What is the name of the diagonal depression on these Colt bolts just behind the lugs?
More importantly, what is the function of these depressions?
(I understand that many FN bolts have a similar depression but with a semi-elliptical sort of shape.)
Thanks.
I’m not sure of the specific name but I believe these are for debris clearance.
It’s from the tool that cuts the chamfer on one side of the lugs.
More oddities noticed:
Why are the letters “MPC” tilted on some bolts, but not others?
Why is the raised ridge between the cam pin hole and the letters MPC apparently flutted on some bolts, but not on others?
Go ask your mother. :jester:
It’s all magic.
Not all of those look like Colt bolts…
these are all machining slop, for lack of a better term. the “fluting” is just where the lug cutting tool grazed the rib.
the stamps are in different spots because they’re just wherever the stamper decided to stamp them
there’s no method to this madness
Poor tooling control on the CNC machine during lug cutting.
Which ones & why? To the untrained eye (meaning yours truly), they all look the same except for the one where the lug cuts extend back into the ring around the bolt body. I know zip about colt parts, so I’m curious what makes them different.
They all appear to be stamped “MPC”.
Doesn’t that make them Colt?
OK, here is a pic of a proported FN bolt with the semi-elliptical depressions behind the lugs. I care not the authenticity of the bolts’ manufacture but I am curious to learn the name and function of these bolt characteristics.
(Mod: If pic is not in public domain, please delete it.)
No. The canted lettering is a giveaway.
I have seen Colt bolts with other types of MP markings. I believe some were MPJ and MPY. I would say that some of those are possibly FN and maybe LMT.
does LMT produce bolts without the lug undercut?
I thought some of their older stuff was, but I am not 100% sure.
Here’s my FN bolts, marked MPF - I believe they are legit.
They have the same semi-elliptical cuts.
Feel free to save this image and use it whenever you like. It’s the best I could do with a cell phone (I spend my money on guns, not cameras :D)
Here’s a shot of the F marked extractors:
Colt bolts marked MP_ or MP__ up to four place stamps.
FN bolts have been MPF with an underscore under one of the letters, usually the F
I have no clue as to the name of the area in question. As far as purpose I would guess that area was trim down to allow more free movement of the bolt inside the carrier causing less jams due to excessive carbon build up.