Case Gauges

[Reloadron]

The following information is aimed at the new hand loader, the individual just getting started in rolling their own ammunition themselves. However, any input and added information from the well seasoned hand loader is most welcome and appreciated.

There currently exist a plethora of case gauges available to the hand loader. It becomes important for the hand loader to understand what these gauges will and of more importance will not do when considering buying a case gauge. Years ago gauges like this weren’t available to the hand loader leaving us to fabricate our own gauges and methods to measure case characteristics. Today case gauges in a variety of designs are readily available from a dozen or more manufacturers who cater to the shooting sports. Working from the least expensive designs to the higher end designs we can start with the basic case length and headspace gauge. Gauges like this are made by a host of manufacturers, L.E. Wilson, Forrester, Lyman and many others.







The above images illustrate a few examples of what is commonly referred to as a “Case Gauge”. When purchasing such a gauge make sure the case gauge you purchase measures the features you wish to measure. The majority of these gauges provide two characteristics of the case. They provide a Go/NoGo indication of the case base to shoulder datum and the case overall length. There are variations that are cut like a chamber to include the case diameter characteristic but the majority does not provide this data. I say they provide a Go/NoGo indication because this type gauge does not provide any quantitative values (no numeric values) about the case being measured.

Another case gauge design which does provide quantitative (we get real numeric values) is the design pictured below. While the below gauges are Hornady Lock-N-Load Headspace Gage 5 Bushing Set with Comparator just as previously mentioned this same or similar design can be found by other manufacturers.



The downside of the above is while when used with a good caliper they give a numeric value but the numbers are sort of skewed. The collets have a slight bevel which mates with the case shoulder. Below is an image of using one in conjunction with a true 1.630’ actual chamber headspace gauge. Note the gauge is reading 1.624” of a full 0.006” below the actual true reading it should be.



The gauge does however function well for its intended use. The idea being to fire a measured case, after firing resize the case to be about 0.002” below the measured value of the fired case. This is commonly called “bumping” the shoulder back and more on that term later. Just do not believe when using the gauge that any numbers you get are anything like your chamber headspace dimension.


A gauge I happen to really like is the RCBS Precision Mic set.



My personal experience is this gauge affords real measurement numbers and does so accurately. I only want to focus on the case measuring ability at this time. The above gauge is the .308 Winchester version and again using an actual headspace gauge for a comparison check we see that using this gauge in accordance with manufacturer’s instructions the gauge reads a true 1.630” or in the image 0.0 which acquaints to 1.630”.



A note about terms I have used here.

Headspace:

The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats. 1. BELT: A type of chamber design in which the cartridge seats in the chamber on an enlarged band ahead of the extractor groove of the cartridge body. 2. MOUTH: A type of chamber design in which the cartridge seats in the chamber on the mouth of the cartridge case. 3. RIMLESS: A type of chamber design in which the cartridge seats in the chamber on the shoulder of the cartridge case. 4. RIMMED: A type of chamber design in which the cartridge seats in the chamber on the rim or flange of the cartridge case.

Headspace Gauge:

A device used in a firearm to determine the distance between the breech face and the chamber surface on which the cartridge seats. Also called Breeching Plug.

Just for further clarification.



Currently many manufacturers are marketing their case gauges as I illustrated above as headspace gauges. While these gauges do not fit the actual SAAMI Glossary as being correct the term is none the less being widely used without discrimination. My objective is merely to point out a few gauges and their use as well as good and not so good points. I am not seeking a war on semantics.

Another popular term being used is bumping the shoulder back. Now if we take a fired case and scribe a perfect line around the case shoulder right on the case body and case shoulder start juncture and then we full length resize the case we will find our scribed line has actually moved up on the case shoulder. The argument becomes it is not possible to bump a shoulder back on a case which has full body case support which is exactly what a resizing die does. So what is really happening? So how is the new shoulder which is closer to the case head formed? As the case is full length sized, a small amount of case material is moved toward the mouth, with the a bit of the old body now forming the base of the new shoulder, and the base of the neck now containing a bit of the "old" shoulder. And as a result of that sizing process, the neck may have grown enough to need trimming. That said a simple Google of “bumping the shoulder back” will bring up countless hits so again a term which is being widely accepted in the shooting community.

Happy Measuring....
Ron

 

[HJ857]

Great write up and thanks for doing it.

I have one notation, when using the Hornady bushing system I have noticed that if a case has a bent rim it will throw off the reading.

I run autoloaders only and will reuse cases until it self destructs in some way and I see bent rims a lot. A slight twist of the case and re-measure can show you differences in case headspace. The difference is typically not very large but can fool you into thinking you haven't sized the case as much as you want to.

 

[Potatohead]

How do you spell "sticky" ?

 

[higgite]

How do you spell "sticky" ?

You spell it "Reloadron's post on the topic 'Case Gauges', dated August 12, 2014, 12:20 PM".

 

[cfullgraf]

Great write up and information.

