If you are having feeding issues, sometime a quick polish on the BB feed ramp can help out. It's also always wise to pop-out one or two BBs after filling your mag.
Here is a before
Dermal for polishing
Here it is finished up
If you have a older LM4 with a upper that is made of multiple pieces ... you can disassemble it making it easier to polish the feed ramp. If you do this, I suggest you JB weld the upper back together making the unit stronger. Be careful to not use too much weld and especially careful with the Picatinny rail as you can mess up how the charging handle slides. I also JB weld all the uppers on my older KWA AEG's
Disassembled ... before and after