Trigger pull to light

Make sure the cocking piece is not loose on the striker threads, that might cause an issue as well.  If it is, you can clean and "tin" the striker threads with solder. 

You also probably know that the trigger pull must be measured with the magazine fitted, otherwise the striker spring is not compressed enough. 

I actually did not say this right, was multi-tasking at the time.  The sear spring serves a dual purpose, it pushes on the magazine release catch and the sear. When the magazine is inserted, it compresses the sear spring slightly (not the striker spring) and increases the trigger pull weight required to move the sear off the bent of the cocking piece.  Make sure the CMP armorer understands this, they normally want magazines removed when weighing triggers. 

Rifles such as the L39A1, do have a lighter trigger as standard, due to the slight change of angle on this surface.

It's worth checking, along with the previous suggestions.

The CMP Vintage Sniper Match rules allow for a minimum weight of 2.5 lbs, but I don’t think that can be safely achieved with the No. 4 trigger design, so I have mine set at 3.5 to 4 lbs. 

At competitions in France, they use a weight,  hang it on the trigger and gently lift it (vertically) off the table. 

It should not release the firing pin. 

You can make a homemade rig with a water bottle filled to the required weight.

That’s what we do here to at matches. 

I tried various methods to “weigh” the trigger but wasn’t satisfied I would get the same reading that the CMP armorers do when they weigh the trigger prior to the match. So, I bought the same NRA “Official” trigger weight system, consists of a 20 inch long rod with a nylon roller that rests on the trigger and weights are then added at the bottom of the rod that are stacked to get 2.0 to 4.5 lbs in 1/2 lb increments. The rifle is held vertically as you described above.  Make sure they don’t remove the magazine for the test, otherwise you will get a reduced weight (happened to me once).  

I keep 5 or 6 cast lead .577 bullets for the Snider Enfield (which weigh about 1 oz) to place on top of the weights to make sure I have some margin above the minimum (3.5 lbs for bolt action service rifles and 4.5 minimum for semi-auto service rifles). 

I’ve learned my lesson to not work the LE trigger down to the minimum of 3.5 lbs set by the rules, I won’t go below 4 lbs intentionally which gives me a comfortable margin. Last thing you want to have happen is fail rifle inspection right before the match.