Can a Carbon Fiber Shouldered Barrel be installed with muzzle flats?

[CMP70306]

Hello All,

I know people machine flats on the muzzle of steel barrels so they can torque them on without removing the action from the stock. However I have yet to see it done with a carbon barrel and I was wondering if it was even possible or would it cause stress in the carbon wrap that could lead to failure?

 

[Shankin]

I’m thinking it would fail. There was a thread started not long ago that was taking about install/removal of carbon barrels, and if I remember correctly, it was said that a barrel vise was required, and that it would need to be locked down on the steel shank nearest the receiver, otherwise the epoxy would crack and fail.

Carbon barrels in barrel vise

 

[TheShooter]

I wouldn’t do it. In fact, I would not do that on a traditional barrel either. If you want flats for easy barrel removal, put them near the breech. Barrels are installed tight. That means you have to apply a lot of rotational force to install. What are the odds that you will be able to keep that force completely along the axis of the barrel? This is exactly the same as putting your action in the vice and hanging on the end of the barrel. I assume you would not want to do that either.

From a pure rotation perspective, a traditional barrel would be fine. However, if the carbon fiber was not perfectly bonded to the barrel, you would have the steel rotate within the carbon fiber sleeve, breaking down the bond and defeating the purpose of the carbon fiber in the first place.

I could say a lot more (I have a masters in structural engineering), but hopefully you get the point.

 

[PinesAndProjectiles]

If you want to easily change barrels, use a Bar-Loc or barrel nut.

I would never rely on the muzzle end for installing or removing a barrel.

 

[CMP70306]

If you want to easily change barrels, use a Bar-Loc or barrel nut.

I would never rely on the muzzle end for installing or removing a barrel.

Currently using both of those methods however the barrel nut requires a vise and I’ve been having some POI shift issues with the barloc that I haven’t quite nailed down yet. However since I’m getting ready to start buying parts for a hunting rifle build I figured I’d consult the experience here on the topic before I dove in only to find out there was a better mousetrap.

 

[CMP70306]

I wouldn’t do it. In fact, I would not do that on a traditional barrel either. If you want flats for easy barrel removal, put them near the breech. Barrels are installed tight. That means you have to apply a lot of rotational force to install. What are the odds that you will be able to keep that force completely along the axis of the barrel? This is exactly the same as putting your action in the vice and hanging on the end of the barrel. I assume you would not want to do that either.

From a pure rotation perspective, a traditional barrel would be fine. However, if the carbon fiber was not perfectly bonded to the barrel, you would have the steel rotate within the carbon fiber sleeve, breaking down the bond and defeating the purpose of the carbon fiber in the first place.

I could say a lot more (I have a masters in structural engineering), but hopefully you get the point.

That was my concern as well, since the carbon is simply bonded in place to put tension on the muzzle and chamber end of the barrel for stiffness rather than becoming a part of the steel itself (like stelite) my concern was that applying the rotational force required to tighten the barrel on the muzzle side would twist the steel barrel inside of the carbon fiber shell thereby destroying it.

I have a bachelors in mechanical so I understand what your saying. I didn’t think it would work but since I don’t know their entire manufacturing process and there is always the possibility of learning something new I wanted to run it by here to check.

Plus I’d prefer to not spend the $1000 a shoulder barrel would cost to test it myself in the event of a failure.

 

[Ledzep]

Just doing some simplistic by-hand calculations sigma= Mc/I and tau= Tc/J, von mises equivalent uni-axial stress and ignoring transverse shear for a steel cylinder that has a .3" diameter thru-hole and a .550" OD (These are merely my guesses on the steel under the CF wrap for a .308 barrel) shows that 50 ft-lb applied at the muzzle doesn't have a chance at yielding the stainless steel liner. Obviously there are some simplifications to the loading scenario and it assumes that a perfect 50lb is uniformly applied to an exactly 12" wrench... But I'm getting about 3000psi being the highest point of stress present-- well within the linear elastic region of the material (again, with the simplified assumed loading scenario). Another thing to consider is that it can take considerably more torque to UNscrew a threaded part than it took to originally install it. 30 ft-lb on could end up being in excess of 100 ft-lb off, especially if corrosion is involved.

My biggest fear would be the twisting of the steel liner exceeding what the bond between the CF and steel can handle. However, I'm not really knowledgeable enough with composites, and have no idea what resin/epoxy Proof and others are using. It'd be inappropriate for me to take a stab at that problem.

My gut feeling is that the barrel would handle it just fine. Putting flats closer to the breech (while maintaining a safe wall thickness) would generate lower stresses in the barrel and pose less risk of twisting and bending, though. Even a couple shallow drilled spanner wrench holes might suffice, and depending on the optic/stock could still allow for barrel changes without further disassembly.

 

[sjc929]

I can tell you that the Proof CFW prefit barrels for AI rifles come with the flats machined on the muzzle end of the barrel as standard from Proof. Obviously, these are primarily for the Quickloc AI actions, so most people won’t be applying any large amount of torque to them, especially compared to someone using a conventional action/barrel interface where the torque is the only thing locking the barrel in place. That said, these same barrels are also sold for the old AE and AW rifles. Based on this I can only assume Proof considers using the muzzle flats as a safe way to torque the barrels on, and I don’t remember any instructions that came with mine saying anything about not using them if installing on the older actions with traditional high torque. I’m not saying it is safe to do it, just that I have seen it done. I’ve never heard of anyone claiming to have destroyed their Proof prefit by using the flats to install the barrel.