.308 Winchester — Large vs. Small Flash Hole Test
Conventional .308 Winchester brass has a large primer pocket with a large, 0.080″-diameter flash hole. Last year, Lapua began producing special edition .308 Win “Palma” brass that has a small primer pocket and a small flash hole, sized 1.5mm (.059″) in diameter. Tests by U.S. Palma Team members showed that the small-flash-hole .308 brass possibly delivers lower Extreme Spread (ES) and Standard Deviation (SD) with some bullet/powder/primer combinations. All things being equal, a lower ES should reduce vertical dispersion at long range.
Why Might a Small Flash Hole Work Better?
The performance of the small-flash-hole .308 brass caused some folks to speculate why ES/SD might be improved with a smaller flash hole. One theory (and it’s just a theory) is that the small flash hole creates more of a “jet” effect when the primer fires. Contributing Editor German Salazar sought to find out, experimentally, whether this theory is correct. German explained: “During one of the many internet forum discussions of these cases, Al Matson (AlinWA) opined that the small flash hole might cause the primer flash to be propagated forward more vigorously. In his words, it should be like shooting a volume of water through a smaller nozzle, resulting in a flash that reaches further up the case. Now that kind of comment really sparked my curiosity, so I decided to see what I could see.”
More Primer Testing by Salazar
You can read more about this test and other primer experiments on RiflemansJournal.com.Salazar Primer Tests: Small Rifle Primer Study | Large Rifle Primer Study
Large and Small Flash Hole .308 Cases — But Both with Small Primer Pockets
To isolate the effect of flash hole diameter alone, German set up a test with the two types of .308 case that have a small primer pocket: Remington BR brass with a 0.080″ flash hole and Lapua Palma brass with a 0.062″ flash hole. NOTE: German reamed the Lapua brass to 0.062″ with a Sinclair uniforming tool, so it was slightly larger than the 0.059″ factory spec. The Remington brass has a .22 BR headstamp as this brass was actually meant to be re-formed into .22 BR or 6 BR before there was factory brass available for those cartridges.
German set up his primer testing fixture, and took photos in low light so you can see the propagation of the primer “blast” easily. He first tested the Remington 7 1/2 primer, a primer known for giving a large flame front. German notes: “I thought that if there was a ‘nozzle effect’ from the small flash hole, this primer would show it best. As you can see from the photos, there might be a little bit of a flash reduction effect with this primer and the small flash hole, the opposite of what we expected, but it doesn’t appear to be of a significant order of magnitude.”
Remington BR case, 0.080″ Flash Hole, Remington 7.5 Primer.
Lapua Palma case, 0.062″ Flash Hole, Remington 7.5 Primer.
Next German tested the Wolf .223 primer, an unplated version of the Small Rifle Magnum that so many shooters use. German notes: “This is a reduced flame-front (low flash) primer which has proven itself to be very accurate and will likely see a lot of use in the Lapua cases. With this primer, I couldn’t detect any difference in the flash produced by the small flash hole versus the large flash hole”.
Remington BR case, 0.080″ Flash Hole, Wolf .223 Primer.
Palma case, 0.062″ Flash Hole, Wolf 223 Primer.
German tells us: “I fired five or six of each primer to get these images, and while there is always a bit of variance, these are an accurate representation of each primer type and case type. You can draw your own conclusions from all this, I’m just presenting the data for you. I don’t necessarily draw any conclusions as to how any combination will shoot based on the pictures.”
Results of Testing
Overall, looking at German’s results, one might say that the smaller diameter of the small flash hole does not seem to have significantly changed the length or size of the primer flame front. There is no discernible increased “jet effect”.
Similar Posts:
- Large vs. Small Flash Holes in .308 Win Brass
- .308 Lapua Palma — Lapua to Introduce a Small Primer .308 Winchester Variant
- Lapua 6.5 Creedmoor Brass Has Arrived at Graf & Sons
- New "Outside-In" Flash Hole Reamer for Large Flash Holes
- Flash-Hole Fix — Clearing Flash-Hole Obstructions in Your Brass
Tags: .308 Winchester, Extreme Spread, Flash Hole, German Salazar, Lapua, Primer
So what was this test, exactly? How the picture of a spark differed? More meaningful data might include velocity es/sd changes between the two cases, as well as pressure data.
