Saftey of rebarreling a Sauer 202 with lug recesses integral to the barrel

[TBerkhouse]

I have done several inquires and gotten differing points of view regarding the safety of doing the following re-barrel. I have received many "gut reactions" but would appreciate any real engineering advice/expertise.

Project summary - install custom barrel chambered in 7mm/.300RCM on Sauer 202 rifle (its barrel has the locking lug recesses built into the back of the barrel (probably something like a Browning BAR).

1. Turn threads off my existing custom barrel (currently 1" diameter threaded section) which will result in .870 diameter; re-thread using 28 or 32 tpi to end up with root diameter of .824-.832. After accounting for the RCM case diameter of .532, that leaves a chamber wall thickness of .146-.150.

2. Cut the chamber area (1.150 OD)and barrel extension (the part with the lug recesses) off the Sauer barrel. Ream out the Sauer chamber area for the newly threaded custom barrel (#1 above). After reaming and threading for the .870 diameter threads on the barrel, that leaves .140 wall thickness for this part.

3. Screw the .146-.150 custom barrel chamber wall thickness and the .140 barrel extension wall thickness together using red Loctite for a total .286-.290 chamber wall thickness.

This entire assembly slides into the aluminum alloy Sauer action and is bolts in with 3 bolts.

Expert/engineer opinions on the safety of this?

 

[John Kielly]

The Australian Sportco/Omark target rifle was built to a similar design back in the 1960s onwards except that the barrel threaded into the action. Subsequently, smiths fabricated units like yours from shot out barrels & later made replacement adaptors.

One issue that was identified was that there was an area where the lugs had been machined out that could be damaged when screwing in the new barrel, depending on how the barrel stub was clamped. As I understand it, the wall thickness was of marginal strength at that point. I don't know if the issue occurred when the new barrel was screwed into the adaptor or when the adaptor was screwed into the action, but I suspect that it was the former - a similar situation to what you propose.

You might like to check those dimensions on the Sauer barrel.

 

[Charles E]

I don't quite fit the bill - expert or engineer -- but will offer this.

After accounting for the RCM case diameter of .532, that leaves a chamber wall thickness of .146-.150.

I'd say not enough for usual pressures. Jim Borden use to offer a case based on the .404 Jeffrery, which has a .543 case head diameter. Worked quite well in a Remington 700, with its 1.062 tenon diameter. With a Winchester 70 (1.00 tenon), he had to cut the chamber larger to keep extraction easy. (Thinner walls expanded enough to exceed the modulus of elasticity of the case.)

And many smiths won't rebarrel a Remington 700 to the Rigby/.338 Lapua chamberings, due to its .580 case head with the 1.062 tenon.

Which suggests that you instincts are right -- you need an engineer to calculate the elasticity of the chamber, and shear load on the lugs, with the pressures you're expecting to encounter.