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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:



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:



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:



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.


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.

Shoot John , I was hoping you’d mention the mark V as well haha

John;
Good morning to you sir, I hope that this finds you and Eileen well and warm on the first weekend in May.

Thanks kindly for the informative read, as usual with your work I learned something and that's always a good thing!

Having been on the receiving end of blown cases in a 788, tang safety Ruger 77 and a No 1, I can agree that the No 1 was the preferred arm when things go sideways.

The old Liberty Model 77 did pretty good work too though.

Both the No 1 and 77 were when a batch of N160 went bad on me - I believe you and I discussed it way back when that happened. Anyway it all caked up in the cases and in the 8lb caddy it was stored in too. The caddy was warm, not hot, but warm enough to cause me concern for sure. In the end I threw out about 150 cases, the worst of it was a bunch of 6.5x55 which were hard to come by up here back then.

Also I should mention that the 788 was just me learning about rear locking actions and resizing dies, so totally operator error and nothing more.

Thanks again for the interesting reading sir. All the best to you folks as we head into warmer weather.

Dwayne

I have had two blown cases that I can recall. One was with a Sako L 691 308 Norma Mag where I accidentally poured some IMR 4350 into a can of MRP......... and then forgot and loaded up some rounds The second was a couple of years ago working with the 270 Win and IMR 4955. Not sure what happened if it was a faulty brand new case but I was below Hodgdon's max and blew a primer. There were no indications of high pressure before that and the bolt opened easily so not sure what happened. I have noticed since that a bunch of other bullet companies have data much lower that Hodgdon with IMR 4955.

The other thing that should be mentioned is people who shoot right hand rifles left handed. Always thought it was a bad idea but people have to make their own choices. What gets me is the guys who are to cheap to buy a proper left hand rifle for their family members and then make them shoot right handed. I doubt many people wear shooting glasses at all while practicing let alone wear them while hunting.

Good article, thanks.

jmd025,

One of the most interesting bolt-action "blow-ups" I've heard about occurred with a Mark V. I didn't personally witness it, but heard about it during the year I lived in Lander, Wyoming (home of the well-known One-Shot Antelope Hunt) in the 1970's.

One of the members of the Wyoming team that year was a well-known Wyoming politician who wasn't a very sophisticated rifleman. He was shooting a Weatherby Mark V, apparently borrowed, chambered in .270 Weatherby Magnum--but somehow ended up with .270 Winchester ammo. During sight-in the first .270 Winchester round fired, and of course split wide-open. The Mark V is pretty good at gas-control, however, and while gas got inside the bolt body, it was diverted into the magazine by the three ports on the underside of the bolt. The floorplate blew open, and there was some splintering of the stock as well, but the shooter was pretty much unscathed.

Probably should also note that Otteson gives the Mark V a very high rating in gas-handling, and explains why in detail.

Hi Dwayne,

Yes, I remember discussing that powder problem with you.

Bet you didn't have any problem with the No. 1! I once made a mechanical mistake when loading some ammo for a No. 1, and when I went to sight-in the rifle, was wondering why the chronograph's reading's were so high. But it was the last of the three Shooting Chronys I owned, and it was the middle of a clear day with the sun high overhead, and Chronys were well-known for wonky results in high sun. Since the first two rounds fired acted pretty much normal, I fired a third--which blew the primer. I took the rest of the ammo home and pulled the bullets, finding that somehow the powder charge was consistently too high. But other than the blown primer, I never noticed any signs of high pressure other than the chronograph readings, and never felt even a hint of powder gas from the action.

Gerry,

Thanks--and a good point on left-handers firing right-handed bolt-actions.

But will note that while most right-handed actions have the receiver-ring gas port on the right side, at least one push-feed action that I know of has the port on the left side of the ring. Dunno if that's a real problem, though, because the receiver ring is a long way in front of a shooter's face.

I have recounted stories of rifles handling severe overloads and the resultant escaping gas, on this site and others. There is no doubt in my mind that the Remington 700 "three rings of steel" really does work. I've seen quite a few examples which were way beyond a leaking primer and the shooter had no idea there was anything wrong until he found he couldn't open the bolt. One of my favorites was the guy who shot a pretty decent black bear with a 7mm STW rifle in which he fired a 308 Norma Mag with 180 Swift A-frame bullet. A one shot kill; which was a good thing since he could not have fired another.
Another action which seems to handle gas exceptionally well, is the Savage 110. Again, shooters who have had a primer blow, or worse, in one of these are frequently not aware there is anything amiss until they find the bolt frozen shut.
For myself, I have gotten some particles in my face a couple of times; both with a Model 70 push feed. Surprisingly enough, when I blew a primer in my Model 54 Winchester (in 256 Newton), I saw smoke curling out of the action but felt nothing at all. Now this action is slightly modified and uses a Mauser 98 bolt stop. I also modified the bolt nose so I could fit the barrel with a counterbore to prevent gas from entering the left race way. On the right side, of course, the extractor cut provides an open route to the outside and, in my case, since I shoot left handed, to my face. Nonetheless, It worked out OK for me.
A non-bolt action which surprised me a bit was a Savage 99 in which the owner had, apparently, fired a double charge of 2400 in a cast bullet load. That primer pocket was about 30 caliber and the chamber was expanded but there were no missing parts and the shooter felt nothing but embarrassment.
When I was shooting competitive BR, I had one rifle I had built on a Wichita Mini action. This action had a shellholder bolt face, three locking lugs, a full diameter bolt body, and no loading port. Blow a primer in this and there was absolutely no clue except the case might be hard to remove from the bolt.
I don't know if one can do anything to cause a problem with a Number One. I've been shooting them since 1971 and, If I wanted to lopad hot, they would be my first choice. My current No. 1 is chambered for a rimmed cartridge and I have never even blown a primer although I have loaded it way too hot. I suspect this may be because the case is almost totally contained in the chamber. Even the extractor cut is minimal. I did blow the primer a couple of times in another No.1 in 6mm Remington but it hurt nothing. GD

