PDA

View Full Version : Pressure Signs and Maximum Loads In the 1895 Marlin Action


7x57
05-20-2009, 11:48 AM
This is a response to a post (http://www.calguns.net/calgunforum/showpost.php?p=2506408&postcount=54) in another thread (http://www.calguns.net/calgunforum/showthread.php?t=183341) about heavy loads in a Marlin .45-70 levergun, but it seemed more appropriate here. Might start some useful discussion with people who have more experience doing this, or, better, save someone from trying to handload a levergun as though it were a bolt action without knowing what they're actually doing.

This sort of thing is also what I like about handloading--you start to learn just how complex an action firing a cartridge really is, and that's interesting.

The lockup doesn't matter, these are symptoms of overpressure that affect the case. Having said that, there are other symptoms that affect bottlenecked cartridges (shoulder splitting).

I retire my cases after about 3 reloads. Not because of failure, just precaution.

I'm not going to argue the point back and forth if you are convinced you know what you are doing, but Mic McPherson knows more about Marlin leverguns and their limits than any of us ever will, and he does not agree with you. For the benefit of whoever cares about very heavy loads in Marlins, I'll repeat the gist of a couple of different articles of his. As there will be a grizzly bear gun in my future someday I'm one of those who cares and I spent some time trying to understand his advice. It's your eyes and your life, you can do what you please with it.

The problem with rear-lockup actions is bolt spring. Rifle pressures can be enough to compress the bolt by a few thousandths even when the chamber will take the pressure--this is why, IIRC, the Enfield has a reputation for poor case life. The cases stretch much more than in a Mauser-type front-lockup action. (Physically the bolt spring is proportional to pressure and to the distance between the bolt face and the locking lugs. That distance is short enough in a front-lockup action that bolt spring is unimportant at safe pressures--the cartridge will fail for other reasons first.) And the problem with this is that the stretching will happen at the head, and failure means head separation. For lurkers who don't know, head separation means potentially 50,000 PSI of incandescent gas or worse (like the bolt, if you've utterly screwed up and done it just the wrong way in a weak antique rifle) coming back through the action at (or through, in the case of the bolt) your face. (Which is also why modern action designers try to deflect that gas elsewhere, such as through the magazine.)

You have on eye protection when you shoot, right? What happens if the cartridge is defective and you get a head separation with a safe handload or factory load? What happens if the static headspace on that surplus rifle is marginal and you didn't bother to gauge it? Just some little thoughts there while we're talking about incandescent gas in the face.

In essence, bolt spring means that the true dynamic headspace is dependent on pressure, regardless of the static headspace measured by gauge. Almost everything we read assumes that dynamic headspace equals static headspace--this is a bias toward Mauser-pattern bolt actions, frankly, and shouldn't be relied on for other actions without careful thought. (It bothers me a great deal that I've never read this explanation in the normal reloading sources, which only discuss static headspace. The terms "dynamic headspace" and "static headspace" are my own, because there doesn't seem to be an equally useful terminology in common use.)

In the specific case of the Marlin, you also have the issue that the chamber is inherently not as strong as a bolt action, so you don't really want to be running at pressures that have much bolt spring at all even aside from the potential for head separation. For one thing, Mic points out that to make room for the magazine tube the Marlin chamber is actually quite thin under the threads. You just don't want to push that chamber as hard as you can a modern bolt-action barrel chamber, and in Mic's hand-reworked leverguns he actually goes to considerable trouble to re-cut the receiver threads to a different profile to allow for more metal under the barrel threads and makes it precise enough to get some hoop strength from the receiver to reinforce the barrel. I believe for his kodiak-bear killer specials he also buys barrels made of stronger steel than Marlin does. That ought to tell you something about how seriously he takes the limits of the factory Marlin chamber.

