Author Topic: rechamber a Spartan 45-70 (Read 1018 times)

GEMSBUCK · « **on:** September 27, 2005, 06:03:09 AM »

is it possible to rechamber the new Spartan SPR22 45-70 to 45-120 or 50-110 and will the pressures be too great for it in the new chambering/ thanks

gunnut69 · « **Reply #1 on:** September 27, 2005, 06:31:20 AM »

I haven't had any dealings with these but the 45/70 version on their website posts a limit of 28,000 PSI and 28,000 CUP as a maximum load. I would bet the 50 caliber rebore is out. There is still the manufacturers mistake of lumping CUP and PSI together. These measurements are NOT equal... Still rechambering to the longer cased 45 caliber rounds would be doable. Reloads would still need to be kept under the specified pressure limits.. Please remember that even at 28,000PSI the 45-70(90 or 100)in a 7 1/2 pound rifle will pound the snot outta whatever's at either end!!

PS-I went back and read the info on the website- These rifles have a chrome lined bore and chamber. That will complicate the rechamber job and increase it's cost. Only carbide tools can handle the chrome lined bores.. Their website address is shown below!

http://www.spartangunworks.com/spr22.htm

GEMSBUCK · « **Reply #2 on:** September 27, 2005, 09:23:53 AM »

I was just "what ifing" I got my hands on an early release SPR22 45-70 and was thinking I could make it into a DG gun on the cheap to use on brown bears,bison,cape buff or such

gunnut69 · « **Reply #3 on:** September 28, 2005, 04:34:10 AM »

It would likely do just fine. A longer chamber might give a bit more room for bullet in a reloading schenario and while pessures have to be limited that's not to big a problem. A DGR is really a close range thing and a 450-500 grain 45 caliber slug at a couple of thousand FPS would be a fight stopper! The 45-90 should just about give the case capacity of the 458(plus a bit). Even the 45-70 is no wuss.. and the price is deffinitely right.. The Weights a little light for heavy loads but weight can always be added, preferably in the for of a mercury recoil reducer!.. How does the rifle perform on paper? What load is the gun regulated for? That may well be a whole nuther problem.. Reloaders working with a double rifle have to work within what the rifles barrel regulation will allow..

260 AAR · « **Reply #4 on:** October 07, 2005, 11:04:40 AM »

I just went to the Spartan site. It says the rifle is also chambered for the 30-06. What is the "normal" operating pressure of a standard 30-06? Last time I looked it was well over 45,000 psi. If they sell one of the MR22s in 30-06 and another MR22 in 45-70 I feel it wouldn`t be too cost effective to use a different action. Thus the conversion could easily be done [with a carbide reamer] if the bores are chrome lined. Just my .02

Aloha, Mark

gunnut69 · « **Reply #5 on:** October 09, 2005, 01:11:33 PM »

I saw the 30-06 chambering but the difference is iun the details. A 30-06 casehead has a considerably smaller area than a 45-70. Thus the force exerted on the standing breech is considerably greater and it will be exerted further from and higher than the hinge point. This increases the unlock load on the action. Of course this is from a manufacturer that mixes PSI and CUP in measureing pressures. 28,000 PSI ain't to be sneezed at in any case and in a rifle that light is surely gonna hurt..

Mac11700 · « **Reply #6 on:** October 27, 2005, 08:12:14 AM »

Not to be argumentative..but my understanding is the 45-70 is one of few cartridges that the PSI rating and the CUP rating is equal...http://www.leverguns.com/articles/saami_pressures.htm

Mac

gunnut69 · « **Reply #7 on:** October 27, 2005, 12:35:26 PM »

There are a couple of ways to measure pressure. The standard was CUP(copper ubits of pressure) as is shown in many of the rounds on the list your link went to. In low pressure rounds lead was i.e. LUP(lead unit of pressure. These used a test barrel with a ported cut into the chamber. a piston was inserted into the chamber above the port and a slug of copper was introduced and the port was sealed. when the test barrel was fired the pressure caused the piston to compress the slug of copper. The amount it was crushed could be used to calculate the amount of pressure that had to have been applied to it. The 'piezo' test method uses a normal barrel and a piezo electric strip which is glued to the barrel over the chamber. This is attached to a computer of sorts and when the barrel is fired and expands the piezo cristal emitts an electric voltage that can be measured and converted into a pressure reading equivalent to PSI. The readings between the 2 methods are almost never the same and are always listed sepeerately. This is the case in the table your link goes to.. If one sees CUP and PSI listed as the same number,,beware..

Mac11700 · « **Reply #8 on:** October 27, 2005, 06:48:54 PM »

Yes...I know the differences...and the 45-70 and a handfull of others show practicly the same...cup...and psi...

Mac

gunnut69 · « **Reply #9 on:** October 28, 2005, 06:23:43 AM »

That may well be and I have no data to contest your assertion, but the link you posted is simply a table of values some of which were obtained using copper crusher method (CUP) and somepiezo method (PSI). What led you to the conclusion that there are cartridges that are the same pressure by either method. Most sources I've read said that the to are to be compared only to themselves and never 1 to the other. Still there may be some rounds that produce the identical results regardless of test method, just interested in your sources..