I think you have headspace issues, some of the older 722 based 40x's the barrel is set back further than the 700 based 40X. Do you know which you have? If it's your intention to use the factory barrels, you may have to have them rechambered. I know that sucks because it defeats the purpose of buying a stripped barrelled receiver. I have one 722/40X that Kiff's bolt would not close either, but it didn't matter to me because I was going to rebarrel anyway. When i unscrewed that barrel, sure enough, the tenon was quite a bit longer than the others. another thing I noticed, the recoil lug was shaped different too, same thickness but fatter width at the bottom. What a friend of mine, Bob, did was is adjust headspace and line up extractor slots (factory barrel) by adjusting the thickness of the recoil lug. in his case it was just the opposite as yours, he had to decrease the thickness, but you can buy oversize lugs, or, you could use a washer. Bob measured the thickness he wanted and I took two lugs to my friend's machine shop and he put in his surface gringer to take them down. Worked perfect, both his rifles shoot great and he's happy. Thanks, Douglas