What Mic does to determine maximum loads for rear-lockup rifles is to use a very clean chamber and cartridges (to prevent the case from slipping and preventing case stretch from measuring bolt spring), and measure the lengths of the cartridges before and after. I believe it was three-shot groups, and any load that produced measurable case stretching on even one round would get backed off by 7%. Stretching *always* occurs, of course, but this procedure limits the stretching to within the elastic limit of the case. It is still springing back to it's original length. According to Mic, that will not only avoid head separation but also keep the pressure within the chamber limits. What Mic is saying is to keep your loads in the regime where the dynamic headspace is not significantly different than the static headspace.

I want to emphasize that the usual pressure signs people are taught to look for assume something that is usually not stated: that the *dynamic* headspace is in spec if the static headspaces measures OK, and that the case will fail before the action. Neither assumption is always true: I've already explained that the first is not necessarily true for an Enfield bolt-action, though I believe the second one is (I've not reloaded for an Enfield so check the chamber strength before doing something stupid.) On the other hand, for my 1893 Spanish Mauser action, the first is true (front lockup) but the second may not be in a pre-98 action so I am always quite conservative and stick with the lower SAAMI pressures and not the ones in about half the books that specify "modern actions only."

Anyway, what Mic is telling us is that *neither* is true in a Marlin levergun, and that has consequences we need to understand. And also that the combination is in one way a blessing--the bolt spring offers a pressure indication appropriate to the chamber strength, if we have the wit to use it. My front-lockup Spanish Mauser doesn't do that, and I think that's more dangerous (OTOH I gather that a catastrophic failure from overpressuring an 1893 action is unlikely, so perhaps it's not really more dangerous.)

The two original questions I asked were to see whether you were aware of the bolt-spring problem in that action, and the second was to see whether you were likely to repeatedly stretch a case until head separation becomes a virtual certainty. With your heavy loads you are definitely operating in the regime where bolt spring is somewhere between possible and probable. I don't like to argue with people about a cartridge they load and I don't, but depending on whether you've measured case stretching to verify your load in your gun (I suspect chamber and perhaps even bolt variations may differ enough from gun to gun to matter, though Mic doesn't say so) your situation could be unsafe (for maximum limit loads I would suspect that you ought to test each brand of case separately because they'll vary in capacity, strength, and tempering, though Mic doesn't say that). If you haven't measured it *and* you were not retiring cases I'd say it's absolutely unsafe, so I'm glad you're careful about repeated stretching.

As it is, unless you've measured your case stretch I don't think either you or I actually know how much margin you have left. Do what you like with the information, but I wouldn't be comfortable with that. It's your gun, your eyes, and your life, but I'd rather be told to mind my own business than to hear of an accident that happened because I didn't say anything.

If anyone cares I could probably dig up the references the above little essay is based on.

Thanks to Pronghorn for making me try to remember Mic's Marlin loading advice, and hopefully he's a good sport about me kind of going off on a tangent based on his post.

7x57

rabagley
05-20-2009, 12:07 PM
Fascinating posting. This should be published in handloader magazine.

7x57
05-20-2009, 12:19 PM
Fascinating posting. This should be published in handloader magazine.

Mic published some of it, though probably in a different magazine. There isn't a copy on the net I know of except people who've typed it in on discussion board threads.

I might email Mic and ask if he would put a definitive copy on-line.

7x57

buffybuster
05-20-2009, 12:29 PM
Pronghorn,

Be careful buddy, I'm with 7x57 on this one. You will not see the typical high pressure signs with a Marlin M1895 leveraction even after you have exceeded the safe working pressure of that action.

You also stated in a previous post and I'm paraphasing something like "if you have your hand on the lever the case will eject automatically".

The action springing open is a classic sign of pushing it too hard....

Stay Safe.

EOD3
05-20-2009, 12:34 PM
Originally Posted by Pronghorn View Post
I've been loading for 15 years. There are several symptoms present long before firearm failure (stuck cases, primer distorsion, etc.). I have not expierenced any of these issues.

It's your rifle and your head, load it any way you like.

