.17 WSM 20 grain dissection - Page 2 - RimfireCentral.com Forums

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  #16  
Old 07-17-2016, 08:13 AM
supermaggin

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Why do you think they use a "death crimp" on these? It's not a heavy recoil load.
To help keep the projectile straight while chambering? I would think the .200 in the neck is enough?

To build more pressure? I don't think it would make that much of a difference?
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  #17  
Old 07-17-2016, 11:48 AM
nvreloader
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Glass 37

The crimp that is used is a taper crimp,
the inside edge of the case neck is pressed into the bullet,
leaving over half the case neck thickness above the bullet.

The area of the crimp is still on the ogive of the bullet nose,
just before the full shank bullet diameter.

A measured 20 gr bullet is approx .602" long,
approximately .380'' of the bullet nose is projecting from the case,
full shank diameter is approx .210",
leaving approximately .392 of ogive on the bullet nose,
where the case neck is crimped on the bullet.

From my sampling.

Tia,
Don
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  #18  
Old 07-17-2016, 12:24 PM
Glass37
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Crimp is right at the .210 full shank diameter. Even with the taper crimp, some of the full shank diameter toward the bullet base is reduced to less than full diameter, correct? Why are these crimped so hard? Winchester must use some kind of collet crimper, they can't slam them into a shaped crimper at line speed, is whatever they use not adjustable???
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  #19  
Old 07-17-2016, 01:55 PM
nvreloader
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Glass 37

On my samples,
The crimp line/indent is at approximately .380",
just before the ogive, (which measures approx .392" in length),
meets the full shank base diameter of .172".

In this .010 to.012",
the inside case neck edge is tapered crimp approx .006" deep into the bullet,
being that the crimp is on the ogive,
the full shank diameter is not reduced to any great amount.

The reason for crimping so hard is,
1. Ammo makers are not sure which type of firearm the ammo is going to be shot from,
a clip/magazine semi rifle imparts different forces upon the bullet nose/case,
than does a bolt action, or single shot etc.

2. The crimp is used to retard the powder pressure,
until it's maximum PSI is developed,
for whatever powder/case combo used etc,
without any crimp,
the bullet would be pushed into the bore by the priming compound,
which would lead to VERY poor ballistic results.

Never having toured the Win factory,
I believe that they have a tapered crimper on the final step,
that taper crimps these rounds/cases,
seeing that the crimp is only .006" deep,
(about 1/2 the neck thickness of .012"),
and approximately .010" long,
it would not take much pressure to crimp the case neck,
as the bullet is softer than the brass case neck.

Those cases speed along at several thousand cases p/hr as they are crimped,
remember that it takes a PINCHED area on the rim to ignite a RF case,
when the crimp is applied, the whole flat base of the case is supported,
I would believe there is some type of safety shield,
in place at that section of production line,
as the ammo does not ignite when slammed home,
when chambered from a semi action type rifle, correct.

They Win and SAAMI set the spec's for factory ammo crimping etc,
depending on powder load spec's etc.

Yes, I would dearly love to see this type of ammo be produced,
a fairly remarkable process.

To get a better view of the crimping area,
USE AT YOUR OWN RISK,
VERY VERY carefully use a tubing cutter and cut a case in half,
DO NOT USE ANY POWER TOOLS THAT CREATE ANY HEAT or SPARKS ETC,
you wont like the results, if you do.

Take the front half and find a drill size 3/16",
drill a hole in a piece of bar stock,
alum works fine, counter sink a hole with a 1/4" drill deep enough,
to hold the case neck/body at the tapered shoulder,
drop the front half into this 1/4" hole,
then use a 11/64" dia rod to drive the bullet thru the case neck,
you can then get a good picture of where/how the crimp is on the bullet etc,
I repeat again,
USE THIS METHOD AT YOUR OWN RISK.

Tia,
Don

Quote:
Originally Posted by Glass37 View Post
Crimp is right at the .210 full shank diameter. Even with the taper crimp, some of the full shank diameter toward the bullet base is reduced to less than full diameter, correct? Why are these crimped so hard? Winchester must use some kind of collet crimper, they can't slam them into a shaped crimper at line speed, is whatever they use not adjustable???
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  #20  
Old 07-17-2016, 03:25 PM
Glass37
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Thanks for the description and info. I used the first half of that bullet removal method and slit the neck with a Dremel. As for the cycling capability of this round, speaking of the bullet crimp only, it would have no problem at full auto, me thinks.
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