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Posted: 2/23/2010 5:50:39 PM EDT
| long story short, my old bolt broke at the cam pin hole. the replacement bolt is extremely tight in the carrier. it will not move with the flick of the wrist.. head space is good. that was the only part changed. unknown maker on the bolt, it came from my aquired parts box. any ideas how to fix? no wear in the carrier. gun has about 600 rounds total thru it. model 1 sales 16 inch stainless bull upper . |
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See if it's tight to the carrier at the back of the gas section, or at the middle of the bolt. Either can be relieved by spin sanding.
Also, check the back bugle section of the gas portion on the bolt. Some are known to not be milled correctly, leaving a high step just before the flair that will conflict/bind with the back of the carrier gas section as that high step tries to enter such. |
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Quoted:
long story short, my old bolt broke at the cam pin hole. the replacement bolt is extremely tight in the carrier. it will not move with the flick of the wrist.. head space is good. that was the only part changed. unknown maker on the bolt, it came from my aquired parts box. any ideas how to fix? no wear in the carrier. gun has about 600 rounds total thru it. model 1 sales 16 inch stainless bull upper . Afterthought - Your bolt BROKE ? Holy hell man, I've swapped out barrels and bolts (always a new bolt with a new barrel) with 15-17K through them and not so much as fracture. Are you shooting FA? Please tell me the 600 rounds you mention were not the only rounds on that bolt. If it were, I suggest calling whoever sold you that piece of "gear" and getting a free replacement. |
| measurements on machined part of the bolt is .5275, the bore of the carrier is .5315. diameter of the ring pack is .5085. the bolt out of a working gun measures .5280 for machined part of bolt, .5315 for carrier bore, .5020 for ring pack diameter. i can now flick it open by hand now. i manually worked it for a while. the bolt seems to get tight when the machined ring on the bolt starts into the carrier. forgot to try it without the rings on. |
| I suggest calling Model 1 and telling them what happened. Given that as a significant safety issue, they will probably send you a replacement. You might mention that their MP inspection process could use a little tweaking, seeing as yours had to have had a fracture when it shipped. There is no other explanation for what happened to your bolt unless you've been using it as a drive pin in the shop. |
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THe MP testing will not pick up if a bolt has been incorrectly heat treated properly.
When heat treated incorrectly, the metal is too brittle without any type of fracturing for the MP test to pick up, and instead of the metal having some elasticity/give to it to allow shock, it shatters like glass in a shot time instead. Agreed though, Get a hold of the supplier for a free replacement since the bolt was defective from the start, and life/use span played no part in it failure of the part |
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Nope... Colt BCG's are just harder to tell someone to go buy as they aren't as easy to find as a BCM. I run Colts in most of my AR's.
If that bolt fractured at 600 rounds, I wouldn't trust the carrier that came with it either. I'd swap the gas rings to see if that makes the bolt move correctly in the carrier and then move that to a spare in the range bag, get a Colt or BCM BCG and run that as the primary. |
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Out the gate, parts are not made by most of the suppliers, but by subcontracts to them. So it may be that the carrier and bolt where not made by the same subcontractor, or even heat treated in the same batch firings.
Next, every suppler (yes even colt) has had a improper batch of heat treated bolts. Granted that Colt tends to have a better track record when you are talking military issued parts, since not only are the parts tested by the subcontract and the supplier (them) as well, but finally batch lot inspected by the government as well (read if the government fails the lot from there sample test, the entire lot is sent back for a new replacement batch at the cost of the supplier). So lets take this same example back to the civilian world. Granted that some bolts have been MP tested, but as stated, MP testing will not tell you if a bolt has been heat treated incorrectly, only if you have a crack in the surface of the metal alone. Here you need shear testing, and until a supplier/sub contractor does batch lot shear testing, and marks such in a way to prove that is has been done (read letter stamping a heat treated part is not the smartest way to go, and will need to laser engrave), then you have no real idea of if the heat treating was done correctly or not (read if the part is going to shatter or not down the line with a very short service life). |
| after looking at the broken bolt, it looks like half of it has been broken for a while. it is dark and almost looks like it was parkerized when it was new. the other half of the break is shiney and looks recently done. will atking my parts to the local machine shop to get them magna fluxed work ? |
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Understand that Mp testing is running a charge through the part and using iron dust to coat the part to check for cracks.
A crack in the metal will disrupt the electrical magnetic flow across the surface of the part, and the iron powder will collect on both sides of crack predominately to show it's location. Yes, you could have a machine shop do this for you, or it's something that you could do at home as well. But to regress, chances are the part was not cracked when produced, but one side cracked before the other due to working stress put on the part through use. Chances are the black that you see on the cracked section is not parkerizing, but fouling that has collect over time until the part totally failed (other side cracked as well). |
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