Dusty Stevens
Shiner
They confirmed the tests palmisano and pindell did to decide on the .059 size
Effects of flash hole size in ballistics and precision
- Thread starter Bryan Z.
- Start date
257ack
Silver $$ Contributor
I have checked the Lapua brass and to get everything the same, I use a 1/16 drill bit. I have heard to leave it alone but the holes in my brass vary a bit so I try to make them uniform to the smallest possible. I have used H4895 at a few times with fair results when 133 (for whatever reason) was not working.
Ned Ludd
Silver $$ Contributor
As I mentioned previously in this thread, Alpha Munitions did testing of their own and found that with .308 Win Palma brass, a 2mm flash hole was just slightly better than the smaller 1.5mm flash hole. In my hands, ES/SDs with Alpha brass are the same I I routinely achieve with Lapua SRP .308 Win brass, perhpas even a tick better. However, the difference wasn't huge. The folks at Alpha were kind enough to send me the test results, but that was some time ago and I don't have them any longer. Perhaps you can get the same test results by contacting Alpha Munitions.
My [limited] experience with .308 Win brass suggests there is little difference between 1.5mm and 2mm flash holes in this cartridge. I would give a very slight edge to the 2mm flash hole, but it's pretty close. Unfortunately, this is only a sample size of "1". I'm guessing that something as simple as switching primers can produce at least as significant effect as flash hole size in a .308 Win cartridge. Different flash hole sizes might well exhibit a larger effect in cartridges of different size, such as the small .223 Rem case, which uses the 2mm flash hole. Alternatively, powder or primer selection might also have an impact on the effect of flash hole size. It is not easy to test with some cartridges such as .223 Rem because only the larger 2mm flash hole is available, but testing in cases where it is possible is really the only way to know what effect(s) the different flash hole sizes might exhibit.
F tests were used. That’s mentioned in the video.
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Know where I can see their data?
Dusty Stevens
Shiner
I doubt youll ever see it. I doubt it was published for external eyes
Rick300
Gold $$ Contributor
I have posted this before - this is what Alpha says about it:
Rick,
First off thank you for purchasing our 308 SRP brass, and for the question concerning our small primer pocket large flash hole setup. There has been a lot of debate back and forth concerning small vs large flash holes, and most of it is just that, debate. It is hard to find any kind of confirmed study. This answer may get a little long, but its a question deserving of such an answer.
First, we have only performed testing on larger volume 308 cases, being the 6.5 creedmoor, 260 rem. and 308 win. There is a lot of history from benchrest shooters who have looked at flash hole size within the PPC family. The results of each case (ppc vs 308) individually cannot be assumed true for the other size cases. Due to gas pressure being highly sensitive to volume (PV=znRT, ideal gas law), and many other factors, it is not valid to assume the results for one particular case must transfer to another case. That said, I'll discuss more what we have seen and found.
Lets hit some background first. People speak of the "jet affect" which was assumed in Percussion Primers, Design Requirements by E.R. Lake, 1970 where he states "as the size of the flash hole is decreased, then the pressure of the [primer] products and the length of their "spit" is increased". Simply put, the smaller the flash hole the greater the length of the jet the primer creates. Going through this report there is zero data backing up the jet affect for our specific application (rifle ammo). A further study, most popular and known in the shoooting industry was performed by German Salazar, 2011 Large vs. Small Flash Hole Test, which presents photographic results which may contradict the "jet affect". Salazar shows images of a large flash hole primer pocket appearing to visually produce more "spit" or "flash" in comparison to the small flash hole. Again, this is all visual results with no quantitative test data.
The reason I wanted to hit on the past research or common knowledge in the shooting industry is that people believe this stuff and speak like it is the 100% undeniable truth, when there is no true data to back it up. We started looking into the large vs small flash holes and have shown the affects of the flash hole on the end result, being the consistency of velocity. Our tests have taken identical cases, except for the flash hole size, and observed the performance characteristics of both. There is a lot of detail I could go into for the setup, but I'll save that for the technical article. We first found a velocity node to shoot well then loaded the same load into the test cases. These were then shot out of the same gun, and recorded using the same chrono (lab radar setup).
In standard conditions we found to have slightly better results (velcoity ES and SD) with the small primer pocket large flash hole setup, now is it a huge difference that would blow everyone away, no. However, testing at extreme low temp conditions we did show the velocity ES difference between the large and small flash holes opens wider.
It is my opinion that there is a balance of both primer and flash hole size to produce the best velocity ES. I think for optimal results you want to use the smallest primer possible which effectively ignites the powder charge. There is too much variance in primer ignition pressures that, I think, leads to much of the pressure variance in firing, consequently affecting the bullet velocities. It is possible (my THEORY.. just a theory...) that the jet affect could actually worsen the inconsistencies of the primer ignition creating greater inconsistencies in the powder ignition.
Anyway, really appreciate the question and I hope this helps!
Thanks,
Andrew Rixon
Director of Engineering and Manufacturing
Alpha Munitions
Rick,
First off thank you for purchasing our 308 SRP brass, and for the question concerning our small primer pocket large flash hole setup. There has been a lot of debate back and forth concerning small vs large flash holes, and most of it is just that, debate. It is hard to find any kind of confirmed study. This answer may get a little long, but its a question deserving of such an answer.
