GL40 is pretty cheap right now, from 290k to 350k depending on the time of day. However, it seems like many people haven't used the GL enough for there to be guides about the launcher. So I made one.
The 40mm rounds travel at 76 m/s which means the drop is insane. Tarkov does not have the ladder sights for the GL40 yet, and iron sights are useless except close range of under 25 meters. There is one way to use zeroing, however. It doesn't make sense IRL, but you can use reflex sights to use zeroing. Your pmc will raise the barrel upwards and the reflex dot will magically be painted at the point of impact at said zeroed distance. Refer to this clip: https://streamable.com/lojlzf You need to be able to measure distance accurately(less than 10 meter error) to hit any targets above 25 meters.
M381/M441 are identical in every aspect. Latter is FiR only, so just buy whatever is cheaper for you at the moment. Peacekeeper sells M381 up to 4 rounds every 3 hours. These rounds have a short arming distance, so you CAN and very often kill yourself with it. It arms at around 3-5m, and it's closer than you'd think. As long as the freedom to kill yourself doesn't seem like a downside to you, this round is superior to the ones below.
M385/M406/M433 are also identical in every aspect. Latter is FiR only. These arm at 15m, and that's further than you'd think. If you're using this round to fight in close ranges, you're always going to hear a "click" instead of an explosion.
M576 is a meme. It's a shotgun round.
All of the above except M576 has the exact same kill radius and maximum range as far as I can tell. Basically, only difference is the freedom to engage closer distances or not.
3. Combat effectiveness
The GL does not kill through walls anymore. However, its shrapnel system sometimes feel unreliable. Generally, it kills anything under 3~4 meters. From the hideout shooting range, if you shoot at the second steel target, there's a high chance you will die.
But generally, you can count on the nade killing the target if it lands within 1~2 second sprint distance.
Long range sniping
GL is actually pretty effective at range, mostly because it doesn't have damage falloff nor does it have to be dead accurate to kill the target. It is very good against ADAD spamming targets at 70~130m.
In squad vs squad firefights, the GL can force enemy groups to fall back, scatter, and take cover. This buys your team valuable time to heal, reload, and relocate.
Tarkov meta has always been aggressively using the peeker's advantage and rushing people's locations while flushing them out with hand grenades. You've probably had experiences where chads were pursuing you into corridors and buildings to kill you. Because of the GL40, this will change.
You can lure the bloodthirsty chads into long corridors where you can ambush them, killing them in a single shot. (https://streamable.com/dh79ml)
Always have MBUS iron sights on the GL. Even if you're using EKP Cobra/HAMR top red dot/PK06 for zeroing, time might come when it's exclusively CQB and need to take the sight off, since their lowest zeroing is 25m.
Remember, it's easiest when you're shooting downwards in height. If you're shooting uphill, it's practically impossible to fight. Do not try to fight in open fields where the enemy is on a hill.
GL is strongest when there are walls around the target, providing multiple surfaces that the grenade can impact to kill. GL is weakest in extremely closed spaces providing less than 5m safe distance for the operator.
If you're going up against one, don't try to rush it. Fall back. Just because you have a meta M4 with a slick and altyn doesn't mean your optimal strategy gets to be "Rush B" in every case. GL is a gamechanger. Respect it as it is.
6. Personal opinion on balance
As an ending note, 40mm does feel very powerful, to the point where it feels like counterplay is simply running away from it.
My personal thoughts on its balance is:
Make the lethal radius much, much smaller.
Make the explosion damage armor greatly. This has two effects: weakening the target, and making GL unattractive when you want to take enemy's armor home.
Make the blast apply extremely heavy concussive effects. Increase utility, decrease lethality.
Make the GL rounds cheaper since it's weaker in lethality.