.155" is .030" over 1/8"(.125") and - .095" less than 1/4" or am I missing something here. .032" difference is closer to 1/32", not 1/8", which is actually 0.125". Quarter inch is .250".
: Even at these measurements, I am sure they are plenty strong enough for moderate loads.
: The muzzles, of course, can be very thin as the pressure at that point is very low with normal loads. I've seen in print that even the quite slow burning IMR 4831 developes it's gross(max) pressure at 13" from the breech in rifle barrels. Faster powders develope their max pressurs much closer to the breech, hense normal contours are safe.