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

Anyway, 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.

You may want to view a few slow-motion videos of an AK firing.

The flexing the AK has in the fire cycle does not relate to the dime/washer drill...I will try it on a few of mine tonight and report back for you.

Again, I have two AKs.  On one of them, the dime stays in place nearly every time.  On the other, the dime almost never stays in place.

When I was in the Army we did this drill by putting a cleaning rod in the muzzle end of the barrel and then balancing the dime on the cleaning rod.  Maybe try that way.. I found it much more difficult but I guess that is the point of the drill.

wait a minute are you dry firing or is this with live ammo?

at first i thought live ammo but even the army can't be dumb enough to put a cleaning rod down the bore of a loaded rifle.....can they?

dry fire....

The point of the dry fire exercise is to detect inadvertent movement caused by poor trigger control.  In theory if the shooter has good trigger control the rifle shouldn't move at all and the dime should stay in place.  Of course this is also dependant on the quality of the trigger and mass of the FCG components.  With a rifle that has a massive enough hammer with enough of an arc to its swing, and a strong enough impact I'm not sure there is much the shooter can do to prevent the vibrations that upset the dime.

I was thinking that one must be one tough mofo that can keep a dime balanced on an AK between rounds!

I like to stand dimes on end and balance them on my muzzle brake while I bump fire.

That only counts if you stand two or more dimes, on edge, one on the other.  Anything less is purely the sign of a major league WUSS!  Of course I've never tried it while bump firing since I prefer rapid controlled fire.  So maybe I'm a little off base in regard to bump firing.

Then maybe these vibrations are throwing off my shooting?  WOuld the bullet already be clear of the muzzle by the time these vibrations could cause any serious problems to accuracy?

Odds are the vibrations/shock from the ignition of the powder would overpower the vibration/shock from the hammer smacking the firing pin, but i'm not a physicist so take that for the fee it cost you to hear it.

Have you tried maybe an RSA FCG to see how it compares?

Excuse me for asking, but wouldn't the vibrations/shock of the ignition defeat any benefit of a good trigger pull?

Have you measured the weight of pull on both rifles? Is the trigger pull heavier on the rifle on which you find balancing the dime more dificult?

Both AKs have the Tapco G2 trigger group.  The one where the dime falls off, the dime always falls off at the time of impact when the hammer slams home.

No, regardless of the form of shooting or the small arms weapon being fired, trigger discipline will always improve the general out come. Trigger discipline can be simply summed up by stating that when the trigger is pulled and the firing mechanism is released, the sight line up does not move continuous post follow through. Trigger discipline with a rifle is not about 1 finger, at the minimum it is about 5 fingers and a shoulder. While you use 1 finger pad to pull a trigger, the other 4 fingers and shoulder support that function in entirety.  

Assume a poor trigger pull creates an arbitrary deductor of 5
Assume a rifle design, in a firing condition, creates an arbitrary deductor of 5

The higher the deductor number, the poorer the end result becomes.

5+5= 10, a person says - fuck it, it's an ak (which we have already assigned a 5 deductor to) and chooses not to employ trigger discipline (again 5 deductor), the sum is 10.
5+0=5, a person says - I know it is an ak, but I will do my part to mitigate the things in which I have direct control over and employ trigger discipline, the sum becomes 5.

Then my guess is that the hammer spring is stronger in that rifle. I've measured the strength of  hammer springs using a length of string around the hammer and an accurate fish scale.

Just tried it with a 1971 Romanian kit build. Tapco G2 trigger. Dime falls when hammer strikes not when sear trips.
ETA: dime falls half the time in front of FSB and never when behind it.

That's my experience; it falls when the hammer strikes.

When placed on the muzzle brake in front of the FSB, it usually stays put.  It never stays on when positioned on the barrel behind the FSB.

But on my SAR-1, the dime always stays on when placed on the barrel behind the FSB.

Strange.  I guess it's just one of those quirks you find from rifle to rifle.