TALES OF "GAS HANDLING"

No, I'm not talking about gastric distress, but how bolt-action rifles deal with hot powder gas blowing into the action and, possibly, the shooter's face when a primer or case leaks. This has been a potential problem ever since the development of metallic cartridge cases, but became a much bigger problem after the appearance of practical smokeless rifle powders in the 1880's, when pressures rose enormously.

While there were some black powder bolt-actions, smokeless brought bolt into widespread use, especially among the armies of the world, because bolt-actions tended to be stronger than other repeating actions. However, a bolt action was essentially a tube within a tube, the bolt within the receiver. If a primer or case burst on firing (and many did during the early years of smokeless evolution), the hot, high-pressure gas could flow through and around the bolt, directly into the shooter's. face.

The big problem, of course, was the case itself cracking. A leaky or even "blown" primer doesn't normally result in nearly as much leaking gas, but cases usually crack just in front of the thicker case "head." Such cracking can occur for several reasons, but probably the most common involves handloaded cases stretching during firing, and then being resized too much, resulting in a little excess headspace.

This isn't all that unusual, partly because the directions for many full-length sizing dies suggest screwing the die into the press until it firmly contacts the shell holder. This does guarantee the resized cases will chamber easily, but usually ensures the case will stretch lengthwise during firing. (Here it should probably be noted that bottle-necked case stretching doesn't normally occur until pressures approach 50,000 PSI. This is why fired .30-30 cases often have primers protruding slightly from the rear of the case: The maximum average SAAMI pressure for the .30-30 is 42,000 PSI, which normally isn't sufficient to cause brass cases to stretch enough to totally fill the chamber. Instead primers back out slightly.)

A rimless case that's sized too much will stretch a little upon firing right in front of the solid head, and repeated sizings and firings just about guarantee the case will crack in front of the head. The "pre-symptom" for such cracking is a bright ring in front of the solid head, though that can sometimes be caused by the sizing die as it squeezes the outside of the head. The surest check is a piece of stiff wire with a small bend at one end. Stick the wire into the case and rub the bent end against the inside of the case wall: If you can feel a depression near the head, the case has stretched enough to thin the case body.

The brass is not only weaker there, but continued firing and sizing will eventually result in a crack in the case wall. Normally, however, the crack only occurs on one side of the case, partly because many actions flex a little during firing. How much hot powder gas escapes depends on pressure and the extent of the crack.

Whether the shooter feels any escaping gas (and perhaps brass particles) depends on both the location of the crack and the design of the action. When I first started full-length sizing cases decades ago (of course following the manufacturer's directions for "adjusting" the die) a few of my repeatedly-fired cases cracked in front of the case head--but I can't recall being aware of the crack until looking at the case afterward. The lack of gas in my face was due to the first two rifles I extensively handloaded for (and in my relative poverty kept reusing the cases as long as possible), a pair of Remington 700's in .243 and .270 Winchester.

Remington 700's are well known for a bolt face with a rim that completely surrounds the case head. Supposedly this kept hot gas contained during a leak, but in reality the bolt-face rim doesn't firmly contact the rear of the barrel, so a little gas can leak. However, the 700's bolt-face tends to limit gas-leakage far more than a controlled-feed action with a long "Mauser" type extractor, where there's no rim at all around half the bolt-face.

Most so-called push-feed actions like the 700 are designed to contain or at least considerably slow most escaping gas, though they also usually have an outlet hole on the receiver ring beside the bolt-face, to divert any gas that does seep out.

How much gas a push-feed action contains depends on whether the bolt-face rim is complete (as it is in the 700, with its inside-the face "ring" extractor) or whether a small spring-loaded extractor sits in a small cut-out in the ring. When the bolt's closed such extractors are situated on the side of the bolt opposite the shooter's face, so the relatively small amount of gas escaping through the extractor slot tends to blow in a safe direction.

Controlled-feed actions with Mauser-type extractors obviously don't block much powder gas. As a result, they're often (but not always) designed to divert gas escaping back toward the shooter's face. They generally still have a port on the receiver, but can also include other diversions. The most famous example is the 1898 Mauser action, often the best at gas-handling more 120 years after it was designed.

The biggest problem with long-extractor bolt actions is the semi-open bolt face tends to divert escaping gas into the left bolt raceway on a right-handed action. It has to, because the extractor sits on the right side of the bolt.

