Who Here Really Breaks Bolts?

[rero360]

I’ve only seen it happen once, was a Squad Designated Marksmanship course rifle that had god knows how many rounds through it, I do know that rifling erosion was visible on most of the guns when we finished the course. The broken bolt in question had two lugs sheared off but was still functional. All USGI, can’t remember if those guns were Colts or FNs.

[lysander]

We say Rockwell C because most people understand the Rockwell hardness scale, same for the word "anneal".
None of the Melonite/Nitride companies I used could get a case depth of .002", all of them vary 60-70c (converted), that would be Bodycote(Berlin), H&M(Ohio), Parker Trutec (sevierville or Arkansas) or Burlington in Ca. ETA- the higher the temp and longer the parts soak the larger the chance that it(nitride) will soften the already carburized parts. If it is raw material being nitride treated the high temps and longer soak should increase the case depth.

I said you can get thicker case depths, I didn't say you were . . .


100 µm = 0.003937 in

[duroSIG556R]

We say Rockwell C because most people understand the Rockwell hardness scale, same for the word "anneal".
Definition of anneal
transitive verb

1a: to heat and then cool (a material, such as steel or glass) usually for softening and making less brittle
Each bar, with its intricate twists, bevels and turns, had to be shaped individually. This shaping made some parts of the bars brittle … . To restore their flexibility, all the bars had to be annealed by heating, and then rapidly cooling them.
— Ivars Peterson

. Yes I believe I said we are looking for a core hardness of 50c so the core remains ductile. Raw 158 or 9310 is around 28-32c so the gas carburizing does increase the hardness at the core from 30 to 50 not "case hardened" but harder. They cut a few bolts from every batch I sent in to check the case depth and core.
Nitriding a raw bolt will not raise the core at all when the lugs are .100" thick. The lugs and the area each side of the cam pin hole are what really matters and both are close to .100" thick. Nitriding a bolt that has been gas carburized will soften the material. When I drill through Nitride treated barrels the case is hard but as soon as the bit breaks through it is like butter. Gas carburizing is not like that, the case is hard and then gets softer the closer to the center of the core.
None of the Melonite/Nitride companies I used could get a case depth of .002", all of them vary 60-70c (converted), that would be Bodycote(Berlin), H&M(Ohio), Parker Trutec (sevierville or Arkansas) or Burlington in Ca. ETA- the higher the temp and longer the parts soak the larger the chance that it(nitride) will soften the already carburized parts. If it is raw material being nitride treated the high temps and longer soak should increase the case depth.

Okay so now I'll tell you how I know what will happen to bolts or barrel extensions that have been nitride treated. I've produced barrels and machined bolts for 14 years. Around 2009 H&M was nitride treating my barrels and they told me it would not effect the barrel extensions. All of the barrel extensions you see on the market that are silver are untreated steel, they aren't stainless like everyone thinks and they will rust if they weren't coated in oil when people oil their BCGs. H&M says the Nitride treatment will make the barrel extensions corrosion resistant. I know I had to remove the extensions clean and re-torque then drill the gas ports.
Apx a year later I get a call from someone I know pretty well, he works up and tests ammo, he says the headspace has increased and returns a barrel and bolt for me to check. He's right, I removed the barrel extension and measure the lugs, they had compressed an average of .007". The gas carburized bolt lugs had not compressed at all. I replaced the extension after timing it to the gas port and returned it to him, as far as I know he is still using the same barrel 10 years later.
Around the same time I am in a discussion with a guy on barfcom, he had said over and over for years melonite can cause embrittlement and those parts can chip, well I've already seen lugs compress so I'm thinking they are soft. I pulled out a nitride treated barrel extension and hit it with a ballpeen hammer, it dented, then smashed it (side to side)with a 8lb sledge. It folded flat but broke at the sides. I pulled out a normal silver barrel extension and hit it with the sledge, it shattered into several pieces. I had already stopped letting H&M nitride the barrel extensions but at that point I was curious so I sent an old treated barrel extension to Paulo Prod that heat treated all of my bolts and asked them to check it for hardness, it was softer and the case wasn't near what it should have been.
I don't really care what anyone buys or uses, it isn't going to affect what I do. I post it to possibly save some people from aggravation, you know when they start blowing primers for what seems like no reason. 5.56s do not create as much thrust as a 6.8 which does not create as much as a Grendel so it may take longer to compress 5.56 lugs. Anyone can send off nitride treated parts to have them tested, don't believe what you read? Check it yourself.

Thanks for your contribution. I love your barrels and bolts. Both have been excellent.

[The Dumb Gun Collector]

I've never broken one in 20 years of pretty dang heavy AR shooting (Although my oldest current gun is only 12 or so years old). Hilariously, even in all the carbine courses I have taken the only bolt I have seen bust was in a KAC! That was in a Vickers class I took in Ohio forever ago. It busted right out of the gate. Just shows you you can be as careful as possible and poof.

[Joe Mamma]

Off of the top of my head, I remember a guy I was shooting with who broke a bolt. It was during a 3 gun competition.

Unknown round count and unknown ammo. He was a pretty serious (and good) competition shooter, so it would not surprise me if he had a lot of rounds on the bolt. But it would also not surprise me if he had an adjustable gas block.

I always carry a spare bolt (a standard mil-spec bolt), so I loaned him my spare, and his gun worked perfectly for the rest of the match.

It was a bolt made by JP, which ironically is still one of the brands I trust.

Joe Mamma