ODG's Velocity Measurements

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rgchristensen
Posts: 180
Joined: Sat Jan 16, 2016 10:51 pm

ODG's Velocity Measurements

Post by rgchristensen »

Bullet velocities were certainly measurable in the 19th century. Ballistic pendulum, rotating disks, Boulenge chronograph, spark drum, probably others. I am sure that top shooters of the time were aware of the velocity of their bullets and noted the effects of velocity changes. But they were not capable of making such measurements as we readily do today, and thus to examine minutely the aspects of loading protocols that we use to get the very small velocity SD's that we are routinely able to obtain.
I have raised this point in order to point out that there is more than one way to skin that cat. We can either go to higher velocities, and pay the penalties of increased recoil and greater wind deflection, or seek ever-smaller velocity SD's, in order to obtain lesser vertical dispersion at long ranges.

CHRIS
bruce m
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Joined: Tue Aug 04, 2009 5:25 am
Location: australia

Re: ODG's Velocity Measurements

Post by bruce m »

chris,
you raise an interesting subject.
one thing we know is that the victorians were not dumb, they just lacked the technology we have today.
they understood physics and the maths that go with it.
i suspect the ballistic pendulum was an earlier innovation, followed by such things as the spinning drum.
big ammunition companies and governments had the money to do such things, but the average joe might well have had no access to such things.
many shooters , more than today, were firing bullets and recording data and comparing it.
my own suspicion is that most guys just kept adding powder until the targets showed the least vert.
they might have found velocity of more interest in relation to sight settings than for s.d.
reading suggests that they even thought of sight settings more in terms of powder charge than velocity.
metford spoke of how much powder it took to change poi 1 moa.
i have found it not hard to get e.s. down to 4 fps with black powder.
is this relevent if there no vert.
we try to predict reduced vert using low velocity variation, but you can predict low s.d. by using small vert in reverse.
to muddy the waters, you can get good vert at 1 range by a thing happening called "compensation", where slower bullets shoot higher than faster, and they all come together at a given range, after which the slower ones shoot lower.
creedmoor was shot over 3 ranges, so compensation would not help unless you used a different load for each range, thus low s.d. is a better choice.
you can also get very low velocity s.d., buy that load will not group.
this is really a can of worms.
it seems that most long range odgs did not compress, but did droptube.
any fireformed case that would not droptube to a certain height was thrown away.
failing to do this was known to demonstrate vert.
the brits looked for 90 gns of their powder, and the americans looked at 100 gns as optimum for 45 cal long range shooting.
later in the era the americans started increasing that up to i have read 112 gns.
these numbers probably come from experience.
another thing that affects s.d. is bullet alloy, particularly with bore diameter pp bullets.
harder bullets bump less into the rifling and have less friction, allowing more consistent velocities.
but too hard an alloy will not obturate properly, causing a plethora of problems.
inconsistent wiping can produce higher s.d.
then we come to blowtubing, a great way to get high s.d. if you don't have it mastered.
all these things were probably of little concern to most hunters and farmers, who would have been more concerned with expense, and so used the least ammount of powder possible.
bruce.
ventum est amicus meus
Etienne Brule
Posts: 209
Joined: Fri Aug 17, 2007 2:52 pm
Location: Quebec city, Canada

Re: ODG's Velocity Measurements

Post by Etienne Brule »

bruce m wrote: Thu Jul 23, 2020 5:04 pm chris,
you raise an interesting subject.
[...]
i have found it not hard to get e.s. down to 4 fps with black powder
[...]
bruce.
WOW Bruce,
I just cannot make it so low...
I will keep reading this post.
Gerald
bruce m
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Joined: Tue Aug 04, 2009 5:25 am
Location: australia

Re: ODG's Velocity Measurements

Post by bruce m »

etienne,
that is for 10 shots repeated.
seating depth and powder charges.
and of course careful thorough wiping for consistent barrel condition.
weighed cases and primer selection, with printer paper in the primer pocket.
hand lapped barrel.
bruce.
ventum est amicus meus
Etienne Brule
Posts: 209
Joined: Fri Aug 17, 2007 2:52 pm
Location: Quebec city, Canada

Re: ODG's Velocity Measurements

Post by Etienne Brule »

bruce m wrote: Fri Jul 24, 2020 5:11 pm etienne,
that is for 10 shots repeated.
seating depth and powder charges.
and of course careful thorough wiping for consistent barrel condition.
weighed cases and primer selection, with printer paper in the primer pocket.
hand lapped barrel.
bruce.
Hi Bruce,

You are just making me busy for some weeks ... lol ...

Thank you !!

Gerald
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