Thanks for advice

[Sullivado09]

......

[ar15barrels]

An out-of-spec buffer tube or buffer will cause this.
The buffer should stop against the inside of the buffer tube before the gas key can impact the rear bridge of the receiver.
It would appear that something is not doing it's job in your case.

[johnnydizzy]

buy one of those extra power springs and put in a H3 buffer? idk.

[toddh]

Can you screw in the buffer tube more ??
Also, measure the length of your buffer, make sure it's not short somehow.

You either have too much travel inside the length of the tube, or a short buffer, this allows the key on the BCG to hit the receiver buffer bridge.

[Sullivado09]

thank you all for the info. Especially AR15BARRELS.
simple fix of putting a quarter or two at bottom of buffer tube to correct an outta spec buffer.

thanks again

[S470FM]

is that an 80% lower? could be out of spec?