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Hot Topic (More than 10 Replies) Matching the bullet to the barrel (Read 9024 times)
JLouis
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Re: Matching the bullet to the barrel
Reply #15 - Nov 30th, 2017 at 9:00pm
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When shopping for a new bullet and if possible it is best to try several designs and sizes from friends before possibly ending up with one that does not quite shoot that well in one's particular rifle. I know there are several here that are more than willing to do so and why I brought it up.

JLouis
  

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bruce moulds
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Re: Matching the bullet to the barrel
Reply #16 - Nov 30th, 2017 at 10:03pm
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red cent,
good question, so i will describe the nose as i see it.
starting at the front of the bullet is the meplat.
on a flatnose or a hollow point, this is flat.
a  spitzer soft point or round nose is hemispherical, defined by its diameter.
a perfect point is self explanatry, but will not work as it cannot hold the skin of air that must accompany the bullet in flight.
an elliptical is almost hemispherical, and can be regarded as such, particularly as most so called elliptical moulds have a hemispheric meplat due to easier machining.
behind the meplat is the ogive, or curvy bit that joins the meplat to the rest of the bullet.
behind the ogive is a paralell section of the bullet.
this can be either the shank of the bullet, if it is groove diameter, or part of the nose if it is bore diameter.
here is where problems can arise with black powder, as this bore riding part of the nose can bump up into the rifling and cause leading.
on a paper patched bullet, this area would be protected by a patch.
keep safe,
bruce.
  

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Red Cent
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Re: Matching the bullet to the barrel
Reply #17 - Dec 1st, 2017 at 3:16pm
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Questions:
"...but will not work as it cannot hold the skin of air that must accompany the bullet in flight."
Are you saying a sharp pointed bullet causes accuracy problems?
"....is the ogive, or curvy bit that joins the meplat to the rest of the bullet."
I always interpreted the ogive as the point where the nose of a bullet goes parallel with bore/bullet.
"...as this bore riding part of the nose can bump up into the rifling and cause leading.
Would breech seating minimize the leading problem.
Roll Eyes Hope nobody is doing this. Smiley
  

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bruce moulds
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Re: Matching the bullet to the barrel
Reply #18 - Dec 1st, 2017 at 4:18pm
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red cent,
yes a bullet with no meplat will not shoot well, as it continually forms and releases the layer of air in the bullet, causing shockwaves which make the bullet unstable.
i apologise for not remembering the name for that layer, or skin, of air.
there is a minimum meplat size known to hold the layer of air, and it is pretty small.
breech seated bullets under groove diameter will bump up to fill the grooves just like fixed ammo.
recovering fired bullets is an interest in itself.
bre riding nose leading can be dealt with by lubricating the inside of the barrel.
blowtubing presents a lubed barrel to a bullet.
when wiping, use of soluble cutting oil can leave a fine film of lube in the barrel if done cunningly.
keep safe,
bruce. 
edit.
the name of the skin of air around the bullet in flight is "boundary layer".
« Last Edit: Dec 1st, 2017 at 7:33pm by bruce moulds »  

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bruce moulds
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Re: Matching the bullet to the barrel
Reply #19 - Dec 1st, 2017 at 6:31pm
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red cent,
i am not sure whether you are talking about using smokeless or black.
what works best for one does not necessarily hold for the other.
firstly, smokeless bullets can readily be loaded to supersonic velocities, where a spitzer type nose is superior.
transonic velocity is from mach 1.2 down to mach 0.8, and is little understood to this day.
we do however know that the spitzer is not the best nose shape for these speeds.
max black powder velocities with longer range bullets are about the top of the transonic range, meaning that most of their fligh is transonic, then going fully subsonic.
if you are shooting out to 200 yds, it is easy to keep a cast bullet above mach 1.2, or truly supersonic, all the way.
secondly, black powder bumps bullets up a lot more than smokeless.
william metford did a lot of work developing hardened lead alloy bullets, and discovered that softer bullets bumped harder into the rifling than hardened ones, to such an extent that the increased friction reduced velocity.
he found that it was necessary to expriment with alloy hardness to establish an optimum balance between reducing friction and still sealing the bullet in the barrel to hold gas pressure and eliminate the gas cutting caused by blowby.
my own experiments reveal that 12:1 lead/tin bore diameter pp bullets will bump up full shank length to take the rifling and seal the bore.
this alloy holds it nose shape better than softer alloys producing higher b.c. and less drop, with reduced wind deflection.
in the day, long range bullets tended to be pp, as they could establish max nose length attainable, the rest of the bullet being protected from the barrel by the patch, giving the least drag possible.
keep safe,
bruce.

« Last Edit: Dec 1st, 2017 at 6:37pm by bruce moulds »  

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Red Cent
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Re: Matching the bullet to the barrel
Reply #20 - Dec 2nd, 2017 at 6:50pm
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Thank you for the explanations. Trying to soak up this stuff.
  

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