For the others that might be inclined to emulate this behavior DON"T DO IT. Reading pressure warning signs on straight wall cartridges is an art, not a science. About the only way to gauge "your rifle or revolver" is by comparison with a case of known (safe) pressure.

A barrel has two characteristics, one being "working pressure" and the other being "catastrophic failure pressure". The proof load for a given chamber is roughly 2X the working load and is calculated to be at the upper end near the catastrophic failure load. Steel gets tired a little bit every time you fire the weapon but, as long as you're at or below the working load it's a tiny amount. Each time you stress the barrel to a point approaching the failure load, it gets tired in a hurry and the catastrophic failure point is LOWERED.

Think of it this way, if you take a piece of steel and beat on it with a tack-hammer you will have very little effect on the steels molecular structure. On the other hand, beating on it with a sledgehammer will alter the molecular structure making the metal more brittle. the exact same thing happens to your brass each time it is fired/stretched then re-sized/compressed which is why you get case splits. after a few cycles.

Happy shooting.

7x57
05-20-2009, 12:48 PM
You also stated in a previous post and I'm paraphasing something like "if you have your hand on the lever the case will eject automatically".

The action springing open is a classic sign of pushing it too hard....


To be fair, what I *think* he meant was that the rifle would kick your shoulder back far enough that the motion away from your hand would naturally open the lever. If he really meant it was springing open on its own.... :shock:


Stay Safe.

Boy howdy.

7x57

EOD3
05-20-2009, 12:50 PM
You also stated in a previous post and I'm paraphasing something like "if you have your hand on the lever the case will eject automatically".

The action springing open is a classic sign of pushing it too hard....

Stay Safe.

I think he was referring to the recoil of the rifle hitting his hand hard enough to open the action.

EOD3
05-20-2009, 12:54 PM
7x57 keeps beating me to the post message button. WHY didn't I ever learn to type?

Very well said by the way.

buffybuster
05-20-2009, 12:55 PM
7x57, EOD;

You guys are probably right on that. I've had my share of "sinus clearing" loads but I've always be able to maintain my grip.

Nevertheless, IF the action is springing open.......... that it TOOO HOT!

7x57
05-20-2009, 12:58 PM
Nevertheless, IF the action is springing open.......... that it TOOO HOT!

"Too hot" in the sense of "carefully clear the gun now, go home, and immediately pull the bullets on every load that hot to guarantee no one ever has a chance to fire one. :thumbsup:

7x57

buffybuster
05-20-2009, 12:59 PM
Pronghorn,

One more thing, the M1895 action is not much more than the M336 action opened up for the 45/70. As a result the amount of steel in the barrel at the chamber/barrel threads is relatively thin. This is a non-issue with standard loads or loads under ~35-40Kpsi. But if you're pushing more than that, it's something to keep a eye on.

DocSkinner
05-20-2009, 1:05 PM
correct me if I am wrong (yes, I know its redundant to say that) but isn't teh Savage 99 the only true rear lockup lever action, where the bolt is held close by engagement of a solid sear, while the other levers all just use some camming action/over center or just multiplication of mechanic force to hold the bolt closed with lever mechanisms themselves?

Only ever own Marlins and Savages -

7x57
05-20-2009, 1:18 PM
isn't teh Savage 99 the only true rear lockup lever action,


I thought the Savage 99 was front-lockup, like the Browning BLR. The latter is essentially a lever-operated bolt action, I thought the former was similar. I may be wrong.

I'm not sure how a traditional levergun's lockup mechanism works, however.

7x57

buffybuster
05-20-2009, 1:23 PM
I thought the Savage 99 was front-lockup, like the Browning BLR. The latter is essentially a lever-operated bolt action, I thought the former was similar. I may be wrong.

I'm not sure how a traditional levergun's lockup mechanism works, however.

