Pressure vs. tight cylinder throats

[leftiye]

Well when you get through contradicting all of the knowledge that has been known since the last ice age, please explore how you got so mislead. Cases that stick are either in dirty chambers, or have been expanded enough to stick. Pressure is necessary to do this.

[leftiye]

The big bullet in a small bore making no pressure increase is counter intuitive.
Likewise the pinched bullet in the chamber making a huge pressure spike is counter intuitive.
The way I reconcile it is to think in the time domain.
If the peak pressure of powder burn is not concurrent with the increase pressure to swage, the peak pressure does not change.
And if the pinched bullet delays the start of bullet acceleration, the increased pressure makes the powder burn faster which increases pressure which makes the powder burn faster ....

This phenomena of large bullets working in a small bore without pressure spikes is documented in P.O. Ackley 1966 "Handbook for Shooters and Reloaders Vol 2" chapter 7 "additional pressure tests":

"..30 cal barrel pressure barrel was fitted to the test gun, but the neck and throat was enlarged to accept the 8mm bullet, with the bore
remaining the standard 30 caliber. A Remington factory 30-06 cartridge with the 150 gr bullet had been tested and previously gave 57,300 psi, for a velocity of 3030 fps. The the bullets were pulled from two more Remington 150 grain cartridges and were replaced with 8mm 150 grain bullets. To everyone's surprise, although the velocity was rather erratic, these loads averaged 2901 fps, with a pressure of 40,700 psi."

I've got a .445 that I replaced the faulty factory cylinder on (un-square front face). The chambers on the original were 1.7** inches long. Loads with a nominal fire forming charge in them stick in the new cylinder. They produced almost negligible pressure signs in the original chamber. I believe the new cylinder has correct 1.6" chambers. I once had a Mini 14 that produced (for a while) 10" vertical stringing at 100 yds. This with 1.5" horizontal measurements. It was blowing primers periodically. I found that the case mouths (uncrimped) were hitting the sharp edge of the chamber opening when feeding. This produced a ding that pinched the bullets and buggered the pressures. I used a cannelure maker and crimped and the problem ceased to occur.

BTW, I agree with (like) your time/ burning rate theories, both of them.

[Char-Gar]

Hi.

I am working up a load for my 6.5" S&W 629.
I am using the Lee 310gr. boolit with GC run through a .430 sizer and cast to 318gr.

The boolits come out as .431 but my cylinder throats are just at hair over .430 so the boolits will make a pretty tight fit in the throats.

I think I am close to the max load using 18gr. VV N110 and an COL of 1.1654.
This gives 1200 fps but without any apparent pressure signs.

The accuracy is pretty good so the question is about pressure vs. the tight throats.

I use the rear cannelure and the boolits are just touching the throats without any "free flight" what so ever.

Is this a bad thing pressure wise?
Like when loading jacketed rifle bullets touching the lands will raise pressure, will this be the case here as well?

I do not think so but would like your opinions about this matter.

Fire away! You are good to go!

[Silver Jack Hammer]

leftiye, Carsten asked if cases falling free of the cylinder without using the ejecting rod is a false sense of security that pressures are safe. To which I said yes. Your comment about cases stick due to pressure or dirt is true but not related to a subject I posted.

Char-Gar has already assured Carsten that the load in question is good to go.

The question raised about gauging pressure by how easily brass falls from the cylinder is a serious one. Although Carsten was referring to his Model 629, he also has a Colt SAA. We need to encourage handloaders to rely on data published by reliable sources rather than false indicators such as how easily brass falls from the cylinder, flattened primers, reside around the mouth and all the other wives tales that are not indicators of pressure, equally true split brass is not an indicator of excessive pressure. Brass falls from the cylinder of my .357’s and .44 Mags which are fired with pressures that are within SAAMI specs in these calibers but are not safe is a SAA nor rated for a .45 Colt.