greydog,

Have also heard from some people that No. 1's can be difficult to open after firing a hot load, but have not experienced that, and have probably owned a couple dozen over the years.

Just a guess on my part but wouldn't the receiver still offer some protection? It seems the bigger potential problem would be gas coming through the action on some of them anyway. I do feel much more comfortable with left hand bolt action rifles but still own a Lee Enfield 303 (as any self respecting Canadian should ) but definitely fire it with glasses on. On a somewhat related note is when I was younger I owned a Ruger 10-22, of course back then no shooting glasses either. I did end up with something in my eye and then decided it wasn't a good idea to fire semi auto's as a lefty. Technically the Browning BLR is a right hand gun but I don't hot rod the thing and definitely wear glasses when working up loads.

Greydog, I bet you have lots of stories from being a gunsmith lol. Probably seen it all. Thanks for the list of strong well built actions.

I would also guess any gas leaving the receiver-ring port would be directly out to the side. Unlike the flange on Mauser bolt shrouds, the port isn't meant to simply deflect gas that makes it around the rear of the bolt, but to provide an exit for at least some of the gas from a blown primer or case.

as did I...thanks John for that interesting read.....

MD,
I suppose, if one had a rough chamber, extraction could be difficult, If there was an error in manufacturing, angles could be off and opening could be difficult. The action was designed with, I believe, 2 degrees of angle on the locking surface, with the face being vertical. If this is right, the breechblock moves away from the case as it drops down. If this angle did not exist, the breech block could drag. Mind you, Martin Hagn makes his actions with vertical movement and a vertical face and I've not heard of any issues. Still, I like the idea of the angled surface.
Back to the bolt actions, it has often been said, in recent years, if one used a Sako extractor in his 700 or 40X, he was signing his own death warrant; especially if he shoots left handed. I've been risking my life like this since 1982 and have gotten away with it. Those who have blown a primer in a Sako may have had the extractor jump ship but it is contained in the receiver ring by the gas block/ rib. In a 700, the extractor is free to take flight but I think this is fairly unlikely if the barrel counterbore is fitted reasonably closely. I have considered fitting a savage-like baffle or a Sako-type rib but have not felt compelled to do so. When I built a bolt for a 40X receiver I had, I built it with a separate bolt head and could have incorporated the baffle but didn't. Just lazy, I guess. GD

MD

"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."
Kuhnhausen, in his Mauser Bolt Action shop manual, pointed out the wider cylinder at the back end of the bolt body provided for a wider bearing surface cocking ramp. Interesting that the wider cylinder is also part of the M98 gas baffling/diverting system.

I was unaware of the small ridge across the front of the rear tang was yet another gas handling refinement of the M98.

Thank you for yet another worthwhile read.

Interesting .

I’d have to pull my mark v out to look but From memory the “gas ports” in the bolt align with the “ejection / loading port “
I always assumed between that , the bolt body being larger than the bolt head , the relatively tight bolt lug area , and the rear shrouds design and material , that a case head separation would be fairly uneventful.... never had the pleasure though

You're right, the 3 ports are on the side of the closed bolt. Apparently the gas that blew open the magazine came under the bolt head.

The other possibility is the floorplate simply unlatched during the violence. As noted, I only heard about the incident, and all the accounts said the floorplate came open.

Either way , I wouldn’t have thunk it !

I have heard of floorplates coming unlatched on Mark V's chambered for the really BIG Weatherby magnums upon firing a round. But all of mine have been chambered for the "smaller" ones, the largest the 7mm Wby.

A lot of the gas handling discussions tend to be focused around military rifles and older classic designs. Maybe as mentioned, since this was a bigger deal back then. The Tikka T3 is one exception, sometimes. I think this is due to the fact the T3 came with a plastic bolt shroud, and this drew peoples' attention and imaginations to this area. I don't usually see people discuss in-depth the gas handling of newer actions like A-Bolts or X-Bolts, Ruger Americans and all the similar budget rifles fat-bolt or not, etc. I do think manufacturers could often do more in this area, because... why not?

Off topic, but the gas handling of a 760 must be pretty good.
Of course the design blocks a right hander.

An acquaintance fired 3 rounds of 30-06 loaded with 57gr of 4198, instead of 4350.
He saw a little smoke on 1 and 2, #3 locked it up, and broke the bolt.




He then looked at his son, and said,

"LETS SEE HOW THESE LOADS SHOOT IN YOUR GUN"!

The first round locked it up and broke that bolt.

760 bolts aren't available anymore!

Unfortunately, this guy does not drink, ever!
And he is a good mechanic and fabricator.

Drunk or ignorant can't apply.

Just a a case of Stewart Pidd.