277 Fury Pressure and modern components - WAS: Impact of shoulder vs nut on strength/max pressure capacity

I attempted a search on this and became a bit frustrated with the nut vs shoulder argument. I'm not looking for any recommendations one way or the other. What I AM looking for is an engineering and/or scientific data driven view or analysis of if one design vs. the other can inherently handle more pressure than the other and if so, by what percentage. Also, not looking for opinion only. Hoping to hear of actual test/experimental or analysis results that would provide useful feedback.

Does anyone know if there have been any studies that show a shouldered barrel can handle more pressure than a barrel nut setup or vice versa?

NOTE: Assumptions are:
1. Using the same action for both setups
2. Using identical barrels for both but ignoring potential weakness in one vs the other due to material/strength variations

If you want to debate the pros/cons of the 2 designs, that is not the intent of this thread - thank you in advance for respecting this.

Consider this. The max chamber pressure from saami you will see on any round is about 65k. 6.5 creed is 62k 300 Rum is 65k. The brass is the limiting factor as it is the pressure containing envelope.

Thanks Cajun - this is historically accurate.

The 277 Sig Fury now has a hybrid case with brass body/shoulder/neck and steel head with a saami max of 80,000psi. Because of this, and because traditional bolt actions have not been leveraged in this way, I am looking to gain the knowledge of how a shoulder vs a barrel nut will impact the max pressure a given action can handle.

nkyshooter said:

Thanks Cajun - this is historically accurate.

The 277 Sig Fury now has a hybrid case with brass body/shoulder/neck and steel head with a saami max of 80,000psi. Because of this, and because traditional bolt actions have not been leveraged in this way, I am looking to gain the knowledge of how a shoulder vs a barrel nut will impact the max pressure a given action can handle.

Click to expand...

I will also say that savage uses barrel nuts on all their actions even magnums. I'm not an engineer but my redneck self would think a barrel nut set up will handle anything you would do. Also with barrel nut setups the normal recommended torque is 45-60 and shouldered barrels it's usually higher fwiw. Typically the nut versus shouldered barrels comes down to esthetics. Some folks don't like the looks of the barrel nut. Now we can have another conversation about shouldered or nut prefits versus machined barrels installed by a gunsmith. I can think of no reason why a prefit with a nut would have any pressure limitations versus a shouldered barrel.

A quick Hoop stress calculation will give you the numbers. The tenon will be the weakest point and equal between the 2. The smaller OD of the nut barrel will be less than the shoulder. The Sig case helps due to the stronger head.
Might ought to look at bolt thrust also.

I guess I'll chime in since I've done some pretty extensive FEA on this-

Bolt thrust is more active in the ability of an action to handle pressure than the tenon seating method. The barrel experiences far more hoop stress (radial) than angular when firing. The bolt, on the other hand is the point in the system that contains the chamber pressure along the barrel axis. I haven't been able to do a good model of the Fury yet since I don't have any cases to section, model, and apply metallurgy properties to. That being said, as Cajun mentioned, brass is the weak point in traditional cartridges. I'm thinking the Fury may actually increase bolt thrust above what a brass case does due to the steel case head not having the same elastic expansion/ tension in the firing process.

The first time I read about the fury, I wondered if they had special bolt heads adapted for the increased bolt thrust.

cajun said:

I will also say that savage uses barrel nuts on all their actions even magnums. I'm not an engineer but my redneck self would think a barrel nut set up will handle anything you would do. Also with barrel nut setups the normal recommended torque is 45-60 and shouldered barrels it's usually higher fwiw. Typically the nut versus shouldered barrels comes down to esthetics. Some folks don't like the looks of the barrel nut. Now we can have another conversation about shouldered or nut prefits versus machined barrels installed by a gunsmith. I can think of no reason why a prefit with a nut would have any pressure limitations versus a shouldered barrel.

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Savage actions (and other actions Zermatt/BHA, Aero Precision Solus, etc..) have a hole (I have seen it referred to as idiot hole, LL ) in their actions that might help reduce/relieve internal/chamber pressure.

The fury pressures were designed to work on a different barrel/bolt design than a standard bolt action.

Their design is similar to an AR where the bolt lugs lock into the barrel extension ( which is screwed/torqued to a shoulder) --- thus taking all the pressure off of the action completely.

People are chambering bolt action rifles in the fury cartridges but so far, I'm not sure any bolt action manufacturer has acknowledged that their action design is "safe" with the 80000psi cartridges--- I know gun smiths are doing it but it's kinda like doing a wildcat at this time--- I'm not sure anyone has done the appropriate destructive testing to find fail points/swl with the new cartridge/action designs.

I know people have done the calculations based on prior destructive/swl 65000psi testing but it seems to be theoretical/mathematical at this time.

Savage has two different tenons a small shank and a large shank. The large shank of course would have more radial strength.

I would think if I was going to chamber a high pressure cartridge I would go with the large shank.

Case in point, how many barrels have you seen ruptured/cracked/distorted at the barrel shoulder or barrel nut?
The action will let go well before damage to the barrel occurs, unless a catastrophic barrel obstruction is the cause of the excessive pressure event.
Is there a difference between the 2 mounting systems and their ability to handle pressure? Yes, thinner metal is weaker than thicker metal, that IS the only difference…

Cheers.

cohunt said:

The fury pressures wete designed to work on a different barrel/bolt design than a standard bolt action.

Their design is similar to an AR where the bolt lugs lock into the barrel extension ( which is screwed/torqued to a shoulder) --- thus taking all the pressure of of the action completely.

People are chambering bolt action rifles in the fury chambering but so far, I'm not sure any action manufacturer has acknowledged that their action design is "safe" with the 80000psi cartridges--- I know gun smiths are doing it but it's kinda like doing a wildcat at this time--- I'm not sure anyone has done the appropriate destructive testing to find fail points/swl with the new cartridge designs.

I know people have done the calculations based on prior destructive/swl 65000psi testing but it seems to be theoretical/mathematical at this time.

Click to expand...

Modern actions are built/designed to withstand 200,000psi pressures without breakage.
Catastrophic failure at less than 200,000psi occurs from detonation which the action cannot handle due to speed of max pressure rise. Handling NORMAL pressure, not sudden explosive detonation, at or beyond 80,000psi is of no concern. In fact many handloaders are pushing the boundaries of 100,000psi without even knowing it…

Cheers.

Those little vent holes in the side of the action and bolt body are very important, if/when there is a case rupture. Otherwise, all those gases end up in your face, made worse by a cone head bolt.

A quick trip to SAAMI finds the following on each page of the Spec.

WARNING:
Maximum Average Pressure levels greater than 65,000 psi may present increased risk of unsafe cartridge case or firearm rupture and thus require cartridge case and/or firearm designs that depart from traditional practices (materials, construction, and other design criteria).

So there is no misunderstanding the cartridge case actually functions primarily as a gasket not a pressure vessel where the case expands into the chamber to seal the chamber. The barrel provides the pressure containment. The only portion of the case that is structurally pressure containing is the case head where it must contain the hoop (radial) stress in the unsupported portion of the case and the axial (longitudinal) expansion of the case/head junction during firing.

In the case of the hybrid cased Fury the stainless case head is used because the thickness of brass required to contain the pressure would be excessive. The balance of the case is similar to normal cases.

Sig currently markets both hybrid case and conventional case ammunition which begs the question as to what pressure the conventional case ammunition is loaded to. To add to this they haven't released any 277 Fury rifles to the civilian market but have released those intended models in conventional calibers (6.5 CM and 308 W). Kinda makes you wonder where all this is headed.