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Thread: Gas Check Boolits without Gas checks ???

  1. #81
    Boolit Master
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    Hi guys!
    Awsome thread!
    Allot!, and I mean "ALLOT" of food/info for thought here!

    I have an observation though.
    (Great! More variables!) lOl!

    Sorry for going a little off topic, but i would like to know your thoughts on this.

    With the large variation of velocity with rifle cast shooting(1000-2500ish), that has to play heck with a given bullets ability to deliver top knotch accuracy.

    By this, I mean, how can a rifle with a fixed rifling twist deliver top knotch accuracy over such a broad range? At some point there has to be a trade off.
    I know for ranges past 1000 yards (with j-bullets), twist & velocity come into play "big time".
    I wonder if going with a bullet more appropriate for the twist/velocity should be a cast shooters first concidreation. Then bore fit, and lube, etc.
    Just some food for thought guys.

    I hope my Rem700 Varmint .308win, will shoot MOA out to at least 4-500.
    but that might be a bit much! Lol!

    Push the envelope, thats where it gets interesting!

    Have fun and straight shootin guys!
    Last edited by Dthunter; 12-05-2011 at 05:00 PM. Reason: More info

  2. #82
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    Quote Originally Posted by Fire_stick View Post
    If your bullet is sized properly for your gun,
    and if the pressure is sufficient to obturate the bullet per the bullet hardness.

    Is there a need for a gas check? Even at elevated velocities?

    From what I have been reading, I suspect the answer is, or could be no.

    Although I also suspect powder burn rates may play a role in determining whether a GC is needed. Maybe it is simpler to use a GC and not worry with all the variables.

    Please help me understand.
    I have had good results making my owne 30 cal. bullets out of a mold that is ment to make gas check bullets.Then i liquid alox the bullets and load them up as to keep them under 2000 feet per second.I dont know what other guns it will work good in but mine works well.

  3. #83
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    Quote Originally Posted by Dthunter View Post
    Hi guys!
    Awsome thread!
    Allot!, and I mean "ALLOT" of food/info for thought here!

    I have an observation though.
    (Great! More variables!) lOl!

    Sorry for going a little off topic, but i would like to know your thoughts on this.

    With the large variation of velocity with rifle cast shooting(1000-2500ish), that has to play heck with a given bullets ability to deliver top knotch accuracy.

    By this, I mean, how can a rifle with a fixed rifling twist deliver top knotch accuracy over such a broad range? At some point there has to be a trade off.
    I know for ranges past 1000 yards (with j-bullets), twist & velocity come into play "big time".
    I wonder if going with a bullet more appropriate for the twist/velocity should be a cast shooters first concidreation. Then bore fit, and lube, etc.
    Just some food for thought guys.

    I hope my Rem700 Varmint .308win, will shoot MOA out to at least 4-500.
    but that might be a bit much! Lol!

    Push the envelope, thats where it gets interesting!

    Have fun and straight shootin guys!
    There are several people that choose a twist based on boolit and velocity area. Most of us just don't have the option of choosing a particular twist and work with what we have. Regardless, twist is part of your fit, so fit always comes first int hat sense. There are multiple threads here about choosing a good candidate for a particular twist/velocity range.

    Hope that helps answer your question.

  4. #84
    Boolit Mold Tallyman's Avatar
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    Remington Model 700 Varmint Rifle

    I have found that a 1:12" twist in .30 caliber works best for me accuracy wise. My Remington Model 700 Varmint rifle has a 1:12" twist although most .308s and 30-06s come with a 10" twist. I also prefer a heavy .30 caliber lead bullet of 170 to 200 grains. I do not gas check my bullets, but lube with Lee liquid ALOX. After the lube dries I add a dab of lithium grease to the base of the bullet as I load it into the case. I keep my velocities under 1800FPS and my shooting range under 150 yards.

