30-06 rims breaking

[swampratt]

I feel lubing the round is a terrible idea..
If you lube it ..the lube will be transferred to the chamber..then when you fire another round any dirt on that next round will transfer
...it will soon be like a lubed mess of dirt dust and carbon..and you create a liquid grinding compound..
You want a loose chamber that is a good way to get one...
Initially it may seem like a good idea...

I have picked up a few winchesters at the range and your issue is shared with others...

 

[Blitzfike]

Try lubricating the rounds before you fire them.

Lubing the chamber is NOT a good idea. Part of the equation of containing the pressure of firing is for the case walls to grip the chamber. Lubed chambers or overly lubed cases increase the pressure on the bolt face.
The rotating bolt on the 742 is one of the weak spots. The bolt doesn't have solid locking lugs, it has a series of thinner lugs that tend to break over the years. Also, high pressure rounds cause the bolt to dig into
the rails in the receiver. Parts for the 742 are extremely hard to get. The difficulty in cleaning the chamber is the cause of most of the deterioration in it. I have owned several over the years, 30-06, 243, and 308.
I made a chamber brush for them by pouring lead into a 1/4" drive socket to hold the brush in place. I then used a small ratchet to turn the brush with a flex extension. Short of disassembling the receiver (which is
a real pain..) this is the easies way I have found to keep the chambers clean on these fine old rifles. (I made a short piece of flat stock to wedge into the operating rod to hold the action open for cleaning.) My experience with these says your main problem is a corroded or rusty chamber, but the higher pressure ammo
is a really bad thing for this rifle.

 

[okietom]

Well I've never had this problem before until this year. I have such great results with Winchester, I'd hate to switch. I had to switch bullet weights out of necessity (they were completely sold out of my usual 150-grain), but I don't think bullet weight from the same manufacturer and type of ammo would make the difference.

I've contacted Winchester Ammunition about it, but I got an auto-reply that they're closed until Jan 2. Maybe they'll give me some useful information, like a return a credit for another box of ammunition (150-grain) this time. If that doesn't work, I may have to switch ammo. If so, I'm thinking Hornady next.

Boy what I wouldn't give for a reloader!!

Bullet weight makes a lot of difference. You should use the same exact load that you or your gun likes. A different bullet weight will sometimes have a different point of impact than a lighter bullet. What I mean is that you most likely would need to zero your scope with the different bullet. You may be lucky and not have to. Even if the zero is the same the trajectory won't be. Shooting at a distance will change.

The different weight bullet will need a different powder charge too. That is where your problem seems to be. I agree that it looks like high pressure.

Go back to the 150gr. loads.