Primer Flash Holes

Lapua is sourced in Europe. In .40 S&W pistol rounds, the GECO headstamp is sourced out of Europe and the primer flash hole is drilled out in a smaller metric size. I know this because my Lyman primer flash hole hand deburring tool always get's caught in the smaller GECO holes but never in American brass. Researched the manufacturerer - sure enough - European & metric. I wouldn't worry about it.
 
2 things....
Lapua is NOT the only one making 6.5x47 Lapua casings.
Peterson Cartridge is also making quality brass for that cartridge.

I had heard about 2 different size flash holes with Lapua brass.
And while i really don't like recommending a different forum on an open forum, a search on Accurate Shooter's forum would possibly have the performance difference answers you seek.
 
OK I prepped a bunch of 5.56 brass. I am doing 2 loads, with 3 10 shot groups. So 60 shots total.

I am doing:
N133 24.8 grains 50 grain SBK
N133 24.9 grains 50 grain SBK

1) Prepped brass with nothing done to primer holes (I measured them, they are near 80k wide)
2) Prepped brass with drilling them to be 81k, making them all uniform.
3) Prepped brass with drilling them to be 100k, making them all uniform.

All debured

I am not sure what will happen, but I am guessing all 3 group very similarly.

I will test in a Bartlien, a Krieger and a Shilen. Whatever barrel shoots these loads more accurately/consistently, I will use for the 60 round test.

Really interested in results, I hear of people drilling out flash holes for decades.
 
My guess is you won't see any performance difference whatsoever. You aren't changing any pressure variables by amending the primer flash hole.
 
However, making the hole 100k wide adds slightly more case capacity to it, and will ignite more powder a fraction sooner since the surface area of powder in direct contact with the primer is increased. I doubt it will matter, like you think.

I was thinking there has to be a reason why industry standard for SRP is 81k flash holes. Who came up with that, and why is it 81k, vs 100k, or 75k, etc. Maybe it just looked good, shot good, and was arbitrary.

I got labradar, and will give it a good go. I hope with the 2 different loads, something can be learned. All the brass is within .5 grains of weight, and all the bullets are exactly the same length. I sorted through a few hundred to get 60 consistent enough to test.
 
2 things....
Lapua is NOT the only one making 6.5x47 Lapua casings.
Peterson Cartridge is also making quality brass for that cartridge.

I had heard about 2 different size flash holes with Lapua brass.
And while i really don't like recommending a different forum on an open forum, a search on Accurate Shooter's forum would possibly have the performance difference answers you seek.
Click to expand...

I did note that Peterson is making 6.5 x 47 in the above post. It cost more than Lapua, so one reason to buy it would be curiosity. The other is to keep various batches sorted as to when they will get annealed. I need ventilation so that will be spring for the first two batches. If I develop cracking I can shift to the third batch until then.

I worked in Light industrial building mechanical/electrical system repair and maint for 35 years.

You will note that I convert 1.5 mm and 2 mm to US .000 format. Something we did fairly regularly as metric equipment got into the system over the years. One of the best tools (fast) I had was the dual US and Metric display micrometer (still do).

It should be noted that Lapua punches the primers (as noted by Unclenick and I confirmed that prior).

1.5 mm is .059 converted to US. The Lapua holes measure .0625. Some a tad tight (so spot on) and some a tad loose but not ..059. .003 larger.

And I don't believe that there is any issue or aspect between metric and US that is relative to what is going on as long as the holes are CONSISTENT. So, if small matters then they should be consistently the same small size (whatever it is).

None of the metric to US conversion is an issue, with US spec devices, you can get to within .001 and that is close enough and beyond a punching tolerance ability. Most of my tests were closer as I checked the size of what I was using.

Ergo, 8 cases at clearly .070 are neither a metric size aspect or anything else other than a mistake. For all reality right between a nominal .060 flash hole and a .080.

So, with .0625 holes (measured by a 1/16 drill bit that is also micrometer checked) and all the flash holes at .0625, that means the nominal 1.5 mm is not being met and either the punch hole device is shifting and batches increase in size or that is the normal punch hole size. .0625 is right at 1.6m. Clearly its not 1.5 mm.

The one test done used .0625 as their standard to Uniform the small flash hole to.
 
My guess is you won't see any performance difference whatsoever. You aren't changing any pressure variables by amending the primer flash hole.
Click to expand...

It could change the pressure build/peak profile and supposedly a large one would for sure.
 
