Bullet Length Effects Theory [Archive] - Glock Talk

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preventec47
06-09-2010, 06:21
I am attaching a portion of Hornady's 4th edition loading data
for their 200gr bullets both hollow point and the shorter non-hollow
point what I like to call solid since it aint hollow.

It is not always good to make assumptions but for the sake
of this message making a point, I'd like to assume that since
both bullets are made by Hornady they would have same diameters
and jacket construction and jacket material etc.
The same cases and primers and powders are used as well.

Take a look at the AA7 and AA9 loads ( the only two that
are appropriate in terms of burn speed vs bullet weight )
using the same weight bullet and notice the
difference in performance, psi pressures and
amount of powder used.

As far as I can tell the only reason for loading data
differences here is the very small difference in bullet
length and the effect on usable case capacity
and the resulting effect on bore pressure.

What I see is that the shorter bullet has higher
velocities because of being able to use more powder
because of the lower pressures.

This is why I have become so sensitive to bullet length.

What other conclusions can be drawn ?

ctkelly
06-09-2010, 08:24
The weight of the bullet will have a direct effect on the amount of pressure that can be safely generated also. If it were as simple as just having more powder room I would load a 200 grain XTP out long for my 610 revolver and shoot it at velocities the 135 noslers can achieve....but it doesn't work this way.

Now of course...assuming same weight, jacket design, etc...then yes a bullet that is shorter in length will free up powder space which in turn will lower pressure. However you typically then have to compensate with more powder to achieve the same velocity. Many have found this to be true when working with the 10mm magnum.

There is merit in what you are looking at however.....if you take a look at the barnes XPB bullets which are all copper alloy, they are relatively long compared to other bullets in the same weight due to the difference in density of lead vs copper. However they will still fly faster than an equivalent length traditional lead core bullet, say 180 or 200 grains because of the difference in weight and pressure produced.

Quickload will show you the pressure curve, where peak pressure occurs, and if combustion is completed before or after the projectile leaves the bullet. Now quickload isn't the bottom line when it comes to things, like anything it makes certain assumptions and isn't 100% accurate...but for intents and purposes it does a pretty good job.

This post is going to seem like a bunch of rambling since its early in the morning and I keep adding stuff...

To get the shortest bullet with a hollow point in a given weight, the ogive is going to have a big part in this as will the size of the hollow point. Ogive will affect the feeding process, size of the hollow point will dictate its ideal velocity for expansion. The base of the bullet will also come into play...the GDHP in 155 grain has a dished or hollow base which will free up some room. However the size of the hollow point is rather large, even if it is bonded......I believe the GDHP has a problem withstanding top velocities and Mike McNett loaded these slightly lower than an XTP in equivalent size.

ctkelly
06-09-2010, 09:10
Hmm something to throw out there for your database...

155 Grn silvertip, .550 in length
155 GDHP .546 in length
165 Precision Delta .546 in length

What I find interesting is the construction of the 155 GDHP and the 165 Precision delta FP. They are both the same in length, but the delta is 10 grains heavier of course. It also has a similar base construction....the GDHP is dished and completely covered, the delta has the core exposed at the base but it is not flat with the jacket...it is in fact dished slightly like the 155 GDHP. The ogive is very different however between the two, as long as they feed reliably this wont affect much.

Then we get to the silvertip vs the GDHP. The gold dot has a large hollow point, but the cavity is rather shallow. The silvertip starts out with a large opening then has a smaller hole bored through deep within the bullet. The silvertip also has a flat base as opposed to the dished base. The ogive is similar but slightly different.

preventec47
06-09-2010, 09:27
[quote=ctkelly;15441330]The weight of the bullet will have a direct effect on the amount of pressure that can be safely generated also. If it were as simple as just having more powder room I would load a 200 grain XTP out long for my 610 revolver and shoot it at velocities the 135 noslers can achieve....but it doesn't work this way.

CT-
I cant tell from your post whether you
examined closely the data presented
which ALL had the identical bullet weight.
So for this post, bullet weights are irrelevant
because they are ALL the same and I dont
even know why you bring it up.
Look again. What you missed ( apparently)
were lower pressures even when greater
amounts of powder was used along with
higher velocities.

Actually yes it is as simple. I dont know if
your revolver could be loaded out long enough
but at some point (maybe even need a
longer case) yes of course you can shoot
the 200gr the same velocity as the 135 with
the same pressure.

I played with Quickload and the other programs
a couple of years ago and they are fun for
a while but while the mathematical models
are likely correct the characteristics of all
the powders are just being guessed at as
the characteristics are not published by
the powder companies and maybe they dont
even know what they are. Thusly, the
results in output are only as good or accurate
as the data inputs. If I remember correctly,
you can only select from a few powders for
each caliber being loaded. What I observed
once was that there was no mathematical
model at all, but simply extrapolations
between commonly available load data when
you changed a varialble such as bullet weight
or barrel length etc.

To prove that you can enter parameters
that you know would change the outcome
and often times the results would not change.
Then you KNOW the results are not being mathematically derived.

Not meaning to knock some of those load
simulation programs because they have
come a very long way and they are quite
helpful to a lot of people apparently.

What I think they are best for is to test
your understanding of internal ballistics
and see if the calculated outcomes or
at least movement of results matches
your expectations when variables are
changed.

preventec47
06-09-2010, 09:42
CT-
you have reminded me of a flaw in my presentation of bullet length.
The simple technique I illustrated assumed
flat bases that would allow for simple
calculations of space displaced in the case.
Where we have bullets with dished bases
and those whose jackets are rolled around
the edge with a depression for the visible
lead base, we would have to compensate
a little to arrive at an "effective" bullet length
for purposes of the calculation.

Actually I think it would be pretty easy to
get real close. Take micrometer and measure
the longest part of the bullet. That would
in all pistol bullets that I know of be to the
outside rear edge of the bullet. ( dont know
of any boattail pistol bullets)

Then take a round ball, something like a BB
and mike the distance from the bullet nose
to the end of the BB that is placed in the
rear depression of the bullet. Then just take
the average of those two lengths after
subtracting the BB diameter and we should
be real close to an accurate usable number
for length to use.

ctkelly
06-09-2010, 10:16
Actually I think I will bow out from your discussions from now on. I think you need to stop asking everyone (that includes the 6-7 other forums you have been trampling all over lately) to do testing for you and go out and do it yourself. In all the posts in various forums I have yet to see you actually post something about results of any load development or testing you have done so far....just a lot of theories and opinions.

preventec47
06-09-2010, 10:37
CT-
I am a little disappointed in the accuracy and childishness
of your comments but thanks for the bullet length info
and other contributions along with the dialog and advice.
The length info was used to update the main list.

"Trampled" huh. Great word choice.

_The_Shadow
06-09-2010, 22:47
I'll throw this out ther to make a point about the different length bullets...

What some have failed to realize is that the longer bullets have more frictional gilding metal surface area to resist being spit out of the barrel. This extra surface area(ever so slightly more) with the increase friction raises the overall pressure in addition to the space for powder being smaller to also increase presures more rapidly.

Now stuff them long boys in your pipe, then smoke'm if you wish!:smoking: