Why dmr is different in team slayer

When I play team slayer de reticle of the dmr opens itself faster when shooting than when I am playing rumble pit, making it less accurate.
What is happening?

There are three different settings for the bloom on the DMR…full bloom, reduced bloom and zero bloom.
From Halopedia:

343 adjusted the maximal reticule expansion on the headshot weapons (DMR, Needle Rifle and Pistol) based on a percent of the original value, set at 100%.
Two current bloom settings exist. They are built into the gametypes and are not configurable in-game. 85% Bloom is the current standard with the TU. Zero Bloom (ZB), as its name suggests, features no reticule expansion, but weapons do retain some spread. ZB is currently used in its own playlist, as well as under the MLG playlist settings.
85% bloom improved the DMR and made pacing much more viable.[1] However, 85% bloom had a different effect on the Needle Rifle. The reticule contracted just as fast as it expanded, making the Needle Rifle indifferent between 85% bloom and ZB. Combined with its automatic fire and stronger aim assist, 343 decided to remove the Needle Rifle from loadouts in TU Slayer Pro gametypes.
ZB had a very strong effect on the pistol, as despite its high spread at long range, it made it very powerful in close-quarters combat with its high rate of fire and bleed-through making it a four-shot minimum. Even with the downgrade back to a five-shot and being removed as a secondary spawning weapon, the pistol is still very powerful at close range. The DMR also benefited from ZB, retaining its long-range combat abilities.

This quote may not mention full bloom but basically when you play Team Slayer is vanilla settings with full bloom. When you play Rumble Pit it’s “evolved settings” with reduced bloom.

Tank you, you’re the best!