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Thread: What is "special vented barrel" in 38 special testing, how does it effect load data?

  1. #1
    Boolit Buddy
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    What is "special vented barrel" in 38 special testing, how does it effect load data?

    Lyman #47 and #49 differ greatly in load data for the 358429 (170 grains) Keith bullet.

    Example #47 max load Unique 5 grains, 860 FPS
    #49 max load Unique 4.2 grains, 841 fps

    same OAL, same barrel length-- difference is "special vented barrel in the #47 manual.

    What is that all about and what data should I use?

  2. #2
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    Well first off you should never start with a max load you should always work your way up.I would suggest you start with a load in the middle of the load data and work your way up from there. Check for signs of high pressure on the way
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    Vented pressure barrel

    https://saami.org/wp-content/uploads...sting-Copy.pdf

    Page 18
    2)Vented barrel velocities are provided for information only.Vented test barrels are used for the establishment of catalog velocity values for cartridges normally chambered in revolvers.

    And sooooo vented means introduction of a cylinder gap

    Mike
    NRA Benefactor 2004 USAF RET 1971-95

  4. #4
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    Quote Originally Posted by poppy42 View Post
    Well first off you should never start with a max load you should always work your way up.I would suggest you start with a load in the middle of the load data and work your way up from there. Check for signs of high pressure on the way
    Yes mom, by the way how do you check for pressure signs in a 38 special revolver?

  5. #5
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    Quote Originally Posted by skeettx View Post
    Vented pressure barrel

    https://saami.org/wp-content/uploads...sting-Copy.pdf

    Page 18
    2)Vented barrel velocities are provided for information only.Vented test barrels are used for the establishment of catalog velocity values for cartridges normally chambered in revolvers.

    And sooooo vented means introduction of a cylinder gap

    Mike
    It doesn't effect pressure but does velocity is what they are saying. The reduction in charges between manuals by Lyman has nothing to do with pressure measured in the two different barrels, but will show slower FPS with the vented barrel.

    No explanation about the difference in min and max charges then? It looks like several powders are effected.

  6. #6
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    Kid,
    A vented test barrel is one that duplicates the cylinder gap like a revolver has.

    A real good sign of high pressure in a revolver is when you have difficulty pulling out the spent cases.
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    Can expect I the velocities in the old manual with the vented barrel to be more accurate then?

    Also what is difficulty in removing the brass? Factory loads in my Blackhawk have to be pushed out but my cowboy loads fall out. "Difficulty" as in hammering out? Do a ladder test and at some point decide it is too "difficult" to push them out?
    In the past I used book velocities and a chrony to keep things in the ballpark. So back to my original question, what data for that?

  8. #8
    Boolit Master VariableRecall's Avatar
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    From my experience with a couple of bad apple handloads, a factory cartridge should require gentle pressure to extract from the cylinder. However, hotter loads require a firm amount of pressure or a good slap to get moving out of the cylinder. Always use factory ammo for reference if you're wondering about the firmness relationship from round to round.

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    when putting together a new load it is always smart and safest to start at the low powder charge listed in a data book and work your load up.
    and when using data that just gives one powder weight, like the Alliant online data, starting load is 10 percent less powder than the max load which is what they post in their online data.
    ill let some of the more experience experts here on the site explain what high pressure indications might be.
    one bad load can very quickly cause firearm damage, injury or even death. reloading in a safe Manner is the only way to live.

  10. #10
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    Quote Originally Posted by farmbif View Post
    when putting together a new load it is always smart and safest to start at the low powder charge listed in a data book and work your load up.
    and when using data that just gives one powder weight, like the Alliant online data, starting load is 10 percent less powder than the max load which is what they post in their online data.
    ill let some of the more experience experts here on the site explain what high pressure indications might be.
    one bad load can very quickly cause firearm damage, injury or even death. reloading in a safe Manner is the only way to live.
    Wow, did you read the questions? Its like calling IT and being asked repeatedly "Did you try turning if off and on?"

  11. #11
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    I read the question, someone else answered it, but with the talk about what load to start with, in my opinion the lowest is what you start with, 4.2q gr, excuse me for butting in on reminding of being safe when reloading.

