Quantcast

Pressure ???

Discussion in 'General Gun Discussions' started by WestKentucky, Jun 11, 2019.

  1. WestKentucky

    WestKentucky Member

    Joined:
    Feb 1, 2014
    Messages:
    7,548
    Location:
    Middle Tn
    I have bought an old 16ga single recently and I really like the gun. So much so in fact that I would really like to make a couple rifle barrels for the frame. One is 22lr which I know is going to be interesting due to offsetting the barrel up or down to allow for the centerfire firing pin to impact the rim of the rimfire round. The other that I want to do is a 32 caliber revolver round barrel, but I can’t figure out where to stop with ridiculousness there. I know .327 is way too hot for this old reciever, but 32long should be very easily contained. I wonder about 32 mag? 38spl? 38SW?

    So what numbers should be compared? Just saami pressure max? PSI on breechface? Just trying to understand what I really want to do before I jump into it.
     
  2. Jim Watson

    Jim Watson Member

    Joined:
    Dec 24, 2002
    Messages:
    25,032
    A common insert barrel in the day was .38-55.

    Maybe if we knew what 16 ga you are starting with.
     
  3. WestKentucky

    WestKentucky Member

    Joined:
    Feb 1, 2014
    Messages:
    7,548
    Location:
    Middle Tn
    It’s an old White Powder Wonder made by crescent. I’m considering making complete barrels rather than doing inserts. I can’t see any way to have any real accuracy with an insert, not to mention shotgun sights are all wrong for a rifle. I would be looking at making a 1 piece barrel block and lug to accept something like a marlin 60 barrel or something of the like. If I disregard the need for an extractor and just leave a lip to get under the rim with a fingernail I should be good to go for most cartridges. I really want to put together a 32swl but sourcing a barrel would be tough and expensive unless I reamed a .308 barrel blank and just loaded .310 lead like I use in my 30carbine... but if I could do that then I could just go with a .30 carbine and do it the easy way.
     
  4. JWF III

    JWF III Member

    Joined:
    Jun 22, 2007
    Messages:
    1,256
    Location:
    Mansfield, Georgia
    Very interesting idea. Thread marked to watch.

    It’d be much more work, but I have a few Stevens 311s. They could make for a “bubba” version of a double rifle. Maybe in .45-70? Even if just Trapdoor loads?

    Wyman
     
  5. lysanderxiii

    lysanderxiii Member

    Joined:
    Mar 21, 2015
    Messages:
    1,434
    Location:
    North Carolina
    It's not the pressure, so much as the bolt thrust. The new bolt thrust cannot be more than the original bolt thrust (within reason).

    Bolt thrust is the pressure times the case head area.
     
    ATLDave likes this.
  6. WestKentucky

    WestKentucky Member

    Joined:
    Feb 1, 2014
    Messages:
    7,548
    Location:
    Middle Tn
    Bolt thrust. That’s the term I was looking for and I couldn’t recall it to save my life.
     
  7. Slamfire

    Slamfire Member

    Joined:
    Dec 29, 2006
    Messages:
    9,357
    Location:
    Alabama
    To be even more cautious, I will claim that not only bolt thrust, which will be in terms of pounds force, but also pounds per square inch on the breechface. There is no reason to assume that the material selected for the receiver was designed to carry a more concentrated load than the base of a shotgun shell.

    This is one reason the Air Force trains and uses load masters for their air craft. A ground pounder might, because the plane is rated for 60,000 lbs, try to place a concentrated load that weighs 60,000 lbs, not knowing, out of ignorance, the floor loading limitations. Sure, the plane might carry 60 kpsia, but the floor will be punctured with 100 psia contact loads. And, of course, never mind the center of gravity issues.A number of crashes in the TV series "Air Diasters" were due to off center of gravity loads causing the plane to lose control. Thankfully I was not on Air Midwest 5481.


    A concentrated load might have been the cause of this trailer hogging. Neither myself or the driver could get past the lock, but,
    57DMvHB.jpg

    instead of distributing 80,000 lbs, the loader might have piled it all in the middle.

    This is a topic not well understood by the general public, but the ground has to support the building. If the earth under the building cannot support the thing, then you end up with the Millennium Tower problem they are having in San Francisco. Maybe the builder expected that friction between the building sides and the turf would decrease "building thrust" . Never grease or oil the walls of a building as that will increase building thrust

    from Wiki:

    800px-The_Leaning_Tower_of_Pisa_SB.jpg
    .
    But, if it is to be a fun project, start off with the pounds force of the shot gun shell, compare to that of the centerfire shell you want, and if the original shot gun shell gives less than or equal to your centerfire cartridge, go with it. And then, shoot enough centerfire shells to see if they create a depression on the breech face. If the case head creates a depression, that's the end of the fun project.
     
