Spare Bolt?

[WVSig]

This bolt failed after 65,000 rounds. Not my bolt but this is the type of round count you have to shoot to shoot a properly made bolt to failure. At todays ammo prices thats $19,500 worth of ammo.

The barrel would have been shot out more than once long before that bolt failed. IMHO So if you are looking to keep spare parts on hand barrels and other wear part might be a better option.

 

[67tempest]

This bolt failed after 65,000 rounds. Not my bolt but this is the type of round count you have to shoot to shoot a properly made bolt to failure. At todays ammo prices thats $19,500 worth of ammo.

The barrel would have been shot out more than once long before that bolt failed. IMHO So if you are looking to keep spare parts on hand barrels and other wear part might be a better option.

That looks to be exactly where my brothers' and my AR bolts broke, at the cam pin hole. We shoot only factory ammo and had no where near 65k rounds through either AR. I don't honestly know what material the bolts were made of. I have assembled 25+ AR's over the years using parts from numerous suppliers so who knows.

I don't own a 5.56/.223 headspace gage and have NEVER headspaced an AR I assembled from a kit. I have never had one that failed to fire. If the headspace is too tight the bolt shouldn't go into battery. If too loose, the brass should exhibit signs of excessive headspace, I never had either happen. Maybe I just got lucky. I think the camming AR bolt design is very forgiving regarding headspace.

 

[Steve912]

That looks to be exactly where my brothers' and my AR bolts broke, at the cam pin hole. We shoot only factory ammo and had no where near 65k rounds through either AR.

Were your two broken bolts from same batch/purchase/pedigree?

 

[67tempest]

Were your two broken bolts from same batch/purchase/pedigree?

I can't say with all certainty that both broken bolts came from the same supplier. We have used parts from several different suppliers over the years. If I had to venture a guess I would say they probably broke due to incorrect material. Everybody and his brother sells AR parts and who knows who actually made them and from what material. I have built AR's using parts from Colt, Armalite, Model1 Sales, M&A and PSA to name a few. Couldn't tell you who's bolt actually broke.

 

[hdwhit]

vonn wrote:
Has anyone ever seen a bolt break? Just curious.

Yes.

• New AR.
• Not mine, belonged to an acquaintence.
• Factory gun, not home-built.
• First magazine.
• U.S. made factory ammunition.
• One of the locking lugs sheared off the bolt during unlocking.
• Apparent manufacturing defect.

I won't mention the manufacturer because I don't know what the ultimate determination of the cause of the failure was.

 

[WVSig]

I can't say with all certainty that both broken bolts came from the same supplier. We have used parts from several different suppliers over the years. If I had to venture a guess I would say they probably broke due to incorrect material. Everybody and his brother sells AR parts and who knows who actually made them and from what material. I have built AR's using parts from Colt, Armalite, Model1 Sales, M&A and PSA to name a few. Couldn't tell you who's bolt actually broke.

If I had to guess you had a stacking issue. Enough parts were sightly out of spec not enough to not function but enough to push the bolt past where it should have been. Were they FA or SA BCGs?

 

[Steve912]

Were they FA or SA bolts?

Carriers? How would that break bolts?

 

[WVSig]

Carriers? How would that break bolts?

You know what I meant. LOL

 

[Steve912]

You know what I meant. LOL

"Oh, Beeee Have!"

No, seriously--how would auto or semi carrier be more likely to snap a bolt?

 

[ameridaddy]

I agree with cyphertext. To the most part they are interchangeable but you could be the unlucky one where the tolerances don't stack up right. Better to grab another, complete rifle or call it a day and head home.

I was an "unlucky one"
Of three AR's builds, one had insufficient headspace by .004"!
Problem wasn't bolt, but the barrel. I'll not mention the name of the company that supplied the upper. I won't buy from them again.
Point is, check headspace or risk a serious problem.

 

[Disabled1]

Thanks everyone for the explanations. And yes, I am new to ARs. I'd like to get a budget version to replace duty on my Universal M1 Carbine. It has been my day/night shooter for wild dogs, coyotes, hogs and other as needed. (Most recently a rattler.) I had been looking at the S&W and Ruger AR or possibly a Hi-Point 9mm or .45 Carbine. I really like the 9mm Carbine as I already have plenty of ammo. I don't plan to buy until after the holidays or February so I'm gathering all the info I can.

That Ruger AR-556 is a mighty fine AR!

 

[CBStuard]

Personally I do not think you need to keep a spare. Unless you shoot a ton the bolt will most likely outlive you. If you still think you need on get a PSA full auto premium bolt for $69-$89.

Palmetto State Armory 5.56 Premium Full Auto Bolt Carrier Group - 8779

Milspec Carpenter No. 158® steel bolt
Shot Peened Bolt
High pressure tested
Mag particle inspected
Chrome Lined Carrier (AUTO)
Chrome Lined Gas Key
Gas Key Hardened to USGI Specifications
Gas Key Grade 8 Hardened Fasteners
Gas Key Staked Per Mil-Spec
Tool Steel Extractor
Extractor Spring
Extractor O-ring Insert
SKU 8779

By the specs it is a better bolt then what came in the Sport II IMHO.

This is exactly the BCG my Swat team armorer SIL recommended I get for a spare last weekend.

 

[WVSig]

"Oh, Beeee Have!"

No, seriously--how would auto or semi carrier be more likely to snap a bolt?

It is not that the BCG caused the bolt to break but I was thinking that the extra weight of a FA carrier might have masked some of the headspace issue which would be why the guns functioned until the bolt snapped.

I fully admit this may not be correct. Please feel free to correct me.

 

[Steve912]

Hmmm...

Assuming the bolts cracking at cam pin area indicates either
torquing or tensile failure, or both--excessive headspace wouldn't seem
to promote either condition.

An FA carrier would presumably accelerate from gas impulse slower, perhaps insignificantly, than a semi carrier. Could a semi carrier, in a worst-case situation--an over gassed carbine, say--impose a violent enough unlocking impulse to the bolt, to snap it at the weak point?

Hmmm...

 

[WVSig]

Hmmm...

Assuming the bolts cracking at cam pin area indicates either
torquing or tensile failure, or both--excessive headspace wouldn't seem
to promote either condition.

An FA carrier would presumably accelerate from gas impulse slower, perhaps insignificantly, than a semi carrier. Could a semi carrier, in a worst-case situation--an over gassed carbine, say--impose a violent enough unlocking impulse to the bolt, to snap it at the weak point?

Hmmm...

You are clearly more technically able than I am so I will differ.

 

[Tinhack]

I don't know; spare parts laying around always seem to morph into another rifle from what I've heard. The same happens with Model T cars. Someone will buy a spare engine or spare wheel and then restore a car around them. It happens a lot. And if you leave two alone in a garage, they multiply like rabbits.

 

[Steve912]

It happens a lot. And if you leave two alone in a garage, they multiply like rabbits.

...like Walmart bags, and coat hangers!

If only ammo would do that!

 

[Mark IV]

...like Walmart bags, and coat hangers!

If only ammo would do that!

^ LOL !!

 

[Steve912]

You are clearly more technically able than I am so I will differ.

I dunno about that

I just try to think it thru, like "sounding out the word" in 1st grade.

 

[2ChihuahuasDad]

From Tire Iron:

BCG should be:
A. MPI
B. HPT or firing tested
C. Melonite, Nitride, or Nickel Boron.

Fail Zero and Aero Orecision both make affordable BCGs that fill the aforementioned requirements, too.