However, making the hole 100k wide adds slightly more case capacity to it, and will ignite more powder a fraction sooner since the surface area of powder in direct contact with the primer is increased. I doubt it will matter, like you think.

I was thinking there has to be a reason why industry standard for SRP is 81k flash holes. Who came up with that, and why is it 81k, vs 100k, or 75k, etc. Maybe it just looked good, shot good, and was arbitrary.

I got labradar, and will give it a good go. I hope with the 2 different loads, something can be learned. All the brass is within .5 grains of weight, and all the bullets are exactly the same length. I sorted through a few hundred to get 60 consistent enough to test.
Click to expand...

An interesting test. Maybe better would be a .0625 flash hole vs the .100. Certainly more than once have used a gross change to see or confirm the affect in the direction of larger (or small).

Fun speculation on how the original size was chosen. Only modern testing equipment could probably even see the difference. Largest size that worked safely in conjunction with Primer movement?

Then there is the small primers but with larger flash holes. hmmm
 
Bryan Litz has already tested deburring of the flash holes.
Came to the conclusion it made no difference on target.
I'm not sure whether the size of the flash holes (as long as all are the same size) is going to show much either.

I don't know that i would try mixing both sizes in the same string for record.
 
I had a different experience, though it was clearly due to a specific set of materials. When I tried using 2520 in 308 in my M1A one year, the 100-yard bench groups grew from the 0.7 moa I had been getting to about 1.2 moa. I experimented around some and didn't have much luck until I deburred flash holes, and that brought the groups back to 0.7 moa. Some caveats: In that gun, deburring flash holes made no difference at all with stick powders, which all shot tightly without taking that step. The 2520 load did not fill the case well, which exacerbates ignition issues. At the time (early '90s) I didn't know using a magnum primer, both because of the extra space and because the older spherical powders are harder to ignite than stick powders, might solve the problem without flash hole deburring, so I didn't try it back then. So, bottom line, it can help with ignition consistency, but usually isn't necessary.

The flash hole size thing is interesting. A number of folks have tested and proven the use of small primers and small flash holes produce tighter groups. But there is also a study of flash hole size and centering you can find online that was done by a graduate student who got Fiocchi to give him unpunched cases to drill and the use of their universal receiver and test barrels. He conclude that of 1.5 mm, 2.0 mm, and 3.0 mm flash holes, the 3 mm (0.118") shot best. So, I don't really know. I'd have to do a lot of testing to separate the variables out.
 
Me?

Sorting out what I am dealing with and shooting (pun intended) to get them the same.

I might play with larger flash hole (.100+) in 30-06 or 308.
 
Unclenick said:
I had a different experience, though it was clearly due to a specific set of materials. When I tried using 2520 in 308 in my M1A one year, the 100-yard bench groups grew from the 0.7 moa I had been getting to about 1.2 moa. I experimented around some and didn't have much luck until I deburred flash holes, and that brought the groups back to 0.7 moa. Some caveats: In that gun, deburring flash holes made no difference at all with stick powders, which all shot tightly without taking that step. The 2520 load did not fill the case well, which exacerbates ignition issues. At the time (early '90s) I didn't know using a magnum primer, both because of the extra space and because the older spherical powders are harder to ignite than stick powders, might solve the problem without flash hole deburring, so I didn't try it back then. So, bottom line, it can help with ignition consistency, but usually isn't necessary.

The flash hole size thing is interesting. A number of folks have tested and proven the use of small primers and small flash holes produce tighter groups. But there is also a study of flash hole size and centering you can find online that was done by a graduate student who got Fiocchi to give him unpunched cases to drill and the use of their universal receiver and test barrels. He conclude that of 1.5 mm, 2.0 mm, and 3.0 mm flash holes, the 3 mm (0.118") shot best. So, I don't really know. I'd have to do a lot of testing to separate the variables out.
Click to expand...
Unclenick. I can relate to what you are saying. But may I offer another possibility. You know what I do and you know my site. All I do is test under as scientific ways as possible for consistency. On several tests, when changing the seating depth on an AR15 as much as 5k only (going from 2.255 to 2.250) the velocity changed, and the groups got literally 50% smaller. Repeatedly. So it was consistent. Such a small difference. Its because that powder is PICKY. It likes a specific area. AA2250 is very picky, and inconsistent, sort of like CFE223. ES is all over the place.