    Last edited: Jun 14, 2019
    ATLDave likes this.
  8. Jim Watson

    Jim Watson Member

    Joined:
    Dec 24, 2002
    Messages:
    25,032
    Greener wrote in 1909 that a double rifle for .303 or nitro express should have the receiver case hardened or fitted with tempered steel disks in the breech face to prevent indentation.

    Converting a shotgun to rifle is a lot of work. Most such use medium grade shotguns like J.P. Sauer.
    If you can do it yourself, make it a .38-55, .45-70, or revolver round, and are prepared to junk it if it doesn't hold up, go ahead with a Stevens.

    Lots of discussion on Nitro Express. The Browning BSS is used. I saw an OU rifle built by Paul Jaeger on a Ruger Red Label.
    http://forums.nitroexpress.com/postlist.php?Cat=0&Board=dblbuild
     
    Slamfire likes this.
  9. bluejeans

    bluejeans Member

    Joined:
    Jan 25, 2015
    Messages:
    284
    Location:
    idaho
    Sounds logical but not actually true. That formula shows wher the pressures are inside the case but the force felt on the outside (chamber walls and breech face) depend on many other factors.
    Ackley in a chapter “pressure” recounts a test for bolt thrust he did by unscrewing the barrel of a Winchester 94 away from the breech face and lengthening the firing pin to fire it with various gaps behind the case head and unless he oiled the case, it never moved rearward even with zero support. He concludes that as long as there is not excessive case taper and the cases are dry, the barrel itself holds all the pressure and the is no ‘bolt thrust’. ( at least in this pressure range of cartridge).
    I couldn’t find his article online for you but someone did a modern recreating of his test with modern testing equipment here https://www.google.com/amp/s/gundigest.com/gear-ammo/ammunition/experimenting-with-bolt-thrust/amp. And confirmed his results... they even exceede sammi spec to load the 30-30 to 46,5xx psi.
    I would ad to that to avoid reduced loads as they may not produce enough pressure to expand the case and grip the walls of the chamber thus truely giving more bolt thrust than most larger rounds.
    Let me back up a bit: when a round is fired, the pressure swells the case walls to fill out the chamber walls. The stiffer the load, (within reason) the better grip the brass has on the barrels chamber and this grip is help until the bullet clears the muzzle and pressures drop. I don’t know at what point the case head will fail busy the test I linked above at least shows that for the 30-30 it would be over 46,500 psi.

    Now to contrast this, I have a Winchester low wall with a cracked receiver because a lubed 22 mag was fired from it.

    @WestKentucky sounds like a fun project. I have considered something similar for my Stevens single shot 12g... I was thinking of a 22 k-hornet. My advice is stick to straight wall or low taper cases and also be aware that reduced loads may produce more bolt thrust than full loads.. and never oil/grease your loads. Whatever you do, just do your research (as you already are) and and keep your eyes open for warning indicators.
     
    Last edited: Jun 14, 2019
  10. Slamfire

    Slamfire Member

    Joined:
    Dec 29, 2006
    Messages:
    9,357
    Location:
    Alabama
    Ackley was a snake oil salesman. His pseudo science tests allowed him to claim that his cartridges were superior to every other wildcatter out there. There were a bunch of attention seeking snake oil salesman selling their cartridge designs back then. Weatherby's claim was that the double venturi shoulders of his cartridge gave it extra speed, Ackley claimed that you could safely add powder because straightening the shoulder walls somehow decreased bolt thrust. The extra velocity these attention seekers achieved, was not by any design characteristic they created, the ultra high velocities they achieved were the result of insanely high pressures.

    I remember a post somewhere, where a reloader had used Ackley's reloading data for one of his AI cartridges, and the post said "you could reprime the case with a shot gun primer". That's how Ackley did it, insanely high pressures.

    Ackley did not invent case friction. Case friction existed before Ackley. I have had stuck cases that I have had to knock out with a cleaning rod, so case friction still happens. Boatwright, a Mechanical Professor, in his blog "The Well Guided Bullet" under mechanical studies, http://www.thewellguidedbullet.com/pdfs/YieldingofBrassCaseWallsintheChamber.pdf discusses how case sidewalls stick to the chamber walls around 13,000 psia, and then start to stretch in the range 13-25,000 psia. If you notice, Ackley's 30-30 test does not have pressure data. Might have been a 10,000 psia test, just low enough that the case stuck in the chamber and did not blow the case head off. He might have also done something to the case and chamber. Tellingly, he did not test one of his 30-06AI cartridges, which in Handloader #1, Ackley claimed "normally" operated at 65,000 cup. That was when the 30-06 was a NTE 50,000 cup, and proof test loads were 70,000 cup. If Ackley had tried the same trick with a high pressure cartridge, the case head would have blown off. Maybe he did, but decided not to report it.

