Hand tight switch barrel accuracy?

[GLTaylor]

I have 2 receivers fitted with the WTO switch lug device. One std bolt face, one mag bolt face. Have 6-7 barrels for them (diff calibers). Change them using a strap wrench. Had my smith put a witness mark on each receiver so i could feel good about them going back in the same place.
So far no problems, rifles shoot very well and consistently. Lubricate each barrel shank rach time i change one.

 

[MagnumManiac]

Race engines, which I build by the way, are a totally different environment to a rifle barrel.
There is virtually zero stress applied to the threads of an action/barrel.
Sure, there is torque applied by the rotation of the bullet and there is vibration. This is for milliseconds.
A race engine has reciprocating masses that change direction, this is WHY head studs require lube under the washers, they actually move.
Also, stretch used to determine pre-load on a rod bolt or head stud is because if it isn't pre-loaded, it will shear if left without that preload.
Stress risers are many on exposed threads, rolled threads, such as those employed by ARP, are far more reliable due to the rolling process compacting the steel rather than cutting and removing it, just like forging does the same thing.
Anyway, there is no need to pre-load a barrel tenon in the way you're thinking.

Cheers.

 

[Alex Wheeler]

At the levels we are torquing a barrel, we are not stretching it the way we do in an engine. Its very easy to tell if a main cap in an engine is moving, you can see fretting between the block and cap. Totally different animal. On a barrel we just need to make sure it doesnt move under the loads it sees, not the loads an engine fastener sees. The torque is some what irrelevant in my opinion so long as we achieve that goal. I build mostly BR rifles, I do not use a torque wrench. But I do have a good feel since I was a mechanic for 15 years. I am in the 75ft lb range. When you get down low enough that it hardly takes any force on the wrench to break the action loose, Id say less than 30 you will start to see fliers. Theres just no reason to flirt with those low torque levels, and no one changes barrels more than BR guys, you will never wear out or hurt an action if the barrels are machined well and lubed correctly.

 

[J E Custom]

I won't argue about if anything is necessary or not, Just present what is the most consistent method for me. I go to great lengths to cut great threads, square and smooth surfaces, Chamber finishes that improve the function of grip and at the same time extraction, precise head space every time so I want the best results when making up a barrel.

While conducting the barrel test, I used a chrome moly receiver and a stainless barrel to avoid the gaulding that can occur when using Stainless to Stainless makeup. To avoid scuffing the threads I used a light gun oil on the threads the first time so the test would have the best chance of being consistent and reprasenitive of any differences. After torquing to 75 pounds I then match marked the barrel to receiver with a zero stamp to get two alignment points and improve the consistency of reading the orientation in degrees.

From then on, a different thread lube was used with a thorough cleaning regiment to remove any existing lube, and then apply the next lube to be tested. Using the match marks an inclinometer was used to measure any differences in rotation. Each lubricant was tested twice for consistency to itself.

The last test was with dry threads (No thread Lubricant) and with the torque the same, it made up with the least rotation and the second test rotated less than the first with some signs of scuffing on the threads. This would likely ruin a stainless to stainless makeup and could/ would gauld and ruin the assembly of the two parts, so dry Is never recommended. using a good thread assembly lube, the assembly of like to like materials showed similar results.

A bit long winded, but a test is only as good as the effort put into it and the results in differences.
There were more parallel test ran to find other differences, Like the amount of torque used, and i will comment on this a little also.

Using less than 35 ft/lbs the consistency fell. using 75 ft/lbs was very consistent with some thread assembly lubes. when we approached 100 ft/lbs of torque we had good consistencies, but encountered some tenon stretch that actually altered head space slightly even though the tenon threads were 1 1/16x16 and the torque was well below the tensile strength of the material. these differences were not a problem but they did prove that there is a point that to much torque can change the loading and is not necessary.

So the procedure discussed earlier Is the way I get the most consistency with all different thread pitches and shank sizes and the assembly lube I use is not affected by heat or solvents So It is my choice for all barrel assemblies even though it may be overkill to some. If I were going to build a switch barrel system I would definitely use this system because of its repeatability.

J E CUSTOM

 

[Greyfox]

Can't say whether it's necessary or not, but I use a torque wrench with a bit of anti-seize in my Bighorn and Savage rifles. Results are "nuts on"....pardon the pun.

 

[ntsqd]

Vibration is vibration; duration, frequency and amplitude determine what the effects are going to be. Not so much the environment where it happens. So yeah, a bolt action rifle isn't an Infernal Combustion Engine (~10 years working in a racing engine machine shop myself), but that doesn't mean that the vibration it sees is any less important.

When I was in high school auto shop our instructor had the burliest guy in the class tighten all of the head bolts on one SBC cylinder head to 100 ft-lbs, as best as he could feel.
He then had a student observe a beam style torque wrench and call out the torque as he loosened each of the those bolts and another student wrote the numbers on the chalkboard.
They were nowhere close to consistent. My now ~30 years old memory of that demonstration is that the torque varied by ±20 ft-lbs. This was a demo that he did every semester, those threads were quite burnished by that point. There would not have been a large difference in all of the surface finishes to have effected the individual bolt's tightness.

His well made point was that you can not tighten by hand with any consistency. I'll go along with the idea that the more that a person does so, the better their consistency will become. But I won't go along with the idea that a person can consistently torque anything to within a specific torque with a narrow tolerance.

 

[MagnumManiac]

As mentioned, I actually do not care what the torque setting is on my switch barrels, witness marks tell me when the barrel is set in place.
Also, as you know, a bolt/nut/stud is a one tightened use. You do not re-use it when tearing an engine down and putting at back together.
I only use studs in the engines I build, bolts just don't cut it.
Anyway, barrels only need to be just tight in my experience.
I switch out barrels during matches every so often when environmentals dictate, I snap the action onto the barrel and have zero issues. In many cases after 100 rounds or so, the barrel will need a vise and action wrench to remove it, they actually tighten past snapped on.

Cheers.