Hello everyone in the forum. I´m new here and from abroad. My English is pretty poor and for that I beg you excuse me. Here is one question to wich I would aprreciate an answer from reloaders:
I have a double rifle chambered for the 45-70 Gvt.; as I don´t trust it enough, I do not want to try with the 45-70´s third reloading level because of (aprox. 50.000 cup/psi) high chamber pressures.
If I could re-chamber it to accept the 45-90 and then come bak and use the 45-70´s third level:
shall I obtain less chamber pressure than the so proclaimed 50.000 cup/psi?
If so, can anyone calculate approximately how much less?
Thanks to all, and thanks for the site.
Oscar


TO HUNT IS NOT TO KILL

Welcome to thet board Oscar X.
First things first If you have not already done so then I would suggest a visiting a compitant Gun smith with the rifle in question for evaluation. Once the rifle has been researched and the condition known then you will have a good idea of what you can and cannot do.

I´d like to ad that the rifle is perfectly ready to accept 45-70´s second reloading level, at least (those intended for Marlin 1895).
Thanks for the welcome Guncotton.
Oscar

Oscar,

Chambering for 45-90 will not necessarily reduce the pressure created by a 45-70 cartridge fired in your gun. It depends on powder speed and crimp and bullet mass? Any reduction it may provide would be better accomplished by lengthening the freebore in the existing chamber because that will keep the bullet aligned better than the longer cartridge case diameter space will do.

Two other things you could check: Does your rifle's manufacturer chamber this gun in .458 Winchester Magnum? If so, and if the external barrel dimensions are identical, then there is a good chance you will be OK with those pressures. Ask the maker what, if anything else, is different? If your barrels were chambered from the same blank stock the .458 is chambered from, and have the same contour you should be OK.

A second thing to learn is what pressure proof load the manufacturer used in your rifle? If it was 70,000 PSI or greater, you are probably safe to go ahead.

Nick

You´re right Nick. What I wanted to say with "re-chambering for 45-90" is what you more correctly called "lengthening
the freebore". As long as case diameter in both calibers is the same.
In other words: I want to give the chamber more freebore (like if I was trying to fire a 45-90) but then use the 45-70. Should that bit of extension reduce the pressure? For your words I think so. But how much?
The question is that I would like to use the 3rd reloading level for the 45-70 but not reaching those 50.000 psi of chamber pressure.
I´ll find out more of those barrels, but I´m more scared about the action, that even being very strong (exposed hammers made in 1927 by Sarasqueta) the lack of a true third lock worries me a little.
Thank you

I am assuming what you are asking is based on using .45-90 cases with the level 3 .45-70 loads? If that is the situation, then your pressure would be reduced, and velocity also, probably to near level 2 pressure and velocity. Since th is the case, wouldn't it be much simpler to just load level 2?

As unclenick said, if what you contemplate is chambering for .45-90 and then shooting .45-70 loaded to level 3, no, you will not see a significant reduction in pressure. Whatever change occured would be completely unpredictable without pressure testing equipment which, if you had, you would not be asking the question! His point about the same model being chambered in other high-pressure calibers with similar case head diameter is also well taken.

Let´s put it this way.
I take a Ruger #1 chambered for 45-70 and I fire level 3 of 45-70. That will (theoricaly) give me around 50.000 psi pressure and around 2.200 fps of MV.
Now I take a Ruger #1 chambered for 45-90 and I fire the same 45-70 level 3.
Being exactly the same load, lenght, weight, etc...
Won´t the pressure come down for having extra free bore?
Well, if it does but speed-energy comes down as well, then I´ll stay in load level 2. But this I don´t know.
Thanks again.
Oscar

Now the situation changes. Before were you talking about a double rifle, or a Ruger #1?

