i have an ar-15 that was assembled fromvarious parts. it is a pwa lower and a fn flattop upper. it has had some gunsmithing done by a very competent smith. the problem is that it will not cycle with lighter bullets and with heavier it will only work for about 50 rounds and then needs a thorough cleaning. i have bben using black hills ammo. 60gr vmax works best. lighter bullets will not cycle reliably at all. this indicates not enough pressure to cycle the bolt. i discussed this with my gunsmith and we decided to open up the gas port about .003". same problem. we have tried three different gas blocks on it. hot loads(worked better but still same problem). i am at the end. the only thing i have not addressed is the bolt/carrier assy.(which was brand new when i started the project). do you think that maybe the spring is too heavy? does anyone have any suggestions? i am thinking of just scrapping it and getting a dpms hi rider. i really like the smooth looks of no forward assist and no ejection port door. TIA

There was a heavier buffer used with the 9mm version, as it was blowback instead of gas operated. There is a chance you have the heavy buffer. I believe the springs were the same.

Other than that, make sure your gas tube is unobstructed and there is a good seal where it mates with the bolt carrier.

What length barrel is it? If it`s under 16 inches, it`s a very common problem. If not, I think you need to really clean your bolt carrier and possibly pull the gas tube off and take a pipe cleaner to it. Use the pipe cleaner on the gas tube on the bolt carrier also. If it`s a 16 or 20 inch barrel, that should fix it. If it`s a shorty, well....good luck.

Do you have a nato chambering or a tighter .223rem.? I've seen feeding problems with tighter chambers.

Have you pulled the bolt out of the carrier and checked the gasrings? Make sure the end gaps are well offset from each other. check the clearance and fit of the gas tube to the carrier key.
Like someone else said check for the proper buffer assembly.There are several other things carrier clearance in the upper and bolt lockup to the barrel extension etc, but they are rare.
good luck
Covey16