Please help: Receiver fit, feeding and cycling issues.

[OnTarget]

Ok, so monday i ordered a BCM middy upper which i installed on my smith and wesson mp15 lower then i ran into a "tremendous" problem as i went to function check. The mag did not catch, so i gave it a good slap and it caught; then when i went to cycle the gun it was kind of hard to pull the charging handle [presumably] because the mag is putting pressure on the bottom of bolt carrier.

The strange thing is that when i put a mag with only three rounds, it catches it without a problem and cycles perfectly. As soon as i fully load the mag, i have to slap it in and pull the charging handle harder -- is this a serious problem or not? How do i fix it?

Thank you in advance for any help. [:D]

[rebelEMPIRE]

Nothing should be 'hard' to do. Odds are something is indeed wrong. If you gotta use brute force to get the magazine to catch or pull back the charging handle, those are clear signs that something is off. You should probably strip your upper to do an inspection before you proceed any further. Perhaps it's the magazine you're using. Try using a different magazine and see if you can duplicate the problem. Next, I would adjust your magazine catch button to make sure it's thread properly. Use a different bolt carrier if there's one available to see if you get the same results.

-rebelEMPIRE

[OnTarget]

Nothing should be 'hard' to do. Odds are something is indeed wrong. If you gotta use brute force to get the magazine to catch or pull back the charging handle, those are clear signs that something is off. You should probably strip your upper to do an inspection before you proceed any further. Perhaps it's the magazine you're using. Try using a different magazine and see if you can duplicate the problem. Next, I would adjust your magazine catch button to make sure it's thread properly. Use a different bolt carrier if there's one available to see if you get the same results.

-rebelEMPIRE
i have tried all this and it still doesnt catch with a fully loaded mag i dont have to use extreme force but its a little harder than normal i seem to be that a fully loaded mag pushes harder when i install the pmag with window i see through the window that when i slap it in i see the spring go lower

[Muddyboots]

How many rounds is "fully loaded?" What side is your top round on?

Do ALL your mags do this?

Trying to help from afar...

Muddyboots

[OnTarget]

Ive tried pmags cmags and colt mags

[5pins]

A fully loaded USGI mag is always hard to insert. Down load them by a round or two.

[Quib]

Scroll down to Post #11:

http://www.weaponevolution.com/forum/showthread.php?1613-FAQ-s-BASIC-INSPECTIONS-AND-PROCEDURES

[rebelEMPIRE]

By now, sounds to me like you don't have any issue with your weapon. However, you should still have someone familiar with ARs check it out just in case. It's a lot easier to dissect in person. If it's only a "little harder" to push in when fully loaded, that is a normal condition,as the spring's potential energy is increased through greater compression. Also, the top round is supposed to contact the bottom of your bolt carrier when the action is closed. When the rifle fires, the carrier goes back, allowing the top round in the magazine to move up, which then allows the bolt to push said round into the chamber. Not sure if you already knew that; please forgive me if you did. However, I felt the need to explain its operation just in case.

-rebelEMPIRE

[Stickman]

Is it any different than when you use your S&W upper?