My rifle 'double taps'

I have just completed new assembly on a Beretta receiver with a new Criterion .308 barrel. Most all the parts are as new and it is sitting pretty in a Boyd's stock set. The issue is when I use old IVI ammo, it will sometimes fire a double tap. It does not do it with Federal Match ammo so I am wondering if the issue is the ammo or some other gremlin. It feels good/interesting when two shots go off almost simultaneously but it is likely not a safe condition by any stretch of the imagination. Any ideas or suggestions of what I should be looking for besides a .308 bolt action to use up a fair bit of this old surplus ammo?

Is your trigger worn- Can you check the pull? Much below 5 lbs? Was a trigger job done? They don't last forever. Sometimes a little too enthusiastic with a stone. Tim did a nice job on mine- it goes off a little under 5lbs and take-up is nice. Haven't used that ammo myself, don't know if it's known for soft primers.

That reminds me- Tim, don't laugh, OK? But do you want to do a trigger job on a mini-14 I just got? .....I said- "Don't laugh"

1. No
2. The ammo change may be what it takes for the right recoil to double.
3. Time to do trigger work most likely. Have you checked the trigger group for the hammer fall test?

What is your headspace and what is your firing pin tip protrusion?
If changing your factory made milspec ammo cures the issue, you will want to double check headspace and firing pin tip protrusion before something more exciting happens than a double tap.

Also, it sounds like you have a new aftermarket stock. Sometimes those can be slightly out of spec as far as trigger housing installed height is concerned and cause "issues", like a double or 8 round "tap".
Have you confirmed that your trigger clearance cut in the stock is deep enough to allow the trigger to reset? A lot of variables with your newly rebuilt rifle.

Also, sometimes milking the trigger will cause double taps even on a properly set up M1/M14 rifle.

Dumped the old IVI ammo and went with some Federal XM80CS. Firing pin is good. Headspace has always been good as it's a new barrel and I do check them all. Trigger resets as it should and passes all the required tests. Tore through 150 rounds this morning and not a hitch. Best part was giving a couple of folks who have never shot a Garand a go at it towards the end of the test firing. Smiles are contagious that's for sure.