Not trying to hi-jack your thread, AtlLaw...just add my tuppence and what was happening to me while I was mucking about.
Got the chamber reamed...it came out much better than the 45-100 rechamber...usually does when things go right and Murphy stays away.
Right off the I saw I needed to throat... the chamber would only handle the 720 gr T-Rex at 3.90" COAL. I ordered the throater this early this am...isn't the net wonderful.
The brass came in yesterday and I also found out quickly that the Norma rim is thinner than all the other 45xXXX brass by about 0.005"...I had the headspace set for 0.005" just in case I ran across rims that were thicker not expecting the opposite to happen, so with the Norma brass it is an excessive 0.010"...should have know Murphy was hanging around somewhere.
Not to worry...when the throater comes in I will face the receiver then install a shim.
I got started on load workup this am and as usual Murphy was buzzing around like flies on a pigs behind, bees on honey and skeeters on a hot body...in other words I had one Murphy after another trying to get my 45-70 Lyman dies set up for loading the 3.25" case. Again...no sweat...just needed a swatter and a little lathe time.
I did fire off 4 rounds...weighed one at 130 gr H20...all the information I have on the 45-120 cases ranges from 113 to 131 gr of H2O...Ty:...this is the reason I don't take information at face value...I/you/we ALWAYS need to check sources and do your own measurements on your own equipment...way too many ways of messing up in this "wildcatting" thing of ours or even reloading the "standards".
The first load I fired was calculated on the 113 gr H2O weight so if the case had a larger volume it wouldn't cause a problem. I used H4895, a 430 gr TRUSHOT bullet, WLR primer, seated to the crimp groove - 3.65" COAL...starting load was 75 gr calculated to be 2100fs at 38KCUP using Load from a Disk 5...after weighing the case and finding it was 130 H2O I recalculated it a ~2000 fs/33KCUP...quite a difference in velocity and pressure.
I fired 3 more loads of H4895 at 5 gr increment increases...starting at 80 gr and going to 90 gr where the case stuck but popped out when it cooled slightly...still the sticking is the stopping point...could have been the sizing wax not getting completely wiped off or could be the extra headspace and the load near the top...I will check it out again when I finish the throating, facing and shimming.
Calculated velocities are - ~(approximately) 80 gr, ~2150fs/38KCUP - 85 gr, ~2300fs/43.5KCUP, 90 gr, ~2450fs/49KCUP...with the throating this will change because of the jump of the 430gr bullet...basically a 0.600" free bore.
The 85 gr load produced ~25-47 ftlbs of recoil...with and without the muzzle brake...5000 plus ft lbs of energy...not too bad for an old girl that's been around for a long time...and still has lots of life in her. There is some wiggle room here depending on the powder used and all the usual factors. This load and bullet would work for ANY game on the planet as long as the bullet was placed right.
I didn't think the recoil was very bad, but I shoot a lot of heavy calibers and don't start getting jumpy until the slap is up around 100 ft lbs.
Here is a pic...I will need to reblue the barrel and blue the brake due to having a solid finger steady rest, not one with rollers.
I did some calculations using the 720 gr T-Rex bullet...at 4.5" COAL, 100 gr H4831, 1800fs the recoil runs about 43 to 76 with and without a brake...but the striking energy isn't much more than the 430 gr bullet...~5000 ftlbs to ~5100 ft lbs, (no nitpicking here...the numbers can change depending on which calculator you use and it is only a close approximation) but the recoil is about twice as much.
The reason is that striking energy increases at the square of the velocity but only increases directly proportional to the bullet weight...in other words going to a bigger slug doesn't get you as much as going to a higher velocity...the good old E=MCsquared thingy...and the reason the high velo rifles get all there oomph...there is a point of balance between velocity and bullet weight for each caliber but finding it can wear out a barrel before you get to hunt with it.
The brake does work and doesn't cause any ear problems as long as you have ear protection, but you get a puff of air and smoke from it as always. Lots of difference between 25 ftlbs and 50 ftlbs of recoil...and going to the 720 gr bullet REALLY makes a difference...up into the 85 ftlb range a 1900 fs without a MB and just below 50 with the brake...
Anyway...it would be nice if others with a BC did this rechamber and posted their experiences.
Luck on your projects
