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Thread: Powder coat and chamber pressure

  1. #1
    Boolit Buddy Driver man's Avatar
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    Powder coat and chamber pressure

    I powder coat my cast projectiles and load them according to the cast lead loading data but find some differences in performance which makes me wonder what effect powder coating has on chamber pressures and whether a new set of loading data be developed. I find in my very light pistol loads (32 S&W Long) 1.5 grains I need to crimp harder or add a bit more powder (to up pressure.I think) other wise there is a loss of accuracy , similar with 38 in my revolver but at top end loads I get improved accuracy (9mm) .

    Has any one done any testing on various rounds and compared them, for example 45acp fmj compared to 45acp .cast and traditionally lubed and 45acp powder coated. Same with 9mm .38 etc, with the same load of powder and weight bullet.

    Does a bottle neck cartridge behave differently and does using them in rifle loads make a difference.

    I think a new set of loading data could be required but unless non subjective tests are done it is only guess work. Has anyone done this type of testing with the correct equipment, would anyone else like to know?
    Last edited by Driver man; 02-05-2021 at 04:41 PM.
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  2. #2
    Boolit Master
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    I think Larry Gibson may have done some powder coated bullets for someone. If he doesn't check in here try sending a PM. I think he is the only person in this forum with pressure measuring gear.

  3. #3
    Boolit Grand Master popper's Avatar
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    The assumption is PC is slick and the bullet leaves the neck easier so more crimp is used to get powder to burn better. I don't shoot revolvers so no crimp groove needed, just set neck tension and remove the flare.
    Whatever!

  4. #4
    Boolit Master
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    Quote Originally Posted by Driver man View Post
    I powder coat my cast projectiles and load them according to the cast lead loading data but find some differences in performance which makes me wonder what effect powder coating has on chamber pressures and whether a new set of loading data be developed.
    PC may be "slick" but it makes bullets fat. I have loaded a Lee 168-358 (discontinued) for subsonic 9mm since 2002 , a few years with Hi Tek coating now. All was good.

    But now that I discovered PC and I like it, that same bullet doesn't work anymore because PC fattens the nose too much. It may chamber every now and then but not really. Pressure will be higher with the fat nose of course.

    I'm using MP Hammer for 9mm subs now.

    In my opinion, a separate PC data still wouldn't work for anyone elses particular barrel / bullet size combination so that's why we start low.

  5. #5
    Boolit Master
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    I've found the same thing that some of my firearms don't like the fatter nose due to PC-- so I resize those after PC and, for me, that solved the problem. In my rifle cartridges I have not noticed any accuracy change with PC-- except for my Enfield that got more accurate when I switched the same bullet from lube to PC. I think its worth taking the trouble to re-do some of the load ladders when switching, just because it makes the bullet a little different. I have not seen any indication of significant pressure changes (that is, no noticeable velocity or primer changes-- I don't have the equipment to check chamber pressure).
    Hick: Iron sights!

  6. #6
    Boolit Buddy Driver man's Avatar
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    At the range yesterday i fired some loads I had loaded in my K frame 19-2 357 revolver. I had loaded a 148gw/c with 3grains of w231 .I loaded 20 with alox lubed and sized 358 and 20 pc with Smokes translucent copper and sized 358 both crimped in the crimp groove with the same die setting. I am using 38 starline brass.
    At 25 yards the pc shot about a 3 inch group an inch higher and an inch to the right ,the alox shot a ragged hole thru the x ring . This is my target load and I have used it for years. The pc had unburnt powder. To achieve similar grouping with pc I have to load up to 3.3 grains of 231. I think there is quite a difference in chamber pressure between the pc and alox lubed wadcutters.
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  7. #7
    Boolit Buddy
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    Quote Originally Posted by Driver man View Post
    At the range yesterday i fired some loads I had loaded in my K frame 19-2 357 revolver. I had loaded a 148gw/c with 3grains of w231 .I loaded 20 with alox lubed and sized 358 and 20 pc with Smokes translucent copper and sized 358 both crimped in the crimp groove with the same die setting. I am using 38 starline brass.
    At 25 yards the pc shot about a 3 inch group an inch higher and an inch to the right ,the alox shot a ragged hole thru the x ring . This is my target load and I have used it for years. The pc had unburnt powder. To achieve similar grouping with pc I have to load up to 3.3 grains of 231. I think there is quite a difference in chamber pressure between the pc and alox lubed wadcutters.
    Did the accuracy improve?

  8. #8
    Boolit Buddy Driver man's Avatar
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    Yes, accuracy improved to nearly the same as alox. I use a rest to test my loads and the pc at light loads is not quite as good. I sometimes dip the pc coated wad cutters in a carnauba /solvent solution and allow to dry for some of my full power loads .
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  9. #9
    Boolit Bub


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    Do you think the wax makes it “stickier” in the barrel and allow the lower powder charge fully burn?