So what I am saying is, I cannot really conclude anything from testing with ball powders because they are picky and not easily repeatable due to their massive sensitively to the environment. Its sort of like testing out brass using 55 FMJ 10 cents a round bullets that are junk accuracy. You can't learn anything about brass when one of the components being used is wildly inconsistent. Or its like using a chrome lined barrel trying to best Berger match bullets and getting 1.5 MOA. You can't learn about match quality bullets and quality brass and quality anything, without using a quality barrel. When you put together quality "everything" and load to precision, I think some evidence can be presented that shows correlation to reach a reasonable conclusion.

This is why, when I conduct tests where I want to learn something, I only use very temp stable stick powders, such as AR Comp, or Benchmark, or Vihtavuori N133, or N135, etc, and neck turn the brass, full case prep, trying to get the lowest SD and ES possible so I can have sort of a control. Then when I get a stable control that operates consistently within a small range, I can change 1 element of it, and then tell you with correlation, the evidence of this. Here is an example of such a test.
http://natoreloading.com/brassprep/

Another one is this one, on neck turning..
http://natoreloading.com/Neck/

When I test across so many loads, and then look at overall, then run other tests like brass prep, it correlates with the neck turning test. It also is probably what you would consider common sense, as it just makes sense prepping brass producing more consistency.

I am not sure how to make the flash holes smaller, because I can only get brass with about a 80k hole in it. I don't have any access to brass that has no hole so I can try like 65k or something.

so back to the 308. I think by changing the dynamic of the flash hole, changed slightly, the pressure inside the case, and since its picky, I am guessing whatever it did, put it past the edge of the node. Its so hard to say, you know how complicated reloading is.

I look forward to sharing the results. I am really hoping there is zero difference, because that is ALL we all need right? 1 more thing to do with brass prep! it already takes long enough! haha
 
You can get 308 in Small Primer/Flash hole size.

I have had a response from Lapua contact. Sounds like a rep as he is passing onto Lapua what I have reported.

He did want to know how many cases were .070, I can only pass on right now that 8 out of the two totally mixed up batches (100 that are prepped) I can report on.

Hopefully in the next two weeks (temperature permitting) I can shoot the 100 I have loaded from those two bathes and get an accurate count.

As they are mixed I will not be able to say they came from one batch or both.
 
9MMand223only,

One way to separate the flash hole cleanup and diameter out from node thresholds will be pressure and velocity testing. If you make the change that improves grouping but doesn't show a decrease in the variation in pressure readings but does show an increase in mean velocity, it is likely the change is node tuning. But if the pressure plots show less variation and mean velocity doesn't change, it's likely to be an ignition consistency improvement that is responsible for the observed effect.

Agree with you on ball powder consistency. Lots of matches have been shot with 748 over the years, but I have no ball powders on my list of best .308 W match performers. 4064 and Varget have been the two best performers for me in that chambering.
 
I love your comment.

I was just going to say, among the powders to use if you dont have stick. W748 is probably KING. AA2230 good too.
 
one of the effects of enlarging the hole will be less velocity on the burning gas from the primer. You will also have slightly lower pressure in the primer cup area. A lower gas velocity may affect the ignition differently on flake, ball, stick powders. Also keep in mind the powder in different cases such as a compressed load in a short case or a 90% fill in a 30-06. There are a lot of factors to be considered
 
Flame tends to spread out a bit wider, too. Whether that is an advantage or a disadvantage likely depends on how easily the flame front moves between the grains. In general, that is easiest with coarse stick powders and hardest with fine spherical propellants.
 
hounddawg:

Taking things to the reality, you assume that the flash you see in the open extended into the powder. Not likely.

We have no pictures of the light off as we can't get them.

So it would be all theory.

I can make a case that with more powder exposed at the bottom with a larger flash hole, the base of the column would light off more evenly.

Or maybe not. We just do not currently know.
 
Ok, here is the answer

Henderson said the team determined that they needed to see what happens to the propellant in the gun during ignition. Since the charge is inside the gun chamber when fired and unable to be observed visually, the team developed a ballistic simulator (BSIM) to aid propulsion development and emplaced it at YPG. The BSIM tube is transparent and bursts at a low pressure, but the few milliseconds of video data before it bursts is critical to the design of the propelling charge.
Click to expand...

Now this is for a 155 mm artillery piece but.....


https://defence-blog.com/us-armys-new-artillery-breaks-the-record-for-highest-velocity/
 
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