Pressure is measured two ways; by the older crusher pressure measurement system or the newer piezoelectric pressure system which uses a sensor called a transducer. The new electronic transducer was revolutionary in that we realized the old system of CUP was not telling whole story. Loads published as safe when tested by the CUP system were showing dangerous pressure spikes with the piezoelectric system.

Leftiye, your comment that jacketed boolits produce higher pressures and lower velocities than equal weight boolits at the same charges with lead is a comment I would not disagree with. But if you posted this in response to my post that Brian Pierce has written that test results with jacketed boolits which are assumabley harder than lead alloy do not increase chamber pressures in tight cylinder throats, we are talking about two different issues. Let me better explain my post. The title of this thread is Pressure vs. Tight Cylinder Throats. I posted that Brian Pierce has data which indicates that reducing cylinder throats does not increase chamber pressures. His data that reduced cylinder throats do not increase chamber pressures do not increase chamber pressure with either cast or with jacketed boolits, which are assumabley harder than lead. I had no intention of indicating anything about comparing the pressure of jacketed boolits to cast boolits.

Dave Scovill has boolits fired from revolvers with oversized cylinders with the barrels removed and captured in a soft stop such as a box of wet newspapers. With Lyman #2 lead the base of the boolits upset and flare significantly. His point is that we have been shooting lead boolits out of revolvers with oversized cylinder throats but the boolits have been swelling to fill the oversized throats thus forming a gas seal. This has been going on since the dawn of the revolver and there have no problems even tho there are those out there that believe oversized cylinder throats reduce chamber pressures and cylinder throats too tight drive up the pressures.

Scovill adds that these boolits which upset at the base forming a gas seal then squeeze down to the smaller bore diameter when they enter the forcing cone and there never has been any danger in this. He suggested that maybe the fact that the boolit has already moved forward from the case when it engages the cylinder throat might be a reason we don’t see this pressure spike.

[Carsten]

Silver Jack Hammer,

Thank you for the explanation.

He suggested that maybe the fact that the boolit has already moved forward from the case when it engages the cylinder throat might be a reason we don’t see this pressure spike.

Which is why I asked the question in the first place.

As I wrote in the first post the boolits are just touching the throats and has no "free flight"

[Multigunner]

Extensive testing of tight bore target barrels and tight chamber throats has indicated that a tight throat will raise chamber pressure, while a tight bore with normal throat dimensions makes little difference in chamber pressures.

Squeeze bore rifles and anti-tank guns were built in the 30's and 40's with no serious chamber pressure issues.

A lightly pitted bore will allow well lubed cast boolits to reach higher velocities at the same charge levels than a comparable jacketed bullet.
The lube fills in the pits as incompressable globules that act like semi-liquid ball bearings. They established that long ago.

I figure a very tight, rough or undersized throat in a revolver cylinder would have to increase chamber pressures.

[leftiye]

[Quote We need to encourage handloaders to rely on data published by reliable sources rather than false indicators such as how easily brass falls from the cylinder, flattened primers, reside around the mouth and all the other wives tales that are not indicators of pressure, equally true split brass is not an indicator of excessive pressure. Quote] SJH

Reloading manuals can get you killed! At the best they only say what was safe in somebody else's gun. One needs to be able to judge pressures to be able to work up (or not) from starting loads safely, even if from a manual. I had a Remington 25-06 fry a case into the bolt face - had to beat the bolt open, and beat the case out of the bolt face - with a starting load once. That load would probly have blown up a Mauser. They are NOT the end all point, and only the starting point if you are lucky.

Actually, if the case comes out easily you are no where near damaging your revolver.

[leftiye]

"Brian Pierce, probably the most published single action writer currently has data which shows reduced cylinder throats do not increase chamber pressures and he has communicated this to Colt."

Only true if boolits fit the reduced throats. Reduced throats would increase pressure if the original boolits were used.