  5. #85
    Boolit Master nanuk's Avatar
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    I have to wonder if the reason GCs are needed above a certain velocity, with GC designed boolits or ANY boolit is that after a certain pressure, the base is deformed enough to not provide a similtaneous exit from the bore.

    a damaged base will allow one side of the base to exit before another, and that is the same as having a predamaged base.

    a GC is much harder, and the base edge simply can withstand much greater pressures.

    one good experiment is someone needs to file a notch in a GC and see how accurate those are. it would support my SWAG

  6. #86
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    I was going to reveal my new adjustable-twist barrel
    but not sure this is the right time...

  7. #87
    Boolit Mold Westerner's Avatar
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    Quote Originally Posted by a.squibload View Post
    I was going to reveal my new adjustable-twist barrel
    but not sure this is the right time...
    I will stick with the tried and true "adjustable RPM" Barrel on my Pedersoli 1874 Quigley Sharps. Case in point; a 405 grain cast flat base flat point molly coated and lubed hard lead bore diameter boolit pushed at 1,100 fps in front of a max Unique load held in by dacron keyholed half the time. A minimum load of H322 left a dirty tube on the first shot and entered the target 3" high and 6" to the right of a 3 shot 3/4" group @ 100 yards. 1,600 fps = the magical 64,000 rpm. Never thought I would love a dirty powder. Never thought it could be done with iron sights either so I tried it all over and had the same results except it opened up a bit, to 7/8". This man loves a hair set trigger and a very long barrel with Soel long range sights.

  8. #88
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    Quote Originally Posted by nanuk View Post
    I have to wonder if the reason GCs are needed above a certain velocity, with GC designed boolits or ANY boolit is that after a certain pressure, the base is deformed enough to not provide a similtaneous exit from the bore.

    a damaged base will allow one side of the base to exit before another, and that is the same as having a predamaged base.

    a GC is much harder, and the base edge simply can withstand much greater pressures.

    one good experiment is someone needs to file a notch in a GC and see how accurate those are. it would support my SWAG
    Sound reasoning and has a basis in fact. If the base of the bullet is below the case neck or there is a great amount of case neck expansion then the base of the bullet can "rivet" and not be square to the axis of the bore on exit. This can happen with PB and GC'd bullets. With the pressure pushing forward on the base of the bullet if the bottom driving band is not thich or strong enough it can be deformed as the edge is pushed forward in the lube groove above it.

    Larry Gibson

  9. #89
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    10 and 12" twists in .30 cal allow a broad range of cast bullet weights to be adequately stabilized for accuracy over a large velocity variation, especially at the lower 300 - 2000 fps range. However, if you are entering the velocity range of 2000 - 2800 fps with medium weight .30 cal cast bullets then a 12 - 16" twist is better with the 14" twist being a good "median" choice.

    If building a .30 cal rifle or rebarreling with HV cast bullet shooting in mind the 14" twist is my 1st choice.

    On the other hand Bret is correct that "Most of us just don't have the option of choosing a particular twist and work with what we have." Understanding the rate of twist we have with a specific rifle and what is needed for accuracy at all spectrums of it's velocity range with a specific cast bullet is essential for best accuracy.

    Larry Gibson

  10. #90
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    Food for thought or comment. last summer I started shooting lead bullets from a revolver for the first time in my life. This was for low speed paper punching. Being new to this and having bricks for brains I made most every mistake one could think of. Soft bullets, very fast powder, undersized , loaded too light....... and painfully more. I was cleaning out lead with a hammer and chisel, jack hammers and various explosives. SLOWLY some thoughts , with lots of reading started me thinking. One of the first things I did that made a stunning reduction in leading was to long seat my bullets so they just barely started into the cylinder. I believe that is from the cartridge sitting on the bottom of the chamber and the bullet having to scrape up over the chamber end to start into the throat. Then I switched to a slower powder, from Titegroup, things got better. Finially, after months , I began to up my charges a little at a time. I had been trying to hold down low for reduced recoil. I got 2 results from bumping speeds up a little . Cases are now clean, no more burnt black sides and accuracy improved. Recoil went up a little but after a little while it made no difference at all. I am as slow and inaccurate as I ever was but the gun can now shoot 200 rounds with just barely a haze of fouling in the barrel.

