I have a Barrett M99 and have had issues with it igniting primers from surplus military ammo.  Today I had numerous FTFs with the Singapore .50 M33 ammo that AIM Surplus was selling last fall.  I have also had issues with the primed WCC brass.  I don't know if my firing pin doesn't protrude far enough, if my firing pin spring is not strong enough, or a combination of both.  My handloads have always fired 100%, so I think it's an issue of the firing mechanism not having enough oomph to ignite the primers on military ammo.

Thoughts?

some of the mil surplus ammo has harder primers.  i think you would sacrifice a good trigger pull to gain the abilty to fire the heavier primers.

How old or new is your rifle? Has it had the firing spring/sear upgrade from a few years ago?
If you bought the rifle used, the previous owner may have not had the upgrade done. If the rifle has the newer brake the upgrade is there..

I've seen Barrett M95s have problems even with CCI#35 primers.  I think the issue was crud in the mechanism.  The Barrett M95 bolts are pretty complicated compared to other 50's so you might wanna take it apart and see if there is come crud in it.  Not sure if the M99 bolts are the same or a similar mechanism.

And I would agree you should see if yours is the upgraded version.  If not, I'm sure Barrett will take care of you with the upgrade.

-David

My M99 was bought back in 2002 - so far the only upgrade I've done is the newer muzzle brake.....that old 82 brake didn't do much for the recoil!

I called tech support and waiting for a call back, hopefully they'll have an answer for me.

ETA - Just got off the phone with tech support.  The tech said the new assembly will solve all the issues with the light strikes, but may see a slight increase in trigger pull.  The assembly was about $120, but will be well worth the cost to make sure the ammo goes bang.  I'll place a follow up report when I get it to the range.