[ Quote Interesting too, Brian Pierce has written that test results also jacketed boolits which are assumabley harder than lead alloy do not increase chamber pressures either. Quote] SJH

But this is in another paragraph with no reference to it being about reduced chamber mouths. Regardless, pressures will always be higher with jacketed than with cast, all things else being equal. If the bullet or Boolit gets jammed into a chamber mouth that is too small, things will only get worse.

[DougGuy]

Hello Carsten, Having cast bullet diameters somewhat larger than the cylinder throats is fine.

"Having cast bullet diameters somewhat larger than the cylinder throats is fine. <<-- DO NOT believe this statement.

I do not buy into the theory that undersized throats do not cause higher pressures than properly sized throats. IF this were true, then consider this.. Recoil with a SA revolver directly affects point of impact of the boolit. Right or wrong? Every sixgunner knows this is correct, even the gun makers know it is correct because they install taller front sights on the longer barreled revolvers to compensate for how recoil affects the longer barreled gun.

Pressure, dictates recoil. Period. This is a LAW of PHYSICS. Every action creates an equal but opposite reaction. Proven, documented, take it to the bank.

Pressure from a hardcast boolit having to be swaged down by a tight cylinder throat will make a revolver shoot as much as 4" to 6" higher than where the sights were aimed, in as little as 25yards. Reaming the cylinder throats and removing the constriction will make the same revolver with the same load strike the target MUCH LOWER than it did before reaming.

IF and I say IF the theory of varying cylinder throat diameters having no effect on pressure was true, which it is NOT, then there would be NO CHANGE of the boolit's impact on the target, since there would be no difference in pressure, and therefore no difference in the amount of recoil generated by firing.

Let's take that a little farther. We all know better than to fire a gun with an obstructed barrel. IF and I say IF an obstruction was great enough, it would cause the gun to to KABOOM! WE all know that this is a very valid explanation for how to blow up a gun. Now... Firing through a constricted barrel OR undersize cylinder throats is firing through an obstruction of sorts. It may not be great enough to cause a KB, but IF the load in question was near max to begin with, and then fired into a constricted barrel, pressures can go sky high. They can spike high enough to cause a catastrophic event. THIS is why it is NOT OKAY to size boolits greater than the cylinder throat diameter.

Like when loading jacketed rifle bullets touching the lands will raise pressure, will this be the case here as well?

I do not think so but would like your opinions about this matter.

Carsten, cylinder throats are made to guide the boolit to the barrel, and they work best when the boolit will slide into the throats with minimal resistance. The true answer to your question is YES. Any resistance provided against the movement boolit will cause pressures to increase as opposed to the same exact load with less or no resistance to the movement of the boolit.

[Piedmont]

Pressure, dictates recoil. Period. This is a LAW of PHYSICS. Every action creates an equal but opposite reaction. Proven, documented, take it to the bank.

Pressure from a hardcast boolit having to be swaged down by a tight cylinder throat will make a revolver shoot as much as 4" to 6" higher than where the sights were aimed, in as little as 25yards. Reaming the cylinder throats and removing the constriction will make the same revolver with the same load strike the target MUCH LOWER than it did before reaming.

With regards to the first paragraph quoted I can load a 200 grain bullet in a .44 mag to higher pressures than a 240 grain and it will recoil less. So I guess that isn't a law of physics.

With regards to the second paragraph quoted, didn't it occur to you that you were likely changing the dwell time in the firearm?

[DougGuy]

Yes the dwell time is partially the cause of shooting to a higher point of aim, but there isn't this huge slowing down of velocity with those loads, so it cannot possibly be all attributed to dwell time. Some of it is from pressure.

I apologize, I did not correctly type out what I meant to say, I meant to say that pressure behind the boolit mass dictates recoil.

[Multigunner]

Well I have a very old top break .32 revolver. I loaded BP loads with a .375 ball swaged down to .314.
When I first fired a cylinder full the hinge pin of the top latch bent loosening the action, the fired cases were difficult to extract.
I examined the throats and found a deep crust of old rust and fouling. I cleaned the throats down to bare steel and polished away some surface roughness. Now the same loads don't bend that now straightened hinge pin and cases eject with ease.