  11. #91
    Boolit Mold ShooterOnTheLine's Avatar
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    I guess we agree to disagree...

  12. #92
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    Does anyone KNOW when you need to use gas checks and when not, what it REALLY does? My mentor Elmer Keith din't use them. Why do I need them??

  13. #93
    Boolit Buddy sixpointfive's Avatar
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    What about using gas checked typed bullets without the gas check for low velocity plinking?

  14. #94
    Boolit Master badbob454's Avatar
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    Quote Originally Posted by sixpointfive View Post
    What about using gas checked typed bullets without the gas check for low velocity plinking?
    this is what i do up to 16-1800 fps without , and above 1800 i use a check , however i have driven many a boolit in plain base near 2,000 fps with good accuracy my sks shoots a 175 gr boolit in plain base very accuratly @ 1800-1850 fps in a .314 diam boolit ...
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  15. #95
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    When IDEAL (Lyman) came out with gas checks, they and most everyone else tested them an awful lot, and the results are for us to enjoy not necessarily reprove. Results of their use can be seen in the record books, of course plain base bullets set records too, but are mostly breech seated and at lower velocity.

  16. #96
    Boolit Master PS Paul's Avatar
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    Quote Originally Posted by NMLRA Guy View Post
    Does anyone KNOW when you need to use gas checks and when not, what it REALLY does? My mentor Elmer Keith din't use them. Why do I need them??
    I know this an old thread, but I believe lasc.us had about the best explanation for using gas checks that I had ever read: to the effect...... gas checks are required when high SPEED and high PRESSURE are BOTH in play. Speed alone is not necessarily THE deciding factor.
    A government that robs from Peter to pay Paul can always depend on the support of Paul.

  17. #97
    Boolit Bub
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    Huh I've checked an if hard enough no cgi needed but softer needs gc

  18. #98
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    This is a good read. Bret comes closest to my view on this. I am new to cb and reloading in general, but did metal failure analysis in extreme environments and motion for 30 years. All of these issues show up elsewhere in machinery failure, manufacture or assembly.

    Please forgive my nerd-speak and understand that I am just excited with this really fun topic. I do not intend to imply that ed-ja-ma-cation is in anyway a substitute for experience, especially in a topic like this one. These are musings, written like I write for fun, and I prolly sound like a pedant or some other horrid ting.

    So, first my explanation of what is happening. Then my explanation of why it is so unpredictable.

    The overall mode of failure is one of my favorite styles: kinematic instability with load and time dependent geometry and material properties. The radical inaccuracy comes from the bullet jack-knifing in the barrel as the sides overstress from pressure, heat, rifling friction force, and supersonic superheated gas errosion of material near the rifling contact line on the bullet. The still solid bullet is then wedged tightly cocked as hard as the gas pressure can get it, with the barrel itself eggshaped elastically from the load. As the bullet leaves the barrel, the last contact point catapults the bullet sideways with considerable spring energy that the barrel and bullet material have stored in the cocking. After that, the wind drag affects the bullet sideways according to the square of the speed and linearly with its cocking angle.

    The situation is very similar to trying to do a hard press fit of a short dowel pin into a softer steel hole. The pin wants to go sideways, gouging the wall of the hole, and the more sideways it gets, the more off center loading it gets. The situation is worsened as the pin swells and fails due to heavy compressive stress.

    With the lead bullet, the situation is so much more complicated. The lead is already very close to its melting point so addition of heat from gas and rifling friction interact with the above-yield stress state at the rifling to push the total lattice energy above the melt enthalpy.So the contact point lead leaves the area, allowing cocking.

    It is so unpredictable because all these exponential effects are combining to eat away at the tiny remaining lattice stability of the lead. And when pushing a rod from the back it is always hard to predict when it will go sideways. The driving force, the powder explosion, is an instability in itself, and varies a lot from shot to shot, day to day, powder to powder. Finally, while we get to hear about the caliber, length and rifling of our barrel, we usually get no information on the surface roughness or actual dimensions of the land and non-land geometry. The non-lands are the flow paths for the superheated gas and grit to rush past the bullet surface adding heat and stress.

