One of the most common issues with an AK build is the bolt carrier jams at the back when it is cycled. This is caused by the bolt carrier cutouts being too long. The design of the AK recoil system takes into account that the bolt carrier will need to be removed for cleaning and maintenance. To keep the carrier on the rails while under upwards pressure from the hammer there is an extension on the back of the carrier that fits into a slot in the front of the recoil spring stop.
When the carrier cutouts are made to the proper length the carrier will drop in with less than 1/32" clearance. When the carrier is cycled the recoil spring stop will keep the carrier about 1/16" forward from the rear trunnion. This means that the front of the carrier will will always be engaged with the rails.
If the cutout is too long the pressure from the hammer will push the carrier up and it will jam on the rails. The easy way to rectify this issue is to install a recoil buffer.
I have found that if I make the cutouts too small and then file fit this issue can be avoided.
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