Failure to feed??

[stormblue]

I have a S&W M&P15T that has a occasional (3 in 200) failure to feed.
The magazines seem to have more front to rear play than a rifle built on a Mega lower.
I'm thinking that this extra play allows the front of the mag to rock down just enough
for the occasional round to miss the ramp and hit the reciever. I observed this once
while manually feeding rounds. I measured the magwell front to back at the top of the
receiver and it's 2.42". I measure my mega lower and it's 2.4".

So my question is, is 2.42" considered to be in spec?

[Robb Jensen]

Please describe you failure to feed a little more.....

What mags are you using?
What ammo are you using?
How much and what lubrication are you using on this rifle?

What weight of buffer do you have?
What length in inches is your buffer spring?

[stormblue]

Unfortunately I've not been methodical in recording the circumstance of each failure.
It took me a little while to decide there might be an issue. I've been fighting this rifle since
I got it and I'm tired of going to the range to diagnose problems. I guess I was hoping
for a "yep it's out of spec" so I can send it to S&W.

I really wasn't ready to discuss circumstances because they are not specific but here they are anyway.

Mags: mixture of new NHMTG and 15 year old D&H, all have green follower.
Ammo: mixture of SA and M855PD
Lub: TW25B, I would say moderate amount

Buffer: It's unmarked, I take it that means carbine.
Spring: 10.75"