may not work.

At another location in this forum I started a thread with an inquiry about converting a Stevens .32 Long RF to some CF version so I could find/make my own ammo and actually shoot the thing. I had just purchased the rifle, but had yet to receive it. Furthermore, I had never owned or shot a Favorite. My question asked specifically about "max chamber pressure", and the answers were in that context.

Lotsa folks - one exception - stated unequivocally that this conversion was a "bad idea". All -  except the one - used "too much pressure" as the reason.

However, when I got my hands on the rifle, it was patently obvious to me that the rifle's receiver and barrel were MORE than adequate to handle ANY pressures I was interested in subjecting the rifle to once converted. The cartridge I was interested in to start with was the .25-20 SS. I was completely happy keeping the chamber pressures down to 20,000 PSI or less. 20,000 PSI being a full 30% lower than the 26,000 PSI of High Velocity .22 RF cartridges which the Favorite shoots without complaint - at least as far as some said.

Since taking receipt of the rifle, I have had a chance to take it apart and study it and talk with an old friend that has "done it". We get along in large part because neither of us take "because" as a reason for not doing something, so when Paul, (yes his name is Paul too ), says it's a "bad idea", I listen. He pointed out exactly why this conversion would very  likely be ill-fated. While I remain absolutley convinced that the barrel and receiver can "handle the load", and much more in fact, I am equally convinced that the ACTION cannot.

As I held the action pieces in my hands, Paul explained that the issue wasn't "strength" per se, it was "design". The linkage is simply not designed to take much "bolt thrust" without "giving". The action isn't harmed by this. However, "flexing" exposes the head of the cartridge. With a thin-walled case - like a balloon-cased .22 RF - the head may separate or leak gasses.

By this time, I had already designed a very efficient cartridge that I could get a 125-grain bullet doing 1900 f/s at the muzzle and keep the chamber pressure right at 20,000 PSI. Nonetheless, once Paul explained the real problem, I was concerned that even this cartridge would be "too much" for the Favorite. But it wasn't necessary to guess about it as calculating the critical value was simple. To put it in a phrase, the issue is "linkage" but the ruler is "bolt thrust". The linkage design of the Favorite is not geometrically optimized, and is simply too 'loose', to allow use of modern centerfire cartridges. That's NOT criticism, just observation. As far as I can tell the Favorite does just fine doing what it was designed for.

I called the new cartridge the ".32 Honest". Here are the numbers:

For the 32 Honest:
20,000 PSI chamber pressure,
0.440" head diameter.
Head area = 0.152 square inches.
Bolt thrust = 0.152 * 20,000 = 3041 pounds. (Head area * chamber pressure).

For the .22 RF:
26,000 PSI chamber pressure,
0.270" head diameter.
Head area = 0.018 square inches.
Bolt Thrust = 0.018 * 26,000 = 1488 pounds.

The "Honest" has essentially twice the bolt thrust of a High Velocity .22 RF. (WRT "bolt thrust" in the absolute, I'm not going to get into how "sticky" the chamber walls are, or whether the case is "tapered" or "bottle-necked". For an exercise in which we're looking for a generalized comparison, considering individual variability between components is inappropriate.) 

Based on these numbers, it doesn't look good for the CF cartridge. It appears, that since metal strength is really not the issue with the Favorite action, the "ceiling" which any "new" potential cartridge must fall below is something like 1500 pounds of "bolt thrust". Even that - 1500 pounds of bolt thrust - is apparently the absolute max figure, as lotsa folks have complained that the Favorite can't really handle a High Velocity .22 RF without flexing.

So...

Thanks to those that took the time to read and comment on my other posts. Truly. I've learned a great deal so far.

Maybe this post will provide some quantitative support for any future queries about the "reasonableness" of converting a Steven Favorite chambered for a rim-fire cartridge to center-fire. Or... AS I'm relatively new here, maybe this has already been pointed out but didn't make it into the other thread because it is "common knowledge". Anyway, now it's my "common knowledge" too.

Thanks,
Paul

There is one other factor that I was taught a long time ago to consider when deciding whether to convert or build a rifle.  Never build a rifle for how you will shoot it, always build it for how the next guy will shoot it.

Thanks fellas.

The demilled .303 barrels is interesting, and opens the door for me to relate what my line of thinking was as I was 'scheming' about the favorite.

First, the fact that ".32 caliber" rarely actually means .32 caliber kinda annoys me. (But then so do a number of other 'trivial' things too.) Nonetheless, as I was looking at potential bullets, I of course found a much better selection of .323" bullets than .312" or .313". That in turn got me to thinking about .323 barrels, and I quickly realized that I have many Mauser 98 take-off barrels. I can't bring myself to throw them away, but I haven't found many good uses for them either. That is "til now. A Turk '38 starts out at 29", and has plenty of meat to end up with a 24" half-round/half-octagonal Favorite barrel. Of course, now, that's not a viable idea for chambering in a CF cartridge, but...

This whole issue of "linkage geometry" has my 'gears turning' (No pun intended.) I'm going to spend some time looking at the Favorite action, and seeing if I can come up with a design that will allow a nice modest-pressured cartridge to be used in a "Favorite-esque" action. I have found a source of reasonably priced 4140 bar stock, and have been itchin' to make a single-shot receiver. The Favorite seems, at least at this first blush, a good place to start. I'm also considering a rolling block, but I don't have one of those in my hand... yet.

Thanks again,
Paul

For what its worth, when figuring total bolt thrust the proper way to calculate it is by using the largest 'inside the case' diameter. This is what the internal pressure 'pushes' against.

Bolt thrust for a .312 dia. @ 20000 PSI# is 1529 pounds.*
Bolt thrust for .22 rf @ 26000 PSI is 1276 pounds. **
 * Assuming a straight case.
 ** Not sure of the inside dia. of the rim cavity, I used .250