Bullet "bump up"

[Naphtali]

What I think I'm attempting to identify is the relationship among smooth relatively force free loading of muzzleloading bullet, obturation during ignition, and accuracy.
***
During ignition any bullet base moves first. I have been informed that included in "moving first" the base expands slightly - perhaps the entire bullet, for all I know. I have been informed, again, that this expansion is anticipated because it is supposed to obturate grooves.

If the previous paragraph is more or less accurate when referring to lubed bullets and/or Minié Balls - yeah, I'm aware that patched balls do not completely obturate grooves -

1. What is the "bump up" for solid base lubed bullets in the .58-.69-caliber range in thousandths or tenths?

2. What is the "bump up" for lubed Minié Balls in the .58-.69-caliber range in thousandths or tenths?
***
If I am asking the wrong questions, please respond, as though I asked, to what are the right ones.

 

[David W.]

How much the base of a Minie ball expands depends on the amount of powder used (no more than 60 gr.) FFg. Otherwise, the base will flare out when it exits the barrel and greatly affect accuracy. The Improved Minie will take a much heavier charge.
Due to the softness of lead, yes, even a pure lead round ball will obturate somewhat, but the ball will NEVER fill the grooves. That's the reason for using a patch, to "grip" the ball so that it will spin instead of skipping over the rifling.

A conical will increase in diameter, and the overall length will shorten at the same time. It is difficult to say how much because how tight, or how loose the conical fits in the bore factors in.

 

[Flash Pan Dan]

That is a tricky question to answer. The amount of obtrusion is relative to the hardness of the material and the overall mass of the projectile. A 500 grain conical of pure lead will obtrude more than a 128 grain round pure lead ball of the same caliber. Other variables also come into play; burn rate, air density, bore condition, etc. Is there a particular application to which you are trying to obtain or are you just musing over the point? Both of which are valid, but trying to find answer to a unique condition would be simpler that a general “rule of thumb” answer to this question.

 

[nkbj]

I suspect that larger bore sizes will get expansion on the ball with a fiber wad and stout charges but I haven't tested out the theory. In reality the "expansion" might just all be south of the equator.
How much plain base conicals will expand just depends on the charge, the projectile hardness and how close the projectile diameter is to the bore and groove diameters.

 

[ken.clements]

What I think I'm attempting to identify is the relationship among smooth relatively force free loading of muzzleloading bullet, obturation during ignition, and accuracy.
***
During ignition any bullet base moves first. I have been informed that included in "moving first" the base expands slightly - perhaps the entire bullet, for all I know. I have been informed, again, that this expansion is anticipated because it is supposed to obturate grooves.

If the previous paragraph is more or less accurate when referring to lubed bullets and/or Minié Balls - yeah, I'm aware that patched balls do not completely obturate grooves -

1. What is the "bump up" for solid base lubed bullets in the .58-.69-caliber range in thousandths or tenths?

2. What is the "bump up" for lubed Minié Balls in the .58-.69-caliber range in thousandths or tenths?
***
If I am asking the wrong questions, please respond, as though I asked, to what are the right ones.

Well”¦.. :hmm:
I think”¦.
It could be”¦.
Although it may be”¦. :redface:
obdurate= yep heard that once (dog gone high falutin’ words) :surrender:
If the Minie (lubed) falls down a clean barrel = it’s too small = you all won’t hit what you want :td:
If the Minie (lubed) has to be lightly pushed down a clean barrel, it’s good = you’ll hit the target. :thumbsup:
If the Minie (lubed) don’t fit down a clean Barrel = you mixed up the rifle’s and Minie’s at home = go on home and get the right one :slap:

:grin:

 

[Dphar]

What I think I'm attempting to identify is the relationship among smooth relatively force free loading of muzzleloading bullet, obturation during ignition, and accuracy.
***
During ignition any bullet base moves first. I have been informed that included in "moving first" the base expands slightly - perhaps the entire bullet, for all I know. I have been informed, again, that this expansion is anticipated because it is supposed to obturate grooves.

If the previous paragraph is more or less accurate when referring to lubed bullets and/or Minié Balls - yeah, I'm aware that patched balls do not completely obturate grooves -

1. What is the "bump up" for solid base lubed bullets in the .58-.69-caliber range in thousandths or tenths?

2. What is the "bump up" for lubed Minié Balls in the .58-.69-caliber range in thousandths or tenths?
***
If I am asking the wrong questions, please respond, as though I asked, to what are the right ones.

Well”¦.. :hmm:
I think”¦.
It could be”¦.
Although it may be”¦. :redface:
obdurate= yep heard that once (dog gone high falutin’ words) :surrender:
If the Minie (lubed) falls down a clean barrel = it’s too small = you all won’t hit what you want :td:
If the Minie (lubed) has to be lightly pushed down a clean barrel, it’s good = you’ll hit the target. :thumbsup:
If the Minie (lubed) don’t fit down a clean Barrel = you mixed up the rifle’s and Minie’s at home = go on home and get the right one :slap:

:grin:

The issue Minie was .015" undersized IIRC. Had to be to load in combat.
If you read Mann's "The Bullets Flight" you will learn that even the 30-40 Krag would produce better velocity and at least equal accuracy with BORE SIZED bullets. These were jacketed an he was shooting early smokeless. Even these expanded and filled the rifling. He referred to lead bullets as "putty plugs" so soft they deformed TOO easily.
Bullets .010 under groove will shoot fine in a BPCR, I have won a number of prizes shooting them and ALL the ML bullets are at LEAST .010" undersized from the GROOVE dimension of the barrel some perhaps .20" if the barrel has .010 deep grooves. Being very near bore diameter keeps them properly centered in bore so when they expand as they start to accelerate they are supported so as to expand "square" with the bore.
The expand BEFORE they move BTW and before any gas reaches the base of the bullet.
Dan

 

[Tumblernotch]

Actually the Minies issued for use in US rifle-muskets were only .005" under bore size. The standard for the .58 was .575 and the one for the .69 was .685. There were however many variations, especially in cast bullets from different manufacturers. I would say that the standard was more closely followed by those who swaged the bullets. But as far as what was called for by the Ordnance Dept. they were supposed to be .005" under.

 

[Dphar]

I am trying to remember where I got the .015 number.
I have a book with the drawings and dimensions of the 58 and 69 Minies and they are as you state.
I have a guy that might know but he is likely in bed.
I might be thinking of the Williams bullet with the zinc base that was used to try to scrape out the fouling. There were several versions of this. None did much.
I know I came across it someplace but in 40 years of reading its sometimes hard to figure where it came from.
Will do some more digging and see if I was dreaming or not.

Dan

 

[ken.clements]

I believe old war department records....
I cant remember if it was because of the Enfields Minies not fitting in the Springfields or vica versa..
old age :redface:

 

[Joel/Calgary]

[soapbox] The pedant in me has to get in here. "Obturate" is a term that occurs in many technical and scientific areas, and it always means to seal or stop-up something. It does not refer to a particular mechanism for achieving this sealing/stoppage. It is a transitive verb - something obturates something else. If no gas escapes past a bullet or ball, the bore has been obturated, whether that is achieved by tight fitting of the ball or bullet & patching, by deformation of the projectile, or by a wad underneath. If a projectile diameter or base is bumped up but fails to seal the bore, then the projectile has neither obturated (period) nor obturated the bore. In ballistics technical literature, the term is always used this way. It is only in informal discussions of internal ballistics that there has been conflation of the effect with one of the possible causes, and that misuse has been a point of long-standing controversy.[/soapbox]

Regards,
Joel