    Handloader recently published a partial reprint of Handloader #1 and there was an article by Ackley on his 30-06 AI, but of critical interest, was a picture. In the picture was Ackley's pressure gage, and Ackley's bolt thrust gage. Just where is Ackley's bolt thrust data? I have never seen it, if you have it, how about releasing it? I am certain Ackley tested his ideas that AI cases reduced bolt thrust, in his bolt thrust gauge and found it false. And then, because that was, and still is a one of his major claims to fame, Ackley deep sixed the data.

    So, by how much do you weaken an action, assuming the case carries some of the load? What is that number? How do you maintain it?
     
  11. Jim Watson

    Jim Watson Member

    Joined:
    Dec 24, 2002
    Messages:
    25,032
    Any serious rifle round, 50000 ppsi or more, the brass will expand to fill the chamber, including stretching back to take up "head clearance."
    As best I can tell, the stretch will take place immediately the thrust against the inside of the case head exceeds the yield strength of the brass. That is given as 19600* psi and there darned sure isn't a square inch of brass in the case walls' cross sectional area at the stretch ring.
    *That is not gas pressure, that is stress against a one square inch bar of metal.

    One gunzine writer concluded that you can get about 1/4 as much velocity increase as case volume increase, assuming same pressure. Which means that for improved cases to show much velocity improvement, they have to be loaded hotter. And don't even think about velocity increases by longer OAL as was popular with the .257 Roberts, because it isn't going to be much.
     
    Slamfire likes this.
  12. rule303

    rule303 Member

    Joined:
    Dec 5, 2010
    Messages:
    1,638
    Location:
    MN
    It's not just pressure and bolt thrust to have to worry about. How is the action going to deal with a case failure? Rare with correctly loaded cartridges, but it happens. The receiver needs to be able to deal with the full pressure being released and following the path of least resistance. For a 16ga shotgun that is 11.5k psi. That frame is case hardened only, and I wouldn't trust it to any cartridge with a higher pressure than that. You don't want to end up with a firing pin in the eye from a ruptured primer.
     
    Slamfire and bluejeans like this.
  13. murf

    murf Member

    Joined:
    Nov 16, 2010
    Messages:
    3,899
    Location:
    arizona
    and the old levergun load pressures were so low that some of the cases did not stretch and, therefore, could not reseat the primer (a sure sign of low pressure in rifle/pistol loads).

    when the primer detonates, the explosion pushes the primer against the bolt face and pushed the loaded round forward into the chamber (newtons third law of motion). the detonation also ignites the powder charge which deflagrates (burns) pushing the case walls outward against the chamber and the breech face. because of the design of the case, the walls get pushed outward (radially) before the walls stretch axially (longways). so, if the pressure is great enough to push the walls out (as little as 8,000 psi) and not great enough to overcome the case wall elasticity (greater than 14,000 psi depending on the design of the case wall), the case will stick to the chamber wall and not stretch back over the primer. the result will be part of the primer proud of the case head. in a revolver this will tie up the gun as the proud primer drags on the recoil shield. in an old levergun, this fired case will be misinterpreted as a sign of overpressure, not underpressure.

    fyi,

    murf
     
    Slamfire and bluejeans like this.
  14. bluejeans

    bluejeans Member

    Joined:
    Jan 25, 2015
    Messages:
    284
    Location:
    idaho
    I hear you. You do well to caution against ackleys loads... however I was not promoting ackleys loads, nor his improved chamber. I merely reference his 30-30 test as a fascinating experiment relating to bolt thrust.. and if you read the recreation of his experiment that I linked you will see they were measuring the psi of each load as well as checking bolt thrust and concluded that ackleys 30-30 experiment was legit. Two fascinating experiments that are beyond what I myself would ever try and both reached the same conclusion. Hm.
    Again. I’m not promoting ackley, these are two experiential reports.
     
  15. bluejeans

    bluejeans Member

    Joined:
    Jan 25, 2015
    Messages:
    284
    Location:
    idaho
    What you say makes mathematical sense. I’m not arguing I want to understand. Can you please tell me your idea why a 46,500 psi load in the test I linked above, did not blow the casehead off or even stretch it back when it was fired with 1/10th” headspace? Their conclusion was “we had proven that the cartridge case of the .30-30 Winchester can contain all of the pressure of a standard factory load without stretching.”
    What is your conclusion?

    I will bite my tongue after this as I don’t think I’m helping the OP and don’t want to rabbit trail his thread.
    Thank you.
     
    Last edited: Jun 14, 2019
  16. Slamfire

    Slamfire Member

    Joined:
    Dec 29, 2006
    Messages:
    9,357
    Location:
    Alabama
    Thanks for the link. I should apologize for not looking at it earlier, I thought it was a link to something I had already read. :oops: I need to read it several times to figure out what they were doing.
     
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice