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Thread: Drilled Flash Hole Test; 44 Magnum and 45 Colt

  1. #1
    Boolit Grand Master


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    Drilled Flash Hole Test; 44 Magnum and 45 Colt

    Drilled Flash Hole Test; 44 Magnum and 45 Colt

    Completed the test yesterday 29 April, 2019. Test firearm was a Contender with a 8.4” barrel in 44 Magnum and a 10” barrel in 45 Colt. A 2.5X scope is on the Contender. All measured data except group size (ctc widest shots) was obtained via the Oehler M43 PBL. I had prepared 10 cases, as previously posted, for each test string; 10 with standard flash holes and 10 with the flash holes drilled out with a #28 drill. Winchester WLPs were used in all cases for both cartridges.

    Testing was conducted from the bench with a Hoppe’s Pistol Rest with the target at 50 yards.
    Temperature was 80 degrees.
    Humidity was 30%
    Barometric Pressure was 29.63

    44 Magnum;
    Bullet was a 429360 cast of COWW +2% tin, AC’d and aged 10+ days before sizing .430 and lubed with BAC.
    Cases were Remington R-Ps sized and loaded in RCBS dies.
    Powder charge; 22 gr of Alliant 2400
    OAL; 1.638

    With Standard flash holes;
    Velocity; 1622 fps (muzzle)
    SD/ES; 13/41 fps
    Pressure; 35,800 psi(M43)
    Pressure SD/ES; 500/1,700 psi
    Group; 3.1”

    With flash holes drilled;
    Velocity; 1599 fps (muzzle)
    SD/ES; 17/47 fps
    Pressure; 34,500 psi(M43)
    Pressure SD/ES; 1,400/3.900 psi
    Group; 3.2”

    45 Colt:
    Bullet was a 452-230-TC cast of COWW +2% tin, AC’d and aged 10+ days before sizing .454 and lubed with BAC.
    Cases were CBC 45 Colt sized in RCBS steel FL sizer and loaded in Hornady dies.
    Powder charge; 7.3 gr 700X
    OAL; 1.598”

    With Standard flash holes;
    Velocity; 1060 fps (muzzle)
    SD/ES; 7/23 fps
    Pressure; 16,300 psi(M43)
    Pressure SD/ES; 400/1,500 psi
    Group; 2.9”

    With flash holes drilled;
    Velocity; 1059 fps (muzzle)
    SD/ES; 4/15 fps
    Pressure; 16,000 psi(M43)
    Pressure SD/ES; 400/1,100 psi
    Group; 3.15”

    From the measured data we see there is essentially no difference. Again the sky did not fall, California did not slide off into the Pacific and still no Trump collusion with Russians……

    Here’s the fired primers…..no difference in “flattening”…….

    Click image for larger version. 

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    Larry Gibson

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  2. #2
    Are you going to try it with black powder? In his book, "Loading Cartridges for the Original 45-70 Springfield Rifle and Carbine," Wolf was very insistent that a drilled flash hold was a necessary ingredient in reproducing original military-style cartridges.

  3. #3
    Boolit Master
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    Thanks Larry, nice test! Now that you have the cases drilled out are you gonna test CCI, Remington and Federal primers? Interested folks want to know!
    It's all chicken, even the beak!

  4. #4
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    Hmm... I wonder if that works the same for smaller cases like the 380ish or 9mm? Does a more confining case act the same? I would bet the same would be true.
    Any technology not understood, can seem like Magic!!!

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  5. #5
    Boolit Grand Master Outpost75's Avatar
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    Thanks for posting this! Results agree with my less scientific empirical experiments.

    Years ago I found a slight, noticable, but not statistically significant advantage in using enlarged flash holes for flush-seated .38 Special wadcutters in the Colt Gold Cup and Hammerli 240. At the time I thought the large flash holes were mostly a convenience because I could eliminate the step of having to clear particles of tumbling media (corncob grits) from the flash holes. I also noticed a slight improvement in ballisstic uniformity when hand-seating primers (Federal 100) in a clean, uniformed primer pocket, versus just taking tumbled, once-fired brass and running through the Star.

    Best ten-shot, 50-yard groups with Remington or Winchester 148-grain HBWC factory bullets in Remington or Winchester wadcutter brass and 3 grains of Bullseye, taper crimping to .375" were in the order of 1-1/2" at 50 yards. Good cast bullets (Saeco #348, wheelweights +2% Sn, sized .359" with 1970s Micro-Lube) prepped similarly would do about 2" +/- over a long-run , whereas the ordinary tumble cleaned, crunched and ground out loads assembled without any extra care were all 2"+ averaging about 2-1/2" with the largest groups around 3".

    Hammerli was more consistent than the Colt, but didn't belong to me, so when it had to be turned in I had built a BSA-Martini Cadet action with .38 AMU/.38 Spl. chamber with heavy bull barrel and Unertl scope blocks, resting the barrel in a V-block and using a return-to-battery rest and letting the gun free-recoil, using the 10X Unertl only to align on the target roll. Later (1980s) I discovered that Bill Davis, Jim Clark and Reeves Jungkind could all build PPC revolvers that shot as well as the Hammerli!
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  6. #6
    Boolit Buddy

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    Good work, please continue your testing, maybe you can shake california loose.....

  7. #7
    Boolit Grand Master


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    Quote Originally Posted by Shuz View Post
    Thanks Larry, nice test! Now that you have the cases drilled out are you gonna test CCI, Remington and Federal primers? Interested folks want to know!
    Other than affecting the velocity/pressures I don't believe there would be any "danger" from the use of another primer with drilled flash holes. I'll post the results of a test I also ran the other day testing Hercules 2400 (the powder I got from you....thanks again) vs Alliant 2400 (a new lot I recently purchased) and 6 different primers in the 357 Magnum.
    Larry Gibson

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  8. #8
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    Outpost75

    I never found the need to drill flash holes in SR/SP primed cartridges as those didn't develop case headspace problems with cat's sneeze loads. Those don't seem to generated enough psi in the primer pocket to set the case shoulder back.

    Certainly might be some additional benefit to uniforming to a large flash hole as you mention. I might have to try that!
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
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  9. #9
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    Thanks for the test.
    There is no difference between communism and socialism, except in the means of achieving the same ultimate end: communism proposes to enslave men by force, socialism—by vote. It is merely the difference between murder and suicide. Ayn Rand

  10. #10
    Boolit Buddy
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    Good test! Thanks for posting! Stuff like this is interesting! I would guess that if you changed one component it would change results. But neat to see that not much changed with quite a bit bigger flash hole.

  11. #11
    Boolit Master
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    This is interesting.
    My question is why do flash holes come the size they do ?

  12. #12
    Boolit Master
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    Larry,
    Thanks for reposting this as a separate thread.



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  13. #13
    Boolit Master
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    Thanks for sharing, interesting stuff.


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  14. #14
    I tested enlarging (drilling) the flash holes on 357 Magnum and 38 Special brass, IIRC, it was a few years back. Before even beginning I'd read a university study on the subject, and they were testing 308 ammo, at near max SAAMI pressures. Again, the sky did not fall, etc.

    My reason for testing was to try and unlock the mystery of trying to determine low or high pressure on low velocity cowboy loads. The standard or most common size flash hole today is 0.080" or a wee bit bigger. Primer flash holes are punched, not drilled, and the size is not super precise. I have noticed that in the 60's the flash holes wer somewhat smaller, as I can recall jamming decapping pins in the odd flash hole.

    Low pressure handgun ammunition is a bit of a funky deal. I assume that most measuring devices would be hard pressed to even measure the pressure. It probably doesn't get to much over 8,000 psi.

    And yet, some primers will be flat(ish) after firing, IOW the back of the primer will show that it has contacted the frame of the revolver. And others almost don't show any contact. I fooled with powder charge but that wasn't or didn't seem to be a factor.

    In an attempt to reduce the variables, I seated primers in an empty case, and fired them that way, no bullet, no powder.

    Interestingly, the result in most instances was a locked up cylinder. The primer would be pushed rearward, hard. My conclusion was that the pressure contained within the confines of the primer pocket were probably higher than normal 38 Special pressures. The flash hole was acting as a pressure valve, a restriction that was too small to bleed off much of the primers pressure. Of course this would increase the velocity and duration of the primer flash, which may or may not be a good or desirable thing.

    So ended that test, locked cylinders aren't much fun.

    So, the unanswered question was; " How big does the flash hole have to be before the primer doesn't lock the cylinder" I increased the size in small(ish) increments and at around 0.101" the primer would not back out, and without any powder or bullet, you couldn't see much or any contact with the frame.

    I then added powder and bullet and you could see when a load was beginning to have enough pressure to show primer contact with the frame and increasing the powder charge would increase the contact area on the primer.

    IMHO there is some performance to be gained with a larger flash hole, and certainly detecting increases in pressure was now possible.

    I did a bit more testing and called it quits. All the cases with enlarged flash holes were crushed in my arbor press and tossed.

    I decided the whole venture was too controversial to experiment any further. It also adds another variable in the load, matching the flash hole to the powder and primer combo just gets to be too much.

    However, it's my belief that gains can be made by changing (enlarging) the flash hole. I also know that if the sky were to fall, the "I told you so" crowd would be shouting from the rooftops. Everyone knows that is a dangerous thing to do. I do not think it's dangerous in low pressure pistols, but it may be a factor in high pressure magnums. I didn't see any use in experimenting there as the chamber pressure of a magnum rifle exceeds the pressure in the primer pocket that the primer makes.

    I've read that the newer "green" or no lead primers are more energetic than lead-styphnate primers and they use an enlarged flash hole when loading green primers.

    Edit: Today 2020/10/02 I found my notes on this test. Seems my memory was almost right. My tests stopped at a flash hole of 0.101", I've corrected my post.

    My notes:

    I emailed the following question to CCI:

    Q: I have a question concerning small pistol primers. I have been loading 38 Spl and 357 Magnum for CAS and most of the loads call for a SP primer. Today I decided to load some full power loads to get a base line measurement of the PRE. When I loaded a top load of WW 231 and a SP (CCI 500) in my 38 Spl case I saw very little pressure indication, ie the primer wasn't very flat. I had just run a test with a powder that calls for a SPM (CCI 550) and I was seeing some primer flattening, very normal considering that it should be a top load. Both loads should have been of equal pressure, but the CCI 550 was flatter. So I loaded both loads, only swapped primers. The 500 with the load that calls for a 550 and visa-versa. In all the tests the 550 was flatter than the 500. I am puzzled, I don't know what I'm seeing.

    I received the following reply from Cody B./Technical Service Rep.:

    A: You are seeing higher pressures being achieved with the magnum primer because this can increase your pressure over a standard primer by as much as 20%. This is why the primers aren't interchangeable with some ball powders calling for a magnum primer as they are harder to ignite. Hopefully this answers your question.

    The reply didn't really explain what I was seeing.

    I tried to think of an explanation and came up with the following hypothesis. What if the primer cup of the 550 SPM primer were harder than the cup on a 500 SP. Perhaps it could resist the impact of the hammer/firing pin and not indent as much. To test this theory I primed one case with a SP primer and another with a SPM primer. No powder, no bullet, and fired them in my revolver.

    • The SP primer looked very similar to what it usually did, perhaps a bit more indented, but not significantly.
    • When I fired the case with the SPM primer, the cylinder of my revolver was locked up. The primer, upon ignition had backed out of the case enough to lock the cylinder. It took some effort to rotate the cylinder and eject the case. Without any restriction, other than the primer hole, the pressure created was enough to show machine marks from the revolver frame.

    I would not have expected that without powder or bullet, this much pressure was created by the primer. It appears as if the SPM primer is indeed more powerful, and is capable of creating a significant amount of pressure on its own, without any powder or a bullet. The primer flash hole is small enough that a significant amount of pressure is being contained. I wondered, if the primer flash hole were larger, and the test repeated, would the pressure be relieved enough to eliminate the pressure indications. In other words could the primer flash hole size be increased to a point where it would look just like a fired SP primer. The test was repeated with the flash hole enlarged to 0.093".

    • With a 0.093" flash hole cylinder lockup was less, less effort was required rotate the cylinder and eject the fired case.

    I repeated the test, with the flash hole further enlarged to 0.101".

    • With a 0.101" flash hole, the cylinder rotated freely and the case ejected normally. By the appearance of the primer it looks like the flash hole is at the size where it is verge of being able to release pressure enough so that the primer is not flat, does not show a significant amount of frame machine marks, not does it back out and lock the cylinder.

    I know of one test, a theses that enlarged flash hole of 223 and 308 ammunition to 3mm (0.118") without creating any hazardous conditions. I was still well within that @ 0.101".

    The next test was to enlarge the flash hole to 0.101" on 10 cases and test with powder and bullets. The load I choose was a mild 38 Spl load, with 3.1gr of Trap 100 and a 147 gr Xmetal cast bullet (painted).

    • With a SP primer in a case with a 0.101" flash hole the pressure signs as indicated by the primer were just slightly more than with an unmodified primer flash hole.
    • The load with a SPM primer and the 0.101" primer flash hole showed slightly more pressure signs, but less than with an unmodified flash hole.

    I did not test accuracy or chronograph the loads. I conclude that the 0.082" flash hole on my cases acts as a significant pressure constriction. I also conclude that CCI SP and SPM primers require more pressure than normal 38 Spl loads to indicate pressure, cannot be used to check pressure.
    Last edited by nitro-express; 10-02-2020 at 11:42 AM.

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    Boolit Grand Master Outpost75's Avatar
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    Quote Originally Posted by onelight View Post
    This is interesting.
    My question is why do flash holes come the size they do ?
    In US manufacturing practice the flash holes are punched on the priming machine and not drilled.

    The size of the flash hole was initially determined by empirical experiment in determining the minimum size punch which would do the job without breaking or excessively deforming the case web and the specs standardized during WW2.

    NATO spec today is 2mm+0.05/-0.00.
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  16. #16
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    Thanks, Larry and Thanks for contributing the story on flash holes to The Fouling Shot.

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  17. #17
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    Quote Originally Posted by nitro-express View Post

    And yet, some primers will be flat(ish) after firing, IOW the back of the primer will show that it has contacted the frame of the revolver. And others almost don't show any contact. I fooled with powder charge but that wasn't or didn't seem to be a factor.

    In an attempt to reduce the variables, I seated primers in an empty case, and fired them that way, no bullet, no powder.

    Interestingly, the result in most instances was a locked up cylinder. The primer would be pushed rearward, hard. My conclusion was that the pressure contained within the confines of the primer pocket were probably higher than normal 38 Special pressures. The flash hole was acting as a pressure valve, a restriction that was too small to bleed off much of the primers pressure. Of course this would increase the velocity and duration of the primer flash, which may or may not be a good or desirable thing.

    So ended that test, locked cylinders aren't much fun.

    So, the unanswered question was; " How big does the flash hole have to be before the primer doesn't lock the cylinder" I increased the size in small(ish) increments and at around 0.125" or 1/8" the primer would not back out, and without any powder or bullet, you couldn't see much or any contact with the frame.

    I then added powder and bullet and you could see when a load was beginning to have enough pressure to show primer contact with the frame and increasing the powder charge would increase the contact area on the primer.

    IMHO there is some performance to be gained with a larger flash hole, and certainly detecting increases in pressure was now possible.

    I did a bit more testing and called it quits. All the cases with enlarged flash holes were crushed in my arbor press and tossed.

    I've read that the newer "green" or no lead primers are more energetic than lead-styphnate primers and they use an enlarged flash hole when loading green primers.
    When a primer detonates, the pressure of the detonation drives the primer back out of the primer pocket and against the bolt face/backing plate. When the powder burns and creates pressure, it drives the case rearward and reseats the primer into the pocket. Without enough powder pressure, the primers won't be reseated and in a revolver this results in a locked up cylinder. It's quite common in very low pressure revolver loads to have the primers remain backed out. You have to find a happy medium of low pressure, but with enough pressure to seat that primer once again.

    The brisance of the Diazodinitrophenol (DDNP) priming compound is much faster than Lead Styphnate. The first attempts by the ammunition manufactures to mitigate this was to enlarge the flash hole to reduce the effects of the much faster explosion. Then they crimped in the NT primers, and some even used a combination of crimped primers and enlarged flash holes. The somewhat final iteration has been to go to small pistol primers for NT handgun rounds. Blazer (Speer) is now producing 10mm casings with small primer pockets for their NT loadings, along with their .45 acp cases.

    I'm not sure where Federal's Catalyst priming compound falls in brisance, and I haven't followed it's development, other than to read some of the literature concerning it's introduction when it was first commercially available. It's being used mostly in training ammunition at this time, and my simple guess is they want to find out how it performs under those rather safe conditions before they market it in defense and LE ammunition for duty use, etc. A failure on the range isn't the same as a failure in the field, so it was probably a smart move on their part. I forget how many rounds were in the initial contract for training ammunition containing the Catalyst priming compound, but it was rather large. It should give them an idea of how it works out.

    Hope this helps.

    Fred
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  18. #18
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    Quote Originally Posted by SOFMatchstaff View Post
    Good work, please continue your testing, maybe you can shake california loose.....
    I'll go for that............
    JMHO-YMMV
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  19. #19
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    Quote Originally Posted by Larry Gibson View Post
    Other than affecting the velocity/pressures I don't believe there would be any "danger" from the use of another primer with drilled flash holes. I'll post the results of a test I also ran the other day testing Hercules 2400 (the powder I got from you....thanks again) vs Alliant 2400 (a new lot I recently purchased) and 6 different primers in the 357 Magnum.
    Cool................
    JMHO-YMMV
    dd884
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    Gary D. Peek

  20. #20
    I dabbled with flash hole size enlarging a few years back and I theorize that there may be gains to tuning the flash hole size on a load to gain performance, that is better Es/Sd and group size. However, the practicality of having cases of the same caliber with significantly different sized flash holes lead me to abandon further experimentation.

    I did observe several interesting things when loading Cowboy ammunition, the lower velocity and pressure loads. I was testing different small pistol primers and noticed that some primers would flatten more than others. IOW, when you looked at the primer, you could see more flattening on some primers. The flattening didn't seem to correlate to the pressure that the load should be producing.

    The flash hole acts like and is an orifice between the primer pocket and the powder chamber. It is a two way valve. In high pressure rifle ammunition,it slows the pressure spike from the powder to the primer pocket. Depending on the pressure duration, it may even limit the pressure reaching the primer pocket.

    But, in low powered cowboy loads, the pressure developed in the primer pocket is greater than the pressure created by the powder in the cartridge case. Primers are an explosive device, there is a fair bit of energy contained in the primer. To test this I loaded case with just a primer, no bullet and no powder, and fired them in my revolver. Well, I was a bit surprised to find that the primer had backed out enough to lock up the cylinder. This happens sometimes if the powder charge is absent. And during competition, a locked cylinder is not a winning deal.

    I opened up the flash hole and did get to a point where the primer would not back out. Of course, if the primer pocket was a bit loose, it would still back out.

    At this juncture I realized the rabbit hole was a bit deeper than I'd like to go, so I ended my experimenting. Interestingly flash holes on the "green" primers is a bit larger than the norm, and I suspect it's to stabilize some pressure issues. I suspect the green priming compound is a bit more explosive than conventional or common priming compounds.

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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