Hey guys, I bought a box of UMC .303 for my new no4, and tried it out for function, and it won't feed...UNLESS I press up really hard on the mag....the bolt head JUST misses the rim of the cartridge if I don't press up, and rides over. Playing around with the mag shows that the mag is not "locking' into place, and you can pull it out without pushing on the latch if you pull hard. However, for giggles I tried my Ishapore .308 mag in it, and it locks home smartly, and incidentally feeds .303 rounds WELL, even though you can only get like 3-5 rounds into the mag before it binds.... I can find NO burrs on anything, and looking CLOSELY can find NO reason why the original mag won't lock home....ALL the notches and stuff are IDENTICAL to the Ishapore mag... The feed ramps look good too, and taking apart the mag shows no deformation to the follower,and like I said, it DOES feed if you press up, there is a very little movement when you do, but the Ishapore locks up tight with no movement. The mag release looks like it is still depressed when the no4 mag is in place, but for the Ishy it's down and locked. THIS is what is throwing me, I could understand if it DID lock and still showed movement, then I could chalk it up to wear, but it's not locking. The no4 mag has what appears to be the Long Branch marking on it, so I believe it's original. Other than buying a replacement mag, what other suggestions do you have that I can try?