A 'TANDEM TEN' LOAD
What happens if you load two
projectiles
(bullets) into a semi-auto pistol cartridge? - Does the gun blow-up,
- do they just lock together as a single slug – or maybe you might
get the result that I was seeking and get two holes in the target for one shot.
When
I came across a story by
Wiley Clapp in
an American shooting magazine (GUNS & AMMO Nov.1990) I was
immediately intrigued by the possibilities suggested by that story
about loading multiple bullets for use in .38s and .357s. Mr Clap
told how to use bullets cast from a Hensley
& Gibbs #333 mould
to wildcat two or even three-bullet loads in a revolver.
#333 Mould and Cast Bullets
It struck me that my favorite semi-auto pistol cartridge – the
10mm Auto, was a little like the .357” in that they both are longer
straight sided cases when compared to a 9mm Luger or the .45ACP.
Perhaps - like the .357”Magnum, - there might be enough room inside
a
10MM brass case for more than one projectile.
- Grabbing a hacksaw
I cut open a case and then shortened two cast pills to approximate
the length that I thought a pair of 100gn x .40”pills would be -
if loaded into the 10MM case. Well they looked comfortable and very
much 'at home' – and there was room for a normal looking amount of
powder to fit behind the twins – so maybe I was onto something
useful.
'MOCK-UP' Of 10MM DUPLEX LOAD
If two 100gn 10mm (.40”) pills
could be safely fired from one round
in a 10MM semi-auto like the
GLOCK 20, and give minimum separation
on a target at short ranges – seven to ten metres – the surface
area on impact would be twice that of a single bullet but still
deliver the same momentum, and reduce over-penetration.
- A problem that I
have experienced in Bowling Pin Matches is that often a decent
on-target hit with the 10MM will splinter the pin and leave it
spinning on the table while the bullet goes straight through without
stopping - and carries on unperturbed to the backstop, - whereas a
slow soft .45” slug will push the pin gently back and off the table
while lodged in the timber pin.
10MM - May be HOT when fired !
I
have a theory about the lack of enthusiasm for the 10MM Auto in
America. - When Col Jeff Cooper was proposing the development of a
powerful cartridge between .45” and 9mm – he should have first gone with
something smaller like the .40”S&W (short & weak !) - Then
later on, had a public 'eureka
moment'
and proposed a magnum
version for real Americans - called maybe THE
.40”AUTO MAGNUM
.
It would be the same
superior, versatile, flat shooting, powerful, and controllable
caliber
for modern handguns as it is today – but with an 'All
American'
name
that even "Bubbers"
could vote for – it's a MAGNUM, an American
Gun.
The
Wiley Clapp .357' double / triple load in
GUNS & AMMO
was worked-up as a defensive load using very short 'wadcutters' cast
from a Hensley & Gibbs #333 Mold. These hard cast bullets weigh
only 66.6gn and measure just a quarter of an inch front to back. This
short flat shape readily allows three pills to be gang-loaded into a
.357" Mag case (and two into a .38”) – and there's no snags to
using a flat nosed wadcutter round in a revolver. - Certainly if I
could find a #333 bullet mould in New Zealand I'd
snap it up like a cold beer in the desert, and would load up rounds
for my six inch barrel
RUGER .357".
– But of-course wadcutters wouldn't
do in a 10MM semi-auto - which would certainly need some
lead-in
from a tapered or round nose projectile to help feeding up the ramp
into the chamber. What I had in mind was a shallow 10mm pill weighing
no more than 100gn with a truncated cone nose profile that would feed in
a semi-auto action when poking out of the front of the case, – but
the same tapered nose, when reverse-stacked (base-to-base) with the
top slug would ease down into the internal tapering case and act like
a semi boat-tail back end for the twins and help them slip into place
without pushing out a bulge on the outside wall.
First I approached some guys who were swaging projectiles requesting
a batch of lightweight 100gn pills,- but they said that they
couldn't swage them small enough for me – So next I turned to a
fellow Pistol Club member who had told me that he'd made his own
mould to cast 9mm Truncated cone pills to feed a GLOCK 19 Compact. -
Robert liked the idea – and in only a couple of days he produced
samples weighing exactly 100gns that looked great except he couldn't
get the lube to sit in the grooves using his homemade sizer /
lubricator - so we tumble lubed the samples for testing.
