Using 316 in place of 4140?

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I am trying to make a gun bolt off of a set of blueprints for a rifle, and the blueprints call for the use of 4140 steel.  My question is what would be the advantage to using 4140 over say 316 stainless?  From the Rockwell charts and properties I have found on both materials, the 316 seems to be harder, and stronger.  Then again I could be reading them wrong.  Be kind but please offer some advice.  The reason I ask is because I have access to alot of 316 but no 4140.  Would the 316 be able to handle the abuse that hardened 4140 could take?Could 316 be too hard possibly and lead to cracking or shattering?  Any help would be appreciated.My Babies:MillerMatic 185Thermal Arc 300SHobart StickMate AC/DC 235/160Dalex Werke Spot WelderOh and the wife and kids are important too!
Reply:Ok well I see that the tensile strength of 316 is much lower.  Are there any other disadvantages?My Babies:MillerMatic 185Thermal Arc 300SHobart StickMate AC/DC 235/160Dalex Werke Spot WelderOh and the wife and kids are important too!
Reply:Hey gigarre,As a retired Master Gunsmith, your query is interesting, although I would strongly recommend some serious homework. There is quite a bit of engineering & planning that go into the entire process of creating a bolt for a high-power cartridge. Even with drawings, the precise fit in the receiver, bolt lug engagement, the forward bolt body that encompasses the cartridge, & the extractor seat, all have to be correctly calculated. Then, you have to set up the barrel & chamber for the correct headspace. If using an existing receiver & barrel, the barrel has to be removed to fit the bolt to the receiver exact. Then, to obtain correct headspace, the chamber area of the barrel has to be shortened, probably at least .100" & re-headspaced with a finish reamer. Next, if all the parameters have been met, then the test firing to determine if any fatigue, failure, cracking, & stretching has occurred. Safety would dictate the firing be done by remote.... at least 50' away & behind a protective wall. A centerfire cartridge such as the 30-06/308 class would produce in excess of 50,000psi in the chamber & against the bolt face & locking lugs. I've seen c/f rifles that disintegrated like shrapnel.... not pretty. Even worse are those that sheared off the locking lugs & rearward travel of the bolt body decapitate the shooter. Believe it.... it has happened. Your best approach would be to get a factory/military replacement bolt body & just re-headspace the chamber. Anyway.... hope this helps & gives you some food-for-thought to ponder....     Good Luck....      DennyComplete Welding/Machine/Fab. ShopMobile UnitFinally retired*Moderator*"A man's word is his honor...without honor there is nothing.""Words are like bullets.... Once they leave your muzzle, you cannot get them back."
Reply:Is this for a modern high pressure center fire cartridge, or something less demanding like a .22 rimfire? More details are needed to know if the question is even safe to discuss here.
Reply:Well this is the deal.  I recently got the book by Bill Holmes on making a .50 bmg rifle from scratch, besides using a surplus barrel.  Anyway, I have access to lathes, mills, and grinders, welders, etc., and although I am not the most experienced machinist, many of the guys there would be able to help and all have years of experience.  The reason for my question is that the book calls out for 4140 which we don't get much at work, my question was whether on some of the parts I could use 316 instead, which we have plenty of.  I will send a link to the online version of the book, hopefully it will give an idea of what I am trying to do.  Safety is first in mind, so if need be, I would go with the 4140, but on less demanding parts I was hoping to get away with 316.I figured 316 would be a long shot, but on parts such as the trigger assembly and reciever tube I was hoping it would work.  You guys are the experts, so I  appreciate the help.Here is a link to the book.  You can actually scroll through the entire book from here.http://www.scribd.com/doc/4484076/fi...ruction-ManualMy Babies:MillerMatic 185Thermal Arc 300SHobart StickMate AC/DC 235/160Dalex Werke Spot WelderOh and the wife and kids are important too!
Reply:Originally Posted by Oldiron2Is this for a modern high pressure center fire cartridge, or something less demanding like a .22 rimfire? More details are needed to know if the question is even safe to discuss here.
Reply:I've been raised in the country with a dad and grandpa that collect just about any type of gun, and have shot a large variety, but could never afford to buy a .50 so never got to shoot one.  That's the reason I was going to make this one.  I would have something my grandpa hasn't shot since the Korean war, and something my dad has no experience with, which means he will want one shortly after.I guess using 4140 would be wise on the bolt and barrel nut, but does anybody see a problem    using 316 for the receiver tube, and basically everything else that doesn't take the blunt force of the bullet?My Babies:MillerMatic 185Thermal Arc 300SHobart StickMate AC/DC 235/160Dalex Werke Spot WelderOh and the wife and kids are important too!
Reply:Lets be honest, how much steel is it really going to take to make that bolt? What's it going to cost you to just buy a small piece from say MSC or Graingers?Now, do you really want to put your head at the other end of what that gun tosses out the front if a "cheap" material isn't 100% up to spec? My lifes worth way more than any savings that small piece of steel could ever cost. Hell even if I had to by Titanium because thats what they recomended at whatever the cost my lifes worth every penny and more. A new name brand .50 cal bolt will cost me $3000. I'd pay that in a minute 3 times over to keep me alive..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:You make a valid point.  I will probably use the 4140 on the bolt.  I am just considering using the 316 for things such as the receiver tube and small parts like the trigger assembly and muzzle brake.My Babies:MillerMatic 185Thermal Arc 300SHobart StickMate AC/DC 235/160Dalex Werke Spot WelderOh and the wife and kids are important too!
Reply:Small parts like the trigger and muzzle brake are probably ok in SS as they are not structural parts ( I'd think real hard on the muzzle brake as it will see quite a bit of force and then I'd want to compare the specs on both materials and just how they have that brake designed. If I had even the slightest doubt I'd go with whats spec'd in the plans). The reciever tube may be depending on weather the bolt locks in it or to the barrel. If the tube is just a carrier that should be no problem since the bolt would lock to a reciever ring or barrel assembly. If the bolt locks on the reciever tube like it does on some rifles I'd go with what they call for..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Get your affairs and will in order, at 50,000-65,000 psi, that’s 25 to 32 + tons of force psi, you’re going to kill yourself. That force is not applied slowly like in a hydraulic jack; it’s an impulse force like a hammer blow. Even after 100 test firings you never know when it will come apart. Have you considered taking up recovering nitroglycerin for fun and profit? Order the 4140 and a toe tag.
Reply:Originally Posted by gjgarreWell this is the deal.  I recently got the book by Bill Holmes on making a .50 bmg rifle from scratch, besides using a surplus barrel.  Anyway, I have access to lathes, mills, and grinders, welders, etc., and although I am not the most experienced machinist...