Perhaps the best run-down of the 98's gas diversion is the first chapter of Stuart Otteson's fine 1976 book THE BOLT ACTION, subtitled "A Design Analysis." The original 98 military action dealt with the left raceway problem in three ways, first with the so-called "C-ring," the inner collar in the front of the receiver with a cut on its right-hand side to accommodate the extractor, but a solid left side to block some of the gas heading toward the left raceway. Many later commercial 98 actions featured an "H-ring" collar, with a cut on both sides. This is cheaper to machine than the C-ring, but allows more gas to enter the left raceway.

Military 98's also had a cut-out in the receiver toward the rear of the left raceway, the "thumb-slot" for pushing a loaded clip down into the magazine. This was also eliminated on many later commercial Mausers, partly because they were almost never clip-loaded, though James Corbett, of MANEATERS OF KUMAON fame, clip-loaded at least the first of his .275 Rigby rifles, made by Rigby on early German 98 actions. But the thumb-slot also cost more money to machine, and a slot-free action was stiffer, important to some accuracy-conscious hunters. Finally, the bolt-shroud had a wide flange to divert any gas that did make it down the left raceway.

While THE BOLT ACTION analyzes a bunch of bolt actions, one of the 98 Mauser's other gas-diversion features isn't mentioned. The bolt-shroud flange works very well--except it can't divert gas that might sneak UNDER the shroud. That's diverted, or at least slowed considerably, by a small ridge across the front of the rear tang. This fits a matching abutment on either side of the bottom of the bolt shroud, and a slightly wider cylinder at the rear end of the bolt body itself. You can see the slight ridge and wider cylinder here:

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This was pointed out to me by the late Dave Gentry, a Montana gunsmith who made 98 Mauser actions of various sizes, quite a few used by well-known gunmakers, including legendary British firms, which did not include Gentry's name anywhere on the action. (Dave didn't really care, because he charged pretty good prices.)

But he was initially puzzled by this "step" in the tang, because it wasn't included in any of the pre-98 Mauser bolt actions. However, after thinking about a while, he realized the bottom of the bolt shroud couldn't be flanged without resulting in some really clumsy modifications. Since leaky cartridge cases were such a common problem in the 1890's, Peter Paul Mauser came up with yet another small, but important, improvement on his previous bolt actions.

However, as brass cases improved in quality and reliability, gas-diversion became less important, especially in sporting rifles. The pre-'64 Model 70 Winchester action is a prime example. While often cited as an "improved" 98 Mauser, in reality the improvements are mostly the trigger and horizontal-acting 3-position safety. There basically is no gas-diversion, from the "coned breech" to the lack of a flange around the relatively slim bolt shroud. But by the time the Model 70 appeared in 1936, brass cartridge cases had improved so much that really wasn't a problem. Here's a photo of the bolt-shroud area of a pre-'64 action, totally lacking any sort of a flange:

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Winchester changed the Model 70 to a push-feed in 1964, with one of those little extractors stuck in a slot on the side of the bolt-face. Some hunters thought civilization had collapsed, but the push-feed 70 proved to work pretty well, in fact so well that couple of noted African professional hunters, Finn Aaagard and Harry Selby, used PF .458's for backup work, and didn't have problems. Selby, however, said he preferred the Mauser action on his beloved .416 Rigby (which by the way, was made on an opened-up standard-sized 98 action--I know this because of getting to shoot the Selby Rigby a number of years ago), and Finn preferred his pre-'64 M70 .375 H&H, though also owned (but used less often) a .458 on a 98 action.

Eventually the clamor for the return of the controlled-feed Model 70 became so constant that Winchester started making a new version in 1991, though at first it was intended as a limited-run deal, with the push-feed the standard model. But apparently so many whitetails had started charging since 1963 that many hunters desperately desired a CRF Model 70, and the CRF model initially called the Classic is now the standard Model 70. However, a "gas-block" was added to the bolt behind the left lug, to at least partially divert anything heading back along the left raceway:

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In the meantime, other manufacturers had started making new models of bolt-actions that used some 700 or 70 features, or some of their own. Many people praised Bill Ruger's Model 77 bolt-action when it appeared in 1968, because it had the long, Mauser extractor. But it was actually a push-feed action, with the bottom of the bolt-face rimmed to help contain gas, and a plunger ejector. It wasn't until after the 77 Mark II was introduced in the 1990's that a true CRF Ruger 77 appeared, and even then the initial Mark II was push-feed. Many other companies produced push-feeds of various sorts, and hunters continue to argue both about their extractors and gas-handling.