The very early lots of the Rem brass was stamped only BR REM and with the .080 flash hole. This brass was indeed meant to be reformed into the 7BR,6BR and 22BR family of cartridges as REM was not producing them commercially. However, the very earliest production of the BR REM brass was produced with NO FLASH HOLE in the brass.This brass was released to Bench rest shooters who were experimenting with the BR Family of cartridges and the flash holes were drilled by the shooters to evaluate which size flash hole was optimum.Suffice to say that by the time the BR REM brass was released to the public, it arrived with the .080 flash hole in the case. You might make any conclusions as you wish.
I bought several cases of this brass when it became available and did a lot of testing with it, across a chrono and in match situations.What I found was that the small primer, REM 7/12, that I was using reached a point of diminishing marginal return in the BR REM case, ..er that is to say that after a certain point, adding more powder did not result in a increase in velocity or pressure, it simply left the barrel full of unburnt powder kernels.The powder that I tested was IMR 4064 and other powders might react differently.I do recall that the point of DMR was about 45 grains of IMR 4064 or so.
Many shooters used these cases and had very good success with them, mostly using IMR 4895 and less than 45 grains in their Palma loads. J.H.Franklin shot them with fantastic results and success.
The most unique aspect of these BR REM cases was their extremely light weight and vast powder capacity.If my memory is correct, the BR REM case was lighter than the WCC 58 cases of lore.I see the major difference between the BR REM and the Lapua Palma cases in not only the flash hole size, but the case capacity also.An inquisitive shooter might simply drill a .080 flash hole in 20 Lapua Palma 308 WIN cases and compare them with the standard flash hole cases.Interesting test.
In closing, with the new powders available today and the reduced capacity of the Lapua case from the BR REM case, there might very well be a MAGIC potion mix for the Palma shooter utilizing the Lapua Palma 308 WIN case.
Roy
I looks to me like in the rem. 7 1/2 primer, the small flash hole did create a smaller flash, but more of a “jet” effect (look closely). It also appears that primers with lesser flash or flame front tend to be more accurate. I’m thinking that the less effect the primer has on the overall load, the better off you are, since the hand loader has no control over the amount of priming compound from primer to primer. Also, I would suggest that the milder the primer, the less significant the size of the flash hole becomes.
I first became acquainted with the Rem BR case in the middle ’80’s due to my interest in the 22 CHeetah. For me IMR 4064 was NOT the powder of choice. IMR 4831 did better, but it wasn’t until I happened upon RL-15 that the cartridge began to approach its potential. I continue to shoot the cartridge today, and velocities of 4350 fps with 52 gr bullets are routine as are velocities above 4900 fps for a good 40 gr projectile. I decided years ago such velocities are made possible through the use of the SR primer because the ignition is large enough to light the powder charge but small enough to allow for more progressive burning than with a LR which flattens the pressure curve a bit. Don’t have any way of truly knowing whether I’m right or even close. What I can tell you is it took 4 years of trying every primer/powder combination before one that worked in every good way appeared. That being RL-15 with the Remington 71/2 primer of 80’s vintage. I still have some, the new one doesn’t yield the same consistency; CCI 450 seems to be better than either however.
I’ve tried the new Lapua case. Capacity isn’t the issue but the fact that the Lapua’s head measures 0.004″ larger than the old Rem BR’s is. My Cheetah chamber is a couple of thousandths too small for a workable fit.
While it may not offer much difference, the price is still less than the projected Lapua 260 Rem prices. Just gotta put up with the shorter neck.
Could the ES change with flasholes due to powder kernel fit. That is, larger flasholes would allow powder to settle/wedge in, where smaller flasholes might not.
Maybe the test should be run with powders of significantly different kernel size, barrel pointed upward, and with a focus on consistency of flash instead of amplitude(given powder difference and search for ES discrepancy).
If your going to test it why make the hole larger?? Seems to defeat the purpose of the test. The Palma brass works great and last forever.