    The good thing is that all of these factors do not involve chaos, relativity, atmospheric corrosion, or radiation. That aside, mixed phase flow, contact stress and friction, dynamic thermal material property change, phase change, three dimensional stress state, and deformation dependent loading are all some of the most challenging stress analysis modelling that can be accomplished, one at a time, let alone combined.

    The tools to prevent cocking are packing, lube, fit, bullet engagement length, bullet strength and bullet melting point. Packing blocks high temperature gas from rushing past the bullet, adding their heat to the lead at its highest stress location. Gas checks are thermal and dimensionally stable packing, also acting as a 'hard point' for high contact stresses. Dacron polyester is a lubricious packing that blocks gas flow in the rifling non-lands. Paper wrap is packing. Really great fit means enough screw thread strength but not too much friction or compressive stress. Lube works as packing and reducing friction and wear. Longer bullet engagement reduces contact force on the rifling and minimizes the ability of the bullet to cock. Hard lead improves the strength and melt point but the best lead is still a dismal failure as a structural material especially around heat.

    All of these solutions are in competition based on cost and effect. At one end the 22lr delivers 130ft-lbs at about 1.5 moa with an annoying pop for $.06. At the other end a 30 cal deer rifle with fmj reloads delivers 3000 ft-lbs at about 1 moa with an ear damaging boom for $.30.

    Gas checks are $.03 and take less than 10 seconds to install. Polymer packing is nearly free and takes about the same time to install. The lead costs about $.04 per 150 gr round, and the best recycling systems are 50-90% effective, due to bullet destruction. The primer is $.03 and the powder is $.07-$.15. We all love making stuff, so labor is free.

    As long as the lead rifling does not fail bad enough to make cocking cause accuracy loss, additional gas checks, packing, lube and bullet sizing are wasted.

    Just my 2 cents on the really cool issue.

    smw

  19. #99
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    Quote Originally Posted by stephen m weiss View Post
    This is a good read. Bret comes closest to my view on this. I am new to cb and reloading in general, but did metal failure analysis in extreme environments and motion for 30 years. All of these issues show up elsewhere in machinery failure, manufacture or assembly.

    <<snipped for brevity>>

    As long as the lead rifling does not fail bad enough to make cocking cause accuracy loss, additional gas checks, packing, lube and bullet sizing are wasted.

    Just my 2 cents on the really cool issue.

    smw
    What a refreshing perspective, and I think I understood about 1/3 of it!! I don't agree with your conclusions 100%... At the very least, I like sizing for uniformity. Boolits from the same mold will drop and age to different diameters, depending on how well I do my part (consistent alloys, closing pressure, temperatures, etc...) One of my 30 cals shoots .309 boolits just fine, so if I stuff a .312 in there then the pressures will be higher, which will affect other things as well... Also, if I'm not careful about the diameter at the bore ride and make it too big, and it wedges in the bore, then I can't extract the live round... Forcing the bolt open sometimes results in the boolit staying in the barrel while the brass is removed... So, at the very least, I'm a fan of sizing when the boolit drops large...

  20. #100
    Boolit Buddy stephen m weiss's Avatar
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    I wanted to think carefully before replying. So, agreed, if there is gross mis-fit resizing is going to be possibly more important than any of the other factors.

    There is this little equation I always remember: Ee=o, well little e is epsilon and o is little sigma.

    E is the modulus of elasticity of the material. Lead and its alloys are about 2e6 psi.
    e is the strain, diameter over diameter
    o is the stress caused by the strain, in psi (pounds per square inch)

    So in your case, that is 2e6 x (.312/.308-1)= 26ksi (1000 psi) well that squashes all lead. So, sending your bullet down the barrel with gas at 1500 atmospheres and god knows what temperature blasting up its shorts when it is already grossly squashed and failing would definately mean cocking. Fixing the fit with resizing would be the first order of business, as you have observed.

    So, if any of the 'tools' are really badly wrong, fixing them first would be most important.

    smw

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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