Just addressing the original question generally. As was said before, yes, the pressure probably will be reduced somewhat, how much is a wild guess. The other factor to consider is the effect this could have on accuracy. Having a bullet insufficiently supported while it traverses the distance from the case to the lead of the rifling, in this case probably over 1/2", usually has a significant effect on accuracy.

Back to the Ruger #1. Is the rifle you are talking about re-chambering a #1? If so, this rifle is much stronger than necessary to shoot any level of .45-70 load. The limiting factor in this action is strength of the brass! The cartridge will fail before the action is strained the least bit. Only the Starline cases are sufficiently strong to stand up to pressures which can be used with impunity in the Ruger #1.

That´s it. That "wild guess" is what I am looking for, as long as it is not a Ruger#1; otherwise I wouldn´t worry about this matter.
It´s an old double expossed hammers´ action, about the same type than the Kodiak IV, thou stronger and of a better manufacture.
But that thing about the accuracy can radically change my mind, as it is something that I will never get to know unless I want to take the risk and do the job in the rifling or a 45-90´s owner could tell me.
Very much appreciated.
Oscar

Oscar,

Welcome to the forum!

The Weatherby's and several other manufacturers have used longer free bores to reduce the pressure. The NEF rifles are pretty notorious about long throats. I can load .360 Dan Wessons in my NEF .357 Mag barrel, but I can use lengths (OAL) greater than the .357 Max.

If you increase the free bore, you should be able to load a longer OAL which is going to reduce pressure, if you don't increase the powder charge.

With the age of your gun, I seriously doubt it will handle level #3 loads. I don't think the .45-90 has any advantage over the .45-70 if you don't use black powder.

I think you risk messing up the regulation of the barrels.... not a trivial thing with a double rifle.

Why not juts leave the gun as is and go with a lighter loading? The 45-70 is a shooter and will definitely suffice with a less than full power load. Personally, I've seen no real advantage in loading the 45-70 to extremes of pressure and velocity. My highwall is newly manufactured and more than capable of loading beyond listed maximums pushing the 45-70 to run with the .458 Winchester Magnum however, there was no appreciable gains.

I'm not fond of using lighter bullets in the 45-70, 430 grain and bigger bullets perform the best and one need not put a whole lot of speed on them unless you're going after extremely large thick skinned game.

My pet load for the 45-70 is a 450gr 40:1 Pb/Sn cast bullet sitting over a full case of 2F blackpowder compressed .330" and a moderate roll crimp. This load runs at low pressure but produces awesome results on paper and in the field.

Gentlemen,
I have an appointement with wild boars and I´m late. I´ll come back to the forum sunday evening (morning in America) and will keep on giving more details. Please try to keep on the main topic.
Good luck and thanks a lot to all.

If you're interested in pushing velocity levels up to hotter .45-70 levels while maintaining the same pressure levels as a more moderately loaded .45-70, then re-chambering to .45-90 and shooting .45-90 cases may well be the way you want to go.

According to the Lyman 48th Edition Reloading Handbook, using the Lyman #457125 500 gr. cast lead bullet, a Ruger #1 .45-70 load with 37 gr. of XMP-5744 will obtain around 1540 fps at 35,200 CUP. The same bullet in the 45-90 with 43 gr. of XMP-5744 will give around 1667 fps at 26,600 CUP (basically the pressure levels for the Win. 1886 and Marlin 1895). Higher volume cases typically keep pressure levels lower for a given velocity, at the cost of more powder.