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    19 FPS difference is within the margin of error. If you want to start out with the max loads, use your Blackhawk. Your gun will tell you if the loads are too warm by hard ejection. Your gun will tell you which load is more accurate if you are shooting well that day. Your question was answered. Different editions of the same manual reflect differences in that days bullets/powder/primer combo tested on that day. No one gave you a bad answer; when you start a post talking about maximum loads, you will- and should- recieve advice about loading safety.

  13. #13
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    As to what data to use? The data from the 49th. Why, I'd say because they actually retested loads for that particular combination and probably measured the max pressure in psi rather than using the old cup method. Not every load is retested with each new manual publication. My 1973 Lyman cast bullet manual shows 5gr unique as max with that bullet at 925fps and 15,800 CUP (7.71" universal receiver). I was disappointed when I got the Lyman Cast Bullet Handbook, and it was clear some cartridges weren't updated, e.g. 45 AR.

    With respect to your pressure question, one way to get an idea for pressure is to fire some factory load and measure head expansion to give you a baseline measurement and compare what you get with a reload of the same cases. Micrometer, not calipers. Not crazy precise, but a method if you don't have a real pressure testing set up like Larry Gibson.
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    I HAVE started with the "max" load in .38 Special cases, but only when shooting them in a .357.
    When working up .38 Spl ammo for use in .38 Spl. revolvers, I try to back off the max load by at least 5% and 10% is usually better. All other things being equal, use the more recent loading data for work-up. Sometimes, between reloading manual editions, one propellant or the other might be reformulated to burn cleaner, meter better, or whatever, and in the process, its burning rate might change. If the burning rate changes, the reloading data will almost certainly change, also.

    "Special Vented Barrels" are a confusiion to me, but appear to be some attempt to approximate the velocity loss experienced when a round is fired from a revolver, vs. an unvented test barrel. Here again, I'm a big believer in the "all factors being equal" proviso, and suggest that the lowest reported velocity be used as the most optimistic estimate of actual velocity for a given load.
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    At the pressure levels generated by .38 Special standard and +P head expansion and primer flattening are not reliable indicators, as these don't come into play until you far exceed proof pressure. Instead I benchmark standard and +P factory loads in in my guns and attempt to approximate those velocity levels for similar weight and shape bullets with approximately equal seating depth in my handloads. Larry Gibson's published pressure data being a sanity check.
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    Quote Originally Posted by Outpost75 View Post
    At the pressure levels generated by .38 Special standard and +P head expansion and primer flattening are not reliable indicators, as these don't come into play until you far exceed proof pressure. Instead I benchmark standard and +P factory loads in in my guns and attempt to approximate those velocity levels for similar weight and shape bullets with approximately equal seating depth in my handloads. Larry Gibson's published pressure data being a sanity check.
    I just wanted to say thanks to folks like you and Larry for continuing to share your extensive actual knowledge and experience as opposed to regurgitating some of the same old misinformation about checking for pressure signs in cartridges that require SAAMI pressures to be doubled or tripled before pressure signs appear.

    I've been loading 45 Colt's since 1968 for 1873 Colts. Recently I've been loadings for a 460 S&W and yes I have loaded 45 Colt brass to the point it shows pressure for use in the 460.. My guess is that's 250 to 300 percent over SAAMI for the 45 Colt. Point in some firearms/cartridge combinations the first sign of overpressure sign is the firearm coming apart.
    Last edited by M-Tecs; 12-03-2020 at 02:36 AM.
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  17. #17
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    "A real good sign of high pressure in a revolver is when you have difficulty pulling out the spent cases."

    A "real good sign of high pressure" for sure!

    With normal chambering these days that indicates 40 - 45,000 or more psi. With older or newer revolvers having burnished chambers sometimes even more.
    Larry Gibson

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    Boolit Grand Master Outpost75's Avatar
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    Having to stretch the crane arbor on an S&W to remove end shake after firing only one box of ammo is a sure indicator of high pressure too!
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  19. #19
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    Quote Originally Posted by clearwater View Post
    Yes mom, by the way how do you check for pressure signs in a 38 special revolver?
    Ah how bout split cases blown out primers and a few other signs. Kinda like checking for precious signs in any cartridge.
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    Quote Originally Posted by poppy42 View Post
    Ah how bout split cases blown out primers and a few other signs. Kinda like checking for precious signs in any cartridge.
    In some low pressure cartridge/firearm combinations pressure signs don't appear until you have damaged or destroyed the gun.
    Last edited by M-Tecs; 12-03-2020 at 11:49 PM.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check