When this tread started out, I thought Mac was full of it. Of course the frame stretched, every body knows that! The more I have read and thought about it, the more Mac makes sense to me. When the BAT action was compared to a Handi, like Mac said it, apples to grapes, both are fruits, but very different. All of the forces in a bolt gun are straight line. The case pushing straight back into the bolt face. As I have stated earlier; the hinge pin is about .75" lower than the center line of the cartridge. This means that the case is pushing on the breech face and is trying to open the action, not just push straight back. Most of the force is against the breech and the hinge pin, in opposite directions (but not straight). The latch and lug is what is keeping it all from flying open. The forces within the action is 1. pushing against the breech face. 2. the latch pushing down on the lug. 3. the lug front pushing against the hinge pin. 4. The frame holding it all together. There are other things going on too, but these are the major ones going on.
1 yes the breech face is going to deflect, given enough deflection, it will crack.
2 The latch and lug relationship - the latch and lug are more or less a straight line force in the vertical holding the barrel shut.
3. the lug in the front pushing against the hinge pin is not straight line, it is angled from the center line of the case to .75" down to the hinge pin.
4. All of these forces are being held together by the frame, mostly in the area between the breech and the hinge pin.
If you have 50Kpsi pushing on the breech face you will have some where in the neighbor hood of 37.5Kpsi pushing against the hinge pin and 12.5 Kpsi pulling up on the latch. As the breech face pressure climbs so will these other forces. The latch is not vertical, it is angled, but the force trying to let the barrel open is pretty much vertical. If the vertical force becomes too great, it will deflect the latch/lug enough to move the lug up the face of the latch. There is much force trying to push the hinge pin through the front of the frame, but the lug that rests against it will crush down, just as the breech face deflects. The lug is soft in relation to the the frame. Soft metal is more putty like than hard metal. As the lug crushes against the hinge pin, it lets the back of the lug ride up the face of the latch, opening the gap in the barrel/breech face. As the pressure increases; the more giving to the lug, thus more barrel opening, or flex. In most cases the lug springs back into it's original shape. In severe conditions, it crushes down and does not return to it's original position. When this happens the integrity of the barrel lock-up has been compromised. Breech face cracks occur when the pressure is so high it deflects it beyond it yield point. Remember these forces are not applied slowly, they are violent. How the gun is held makes a difference it the over all scheme. Think of a sledge hammer(case) hitting a concrete block(breech face). If the block is setting on a concrete slab(mechanical holder) the hammer(case) is going to do more damage than if the block was setting on top of 4" of high density foam(your shoulder), floating in the air(nothing in back of you).
It was suggested that the lugs are the same on SB1 frames and SB2 frames. This is true, but the SB2 frames have been heat treated to make sure they do not deflect. If you have an SB1 frame it will deflect right along with the lug and latch and breech face. This increases to the point of unacceptable and may actually damage the frame.
The latch/lug deflects, the breech face deflects, the lug front deflects against the hinge pin. This is going to happen! And this is where the the gun gets it's flexible reputation from. How much all of this happens depends on how much breech face pressure it sees. The frame is not flexing or stressing or yielding or anything else for that matter, it is all in the other relationships. Even a 22 hornet will set these forces into action, but it so small that it is barely noticeable. As the cartridge intensity goes up, the deflection goes up. I am talking the deflection of the lug, breech face and latch. It depends on how intense the cartridge is to how much deflection is taking place. in some cartridges/loadings, full length sizing is needed every time because the case was let to be stretched enough that the next time it will not be able to be chambered and shut. This is reaching the outer limits of the action.
I have covered a lot of ground here. Mac I hope I have told the truth here of what is happening. I did this as much to clarify for me what is happening as much as anyone else.
