Search results

Search the forum Search Articles
  1. J

    Sidearms & Scatterguns Favorite handgun type

    A matched pair of fully custom CZ-52's in full-power 7.62x25 mm Tokarev. Single-action triggers are crisp at 2 pounds. Thumb safety works fine, but decocking feature has been surgically removed. Recoil springs are 18.5 pounds. I completed all of the needed factory machining steps and polished...
  2. J

    Rifling Twist-Rate Effect on Chamber Pressure

    I have revised the original paper to make it more readable and added a table showing typical results as calculated by QuickLOAD(c). Both the chamber pressure increases calculated for faster twist-rate barrels and the associated slight losses in muzzle velocity are practically negligible until...
  3. J

    Rifling Twist-Rate Effect on Chamber Pressure

    Here is a PDF of a "revised and extended" version of this paper which should be more readily understandable. EDIT: I updated the PDF to the published version on 3-1-22.
  4. J

    Rifling Twist-Rate Effect on Chamber Pressure

    With skill and care, I believe the CNC turning of "free machining" (C145 or C147) half-hard copper bullets can be done maintaining +/- 0.0001-inch tolerances in turning diameters. The bullet makers do this primarily to maintain consistent bullet weights. Everyone seems to weigh their expensive...
  5. J

    Rifling Twist-Rate Effect on Chamber Pressure

    Yes, compared to rifle bullets, most large military gun projectiles are of much lower average density, lower scaled weight, lower scaled strength of construction, and even often lower sectional densities. [Liquid payloads must be particularly difficult.] That is why I stick to flat-firing of...
  6. J

    Rifling Twist-Rate Effect on Chamber Pressure

    I tried 0.0006-inch and 0.0004-inch over-diameter solid copper rear driving bands (having no drag producing "relief grooves") and found them to be too large (12 and 10 ksi Shot-Start pressures, respectively). I went to a 0.0002-inch oversize RDB and solved the copper bullet engraving problem...
  7. J

    Rifling Twist-Rate Effect on Chamber Pressure

    Yes, Frank, the concerns you mention (along with several others that we have discovered) are valid for monolithic copper bullets, but there are ways around all of them, and the results are worth making the efforts. I have developed and patented a turned copper ULD bullet design which offers...
  8. J

    Rifling Twist-Rate Effect on Chamber Pressure

    Here is a PDF of a paper I just wrote detailing the derivation of this formulation for effective bullet weight increase when fast-twist rifle barrels are used. The bullet weight increase is only 0.959-percent when a very fast 20 calibers per turn barrel is used such as my 6.6-inch twist Bartlein...
  9. J

    Rifling Twist-Rate Effect on Chamber Pressure

    Starting the engraved bullet into rifling having a steeper helix angle DOES increase the peak chamber pressure a little, but not nearly as much as many seem to think. I just wanted to quantify that increase so you can make more informed decisions. I am neither for nor against using gain-twist...
  10. J

    Rifling Twist-Rate Effect on Chamber Pressure

    Thanks for the information guys. I never said anything about "bullet damage" due to gain-twist barrels. If I am reading the barrel stamps correctly, the rifling of this 6-groove .366/.375 barrel starts at 16-inch/turn twist-rate an increases to 7.78-inch/turn near the muzzle. The rifling helix...
  11. J

    Rifling Twist-Rate Effect on Chamber Pressure

    Just saw a mention that some new gun shown at this year's SHOT Show comes with a 3-inch twist rifled barrel. Some barrel makers have made those kind of twist-rates for ballistic test barrels used for short-range, reduced velocity testing of subsonic...
    • Thread
  12. J

    Rifling Twist-Rate Effect on Chamber Pressure

    This thread was really about showing riflemen how to quantify the peak chamber pressure increase which would be caused by selecting a faster rifling twist for a new barrel. Just multiply your expected bullet weight by a factor of {1 + [(2 Pi/n)*(kx/d)]^2} and run that bullet weight in QuickLOAD...
  13. J

    Rifling Twist-Rate Effect on Chamber Pressure

    I have no data on hand showing bullet twist upon firing from a gain-twist barrel, but I trust the observations of Mic McPherson, cited above. It also makes sense mechanically to me. The differential torque applied to the bullet shank by the rifling would be enormous in traversing a GT barrel...
  14. J

    Rifling Twist-Rate Effect on Chamber Pressure

    I thought so too, JB, until I talked with Mic McPherson, who actually used them with lead bullets and black powder--and then recovered some of the fired bullets. He said that the engraving marks were clean and just one land width and with the helix angle of the final twist-rate. I have no...
  15. J

    Rifling Twist-Rate Effect on Chamber Pressure

    Not much is written concerning interior ballistics except for obtuse military engineering studies. I would suggest (1) using QuickLOAD(c) interior ballistics software for load development and (2) recovering bullets fired (at >45-degree angle) into the deep end of a swimming pool for visual...
  16. J

    Rifling Twist-Rate Effect on Chamber Pressure

    Yes, Shot-Start pressure (required bullet engraving pressure) is seriously affected by throat angle and smoothness, bullet jump (if any), bullet hardness and possibly by anti-friction surface coatings. It is almost independent of rifling twist-rate selection. Higher SS pressure is deleterious in...
  17. J

    Rifling Twist-Rate Effect on Chamber Pressure

    I corrected my OP to bring my derived expression for the torque/force relationship into agreement with Shigley. I mentioned that this question was kind of tricky. The rifling twist effects on chamber pressures are even smaller than I had first thought (0.85-percent increase in effective bullet...
  18. J

    Rifling Twist-Rate Effect on Chamber Pressure

    I have never written seriously about gain-twist rifle barrels. My good friend and mentor, M. L. (Mic) McPherson of Colorado, told me privately that the recovered hard cast 50-caliber bullets they fired at one mile from Sharps rifles showed them to have been twisted by gain-twist rather than...
  19. J

    Rifling Twist-Rate Effect on Chamber Pressure

    Just saw a mention that some new gun shown at this year's SHOT Show comes with a 3-inch twist rifled barrel. Some barrel makers have made those kind of twist-rates for ballistic test barrels used for short-range, reduced velocity testing of subsonic bullet behavior or extreme range terminal...
  20. J

    Dope shooting uphill - tell me why I'm wrong

    I apologize for using too many big words, but the concept seems quite simple to me. It is another implementation of exactly the Sierra calculation which ptosis admired along with a simple physical explanation of how it works.
Top Bottom
Back
Home
Forums
Merch
Alerts