by Dana Delesoy
GunsmithUSA Contributor
In my early years as a firearms owner, the first two guns I owned were a shotgun and a rifle. The next gun on my wish list was a light-weight, backpackable, survival type rifle chambered in .22 Long Rifle. Being an avid shopper at Cabela’s (via the internet), I looked at their offerings and noticed a Henry US Survival Rifle that fit all of my requirements, so I purchased it. This gun has been manufactured for years as the AR 7 by several manufacturers. Overall it has proved quite reliable straight from the box. Personally, I think it’s a neat little piece and really like it for what it is.
Recently I realized the Henry US Survival chamber has an undesirable factory design I refer to as “unsupported case area” (or unsupported chamber area). It is located at approximately the 3 o’clock area of the chamber (the same area as the extractor groove/cut on the barrel). The unsupported case area is .031″ (1/32″) depth and .125″ (1/8″) width (same width as extractor groove on the barrel). I say “factory design” because every Henry US Survival chamber I’ve seen photos of on the internet show they all have the same design, plus a friend has the same gun and it has exactly the same unsupported chamber area.
Does the unsupported case area of the chamber pose a problem? Potentially yes, if not already. Why? Like most cartridge cases, .22 rimfire cases are made of the relatively soft metal brass. When cartridges are fired, pressures occur inside the cartridge case which are forceful enough to expand brass. Since the chamber surrounds the cartridge case, it is the chamber that limits the amount of brass expansion in both diameter and length. The unsupported case area of the chamber provides an avenue for the brass to continue expansion. This has the potential for the brass to expand to the point of bulging, or rupturing, depending on both the size of the area and the chamber pressure of the particular cartridge.
Bulged and ruptured cartridge cases are analogous to the inflation of a balloon. Inflation (from gases) induces pressures within the balloon which cause it to expand. The larger the balloon expands the thinner its material becomes. If there’s nothing supporting the balloon’s material (unsupported balloon) to limit its expansion and pressures exceed the material’s expansion capacity, the balloon will burst. Everything has its limits and, like the balloon, brass is no exception.
Bulged and Ruptured Cases
Because the unsupported case area is in the same location the extractor hook rests during battery, a bulge forming in the same area can prevent the extractor’s hook from being able to get enough purchase on the case rim to hold it on the breech face until the ejector hits it.
In the event of a case rupture, a pressure leak occurs that is forceful enough to bend or break the extractor. A rupture is a worst-case scenario because gasses and/or fragments (brass, extractor material) can travel, and DO, in the direction of the shooter (or bystanders) and can cause injury. This is one reason we as shooters (and bystanders) should wear appropriate eye protection at all times when guns are going off around us.
When a bulge has formed and pressures subside, the bulge may make the case stick in the chamber and hard to extract in a locked breech gun. In this situation, the extractor’s hook may tear through the case rim while trying to extract the stuck case, especially if the hook has good, positive engagement on the case rim and/or if the hook is sharp.
It can also keep the case from extracting itself in a blowback operated gun like the Henry (AR 7). In this case, when a spent cartridge case sticks in the chamber, the rearward expansion of the base of the case can impart enough energy to the bolt to move it rearward far enough to pick up the rim of the next round in the magazine and push its nose into the case still stuck in the chamber. Obviously this results in a jam. In shooters’ terms, we refer to this as “a bad thing”.
For clarification of the terminology I use throughout the remainder of this article please refer to the pictures, in particular “Chamber-end view of Factory Barrel”.
Another area of concern
At the 6 o’clock area of the chamber the factory put what I consider an over-chamfer. The intention here is to provide a feed ramp to assist cartridges (in this case round nose lead bullets) in transitioning into the chamber. There’s no doubt an edge (particularly a sharp edge) at this area of the chamber can interfere with the feeding of cartridges into the chamber but the over-chamfer designed into this chamber has induced a fair bit of unsupported case area. The picture “Chamber-end view of Factory Barrel” above illustrates the over-chamfer.
The oval-shape of the over-chamfer spans from approximately the seven o’clock area of the chamber’s edge to the five o’clock area. The oval tapers into the chamber (like a funnel’s taper) approximately .020″ in depth. The oval and the taper are the actual unsupported area that has been created in the chamber.
A further look into the chamber’s state
Although my gun has not experienced case bulges or ruptures, I explained its situation (and my concerns) to Master Gunsmith Ken Brooks. He stated that given the amount of unsupported case area he’s surprised the gun hasn’t experienced any bulged or ruptured cases. I asked Ken if the unsupported area should be removed and Ken categorically answered “Yes, it should be fixed.” Ken is “An ounce of prevention is better than a pound of cure” type of person, and rightfully so.
I asked Ken how he would proceed with the fix. He said the process is simple for this gun, and kindly explained to file the barrel until the unsupported case area is removed then square the barrel to the bolt. This led to another question for Ken. I asked: “As the unsupported case area is removed the chamber is proportionately shortened. How much can the chamber be shortened before it becomes too short and mandates a re-chambering? How do I discern this?”.