    Quote Originally Posted by Driver man View Post
    Yes, accuracy improved to nearly the same as alox. I use a rest to test my loads and the pc at light loads is not quite as good. I sometimes dip the pc coated wad cutters in a carnauba /solvent solution and allow to dry for some of my full power loads .
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  10. #10
    Boolit Buddy
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    Quote Originally Posted by Driver man View Post
    Yes, accuracy improved to nearly the same as alox. I use a rest to test my loads and the pc at light loads is not quite as good. I sometimes dip the pc coated wad cutters in a carnauba /solvent solution and allow to dry for some of my full power loads .
    I see you're in NZ.I get my non TGIC PC from Resto supplies...

  11. #11
    Boolit Buddy Driver man's Avatar
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    If I use a HBWC in my 32 and 38 that has been powder coated the skirt will clamp itself to the inside of the case when fired and split the boolit in two regardless of load levels and just the boolit head will leave the case.
    By applying my wax it shoots very accurately and in one piece . I used to swage my 32 HBWC untill I got a dewc mould from Mihec which shoots just as good. I think powder coating alters the load dynamics in many and varied ways.
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  12. #12
    Boolit Mold RobClarke's Avatar
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    if you have to seat deeper because of the PC then yes there will be increased pressure

  13. #13
    Boolit Master
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    Quote Originally Posted by Driver man View Post
    If I use a HBWC in my 32 and 38 that has been powder coated the skirt will clamp itself to the inside of the case when fired and split the boolit in two regardless of load levels and just the boolit head will leave the case.
    By applying my wax it shoots very accurately and in one piece . I used to swage my 32 HBWC untill I got a dewc mould from Mihec which shoots just as good. I think powder coating alters the load dynamics in many and varied ways.
    Thanks, that is very interesting. I just coated a bunch of 38 HBWCs guess I’ll try lubing them.

  14. #14
    Boolit Buddy Driver man's Avatar
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    Quote Originally Posted by JimB.. View Post
    Thanks, that is very interesting. I just coated a bunch of 38 HBWCs guess I’ll try lubing them.
    Wondering how your pc HBWC lubed shoot for you
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  15. #15
    Boolit Master


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    Several years ago I had Donnie Miculek coat some of my boolits for an Area USPSA match. I had never shot coated boolits before but was trying to keep the gun clean for the duration of the match. Never gave a thought to the other consequences of coating the boolits. When I got to the chronograph station the first 5 rounds failed to make the required velocity for the power factor by half a point (power factor of 164.5). The rules allow for a second try and that attempt passed by less than one full point (power factor of 165.2). The reduced friction of the coating kept the ammunition from developing the pressure that I got using a conventional lube. The same load with a conventional lube made power by over 5 points; over 170.

    Slicker boolits need a harder crimp, more powder or maybe a little of both to reach the same velocity.
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  16. #16
    Boolit Buddy


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    I loaded some 150gr MP 9mm PCed and sized to .357 using 147 jacketed load data for a similar profile bullet, seated to the same depth. Predicted velocity was 975, Quickloads said the same and predicted a chamber pressure of 34kpsi. When I actually pressure tested these they shot 1008fps avg with an average pressure of 28kpsi. I have been using jacketed load data for several years and noticed that *almost* (thats a legal term, ymmv) always the velocity will be slightly higher and the pressure lower for a similar bullet weight, profile and powder charge.

    *Edit. I have had one or two issues with bullet set back in autoloaders over the years so I use a decent Lee factory crimp on almost everything.

  17. #17
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    Coopaloop86 your figures "almost" the same as I stated 6 years ago in my testing. Pc'ed bullets will generally shoot 4 to 5% faster than lubed or jacketed at same powder charge. Also generally you will need to rework any old load your using as barrel harmonics changed with speed increase.
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  18. #18
    Boolit Buddy Driver man's Avatar
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    Are you suggesting that powder coated boolits could be loaded using FMJ data plus 5 or 10%extra powder.
    Might be interesting to do a test
    The Bird of Time has but a little way
    To fly-and Lo! the bird is on the wing

  19. #19
    Boolit Master
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    The only direct comparison I have with ammo loaded on the same day with the exact same powder and die settings is with 450 Bushmaster. These were light loads with a 304 grain bullet and 11 grains Unique. The mold has 2 cavities for gas checks and 2 cavities plain base. The Lubed bullets shot 10 to 20 FPS faster.

    304 Lubed Lead Plain Base 1,149 FPS
    304 Lubed Lead w/ GC 1,150
    304 PC No GC 1,127
    304 PC Plain Base 1,139

  20. #20
    Boolit Bub
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    This is truly an interesting thread. Shot 2 batches of my 1st PC'd bullets--Noe 234 gr RF TL. 4.5 gr BE. The tumble lubed bullets (using lsstuff alox) was more accurate and recoil was milder.

    The pc'd bullets were not as accurate and recoil was more noticeable. I shall try upping the charge by 0.3 grains.

    Leaning something new every time.

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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