Thinking
'all care'.. I decided to use brand new
Winchester
10MM cases and hand seated the Winchester large primers using a
LEE
Ram-Prime. I ran all the new cases through the sizer die before
priming and bell-mouthing them. The 100gn bullets were covered with a
slightly tacky coating of lubricant so I wiped clean all the bases
using a rag on a flat surface to ensure the sticky brown lube didn't
glue them together as one slug.
The first five cases were loaded with o
ne
only 100gn projectile over a light charge of Winchester Superlight
(WSL3) – really just to ensure that the cartridges would feed in &
out of the GLOCK 20 chamber and confirm that the bullets 'truncated
cone' shape would work. - Robert had sized the castings to .401”
and I seated them down to give an overall cartridge length of 1.160”
which looked right and they barrel-dropped and fed up from the
magazine when hand-cycled through the action.
Glock 20 10MM - Functional & So Good-looking !
Not wanting any complications caused by a compressed powder load, I
had measured the powder space below the duplex load which indicated
that a maximum powder charge of WSL3 might be 5.0gn. I also needed to
ensure that more than half the capacity was filled behind the bullets
to eliminate the chance of the propellant flame 'flashing' across the
powder surface and resulting in an instant detonation with high
pressure – so I chose a bottom limit powder charge of 3.0gn WSL3.
Hand weighing each charge on scales I loaded five duplex loads each
of 3.5gn, 4.0gn, 4.5gn. & 5.0gn powder charge and the paired
100gn pills balanced and fed easily into place for the crimp to be
applied to each case just like bought ones before sealing them into
clearly marked plastic bags.
When I got to the outdoor range it was a dull day with just enough of
a breeze to blow my note paper away every time I forgot to weigh it
down with a rock. - I set-up two IPSC buff targets and stuck a large
black patch in the A-Zone as an aiming point and fired the five 100gn
“singles” - making a fair group but had to hand eject as they
were too light to work the
GLOCK 20 action.
- The first twin-load chambered -
and POP
as
two 'snake eyes'
appeared near enough
to the black patch. - Yeahh!, quickly in with the magazine holding
the remaining four 3.5gn loads – and a nice set of paired holes
built up on the cardboard target – this was getting to be
fun . - The big 10MM
GLOCK 20 was running like an Austrian watch on these twins and the
paired holes were appearing right where they should.
- It wasn't
until I got to the 4.5gn loads that the “plastic
phantastic”
began to feel like a 10MM – and the 5.0gn loads did get the GLOCK
to move a bit - ejecting the spent cases three or four metres to the
side. A bit far to retrieve them conveniently - but no excess
pressure signs. The 10mm brass is a lot easier to find than lesser
cases – try picking 9MM cases from the gravel when they're mixed in
with all those broken bits of Desert Eagle in the dirt!
-Having used all my test loads at seven metres I had to go home and
load more to try on bowling pins – and I also needed to check
the spread at longer ranges and pick a standard powder charge to run
with. - Close examination of the targets showed that some of the
hottest 5.0gn loads had tumbled and gone through the target sideways
– and the lighter charges had given the widest separation on the
target, suggesting that a powder charge somewhere between 4.0gn &
4.5gn as thrown by my
LEE Powder Thrower should give
the optimum result.
I loaded fifty more of the
'tandem tens' again using new
Winchester cases with a thrown powder charge of 4.3gns
of the
WSL3 propellant. I was working the next couple
of weekends but in due course I got to the range and set-up another
clean IPSC Target at 25 metres and test fired five rounds - with the
paired holes ringed by felt pen between each shot. - the widest
spread at this 25metre range was 135mm (5.5”) and the friendliest
pair were only 20mm (0.5”) apart.
- So far, so good – but the big
test was to see how bowling pins reacted to my home-made pin-
pushers. - setting-up a couple of slightly used pins and carefully
aiming ..'whack'
- the twin loads certainly knocked the plastic coated pins back and
off their table – with all the 100gn pills staying under the
plastic coatings rather than blasting splintered exit holes. - I'd
have to shoot pin matches to prove the load, but certainly the duplex
rounds demonstrate the versatility of Col. Coopers ideal calibre for
semi-auto pistols. It would be hard to develop a similar load for
shorter
auto calibres such as the 9mm, .40”, or .45”.
Marty K
After researching & writing 1,036 blogs I've got something NEW to try .. I've signed-up to Patreon. - In over five years I've not made one cent from this .. NOW you can send me a wee support $ - starting from $1. to get all this stuff from New Zealand - over a year that's nearly the price of one Shooting magazine. - Am I worth it?
https://www.patreon.com/user?u=16618870
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