Ken’s answer was (as paraphrased by me); “Removing .031″ is not a huge amount. To check if the chamber does or doesn’t need re-chambering, point the muzzle to the ground and drop a brand new cartridge into the chamber. If the cartridge enters all the way on its own, the chamber is long enough. If the chamber is shortened too much, the cartridge won’t fully enter on its own and a kiss with a chamber reamer is necessary.”
Thinking through the repair
When the gun is in battery, the front of the bolt stops against the chamber end of the barrel. This means that however much the chamber end of the barrel is shortened, the bolt will move equally forward. Filing .031″ off the chamber end of the barrel allows the bolt to move .031″ further forward. Will this pose problems for anything? Well, let’s see . . .
When the barrel is removed from the receiver the bolt moves forward, pushed by the recoil springs, until the operating handle contacts the receiver and stops further bolt travel. This is why the operating handle must be removed from the bolt in order to remove the bolt from the receiver. When the barrel is securely fastened to the receiver, the bolt is shoved back and the operating handle is .120″ from the front of the ejection slot. Simple math indicates that shortening the chamber end of the barrel .031″ leaves .089″ (.120″ minus .031″ = .089″) clearance between the operating handle and the receiver. Operating handle clearance is not an issue with .031″ shortening of the barrel’s breech end.
My theory regarding the repair
Since my gun isn’t bulging nor rupturing cases with the .031″ unsupported case area it already has, any reduction is better than where it’s at now. I do not have a .22 Long Rifle chambering reamer so I’ll play on the conservative side of the situation and set out to shorten the chamber .015″ rather than removing the entire .031″.
Supplies for the job
This is not a machining project by any means. The work will be performed mainly with hand tools. For those with access to and who are adept with machining equipment, this project should be easy. A flat file will be used for the bulk of removal of metal. A sanding block will be used to remove scratches left from filing. A Foredom tool with a sanding and polishing mandrel will be used to do the finishing touches.
Checking for chamber smoothness
The first step I recommend is to determine if the gun’s chamber is rough or smooth because a rough chamber can provide a false reading when checking for cartridge seating depth following the repair process.
Check chamber smoothness by pointing the muzzle vertical to the ground and drop a new, unfired cartridge into the chamber. The chamber is smooth enough if cartridges can freely slip into and fully seat into the chamber via gravity and the cartridge should freely fall out of the chamber when the muzzle is pointed straight up. If the chamber is rough the cartridge will not freely drop in or out of the chamber under the force of gravity. A smooth chamber is always a benefit to a gun anyhow.
Polishing the Chamber
The Henry’s barrel removes/installs easily, which makes the task of polishing the chamber quick and easy. The supplies and equipment I use for polishing is 400 grit silicon carbide sandpaper, spring steel stock for the mandrel (the part the sandpaper wraps around) and a Foredom Tool.
The sandpaper is taped to one end of the mandrel and the other end of the mandrel inserted into a rotary tool. I wrap the sandpaper the opposite direction the mandrel spins so it doesn’t unravel as it spins in the chamber and it ensures proper polishing action.
The sandpaper needs to be a length that when wrapped around the mandrel is large enough in diameter to fit slightly snug when inserted into the chamber. The photo “Mandrel and sandpaper used to polish the chamber” shows the first length of sandpaper was cut too short (2 1/8″) thus not being large enough in diameter to effectively polish the chamber. I had to add (by taping) another length (1 1/2″) to the short length.
The sandpaper needs to be approximately 3 1/2″ in length, based on the .068″ diameter mandrel I use. A 1/8” dowel with a 5/8” slit in the end will work as well. Since this gun is chambered for .22 Long Rifle I cut the width of sandpaper the same length as a .22 Long Rifle case (5/8″ or .610″) or slightly longer (3/4″ or .750″). In any event, the sandpaper width is the same or slightly longer than the cartridge CASE length.
Avoid sanding the chamber throat and rifling while polishing the chamber! Having the sandpaper a similar length as a .22 long rifle case will serve as a depth indicator. If you can’t see the sandpaper during polishing you have inserted the mandrel too far and will be polishing the rifling. Wrap the sandpaper snugly around the mandrel and insert it into the chamber. While keeping the mandrel in line with the bore, spin the mandrel and slightly move it in and out of the chamber while keeping an eye on the depth indicator.
The process only takes a few seconds, so go slow and check often. You don’t want to enlarge the chamber diameter nor oval the chamber. When a cartridge will freely drop in or out of the chamber the job is done.
Filing process
A bevel of approximately .040″ depth surrounds the outside of the breech end of the barrel. This gives you a good reference for seeing how filing is progressing. I clamped the barrel in a vice with padded (rubber or wood) jaws and leveled the surface to be filed (end of the barrel).
Plug the chamber with a Q-tip or cleaning patch to keep it and the bore free of excess filings. I used the largest width flat file I had on hand (.850″) which is slightly narrower than the area to be filed. The end of barrel is .900″ in diameter. A file slightly wider than .900″ would make the task quicker and easier to perform.
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