You are correct to some extent, given the 45/70 and 45/90 are loaded equally, you should expect a pressure drop in the 45/90. This is do to increased case capacity not free bore, however there are things you can do to take advantage of free bore such as not crimping the bullet and decreasing the seating depth. I caution this practice in a double because the second bullet may jump further out of the case (under recoil) and engage the rifling, which could lead to an impressive pressure spike.
The case of the 45/90 is 2.4” in length vs. the 45/70s 2.1” not a big increase so I would not expect huge pressure drops. Have you considered 45/120? It’s also known as a 45 3 ¼ sharps. This cartridge actually was introduced after and Sharps closed their doors in 1880.
It’s European cousin is the 450 3 ¼ Rigby. The Rigby was originally a Black powder round that made the transition to cordite in 1897. It was first big bore “Nitro Express” round and became a bench mark for some time to come.
The Hodgdon website (http://www.hodgdon.com/data/cowboy/lrrd.php#45-120) lists the 45/120.
They list a 500gr bullet at 1809fps while keeping the pressure to 28,500. The Rigby double fired a 480gr bullet at 2050fps when released but was soon increased to 2150fps. I think this is certainly worth consideration assuming your rifle will accept this chambering. Here is a place with a lot of info on big bore nitro rifles (http://www.nitroexpress.com/).

If you haven’t already, I would also visit Garrett’s site and check out the articles (http://www.garrettcartridges.com/). His loads have been used to drop every large thing on the planet.


Do you have any pics of your rifle?

To be sure we are on the same page, I have posted a crude image of the .45-70 chamber, the .45-90 chamber, and the .45-70 chamber with its rifling's freebore moved forward 0.3" so a long bullet may be seated out to match the length of a .45-90. A Lee factory crimp die would likely be required to prevent bullet backout in the unfired chamber under recoil.

The extra case capacity in the .45-90 requires the addition of more powder to achieve the same pressures. With the 450 grain Barnes belted solid, the .45-70 needed 29.4 grains of H4198 to reach 28,000 psi, while the .45-90 needs 34.2 grains to make that pressure. That extra powder made more energy available to transfer to the bullet. More gas was generated, and so the pressure curve sustains a bit longer. Interestingly, the more sustainged pressure caused a higher percent of the powder to burn in the biggest charge. You can see the velocity gain in the .45-90. This is for a 24" barrel with a peak pressure of 28,000 PSI.

45-70 oal 2.550 Charge: 29.49 gr. H4198 Velocity: 1418 fps 88.1% burned.
45-90 oal 2.880 Charge: 34.23 gr. H4198 Velocity: 1518 fps 91.5% burned.

Unexpectedly with this bullet, moving the freebore forward and seating the bullet out to 2.880 had even more effect than using the .45-70 case (I designate this 45-70LT, for Long Throat):

45-70LT oal 2.880 Charge: 35.72 gr. H4198 Velocity: 1544 fps 92.4% burned.

In another run on the computer with the same bullet but letting the pressure get up to 34,000 PSI using Vihtavuory Oy N130, the 45-70 achieved 1575 fps, while the 45-70LT got to 1700 fps This was very efficient, predicting over 98% of the powder burned. I don't want to post the calculated loads here because they are over SAMMI would be dangerous in some guns, and are only computer predictions based on an un-verified case capacity. I will say it took about 7 grains more powder with the bullet seated to 2.880 rather than 2.550"

Also note, while the .45-90 is 0.30" longer than the .45-70, the difference in maximum OAL is 0.33". I don't know why. For this reason real results will be a bit different.

Oscar, you might want to invest in the RSI Pressure Trace. It's strain gauge load cells are removable without damaging the gun finish. You could use a known accptable second level load, then after having the freebore moved forward .3 in. (7.62 mm) use that reading to match pressure in the new freebored chamber. You will apparently be able to gain about 32 m/s without increasing pressure if you use this technique.

Good luck.

Nick

http://img513.imageshack.us/img513/4521/457045906dl.gif
http://img510.imageshack.us/img510/6907/4570lt90resized3hq.gif

After reading all this, what else can I add? I will compile every given answer and find out how deep I can go in this matter.
You all please forgive my lack of knowledge but in reloading we are still (in Spain) in the Stone Era. That´s the reason why I directed my questions to this forum.
In the meantime, gentlemen, it has been a real plessure to listen and learn from you. I´ll be back soon.
Good shooting.
Oscar


TO HUNT IS NOT TO KILL