If hardened fouling in the throats can raise pressure then a too small dia throat can raise pressure.
Of course BP has different burning qualities than modern smokeless powders.

[leftiye]

Yes the dwell time is partially the cause of shooting to a higher point of aim, but there isn't this huge slowing down of velocity with those loads, so it cannot possibly be all attributed to dwell time. Some of it is from pressure.

I apologize, I did not correctly type out what I meant to say, I meant to say that pressure behind the boolit mass dictates recoil.

Basically true. Pressure, probly velocity achieved, amount of powder/burning rate has effect (jet of gasses at muzzle produces recoil), and projectile weight pretty much cover recoil. Your logic carries regardless, a good explanation IMO.

Firearm weight coupled with this produces felt or free recoil (if I have my terms right).

[Silver Jack Hammer]

A .32 loaded with BP would generate very low pressure, 18 grains of FFg would send a 100 gr. boolit about 800 fps, within the 12,000 CUP range when .357 magnum loads are rated at 35,000. BP is dirty, and SASS shooters shoot lots of BP at 100 + round matches, I have. BP does cause fouling and cases to get sticky, that's why Colt's put the big round bullseye head on the end of the ejector rod - to eject the sticky cases even when the fouling builds up. These Colt BP guns were used in the dirtiest of conditions from the American frontier to Cuba to SASS matches. I don't believe the fouling restricted the chamber mouths to build up pressure.

DougGuy, leftiye, we need to clean up our language. Your comments about cylinder throats referred to them as "undersized." Your familiarity with Rugers likely defaulted to your having seen lots of Rugers with "undersized" chamber throats. The solution is to bore them out to proper dimentions. I'm talking about Colt's and use the term "tight" cylinder throats. In the Colt world our .45 cylinder throats tend to run about .456" - .457" from the factory. .44 Special cylinder throats run about .434" - .455" from the factory. Us Colt guys buy .38 cylinders and have them bored to proper .452" in the .45 and .431" in the .44 Special. USFA was very proud of the fact their guns came from the factory with cylinder throats on par with custom work. If we refer to cylinder throat size by the numbers clarity might materialize.

I have a custom cylinder in a .44 Special Colt, and I have a factory cylinder for the same gun, plus a .44-40 cylinder for the same gun. Maybe I have too much time on my hands but I shoot different loads, different powders, different boolits etc., through this gun and I keep the targets. The cylinder with "tight" throats .431" hits the same elevation to the same point of aim the same as the factory cylinder with "oversized" .434" diameter cylinder throats when I compare the same loads through the two different cylinders. Believe me I am testing for the magic combination for the tightest group.

If boolits cast with Lyman #2 upset at the base to form a gas seal when fired through an "oversized" .456" .45 and .434" .44 Special cylinder throat, then firing the same boolit through a "tight" cylinder throat .431" .44 Special would only also form a gas seal too. There would be no overpressure because both boolits sealed the cylinder throat regardless of it's diameter. That's what Skovill was saying when he fired different boolits through revolvers with the barrels removed. The base of the boolits expanded - a lot. More than the diameter of the oversized cylinder throats. I cast with ww, and I mix 4 parts Linotype with 6 parts ww, and I've cast with straight Linotype. I have sized .44 Special to .429, .430 and .431" and I've sized .45 Colt to .452" and .454" but my point of of impact does not change. I am persuaded that Scovill is right.

I have read Brian Pearce for years and he publishes results of tests on cylinders from the M29, SBH, SRH, USFA, Colt and Smith including the incredible results of the 5 shot L frame. I'm confident none of what he has said refers to "undersized" cylinder throats, he is talking to us SA shooters who spend money on having custom cylinders bored out and fitted to our guns and compared to factory cylinders. If it's Colt, the cylinder throats are not undersized. Colt barrels are tight. I had a .45 with a bore diameter of .450". It's cylinder throats were .456". Colt barrels are .427. I'm referring here to the SAA Model.