7x57

No, the Savage M99 IS a rear lockup action. The rear face of the bolt locks into the back of the ejection port. But since the rear of the actual bolt is the lock, it is a fair degree stronger than leveractions, though it too will stretch cases.

ArticleTheFourth
05-20-2009, 1:27 PM
I thought the Savage 99 was front-lockup, like the Browning BLR. The latter is essentially a lever-operated bolt action, I thought the former was similar. I may be wrong.

I'm not sure how a traditional levergun's lockup mechanism works, however.

7x57

correct me if I am wrong (yes, I know its redundant to say that) but isn't teh Savage 99 the only true rear lockup lever action, where the bolt is held close by engagement of a solid sear, while the other levers all just use some camming action/over center or just multiplication of mechanic force to hold the bolt closed with lever mechanisms themselves?

Only ever own Marlins and Savages -

I don't know exactly how all of the other lever action rifles lock, but my Savage 99 (oldie from dad) locks at the rear of the bolt giving the action some 'spring'.

Doc, thanks for helping us 'outdo' last year's Friends of NRA! :thumbsup:

EOD3
05-20-2009, 1:43 PM
Some of the older Winchesters have a "toggle" bolt and dual locking bars that hold the bolt.

buffybuster
05-20-2009, 1:48 PM
correct me if I am wrong (yes, I know its redundant to say that) but isn't teh Savage 99 the only true rear lockup lever action, where the bolt is held close by engagement of a solid sear, while the other levers all just use some camming action/over center or just multiplication of mechanic force to hold the bolt closed with lever mechanisms themselves?

Only ever own Marlins and Savages -

Doc,

You are partially correct. What you are referring to are the original leveractions:

Winchester 1860 (Henry), 1866 (Yellow Boy), 1873 and 1876
Marlin 1881

These actions used various toggle link and cam over linkages to keep the action closed. These actions are NOT suitable for smokeless powder loads in DESIGN nor MATERIALS. They were made primarily of brass (1860, 1866) and wrought iron/low carbon steel.

The latter actions designed:

Winchester 1886(Browning), 1892(Browning), 1894(Browning), 1895(Browning)
Marlin 1893, 1894, 1895

These model had a superior lock-up system that used some variation of a vertical locking lug/lugs that fit into cutout/s in the rear of the bolt. These original models were suitable in design for smokeless powder loads but NOT IN MATERIAL, as they used low carbon indifferently hardened steels.

Later on by the early 1910's steels were improved and smokeless powder loads could be used.

The Winchesters have been in/out production either through Winchester/USRA or Browning (Miroku).

The Marlin models were changed and evolved. The original 1893 became the M36 and eventually the M336. This action also became the basis of the new M1895. The original M1895 action which was quite a bit larger was never reintroduced. The M1894 was updated and reintroduced for use with pistol cartridges.

ar15barrels
05-20-2009, 1:55 PM
Chamber pressure is not the issue.
Boltface thrust is the issue.

Play with my backthrust calculator and you will see that smaller case heads can certainly be run to bolt action pressure levels, but the larger case heads have to be kept in-check.

www.ar15barrels.com/data/thrust.xls

Pronghorn
05-20-2009, 2:07 PM
A few things.

Yes, the recoil + my hand causes the action to open. It is not springing open.;)

I have played with alot of different calibers, and loaded 10's of 1,000's of rounds. I would never risk injury by pushing the rifle too far.

The pressure limits are known as "Lawyer Levels", and far below the failing point. Some commercial custom loads have a warning on the box stating that the factory pressures are exceeded (Gold Dot LE 9mm +P+, Double Tap, Buffalo Bore, etc.).

Do not take my posts as reloading advise, use your own judgement.

Carry on.

Pronghorn
05-20-2009, 2:17 PM
Thanks to Pronghorn for making me try to remember Mic's Marlin loading advice, and hopefully he's a good sport about me kind of going off on a tangent based on his post.

7x57

No tangent, bud. I'm always learning.:)

Having said that, I have expierenced instances that contradict your facts.