Home Forums Reloading Varmint Rifles flash holes in brass

Thanks for the update Swifty. I was unaware of the SAAMI guidelines on primer holes until you posted it. (You did post that on the first page and I plain old forgot about it until I went back and reviewed from the beginning)

To address your concerns about a baseline.

"Either way without some control set or baseline to validate what the changes did or didn’t do, makes the whole thing as Willy nilly play time"

The base line was shooting the ammo I loaded with the primer holes of LC16 and LC17 pre fired brass as drilled or punched into the brass by the manufacturer. In one of my first postings I talked about the primer holes of previously fired brass (predominately LC brass) being anywhere from .076 to .080 in diameter and did changing the diameter of the primer hole change pressure issues with the brass and secondary did it improve accuracy. Since previously fired brass (range brass) is my primary form of getting .223 ammo I thought that would be a good place to start because it was what I had the most of.

I certainly wish I could afford brand new high quality virgin brass every time I set out to load some more ammo. I just don't have the money and resources to do that. And, why would I do that when I have access to gobs and gobs of once or twice fired brass that is free to me as left behind on the range. With that in mind, I did compare unmodified factory range brass to the brass I drilled the primer holes in to different dimensions. (.086, .093, .098 and .101) I used the unmodified brass as my base line. It was the first group I shot at the top of target. Since this brass was fired twice before I was looking for pressure issues first and was it more (or less) accurate than the primer hole modified brass ?

On 09/14/21 NVhunter introduced us to a masters thesis as written by Nicolaas Martin Schrier. Nicholas wrote this thesis in 2015. (This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources) https://scholarsmine.mst.edu/cgi/viewcontent.cgi?article=8415&context=masters_theses

The question about the pressure (which was my primary question) issues was eventually solved the third time I went to the range on 10/05/21. I discovered that the larger the primer hole the more likely I was going to have case separations. (case separations indicate pressure issues to me, I assume it means pressure issues to you as well) When I had 5 cases out of 20 that had obvious separations inside of the brass that could be seen with a bore scope in the brass I drilled to .098". The brass I drilled to .101 I only fired at the second outing. (10 rounds) AS I recall the primers were very flat on that brass but the primers were not punctured. I simply tossed that brass without looking at the inside of the case. I can only imagine what it looked like internally had I looked.

If it weren't for one vertical line on one piece of brass I probably wouldn't have looked as I was only looking at the primers. Since I was shooting a bolt gun I saw no swipe marks on the base of the brass nor did I see any ejector marks on the brass. After checking all the brass I found 4 more cracked cases on the brass I drilled to .093". All of those cases were tossed into the scrap bucket.

I also mentioned that I took the rifle apart to lighten up the trigger. I did lighten the trigger but I should of left it alone. This ultimately was a huge mistake on my part as I could not get the stock screw torque to settle in and the rifle did not shoot as well on my second trip to the range with the Ruger American as my first trip to the range with the RAR. I introduced a variable that I could not correct. I did use 8 rounds per group to find this "sweet spot" again which left me 12 shots per target. (Next time I will try not to be as dumb)


There were no pressure signs on the brass either outside or inside that was drilled by the factory. (.076 to .080") (I shot 12 rounds per group but 20 rounds total)
There was 1 case that had started to separate that had the primer drilled to .086" out of 20 rounds shot. (12 shots per group and 20 rounds total)
There were 4 cases that started to separate out of 20 rounds shot that had been drilled to .093" (12 shots per group and 20 rounds total)
There were 5 cases that started to separate out of 20 rounds shot drilled at .098". (12 shots per group for 20 rounds total)

I got my best accuracy out of the cases that had the primer hole drilled to .086. I think mostly because every primer hole was the same and it was relatively close to the factory dimensions.
The next best accuracy was the target with the factory drilled primer holes.

The brass that had the primer holes drilled to .093 and .096 had flyers. Some worse than others. So, along with the pressure issues and the flyers, there appears to be no value in drilling a primer hole that big in .223/5.56 range brass if keeping pressure in check and if accuracy is your goal.



Making the primer holes uniform in size is a good thing if you have previously fired brass that has been unmodified and has various sized primer holes.

There are probably going to be pressure issues if you go too large. I consider too large .006" over the .080 in .223/5.56 brass because there is a chance a person can start getting pressure stressed cases. Even though the primers do not look stressed. The ammo I drilled the primer holes out to .086" was my most accurate ammunition.

IN order to make all holes uniform I have been using a #45 drill bit that gives me .082" sized holes. I understand this is .002" over the SAAMI recommendations as provided by Swifty but checking with the bore scope I am finding that the .082 holes remove a vast majority of irregularities inside of the brass case and make for nicely smooth primer flash holes.

I may pick this up again next spring. But, enough for now.
kwg