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From left, bolts from a Remington 700, Franchi Momentum, Tikka T3, original Ruger 77, and 98 Mauser.

If you've read Otteson, it's pretty easy to see how many new bolt rifles have borrowed from various previous designs. Most push-feed actions, like Remington 700's, pretty much try to contain and divert leaking gas at the bolt-head, while controlled-feed designs can vary from the extensive diversions of 98 Mausers to the near-zero provisions of the pre-'64 Model 70.

Experiencing a few "gas accidents," however, often reveals more. I've been unfortunate enough to encounter a few myself, mostly when I was a younger, dumber handloader, but a few occurred with factory ammo.

In the early 1990's the late George "Doc" Daugherty was my stepfather-in-law. He'd grown up in Pennsylvania and hunted deer there--but never got one, for reasons I eventually understood. After marrying my wife Eileen's widowed mother in Ormond Beach, Florida, where they'd both retired, he met me when he and Cece came to Montana for a visit. During the visit he decided to hunt with me, and after heading home to Florida he shipped me his rifle so I could mount a scope, because his eyes weren't what they used to be. The rifle was a J.C. Higgins .270 Winchester, one of the Sears-brand models based on FN Mauser commercial actions.

Doc also included a box of pretty old Winchester factory ammo, which he'd had for a long time since none had been fired at deer. I mounted an inexpensive 4x scope and started sighting-in the rifle. The ammo looked fine, but apparently decades in the salt air of the Florida coast hadn't done it any good. On about the third shot I felt a distinct blast of warm air and brass particles on the left side of my face, back toward my ear, and after extracting the case found a quarter-inch slot blown through the body, just in front of the solid head. The action was a typical modern H-ring with no thumb-slot, but due to the flanged bolt-shroud the gas had mostly been diverted.

I then handloaded some ammo for the rifle in brand-new Winchester cases, which worked fine. We went hunting in Montana that fall, and it turned out there were reasons Doc had never gotten a deer in Pennsylvania, mostly involving noise, too much movement and not liking to be in the woods during twilight. He decided to quit hunting again, and I ended up with the J.C. Higgins.

Another incident occurred when well-known gunsmith Charlie Sisk and I conducted some experiments on his indoor range, then in Texas. We hooked up a Model 70 Classic in .308 Winchester to Charlie's Pressure Trace, and after making sure it was functioning correctly, started running various tests. One involved how many times a single case could be fired at maximum pressure, with the primer pocket remaining tight.

We kept loading the same case over and over (I can't recall the brand anymore, but it was common) and the primer pocket stayed tight, and pressures and accuracy stayed consistent. We reloaded the case together, and I did the shooting while Charlie rode herd on the Pressure Trace, and on about the 12th firing the primer blew.

I got a face full of gas and a few brass particles, despite the gas-block on the left side of the bolt, but was wearing glasses (as I always do, due to being myopic since age 10) and no real harm was done. The Pressure Trace read extremely high, and even in a professional gunsmith's shop we had some trouble getting the bolt open, but the rifle was apparently unharmed, with headspace right where it should be. The load was a lightly compressed charge of powder, so the blown primer wasn't due to a big overload, and we didn't experience any problems reloading or chambering the round.

I've also blown some primers in Remington 700 actions, along with one 722, the predecessor of the short-action 700. One handload blew the primer so severely the head-stamp of the case was pretty much obliterated, and the primer pocket might have accommodated a shotshell primer. I have an idea why it happened, but my suspicion wouldn't have involved nearly as much pressure as the case indicated. Again, there was some trouble getting the bolt open, but the rifle was unharmed.

The other instances weren't as bad, but obviously something was very wrong in each. But none of the other 700's were harmed, and even though the bolt handles had to be opened with a wooden mallet, none came off. I didn't feel ANY powder gas in ANY instance (though I do have a good friend who claims he did feel face-gas when one of his handloads blew a primer in a 700).

From all of this I've concluded that I'd rather have my face behind any sort of 98 Mauser or Remington 700/722/721 than a Model 70 Winchester when a case blows. But I still own both pre- and post-'64 Model 70's, and don't worry about it much, because I don't perform so many experiments anymore, either intentional or inadvertent.

However, the centerfire rifle I'd trust the most when a case blows is the Ruger No. 1. But that's another story.









“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck