If the bolt is cycling to fast it could be moving so fast it is out running the mag spring. Not giving the spring enough time to raise the mag follower to catch the bolt. The H-2 buffer would slow the bolt speed and let the follower rise enough to catch the bolt.
With an adjustable gas block I would attempt to set the gas block to lock open after firing one round with an empty E-Lander mag in the well. If you can’t get the bolt to lock open with the bolt catch with an E-Lander mag regardless of gas setting I’d suspect a faulty E-Lander mag. As previously mentioned E-Lander mag springs are very stiff when new.
With an empty mag in the well does an E-Lander mag catch the bolt when pulling the charging handle completely to the rear and releasing. If the mag engages the bolt catch you might have inadequate gas with the stiffer E-Lander mag spring. A barrel port to small or a gas block not centered over the port might provide enough gas for the CPD mag but not enough gas to lock back with a new E-Lander mag. Very fine line but many times it is difficult to tell if an AR-15 is over gassed or under gassed.
If an empty E-Lander mag will not lock the bolt back when pulling the charging handle to the rear and releasing you probably have an out of spec E-Lander mag. The CPD mag functions in the lower so the lower is probably gtg.
With an adjustable gas block I would attempt to set the gas block to lock open after firing one round with an empty E-Lander mag in the well. If you can’t get the bolt to lock open with the bolt catch with an E-Lander mag regardless of gas setting I’d suspect a faulty E-Lander mag. As previously mentioned E-Lander mag springs are very stiff when new.
With an empty mag in the well does an E-Lander mag catch the bolt when pulling the charging handle completely to the rear and releasing. If the mag engages the bolt catch you might have inadequate gas with the stiffer E-Lander mag spring. A barrel port to small or a gas block not centered over the port might provide enough gas for the CPD mag but not enough gas to lock back with a new E-Lander mag. Very fine line but many times it is difficult to tell if an AR-15 is over gassed or under gassed.
If an empty E-Lander mag will not lock the bolt back when pulling the charging handle to the rear and releasing you probably have an out of spec E-Lander mag. The CPD mag functions in the lower so the lower is probably gtg.