I tried posting this in the GD, but realized that the training forum would be a better place to ask.

So I was doing some dime drills with my AK (a SA-M7 A1R) because I thought my trigger pull has been problematic recently.  When I did this, I observed the following.

I began by balancing the dime on the portion of the barrel between the gas block and the front sight block. Nearly every time I pulled the trigger, the dime slid off the barrel.

But then I moved the dime and balanced it on the flashhider and found that the dime stayed put every time I pulled the trigger.

I then did the dime drill on my .30-06 and SAR-1. I tried both rifles with the dime balanced at different points along the barrels of both and the dime almost never fell off of either.

Any ideas what's going on? All I can think is that because the SA-M7 A1R barrel is very smooth as compared to the .30-06 (matte finish) or the SAR-1 (small ribs on barrel), the dime is less stable there and is more prone to falling off. Either that or my SA-M7 A1R action is somehow much more violent than that on either of the other rifles.

Again, any ideas what might be happening?

Thanks for your input.