PDA

View Full Version : 45-70 chamber & bullet configuration



leftiye
01-18-2007, 07:17 PM
I recently got an NEF Handi Rifle cal. 45-70. Way back, I had a Marlin 1895 which I got rid of due to recoil, and because it can't shoot as far as I can see- which is a ways out here (I was young then). So I plan to use cast boolits mostly, and try to come up with a round nose hollow point gas check soft lead load about 400 grs.boolit/ @ about1400 fps. which will expand reliably. I've researched a little, and found several loads that are supposed to achieve 1400 fps. while producing around 15000 CUPs with a 400 grainer.

First off, I did a chamber cast. No freebore, no leade. Case ends, rifling begins. I can see that with a repeating rifle this might be one way of doing it (what with operating length), but it still wouldn't be the best even there, especially with a .486 chamber neck area. What keeps the boolit straight on, and concentric as it engraves? (nada) So the first question becomes "how much throat/ freebore"? About an hour later I ordered a throating reamer from Brownell's (.460 throat, 2 degree included angle).

I'm somewhat obsessed right now with keeping the boolit straight on as it begins it's journey, and supporting the (soft) boolit against obturation as ignition occurs, and it transitions into the rifling. Would seating the bullets just barely (don't read too much into this) into the cases, and letting them jump .100" or .200" into the leade whilst contained in a freebore the same length as the cylindrical portion of the boolit work? It looks to me as if- what with the soft lead, a boolit with a short nose, goodly length bearing area, and fired with a low pressure load it might just do. Plus if we set it up for 300 grain boolits with a .500" long freebore, it might work well for 400 grainers (maybe 500 grs. )too?

Your ideas and advice will be appreciated. Ted

Scrounger
01-18-2007, 08:57 PM
Get the Lyman 457122 which is a 330 grain hollow point bullet. It is plain base but at 1400 FPS that shouldn't be a problem.

Bass Ackward
01-18-2007, 09:51 PM
First off, I did a chamber cast. No freebore, no leade. Case ends, rifling begins.
So the first question becomes "how much throat/ freebore"? About an hour later I ordered a throating reamer from Brownell's (.460 throat, 2 degree included angle).

I'm somewhat obsessed right now with keeping the boolit straight on as it begins it's journey, and supporting the (soft) boolit against obturation as ignition occurs, and it transitions into the rifling.

Would seating the bullets just barely (don't read too much into this) into the cases, and letting them jump .100" or .200" into the leade whilst contained in a freebore the same length as the cylindrical portion of the boolit work? It looks to me as if- what with the soft lead, a boolit with a short nose, goodly length bearing area, and fired with a low pressure load it might just do. Plus if we set it up for 300 grain boolits with a .500" long freebore, it might work well for 400 grainers (maybe 500 grs. )too?

Your ideas and advice will be appreciated. Ted

Ted,

If you established your maximum velocity level to avoid recoil, then your enemy is case capacity and poor ignition. Why would you want to throat out unless it was to gain case capacity? You can simply taper the end of your rifling with that 2 degree reamer and seat up against it. The cartridge will remain centered.

If you wanted a ball seat area, I would just kiss it enough to allow the bullet to snug up and hold the front of the case in what appears to be a large or sloppy chamber. Something on the order of .050 MAX. Personally, I would have chosen a .462 throater myself to just angle the entrace to the throat. Then your loaded rounds would come closer to sealing your chamber. But this would involve custom molds and sizers.

Right now you can simply taper the end of the rifling and shoot what ever factory mold you want. But why not test it a little at a time and tell us what YOU think. You own the reamer now. Just start and play with it until you see how it performs. Remember, once it is cut, it's gone for ever.

leftiye
01-18-2007, 11:05 PM
I forgot to mention that the groove dia was .458, as it should be. It sounds good to me to start by conforming to all of the standard practices as much as possible. this goes to .459, or .460" freebore, and bullet diameters. I already have the Lyman 457122, and that's where the .500" freebore idea came from. I feel that the way-oversize case neck area might be a problem to initial bullet alignment. That was the main purpose in creating a throat ( also to control bullet deformation). I understand that even 4831 burns well enought to fill the case and get this velocity, probably with even lower pressures.