I thought that the 5.45X39 cartridge was the 7.62X39 necked down to 5.45. The only difference, what I'm told, is the neck, and also the case walls before the shoulder are straightened out to increase case capacity. If so, why wouldn't the rails be the same?Thanatos said:I think if you want to use the TAPCO rails for an AK-74 you do not have to trim the rails. I think it's only for an AK-47 that you have to trim the rails. They are already cut for the smaller case.