Bolt thrust
- Thread starter TAJ45
- Start date
i doubt the lugs would fail. More likely barrel would come apart but anything is possible.
As JMayo said KNOW SIGNS OF HIGH PRESSURE!
1) Heavy hard bolt lift.
2) Ejector marks (small shiny circle marks). on case head
3) Super flattened or pierced primer.
Always carefully check these with any new load.
Better safe than ?$#@^&(*
As JMayo said KNOW SIGNS OF HIGH PRESSURE!
1) Heavy hard bolt lift.
2) Ejector marks (small shiny circle marks). on case head
3) Super flattened or pierced primer.
Always carefully check these with any new load.
Better safe than ?$#@^&(*
dellet
Gold $$ Contributor
This might be a good start, a good look at the basics.
riflebarrels.com
A Look at Bolt Lug Strength - Lilja
All action designers are concerned primarily with producing a safe and functional product. All other considerations such as weight, finish, eye appeal and other cosmetics are secondary. From a safety standpoint, the strength of the bolt lugs is of prime concern. Bolt lug shear strength depends...
jackieschmidt
Gold $$ Contributor
you might be correct, considering the lugs and their abutments are the thickest linear portions of the action.
But you can sure get enough in to split the receiver. There are numerous examples of this.
Explosions generally follow the path of least resistance.
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This is a perfect example of how not to measure bolt thrust or excessive pressure. Know your signs of excessive pressure by measuring head diameter from the beginning with new brass. Find what is maximum for your rifle, .0008" head expansion is maximum! When you get to hard bolt lift you have gone past max and you are not going to save that brass without a considerable amount of needless work. Go to Hornady website for a clear explanation of how to measure excessive pressure. Sorry that is the Hodgdon web.site
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That,s something I would not say. Tommy Mc
I am quite sure some overachiever could get it done! Be careful and don't be that person!!
Paul
JSH
Gold $$ Contributor
I forget who did some test on what we deemed pressure signs. They used one of the epoxy on strain gauges. The “signs” many believed to be start of high pressure were way higher than what was always believed.
Then there were no constants. Pressures were through the roof, bolt lift was normal brass showed no visible signs or measurable signs of pressure.
I have been bashed on this subject before. By gosh and by golly attitude towards what we guess as pressure is just that a guess, no more no less. Unless there is some piece of equipment hooked to your rig for measuring pressure, it’s just a guess.
Look at the 280AI. When it was a wildcat it did some amazing unheard of things, all with “no pressure signs”. So for years it was deemed safe and many folks used it with no ill effects. Fast forward a number of years and it was legitimized. But to get it to pass SAMMI spec it had its “teeth pulled” and does little over its parent cartridge.
Then there were no constants. Pressures were through the roof, bolt lift was normal brass showed no visible signs or measurable signs of pressure.
I have been bashed on this subject before. By gosh and by golly attitude towards what we guess as pressure is just that a guess, no more no less. Unless there is some piece of equipment hooked to your rig for measuring pressure, it’s just a guess.
Look at the 280AI. When it was a wildcat it did some amazing unheard of things, all with “no pressure signs”. So for years it was deemed safe and many folks used it with no ill effects. Fast forward a number of years and it was legitimized. But to get it to pass SAMMI spec it had its “teeth pulled” and does little over its parent cartridge.
Bolt thrust is not bad or good it is a part of the physics of firing a cartridge in a chamber.
Zero reason to be concerned about it, you have no way to accurately measure it and as long as you stay with reasonable loads its a moot point.
On modern rifles If you get to the point of setting back or even shearing the lugs the case head would have failed way before that.
Zero reason to be concerned about it, you have no way to accurately measure it and as long as you stay with reasonable loads its a moot point.
On modern rifles If you get to the point of setting back or even shearing the lugs the case head would have failed way before that.
Scientifically correct. Practically? Not so much.
Bolt thrust is not a concern unless you are designing the sections of an action, or trying to fit a cartridge to an action that wasn't designed for it.
A closed bolt is the strong part of the action.