First, we have only performed testing on larger volume 308 cases, being the 6.5 creedmoor, 260 rem. and 308 win. There is a lot of history from benchrest shooters who have looked at flash hole size within the PPC family. The results of each case (ppc vs 308) individually cannot be assumed true for the other size cases. Due to gas pressure being highly sensitive to volume (PV=znRT, ideal gas law), and many other factors, it is not valid to assume the results for one particular case must transfer to another case. That said, I'll discuss more what we have seen and found.
Lets hit some background first. People speak of the "jet affect" which was assumed in Percussion Primers, Design Requirements by E.R. Lake, 1970 where he states "as the size of the flash hole is decreased, then the pressure of the [primer] products and the length of their "spit" is increased". Simply put, the smaller the flash hole the greater the length of the jet the primer creates. Going through this report there is zero data backing up the jet affect for our specific application (rifle ammo). A further study, most popular and known in the shoooting industry was performed by German Salazar, 2011 Large vs. Small Flash Hole Test, which presents photographic results which may contradict the "jet affect". Salazar shows images of a large flash hole primer pocket appearing to visually produce more "spit" or "flash" in comparison to the small flash hole. Again, this is all visual results with no quantitative test data.
The reason I wanted to hit on the past research or common knowledge in the shooting industry is that people believe this stuff and speak like it is the 100% undeniable truth, when there is no true data to back it up. We started looking into the large vs small flash holes and have shown the affects of the flash hole on the end result, being the consistency of velocity. Our tests have taken identical cases, except for the flash hole size, and observed the performance characteristics of both. There is a lot of detail I could go into for the setup, but I'll save that for the technical article. We first found a velocity node to shoot well then loaded the same load into the test cases. These were then shot out of the same gun, and recorded using the same chrono (lab radar setup).
In standard conditions we found to have slightly better results (velcoity ES and SD) with the small primer pocket large flash hole setup, now is it a huge difference that would blow everyone away, no. However, testing at extreme low temp conditions we did show the velocity ES difference between the large and small flash holes opens wider.
It is my opinion that there is a balance of both primer and flash hole size to produce the best velocity ES. I think for optimal results you want to use the smallest primer possible which effectively ignites the powder charge. There is too much variance in primer ignition pressures that, I think, leads to much of the pressure variance in firing, consequently affecting the bullet velocities. It is possible (my THEORY.. just a theory...) that the jet affect could actually worsen the inconsistencies of the primer ignition creating greater inconsistencies in the powder ignition.
Anyway, really appreciate the question and I hope this helps!
Thanks,
Andrew Rixon
Director of Engineering and Manufacturing
Alpha Munitions
NorCalMikie
Gold $$ Contributor
And for those that won't believe it till they see it? (I'am from Missouri)
Do it yourself. Work up your best accuracy load, THEN...
Get 20 cases of your choice, weigh them, measure them or do whatever floats your boat, 10 with small and 10 with larger flash holes.
Load each "EXACTLY" the same. Same powder, same OAL, same case length, same same.
Remember, all are EXACTLY the same "except" for the flash hole size.
Shoot them and see what the results care.
And if I'am at the bench next to you, while you're messing around with trying to figure out flash hole size, I've already fired off 100 rounds, all going in the same hole and am reaching for another box or rounds.
Shooting buddy (brother from another mother) kept records of EVERY load and round he ever loaded and fired from each of his rigs.
While he was busy writing, I was at the next bench firing round after round and all going in the same hole. Hard backed binder he kept that he must have taken with him when he died. He IS missed.
Do it yourself. Work up your best accuracy load, THEN...
Get 20 cases of your choice, weigh them, measure them or do whatever floats your boat, 10 with small and 10 with larger flash holes.
Load each "EXACTLY" the same. Same powder, same OAL, same case length, same same.
Remember, all are EXACTLY the same "except" for the flash hole size.
Shoot them and see what the results care.
And if I'am at the bench next to you, while you're messing around with trying to figure out flash hole size, I've already fired off 100 rounds, all going in the same hole and am reaching for another box or rounds.
Shooting buddy (brother from another mother) kept records of EVERY load and round he ever loaded and fired from each of his rigs.
While he was busy writing, I was at the next bench firing round after round and all going in the same hole. Hard backed binder he kept that he must have taken with him when he died. He IS missed.
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Thanks Bryan for great test and the time and effort you put into it.
The only other possible question I would have is if the slightly larger
flashhole size might improve ignition in colder temperatures.
I was shooting a 260AI all summer and fall in Minnesota a couple years ago
with Lapua small rifle primer brass with no issues.
Then one day after the outside temperature had dropped overnight down in the
single digits, I had mostly failure to fires on the exact same loads that worked
those several months previously.
Have wondered since about that question.
Thanks again.
The only other possible question I would have is if the slightly larger
flashhole size might improve ignition in colder temperatures.
I was shooting a 260AI all summer and fall in Minnesota a couple years ago
with Lapua small rifle primer brass with no issues.
Then one day after the outside temperature had dropped overnight down in the
single digits, I had mostly failure to fires on the exact same loads that worked
those several months previously.
Have wondered since about that question.
Thanks again.
Looks like my test merges with what Jack said. Would be great to see the actual data from these tests. Be even better if it all was easily available. I understand that some of it was done under the guise of product testing by private manufacturers and they do not want to circulate that data freely so as to exhibit the basis for their trade secrets but otherwise it would be nice.
Don't go too big, you need an edge for the primer anvil to seat on!!Open those beautiful flash holes!
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