What is the pressure disparity between BP and smokeless?

P

Pond James Pond

New member
In a thread about things not to do with BP the name Kirst Conversion came up. Seems to be a swappable centrefire cylinder for BP revolvers. This got me thinking about how safe it would be.

I imagine that most pressure is felt in the cylinder but all the same, can anyone give some idea of the psi a BP load could produce in a revolver, what a cowboy action load of smokeless could produce by comparison and finally what modern smokeless loadmight produce.

Let's take 45 Cot as a case study.
 
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About 10X, but its not just the peak, but the speed at which the 2 rise to peak from half peak & drop back. B/P has a shallow (comparatively) steady curve, but smokeless has a much shorter sharper peak even if you back off to the same peak pressure level.
 
it depends on what powder your compairing BP to as well as what charge your making the comparission with . there are many diffrent types of smokless powders .
 
This raises the issue of whether the Kirst or other conversion cylinders can handle SAAMI spec ammunition? I would assume they would, but don't want to be the trial balloon.
 
B/P has a shallow (comparatively) steady curve, but smokeless has a much
shorter sharper peak even if you back off to the same peak pressure level.
Click to expand...
and TrailBoss has the sharpest-rise peak of all... almost a sharp "smack" by comparison.
 
Can I use....

...Trailboss in cartridges?

I shoot .38 special, .357, .44-40, .45LC, .44 and .45-70 with BP.

Does it like compression?

For lighter loads is cornmeal okay?

Thoughts.
 
In modern-steel guns, TrailBoss is the cat's meow.

Do NOT (repeat, NOT) compress it. And by the same token do NOT use any filler.
(Measure your seated-bullet shank depth, and never fill the case more than
90% to that mark.

Used that way it's entire dependable and a great large-case powder for the cartridges you mentioned. :D
 
This raises the issue of whether the Kirst or other conversion cylinders can handle SAAMI spec ammunition? I would assume they would, but don't want to be the trial balloon.
Click to expand...
I believe you'll find they are restricted to "cowboy action" loads, considerably less than modern SAAMI.
 
This raises the issue of whether the Kirst or other conversion cylinders can handle SAAMI spec ammunition? I would assume they would, but don't want to be the trial balloon.
Click to expand...

The Kirst FAQ page specifies a maximum pressure of 12000 PSI -

http://www.kirstkonverter.com/FAQs.pdf

SAAMI specs for .45 Colt are in the neighborhood of 15000 PSI -

http://www.saami.org/specifications_and_information/VelocityPressureData.pdf

It is not clear whether the cylinder is the limiting factor..... perhaps the Italian-made frame is the "weak link in the chain"?
 
...Trailboss in cartridges?

I shoot .38 special, .357, .44-40, .45LC, .44 and .45-70 with BP.

Does it like compression?

For lighter loads is cornmeal okay?

Thoughts.
Click to expand...


Trailboss IS NOT, I repeat, IS NOT a Black Powder substitute. It is a Smokeless powder specifically formulated to take up a lot of space in large caliber cases that usually have a lot of empty space in them with most Smokeless powders.

DO NOT use fillers or compress it.

Follow the recipes in a recognized, published manual, or go right to the source.

https://www.hodgdon.com/basic-manual-inquiry.html
 
Dang!!!

I must have gotten good ones, my info said 1000fps or less and all I load is 830 - 900+fps. All my guns eat the same diet.
The loads listed in the data sheets all stay on the "safe pressure side" and I've had an awesome time with these conversions!
I can't imagine anyone offering any type of cylinder for a revolver that wouldn't be safe with off the shelf ammo. It would be manufacturing a law suit! !!
Heck, I'm about to venture down that road and they will handle tier 2 ammo.

Mike
www.goonsgunworks.com
 
"smokeless has a much shorter sharper peak"

A common belief, but not true; black powder is a true explosive that burns very rapidly and has a short burning curve. Smokeless can have a much higher initial pressure but also is progressive burning and keeps that pressure on longer. That is the reason shotguns with old Damascus barrels fired with smokeless powder usually don't burst at the chamber but at the point where the barrel gets thin (and where the shooter's off hand is holding the gun).

That means little in most handguns, though. Millions of rounds of factory smokeless powder loads have been fired in old guns made in the BP era.

But conversion cylinders can present another problem when used with the open top Colts unless pressure is kept very low. When a percussion revolver is fired, the entire cylinder recoils back onto the recoil shield part of the frame, which is in the center of the frame boss where the frame is fairly strong. But when a cartridge revolver is fired the cylinder does not recoil; instead the cartridge case impacts the recoil shield and does so further up on the frame. The leverage tending to bend the frame (actually to straighten out the bend) is greater and the stress on the frame is much greater.

That is the main reason Colt's efforts to sell open top cartridge revolvers were unsuccessful. The problem was ultimately solved by using a top strap.

Jim
 
"smokeless has a much shorter sharper peak"
Click to expand...
not true...black powder is a true explosive that burns very rapidly
and has a short burning curve. Smokeless can have a much
higher initial pressure but also is progressive burning and
keeps that pressure on longer.
Click to expand...
Yes... and no.
It depends.... ;)

" In general, smokeless powders like Blue Dot and 2400 give approximately
the same pressure curve as black powder FOR THE SAME VELOCITY AS BLACK
POWDER AND THE SAME BULLET AND BULLET WEIGHT. Smokeless powders
with a faster burn rate like Unique, Trail Boss, Bullseye, etc. will give a higher,
sharper pressure spike. Slower smokeless powders like IMR 4227, IMR 3031,
RL-7, etc. will give a lower, rounder pressure spike. Sherman Bell had some
good articles on this a few years ago in the Double Gun Journal. Others have
posted pressure curve comparisons. Some examples are [in the link] below:
http://img.photobucket.com/albums/v497/3855Win/45_70_pressures.jpg

BTW: Note the TrailBoss curve. :eek: :mad:





See source article/subject here: http://www.levergunscommunity.com/viewtopic.php?f=1&t=27410
 
I read about this , lets call it frame warping of open top revolvers before I did my conversion. Since I chose to use an older , well used Uberti , I have tried to keep an eye on it so as to see if it was happening . I have to date fired just over 600 rounds of smokeless through my 1851 Uberti . There has been no change in either the angle of the recoil shield or for that mater the distance or angle of the backer ring when mic’ed from the waterline or recoil shield to front pins .


Unless they have stoped selling them Uberti makes open top models with Mason conversions suitable for standard factory loads

Dang!!!

I must have gotten good ones, my info said 1000fps or less and all I load is 830 - 900+fps
Click to expand...

same here . fired alot of millitary issue 45 ACP that were also right in theat ball park . just becouse its slow doesnt mean it wont totaly mess up your day. that would also be before the SAAMI current max pressure numbers
 
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I would like to see some actual pressure information, not "estimated". Bullet velocity is not a good way to determine pressure.

Jim
 
Jim K,
Not determining pressure, I don't know of any manufacturs that load more than 1000 fps fodder (250 gr. Bullets) in the "reg" loading (which is in the safe zone for all S.A. type guns ,not Ruger only stuff). I happen to know these cylinders will handle factory stuff. The rest is for the lawyers. Shoot what you're happy with but I like the loads I shoot and warmer sometimes.
If your not comfortable with something, don't do it.

Mike
www.goonsgunworks.com
 
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