Cartridge pressure is more of a concern, because it acts radially outwards between the bullet and the bolt face, pushing the chamber apart from the inside. The chamber is much weaker than the closed bolt, so it blows up first.
A closed bolt is the strong part of the action.
Cartridge pressure is more of a concern, because it acts radially outwards between the bullet and the bolt face, pushing the chamber apart from the inside. The chamber is much weaker than the closed bolt, so it blows up first.
In my - unlearned - opinion, lube is not going to help overcome the radial force of cartridge expansion in the chamber to permit the entire cartridge to slide backwards on ignition.
If that was possible, all we have to do to avoid case head separation is lube the cases.
The closed bolt in the action forms a pressure vessel with the chamber. The weak point is the chamber wall.
I'm not sure what the use case could be where it becomes practical to worry about bolt thrust before chamber pressure.
DaveTooley
Gold $$ Contributor
Mike Walker couldn't do it when he first tested the action at Remington.
DaveTooley
Gold $$ Contributor
There is almost no chance of shearing the lugs off regardless of chamber pressure. The brass case acts as a safety valve. It ruptures reducing pressure before the bolt thrust exceeds the amount of pressure required to shear lugs. I have some examples of serious "Oh Sh_t what happened" in the shop and there was never an indication that the lugs moved. I had a Rem 700 22-250AI that the guy tried to blow up. Bolt nose was pretty much gone, chamber expanded .009". A new bolt and a barrel setback and it was up and running again.
I had one rifle come through the shop that I knew had had a steady diet of very high pressure rounds over the span of several barrels. The bolt lugs were fine. The action lugs had been set back/deformed to the point of intruding into the bore of the action.
I had one rifle come through the shop that I knew had had a steady diet of very high pressure rounds over the span of several barrels. The bolt lugs were fine. The action lugs had been set back/deformed to the point of intruding into the bore of the action.
I have never seen a bolt fail where the chamber/reciever itself didn't blow first. That wasn't a function of rearward thrust, you can calculate that. You'd never generate enough force to shear lugs before the pressure is so high the chamber gives.
Looks like we're talking bolt actions so far.
An AR15 is a different story altogether. There are numerous examples of bolt failures in them. Ironically
,max load data for them is adjusted by the same factor as bolt thrust increases. IOW, a larger case head ID generates more thrust than a smaller one, at the same pressures. i.e....Grendel or ARC vs 223. If you calculate the bolt thrust for both, they are pretty much the same...at max recommended pressures for each. If you try to run a Grendel at 223/556 chamber pressures, bolt thrust is considerably higher and is how a lot of A15 Grendel bolt failures happen, in the first place. People try to load a Grendel or ARC to 556 pressures without accounting for the additional bolt thrust of the larger cases. Works fine in a bolt gun, so it's not the cartridge, but the AR15 platform's limitations for handling that additional bolt thrust. It's also not the thinner rim around the bolt itself. It is bolt thrust.
Just my 2 cents.
Someone already posted a link above to Dan Lilja's site/article on bolt thrust and how to calculate it if you want to confirm or play with the numbers a bit.
An AR15 is a different story altogether. There are numerous examples of bolt failures in them. Ironically
,max load data for them is adjusted by the same factor as bolt thrust increases. IOW, a larger case head ID generates more thrust than a smaller one, at the same pressures. i.e....Grendel or ARC vs 223. If you calculate the bolt thrust for both, they are pretty much the same...at max recommended pressures for each. If you try to run a Grendel at 223/556 chamber pressures, bolt thrust is considerably higher and is how a lot of A15 Grendel bolt failures happen, in the first place. People try to load a Grendel or ARC to 556 pressures without accounting for the additional bolt thrust of the larger cases. Works fine in a bolt gun, so it's not the cartridge, but the AR15 platform's limitations for handling that additional bolt thrust. It's also not the thinner rim around the bolt itself. It is bolt thrust.Just my 2 cents.
Someone already posted a link above to Dan Lilja's site/article on bolt thrust and how to calculate it if you want to confirm or play with the numbers a bit.
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