BeeKay Posted January 25, 2023 Report Share Posted January 25, 2023 Just curious about what the inside story is on bolt production. It seems like it's a part with very exact tolerances and metalluryy specs so they must come from a central source .... Just guessing. I'd be interested in finding more info on that. Quote Link to comment Share on other sites More sharing options...
jtallen83 Posted January 25, 2023 Report Share Posted January 25, 2023 Toolcraft makes big portion of them on the market. D Wilson was a maker years back that gave a forum discount, he in the precision business making them for other companies, doesn't sell to the public any longer though so I don't know if he still puts out BCG's Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 25, 2023 Report Share Posted January 25, 2023 Toolcraft is is biggest supplier to OEMs. Back in the day CMT was the biggest supplier to OEMs on 5.56 stuff. Continental Machine Tool. One of the companies under CMT was Stag Arms. Dad owned CMT, son owned Stag. That's different now. White Wolf Capital. Here's a rundown on that stuff: This all went down around the timeframe that Aero "started using their own BCGS" in their guns, rather than using ToolCraft BCGs. Makes sense, connecting the dots. Quote Link to comment Share on other sites More sharing options...
BeeKay Posted January 25, 2023 Author Report Share Posted January 25, 2023 (edited) I have three BCGs and two of the bolts are marked with MPI and the other is marked with MP. I'm not sure whether that indicates the manufacturer or some other spec. I do get correct headspacing when I use the MPI bolt with a particular .308 barrel, When testong it with GO / NO-GO Gauges. But the bolt that works with that Barrel isn't the one that originally came in that Bolt Carrier. It seems to be a proper fit, though. I have a couple side charging BCGs and the other is a rear charging so swapping the entire BCG is out All feedback appreciated Edited January 25, 2023 by BeeKay Quote Link to comment Share on other sites More sharing options...
shooterrex Posted January 25, 2023 Report Share Posted January 25, 2023 MPI stands for magnetic partical inspected. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 25, 2023 Report Share Posted January 25, 2023 1 hour ago, BeeKay said: I have three BCGs and two of the bolts are marked with MPI and the other is marked with MP. It's MPI and HP. Not MP. Magnetic Particle Inspected, AFTER firing a High Pressure round - HP - a "proof load". That does not indicate a manufacturer, it's just proof that it's tested for MPI after HP - if it's even done. Lots of manufacturers pay for that process, and mark their bolts as such. It's also not done on every bolt in the batch, for alot of manufacturers - that's what "batch testing" is about in this industry. They might test 2 out of 100, 47 out of 50 - you don't know unless you contact them directly and ask. Closest I can find, and they cut off the MPI to MP... Quote Link to comment Share on other sites More sharing options...
willbird Posted January 25, 2023 Report Share Posted January 25, 2023 10 hours ago, 98Z5V said: It's MPI and HP. Not MP. Magnetic Particle Inspected, AFTER firing a High Pressure round - HP - a "proof load". That does not indicate a manufacturer, it's just proof that it's tested for MPI after HP - if it's even done. Lots of manufacturers pay for that process, and mark their bolts as such. It's also not done on every bolt in the batch, for alot of manufacturers - that's what "batch testing" is about in this industry. They might test 2 out of 100, 47 out of 50 - you don't know unless you contact them directly and ask. Closest I can find, and they cut off the MPI to MP... One issue that happens with steel is a flaw of some kind that was in the original poured billet. That billet gets rolled out into bar stock and the flaw will often be present in every bar of steel rolled out of that billet. At a prior employer we made some fairly large parts out of 4140 pre heat treat which is typically 28-32 rockwell hardness. Parts maybe 24" diameter with a LOT of cnc lathe and mill work on them. Far more than once partway through the process they would find cracks in the parts being machined. A pistol smith I know used to make a lot of 1911 muzzle brakes, again 4140 pre heat treat steel. He had a half dozen of them that he had a lot of hours into and a crack showed up after bluing, it was in the same exact area on each brake because that flaw ran throughout the whole bar of stock he had purchased. Bill Quote Link to comment Share on other sites More sharing options...
BeeKay Posted January 25, 2023 Author Report Share Posted January 25, 2023 Thanks - I'm familiar with a some of the basics of metallurgy and manufacturing so this all makes sense to me. At least - Now I have a bolt / barrel combo that headspaces correctly so I'll go with that . Quote Link to comment Share on other sites More sharing options...
StarWolf Posted January 29, 2023 Report Share Posted January 29, 2023 I don't know of any reason why you shouldn't be able to swap out 'standard' bolts from one carrier to another. That's regardless of whether the carrier is side charging or rear charging. There may be some 'optimized' or proprietary bolt designs that don't swap without swapping the cam pin as well but those are pretty few and far between. If you have one of those you probably know it. Quote Link to comment Share on other sites More sharing options...
BeeKay Posted February 10, 2023 Author Report Share Posted February 10, 2023 (edited) Thanks - I'm familiar with a some of the basics of metallurgy and manufacturing so this all makes sense to me. At least - Now I have a bolt / barrel combo that headspaces correctly so I'll go with that Double post Edited February 10, 2023 by BeeKay Quote Link to comment Share on other sites More sharing options...
MaineMan2 Posted February 11, 2023 Report Share Posted February 11, 2023 On 1/25/2023 at 12:30 PM, BeeKay said: Thanks - I'm familiar with a some of the basics of metallurgy and manufacturing so this all makes sense to me. At least - Now I have a bolt / barrel combo that headspaces correctly so I'll go with that . I have three 308 AR uppers. Two Faxon “identical” barrels and one Criterion barrel finished by Fulton Armory. Three Aero Precision bolts. I had to mix and match bolts with barrels and was lucky enough to find 3 good combinations in terms of headspace. 2 combinations wouldn’t close on the GO gauge. One combination would easily close on the NO GO gauge. Clearly there were variances over .004” between the bolts and barrel chambers. Like powders - only 308 upper on the bench at a time! Quote Link to comment Share on other sites More sharing options...
98Z5V Posted February 11, 2023 Report Share Posted February 11, 2023 ^^^Truth right there. 5.56 - fuk head spacing those things, the platform has been in production for half a century, and every manufacturer has the prints. That's easy. Large Frames, though? Better head space check these big bitches. I'm just sayin'... Quote Link to comment Share on other sites More sharing options...
StarWolf Posted February 16, 2023 Report Share Posted February 16, 2023 Just got the gauges for .308 Win. Offered to use them on a coworker's build and he declined. A different coworker planning a build he wants me to assemble was glad to hear I'd picked up the gauges. Years ago a friend who owned a gunshop was working on getting his manufacturer's FFL. At that point it's a darned good idea to gauge anything and everything including the 5.56. Different level of responsibility. Quote Link to comment Share on other sites More sharing options...
BeeKay Posted March 2, 2023 Author Report Share Posted March 2, 2023 I created another post before this one on the topic of headspacing. I've only fired a few hundred rounds through the barrels in question and now I have a bunch of brass that's fireformed through chambers that are too loose by .002" or maybe even bigger.... So we'll see how this plays out.... Reloading that brass is going to put this through the acid test . I do have one Barrel / Bolt combination that headspaces correctly using the gauges I have - Clymer ... But Gosh Oh Golly... Wouldn't you know it, the gas block position is out of spec on that one . So I'll see how it shoots and if it's accurate, I'll dig uo a longer gas tube . Thanks to anyone who contributed to the discussion Quote Link to comment Share on other sites More sharing options...
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