I managed to break several decapping pins on some Alexander Arms and Lapua brass before I found that they are using a smaller than normal flash hole. Roughly speaking, large flash holes are about .080, and small flash holes are around .060. Using a small decapping pin, I found that I was breaking them with a high degree of frequency, and even though I was able to push the spent primer out, there was a noticeable interference fit. Looking around the internet (always risky), I found that the Lapua flash hole is around .057 or .058. I called RCBS and spoke with a Mr. Meyers. What a guy! He sent me replacement pins for the ones I had broken, and explained that while they don't make a specific decap die for the smaller than normal Lapua flash hole, he would make up something using a warranty returned 7mm seating die. All this for no charge. That's Customer Service!!! I continued to look into the reasoning for the Lapua flash hole size and found several posts from a gentleman that worked for Lapua. This individual indicated that the smaller flash hole contributes to a better flame front, lower standard deviation and extreme spreads. At this point I began to wonder how much difference there would be, and why everyone hasn't gone to .058 flash holes. I took 20 pieces of Lapua brass and used a Sinclair flash hole deburring tool to open up the flash holes to roughly .080 (measured at .078). I decapped, resized (setting the shoulder back .002), and cleaned the standard and modified brass. Both samples were loaded with 28.3 gr of Varget (soft load), and then seated a 123 gr Lapua Scenar bullet to an OAL of 2.25 inches. At this point I headed to the range with the reloaded small (stock) and modified flash hole brass, plus a handful of Alexander Arms 123 gr Lapua Scenar ammo (control group). I set up the chronograph 10 feet from the bench, and set up 5 targets at 100 yards. The first target was for the factory ammo. The other four were labeled Small Upper Left, Large Upper Right, Small Lower Left, and Large Lower Right. I then fired eight factory rounds and recorded the velocity. To minimize any barrel heating impact, I would fire a small (factory Lapua flash hole) round at the upper left target, followed with a modified flash hole at the upper right target, then small at the lower left target, and then a modified round at the lower right target. Then repeated that sequence for all remaining handloads. The following were my results:
Alexander Arms
Std Dev 29.3
ES 72.5
Avg 2567.5
Standard Flash Hole Lapua Brass
Std Dev 25.6
ES 77.5
Avg 2364.7
Modified Flash Hole Lapua Brass
Std Dev 25.1
ES 82.8
Avg 2368.9
In my opinion, the size of the flash hole doesn't seem to make any real impact. While I didn't take any photos of the groups, or measure them for size (not the intent of the test), the target was an orange target spot 1" in diameter. All groups were well under an inch in size. There was some obvious difference in point of impact which I attribute to the 200 FPS difference in the factory ammo over the handloads. I may rerun the test one more time as a check and balance, but pending some widely differing results, I plan to open up the flash holes on my remaining Lapua brass to eliminate messing around with a .057 decapping pin. The purpose of this test was for my own information, and not meant as a recommendation. As is always the case, your mileage may vary.
Alexander Arms
Std Dev 29.3
ES 72.5
Avg 2567.5
Standard Flash Hole Lapua Brass
Std Dev 25.6
ES 77.5
Avg 2364.7
Modified Flash Hole Lapua Brass
Std Dev 25.1
ES 82.8
Avg 2368.9
In my opinion, the size of the flash hole doesn't seem to make any real impact. While I didn't take any photos of the groups, or measure them for size (not the intent of the test), the target was an orange target spot 1" in diameter. All groups were well under an inch in size. There was some obvious difference in point of impact which I attribute to the 200 FPS difference in the factory ammo over the handloads. I may rerun the test one more time as a check and balance, but pending some widely differing results, I plan to open up the flash holes on my remaining Lapua brass to eliminate messing around with a .057 decapping pin. The purpose of this test was for my own information, and not meant as a recommendation. As is always the case, your mileage may vary.
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