Different weapons, military M4s, ran into two strange things today and figured I would take the opportunity to learn, sorry no pictures.
First was a guys rifle we couldn’t get zeroed, I tried shooting it because we figured it was just him being awful and it took WAY too much force to pull the trigger, I don’t know exactly how much but it felt like I was squeezing as hard as I could. All I could figured to do was hose it down with CLP and drive on, which did help significantly. His lower was filthy (not his fault), but I’ve never had trigger issues before, thoughts?
Second was my own rifle, as I was disassembling it I could not get the retaining pin out, it took a pair of pliers to pull it out and it came out looking like a banana with the round outline of the firing pin gouged into it, I could not straighten it out well enough to get it back in so off to maintenance it goes. What could have happened?
Obviously I don’t have to fix these, but for my own knowledge I would love some insight from those smarter than myself.
As for your firing pin retaining pin it sounds like the firing pin wasn’t all the way forward the last time you put the retaining pin back. Each drop of the hammer was ramming the shoulder in the middle of the firing pin into the retaining pin.
I have seen this issue with the firing pin retaining pin before. In my case I suspect it may be due to pressures from the suppressor, but I never really dwelled on it.
As for the trigger- all it takes it for a primer, anvil or sand/grit to get stuck down there. If it’s especially dirty who knows what is lurking down there. It’s always a good idea to use some compressed air to blow that area clean.
The retaining pin will also groove out if the hole for it in the carrier is a smidge low.
Takes a lot to get it going to a point where it becomes a thing though.
Putting the pin in with the loop horizontal can help as the way they are made leaves the pin narrower that way.
A rough firing pin between the shoulder and mushroom will do it as will a worn cam and/or bolt drillway which will allow the firing pin to floats more than it should.
You’ll likely see corresponding marks in the firing pin from the retaining pin also, but as the FP is much harder steel, it doesn’t get tore up like the RP.
Interesting you didn’t notice it before during regular maintenance as the ones that dink up the pin are pretty consistant about it.
AFA the stupid hard trigger, likely the filth you described had a clump, chunk, or piece of something under the trigger and lubing it more or less flushed it out from under there.
Just guessing on that dirt thing of course but am quite confident regarding the retaining pin.
Not all FP retaining pins are made from the same material. Suppressor use and overly large gas ports exacerbate wear/bending as does poor fitment between the tail of the bolt and the carrier.
In my case it was result of ovepressure from shooting out bullet stuck in barrel with next round. You probably did not have something so serious to do that in one round, but some overpressured ammo or increased pressure from suppressor can make it over time.
My HK MR223 was used to teach by other instructor. He had rifle not cycle, so tap, rack and BAAAAAAANG!!! Two bullets came together damaging muzzle device and BCG got so much energy that firing pin shelf bent (and broke) FP retaining pin. Actual damages was noticed when he gave rifle back to me. We settled that he keeps rifle and buys me new one. AFAIK he still uses my old one with no problems. Actually guy managed to blow away some other rifles (DI ARs) as well. Needless to say I do not let him put hands on my gear anymore
