about obturation and perhaps management of fouling or charge compression.  On point of my comments about small balls and patch thickness, the rifle shoots on average about 2" groups of 5 at 50 yards. Sometimes a bit less and sometimes a bit more.  Patch thickness does not seem to influence that within those narrow parameters.  I'll hunt with either, any day of the week, and keep my shots within that range until I demonstrate suitable accuracy at greater distance. The image below is somewhat representative of what I'm speaking of but the load specifics are not immediately available. Maybe one patch or the other, not sure.  Same day in any case.



Whether I'm skilled at offhand shooting is another question entirely but the target below was fired on the same day and it largely self explanatory.  Together, the targets represent my standard with each rifle and how I employ each for field use.



I guess the thought I had was this:  If a .440" ball shoots sufficiently well at a given distance and comparably to a load differing only by greater patch thickness, why? There is an introduced variable that does not seem to have any great effect.  Is it the result of obturation or magic?

I was just looking at a couple of balls recovered at the range after a days shooting and pass this along without any conclusions whatsoever.  One measures .455" in diameter over what would correspond to the groove diameter, or the raised portion of the engraved rifling pattern.  I don't know the groove diameter in the barrel but the bore was pin gauged at .450" and I'll say that is accurate +/- .001".  The patch material is very fine weave, type unknown, measuring .010" in thickness. Similar thread count to silk in any case, and it left no discernible weave impressions on the ball. The ball is noticeably flatter on the base than forward part of the ball.  It looks like the result of obturation but I won't make that claim, simply because of the nature of the media than stopped it, very soft white fluffy sand. The ball is not appreciably deformed otherwise. The engraved portion of the ball measures ~.015" in length. 

The second ball is not so substantially engraved and is likewise unmarred so far as visual inspection reveals. It does not have the appearance of upset.  The engraved portion is ~.010" in length.  Both were recovered during an early phase of load testing when the charge quantity ranged from 30-50 grains of Goex fffg powder.

Collectively they say nothing concise about the matter of obturation, but at this point, and in context of the thread, they give reason to pursue the question so far as I'm concerned.   

I am inclined to query what is going on inside the breech end of my rifle since Dan brought it up.  Along the way I'll let you know what comes of it.

Dan the Other

[Daryl]

Good shooting offhand - the only rifle I've been able to shoot offhand like that is the .69.  It's short, but heavy barrel just seems to stop in the target - good trigger and instant ignition surely helps.  The flinters, both with some muzzleweight, seem to wander constantly and are most difficult to shoot due to the timing required - to tough off as they're coming in - variations in ignition timing will throw shots out.  Flinters are certainly a challenge.  Of course, they all hold better when they're empty.