[DougGuy]

I had a 4 5/8" BH convertible in the 90s, it shot horribly and leaded the daylights out of the barrel. I found the throats were .456" on both cylinders. I don't remember which came first, firelapping or Ruger replacing the cylinders with two that had .4515" throats as requested. I shot .451" boolits back then, mostly linotype, I mostly didn't know much about the throat to bore relationship except that it really turned it around and made a great shooter out of it afterwards. Had I known how to slug throats and/or barrels, had I known what a thread choke was, I could have been much more ahead of the game but I was such a newb to revolver dimensions then. I knew it was a total DOG to shoot and clean, and then it improved immensely after getting properly dimensioned throats. I should have kept it.

I had 5 or 6 1st Gen Colt SAAs that were awesome guns. None of them shot as badly as the Ruger, none of them leaded like the Ruger. Should have kept those too.

[leftiye]

I just gotta say "So what?" PS, there's a whole new world out there, just for looking. Where people only vaguely know of Brian Pierce. And haven't yet been mislead by him.

[Silver Jack Hammer]

leftiye, your attempts to discredit what I've posted you've had to turn my words around into saying things I did not say. The current White House occupant does that too and it's very tiresome.

Brian Pearce is well published, has been for about 10 years that I know of. He has a readership that verifies his work.

As far as your suggestion that I look into a whole world out there, film crews have come from New York and Los Angeles to document things I've done in my profession on 4 separate occasions. It's because my life is intense that I enjoy the recreation of shooting.

[DougGuy]

If we refer to cylinder throat size by the numbers clarity might materialize.

True dat... In the last 75 or so Ruger cylinders I have done, probably 50 of those have been .45 cal, about 40% of those have been .45 ACP.

I am finding patterns of consistency. Some good, some notoriously bad, but consistent none the less.

For the most part, not all, but say 80% of the recent production medium framed guns, their throats are running right at .4505" and .451" with the occasional .4515" throat in the middle of a cylinder full of .451" holes. Unfluted cylinders run tighter, .4505" and the rollmarked Bisley cylinders are the tightest, average pilot size for the reamer is .450" for these. Older BH cylinders can be all over the place, most cylinders have uneven throats requiring me to switch pilots to maintain the very snug fit needed to keep the reamer on center.

The unfluted .44 cylinders are the most uneven. Some of them will have two of six throats .002" larger than the other four, I have to use a custom reamer sized .4324" on these old girls, as I do not like them to leave my shop unless the throats are within .0002" of each other. Not uncommon to have to use 3 different pilots on these cylinders since Ruger used 3 different reamers.

.41 cylinders show the same variances the .44 cylinders do, you have to check them for uneven throats and use the tightest fitting pilot sometimes having to switch pilots. Diameters for these range from .409" to .411" with no sense of regularity at all.

.357 cylinders are usually right at .357" and many shooters simply want to shoot .358" or .359" with the occasional request for the cylinder to be able to take .360" boolits compatible with the owner's levergun.

[leftiye]

leftiye, your attempts to discredit what I've posted you've had to turn my words around into saying things I did not say. The current White House occupant does that too and it's very tiresome.

Brian Pearce is well published, has been for about 10 years that I know of. He has a readership that verifies his work.

As far as your suggestion that I look into a whole world out there, film crews have come from New York and Los Angeles to document things I've done in my profession on 4 separate occasions. It's because my life is intense that I enjoy the recreation of shooting.

You must have failed to communicate. I cut and pasted those quotes. Didn't twist or even mis quote anything (though it seemed to me that your responses have had gobs of drift). Movie stars think they're experts on everything too. It's called false transference of authority.

[Silver Jack Hammer]

There, you did it again.