How Do You Safely Duplex Load With Slow For Cartridge Powders?
- Thread starter yodogsandman
- Start date
yodogsandman
Well-Known Member
Are you guys duplexing IMR 7383? I wouldn't do that from what I've read about it.
Jeff Bartlets description of it...
IMR7383 This is a slow burning stick powder originally used for the Cal. .50
M48A2 Spotter/Tracer round. This is not the same case as that known as
the .50 Browning Machine Gun cartridge. This powder is NOT recommended
for the .50 BMG round. It is a very bulky, single-based powder, composed
of 85% nitrocellulose and 15% stabilizers, flash inhibitors and graphite;
that was developed to replace the IMR4831 powder that was being used.
It has about the same propellant energy as IMR4831 when compared in equal
volume. IMR4831 data can be used. Begin with starting loads, reduced 15%
by weight.
This is new powder, not pulldown.
$60/7# jug
Jeff Bartlets description of it...
IMR7383 This is a slow burning stick powder originally used for the Cal. .50
M48A2 Spotter/Tracer round. This is not the same case as that known as
the .50 Browning Machine Gun cartridge. This powder is NOT recommended
for the .50 BMG round. It is a very bulky, single-based powder, composed
of 85% nitrocellulose and 15% stabilizers, flash inhibitors and graphite;
that was developed to replace the IMR4831 powder that was being used.
It has about the same propellant energy as IMR4831 when compared in equal
volume. IMR4831 data can be used. Begin with starting loads, reduced 15%
by weight.
This is new powder, not pulldown.
$60/7# jug
RBHarter
West Central AR
As a historical foot note only .
The 30-06 was briefly , for experimental purposes and later intensively , fitted with flash tubes to carry the primer flash to the top of the powder charge rather than the bottom . In the tests at Springfield armory it was found to make the shot to shot slightly more consistent and to raise velocities slightly . It was ultimately decided that the gains were not sufficient to out weigh the labor for even match ammo . As such it remains only in large cases like the 3"-50 and up .
Oh it was also referred to as duplexing . The reason was due to having multiple ignition points within the charge . I want to say Askins was involved in the tests , but that names may not be correct ...... The fellow that was there when the stamped 03 stocks had FJA on them was in on it .
The 30-06 was briefly , for experimental purposes and later intensively , fitted with flash tubes to carry the primer flash to the top of the powder charge rather than the bottom . In the tests at Springfield armory it was found to make the shot to shot slightly more consistent and to raise velocities slightly . It was ultimately decided that the gains were not sufficient to out weigh the labor for even match ammo . As such it remains only in large cases like the 3"-50 and up .
Oh it was also referred to as duplexing . The reason was due to having multiple ignition points within the charge . I want to say Askins was involved in the tests , but that names may not be correct ...... The fellow that was there when the stamped 03 stocks had FJA on them was in on it .
yodogsandman
Well-Known Member
So, Never use IMR 7383 for duplex loading! Too squirrelly (pressure excursions) all by itself.
Maven
Well-Known Member
yodog...., When IMR 7383 first became available to reloaders, we knew little about it, except that there were 3 lots, which varied by "speed." It was also thought to be a triple based propellant. Shady Grady on the Boolits site citing military data (cutting & pasting in fact) showed that to be false. Buckshot and others suggested it was "peaky" and cautioned us to treat it akin to IMR 4064 as a starting point. Using a chronograph, I found it to be slower than 4064, i.e., with jacketed bullets it approximated the burn rate of IMR 4350 in the .30-06 and IMR 4831 in the ..243Win. Treat it with respect since it isn't a canister powder, which means no undue compression, no overloads (almost the same thing), no duplexing, and don't stuff your cartridges full of it when the ambient temps. are >80 deg. F. Don't observe these common sense cautions and "squirrelly" pressures will be the least of your concerns.
What about 7383 and cast bullets? In cartridges such as the .308Win., 7.5 x 55mm, .30-06, and 8 x 57mm, it performs very well with heavier CB's and charge weights of no less than 37gr. (If you have a .308Win./7.62 x 51mm, you may want to check this figure). "Jim," who left Boolits and established his own site, developed a simple method to determine the max. charge of 7383 for a particular cartridge. To wit, take the cartridge in question, deprive it, then drill out the primer pocket. Seat the CB you intend to use to the OAL you typically use, then trickle in the propellant until it reaches/is level with what was once the primer pocket. Dump it out and weigh it; repeat this 3 or 4 more times, and you'll have a good approximation of a max. charge for that cartridge and CB combination. Btw, I've done this with both the 7.62 x 39mm and the 8 x 57mm and it works very well as it is a conservative measure since there's almost no powder compression.
Hope this helps!
What about 7383 and cast bullets? In cartridges such as the .308Win., 7.5 x 55mm, .30-06, and 8 x 57mm, it performs very well with heavier CB's and charge weights of no less than 37gr. (If you have a .308Win./7.62 x 51mm, you may want to check this figure). "Jim," who left Boolits and established his own site, developed a simple method to determine the max. charge of 7383 for a particular cartridge. To wit, take the cartridge in question, deprive it, then drill out the primer pocket. Seat the CB you intend to use to the OAL you typically use, then trickle in the propellant until it reaches/is level with what was once the primer pocket. Dump it out and weigh it; repeat this 3 or 4 more times, and you'll have a good approximation of a max. charge for that cartridge and CB combination. Btw, I've done this with both the 7.62 x 39mm and the 8 x 57mm and it works very well as it is a conservative measure since there's almost no powder compression.
Hope this helps!
yodogsandman
Well-Known Member
Seems like IMR 7383 powder deserves a thread of it's own to prevent confusion with powders that can be duplexed. I wouldn't want a new reloader, that started reading from this page, to get this wrong.
9
9.3X62AL
Guest
Very gracious of you, Josh. I gave away the 7383 I had at the time I moved from Ridgecrest to San Diego, and won't be re-exploring that niche again.
F
freebullet
Guest
The flash inhibitors & graphite are the drawback with 7383. From my understanding it was designed for use at 38,000psi. Less & it burns dirty leaving moocho powder in the bore. When pushed beyond 38k it gets squirrely & unpredictable. The flash inhibitor Nitroguanidine is an explosive. When pushed past the design parameters unique things happen.
My weirdest experience with it was in 223. Once it gets a good compression you'll notice pierced primer edges. A pretty good indicator your done working upward.
I try to use it in cases where 85-101% fill gets the pressure it needs to burn as clean as it can.
My weirdest experience with it was in 223. Once it gets a good compression you'll notice pierced primer edges. A pretty good indicator your done working upward.
I try to use it in cases where 85-101% fill gets the pressure it needs to burn as clean as it can.