In a recent post, I talked about getting corn cob media in flash holes when brass is cleaned in a vibrating tumbler. I always clean it out with an ice pick, but wondered if it really would make a difference if I missed one.
You can see that here: Polishing Media in Flash Holes
But to our surprise, we found that it not only didn’t seem to matter, but the groups “with” the media in the flash holes seemed to actually shoot a little better.
Now I’ve shot a few groups in my time, and I know there are a lot of things that affect the size of groups. Even something like wind speed from one day to another can make a difference. I was not sure that the “apparent” improvement was actually there, or if it was just coincidence.
In the discussion on AR15.com, a couple of friends made jokes about how they needed to start sticking media in their case flash holes to improve their groups.
But then my friend Keith_J said:
“There is a tiny volume between the primer and the pocket that can let some powders in, battery cup primers for shotguns have a thin foil over this chamber (which is much larger) to keep powder out for pressure reasons.
Wonder if you stumbled on the next benchrest fad? Foil sealed primer pockets.”
Even though he was kind of kidding, I began to think about it. What if some kind of easily burned barrier was put in front of the primers? Would that improve groups?
I happened to visit my old buddy Ted, (who I call Chief because he is a retired Chief Petty Officer from a nuclear submarine)
I told him about my idea and asked, “Chief, do you have any idea how we might be able to cut some tissue paper the same size as the small rifle primer?”
He went to a drawer in his shop and got a spacing pin from an AK-47 and said, “This ought to be close.”
He used a rotary sander to sharpen up the edge of the hollow pin and, voila, there it was, a perfect punch.
We used a plastic base and used a hammer to cut a bunch of perfect patches from some tissue paper.
I bagged them up and took them home.
I will be honest, fellows, this was a tedious business.
The little patches had to be carefully placed into the primer pocket, and then pushed down to seat them on the bottom of the pocket.
Some tweezers helped do the job.
I then primed them with some Federal Small Rifle Primers. I did 15 rounds, with a couple of extras.
I then primed 15+ without the tissue paper, and kept the two groups separate.
Then to the loading bench, where I loaded the two groups of .223 cases with exactly the same powders, same grains of powder, and same bullets.
It’s time to go to the range.
What do you think will happen?
I will shoot them from my Savage Model BVSS in .223. I will shoot 3 groups of 5 shots with each load, one with and one without the tissue paper.
It was a little windy today, and that might cause some horizontal spread of the groups.
My good buddy Steve met me there and brought his chronograph so we could look at the velocities of the loads. Here’s the set up.
Time to shoot.
Groups A are without tissue paper, and Groups B are with tissue paper.
And here are the results.
Group 1A – 3308 fps avg, 49 fps spread
Group 1B – 3306 fps avg, 49 fps spread
Group 2A – 3290 fps avg, 49 fps spread
Group 2B – 3293 fps avg, 32 fps spread
Group 3A – 3292 fps avg, 32 fps spread
Group 3B – 3279 fps avg, 56 fps spread
- I do not see much difference in the groups. The paper did not seem to make any real difference
- This makes me doubt that the corn cob in the flash hole really made any real difference either. I believe the better groups were basically a fluke.
- As sometimes happens, this turned out differently than I expected.
- These loads were safe in my rifle, but I do not suggest that anyone else try this experiment, as it could lead to unsafe pressures in your rifle.
- It’s fun to shoot stuff.