Home Forums Reloading Varmint Rifles flash holes in brass

ON Monday October 25th I got the chance to finish this primer hole size comparison. The day was sunny and cool with light and variable winds. I was still using my Ruger American in .223 for the testing. My primers were Winchester small rifle and the powder was 24.4 grains of IMR 3031 and a 55 grain Hornady soft point as the bullet. All shots were made at 100 yards.

I have always thought of IMR 3031 as a great powder and can make almost any rifle accurate. I know it is stick powder and with that in mind it is not the perfect powder for use in most powder measures. With that in mind after I dropped the powder into the LC17 cases, any case that appeared to have more or less than the “average” amount of powder in it, I dumped it out and re poured it. Using just a visual check I was pretty happy that I got very close to 24.4 grains of 3031 in each case.

I did run out of LC 17 cases. With that in mind in the cases where there was NO modification of the primer hole I used LC 16 cases. To re-cover some already plowed ground, the LC 16 and the LC 17 had a primer hole between .076 and .080” in diameter. The LC 17 cases I drilled out to .086”, .091” and .096”. In just a minute I will talk about stock screw torque.



I shot 8 additional rounds at every 1” target that I started on Tuesday October 5th for a total of 12 rounds on each target. With the factory drilled (punched) holes I got a 2” group and 3 flyers that took the group to just over the 3”.
The 12 shots made at the #2 target were with LC 17 brass and the primer hole was drilled to .086”. This was my best group. Just like on Tuesday the 5th. 11 shots fell into a 1.725” group. I had one called flyer that took the group to right at 2”.

Group #3. This brass had the primer holes drilled to .091”. 7 shots were into a group at 1.52”. The other 5 shots were flyers with the furthest shot being 2.60” from the point of aim. Similar to what I experienced on Tuesday the 5th.

Group#4. This brass had the primer hole drilled to .096”. 8 shots were into a group at 1.58”. The other 4 shots were flyers with the furthest out at 2.75” from the point of aim.



I mentioned stock screw torque. I pulled the stock and the action apart after shooting on Tuesday the 5th to see if I could get the trigger pull reduced. With the turn of an Allen screw I did get the trigger pull reduced on the Ruger American factory trigger. It appears the lowest trigger pull weight a person can get with a factory trigger spring setup is 3.5 lbs. That seemed to be the results I got. Although, I did get just a bit of trigger creep after turning the weight down.

An even more frustrating problem is getting the screw torque back to where it was before taking the gun apart. Before shooting for groups I had to play with the stock screws in order to find that torque “sweet spot” I had before. This required firing a group and then checking the size. I never got back to where I was before taking the two halves apart. I don’t own a torque wrench, at least I didn’t then, but I do now. I bought one from Midway and I’m waiting for it to arrive. I’m sure this added to the dismal group size I eventually got. Yes, I did create a variable. A big ugly variable. In retrospect I wish now I’d of left the trigger alone.



I have always had good luck with 3031 and getting good groups. I’m not sure the combination of the 55 grain Hornady soft point and 3031 was the right bullet, primer and load for this rifle. If I continue to play with primer hole size I need to change up the powder/primer/bullet combination.



After firing each 4 shot string I checked the primers for flatness. I had no primers punctured. Even with the .096” primer holes. The primers were flat with the base of the brass, but no punctures. I did notice some horizontal lines on the brass that had the primers drilled out to .096”. When I got home I checked the insides of the brass with my bore scope. I found 5 of the 3 times fired brass with the beginnings of a case separation out of 20 pieces of brass (25%) The brass that was drilled to .091 had 4 pieces that were beginning to separate and the brass that was drilled to .086 had one piece that had the beginnings of a case separation. There were none in the brass that had the factory punched holes. Again, this was brass that had been loaded twice before and this was the third fired load.



I should of never pulled the stock from the receiver to adjust the trigger. This changed everything as far as accuracy goes. Hopefully, finding that sweet spot again comes quickly after getting the torque wrench.

Making the primer holes uniform in size did seem to pay off, as long as you don’t go too far. The .086” holes performed the best. This is between .006 and .010” larger than the factory punched holes. The primers were not flat or punctured but apparently it did change the dynamics of the powder ignition and caused a near separation in one piece of brass. The larger the primer holes the more brass that was very close to separating.