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New M4, is this a regular amount of bolt tail peening?


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I recently picked up a new M4 which had a few issues in break in (first 100 or so rounds would have the bolt stick open on the 3rd round in the mag). Sent it to Benelli to be inspected, who found no faults and had their tech shoot it about another hundred times, sent it back again after finding their tech ruined the finish by putting a dent and gash in the magazine tube extension, and after getting it back the second time it seemed to be working correctly. In total the gun is about 3-400 rounds old at this point and I ran another 50 today.

When it was still new and jamming I had noticed the gun developed a squeak if easing the bolt backward, which I think was the tail shaft on the bolt peening itself against the tougher steel of the recoil tube. The sound is now mostly gone and the recoil tube is undamaged so I assume this is a case of those parts wearing in still.

Anyway, I have attached pictures of the bolt tail when I was cleaning it today. It seems like there is a little bit of mushrooming where the tail meets the recoil spring plunger, and some burrs where the diameter of the metal tail shaft exceeds the sizing of the recoil plunger (to be expected then). Are these levels of wear normal for post break in? I assume if the bolt tail had bad heat treating it would have bent or broken rather than peened like this.

Rather hoping I don't need to send it back again just yet as I have had maybe four days of ownership in the month I have owned it at this point so would like to spend more time using it rather than having somebody else do so.

Also should I deburr these marks or let them grind themselves to a polish on their own?





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