Maybe after this thread has run its course it could be moved to the "Reloading Library of Wisdom". Easy to find and does not fill up the sub-forum page one with stickies.

 

[Reloadron]

Thanks peoples and let's keep additional information coming. The good and bad points of the different types of these gauges.

Ron

 

[sirgilligan]

Thank you.

What I have learned is that you must have some way to check headspace while setting up your resizing die. The directions that come with the die for setup do not guarantee that the shoulder will be set correctly. If the shoulder is pushed down the case from the neck to the head too far the case is essentially shortened and the space between the bolt face and the head of the case can be too much and problems may occur, problems that can be very dangerous.

I learned that this week. I am new at hand loading.

 

[cfullgraf]

The Sinclair Bump gauge is similar to the Hornady Lock n Load gauge shown above. But, the main difference is the Sinclair gauge measures changes in shoulder position as opposed to actual shoulder position.

With the Sinclair gauge, you measure the case before resizing and then after. It will tell you how far you have pushed the shoulder back.

 

[HJ857]

The Sinclair Bump gauge is similar to the Hornady Lock n Load gauge shown above. But, the main difference is the Sinclair gauge measures changes in shoulder position as opposed to actual shoulder position.

Thank you for posting that and explaining so well. I've heard of it but never understood exactly what it did that was different from other gauges. I'm going to go look that up right now and probably order one!

 

[Reloadron]

The Sinclair Bump gauge is similar to the Hornady Lock n Load gauge shown above. But, the main difference is the Sinclair gauge measures changes in shoulder position as opposed to actual shoulder position.

With the Sinclair gauge, you measure the case before resizing and then after. It will tell you how far you have pushed the shoulder back.

Thanks Chuck for that piece of valuable information.

Ron

 

[TBH]

I use the RCBS mic. The only thing I might add, would be for the new rifle reloaders.

There are two ways to adjust a sizer die. 1- per die directions ( sized to SAMMI specs).
2- adjust the sizer die to push the shoulder back on fired brass from a specific rifle .002-.003"

The benefit of the first way is the loaded ammo should work in any modern rifle of the same cal.
The benefit of the second way is accuracy and ease of reloading. Also reduces the risk of stuck cases in the die! But only use in the rifle the brass came from.

 

[Potatohead]

My little tid bit to add, and this would be aimed at us new guys, obviously, is after you have your case inserted into the gauge, run your finger across the case head to "feel" where it sits on the gauge. My instructions didnt mention this, only to use a straight edge and to use your eyeballs. Feeling whether it passed or failed, and into which step it is closest to, is much easier then trying to see it IMO.

This might be natural to some , but I didnt think to try it until after my eyeballs had crossed and I had a migraine from squinting

 

[Reloadron]

My little tid bit to add, and this would be aimed at us new guys, obviously, is after you have your case inserted into the gauge, run your finger across the case head to "feel" where it sits on the gauge. My instructions didnt mention this, only to use a straight edge and to use your eyeballs. Feeling whether it passed or failed, and into which step it is closest to, is much easier then trying to see it IMO.

This might be natural to some , but I didnt think to try it until after my eyeballs had crossed and I had a migraine from squinting

Good stuff and something else mentioned, when using certain gauges like the RCBS Micrometer types make sure the case heads are free of any burrs or dings. When I was taking pictures I ran a 223 case where the extractor put a burr on the case head. That burr amounted to .007". Since I ended up going with a 308 case for the pictures I forgot about that 223 case example.

Ron

 

[Potatohead]

True that, my little rinky dink Lyman also.

 

[R.W.Dale]

http://www.sheridanengineering.com/index-2.htm

The Sheridan gauges are unique in that they have a slot that allows you to visually see what about the shoulder is preventing chambering, be it insufficient sizing or a slight buckle from over enthusiastic crimping.

It also has THREE steps cut into the face, go and nogo as well as SAAMI brass minimum. It also measures diameter as well which it's worth noting that all case gauges do not do.

 

[fguffey]

My instructions didnt mention this, only to use a straight edge and to use your eyeballs.

My instructions go back to 1956, back then a pocket rule was as common as a shirt pocket. Once I found a gap, I reached for the feeler gage. Without a straight edge/pocket rule? All a reloader needed was a flat surface, stand the case on the flat surface then place the gage over the case and measure the gap between the bottom of the gage and top of the flat surface.

A reloader needed to understand the Wilson case gage was a datum based gage. Slight difference, a datum is not case friendly, it has a sharp edge, the Wilson case gage has a radius on their datum to prevent the round mark around the shoulder as in measured from.

F. Guffey

 

[oldfortyfiveauto]

http://www.larrywillis.com

I have this one and am very happy with it. Also like the RCBS mic setup.

 

[gamestalker]

Making a gauge to use as a reference for shoulder height.

Using several once fired pieces of brass from a dedicated chamber, I resize, precision trim, ream / chamfer, and slightly over bell a piece of dedicated handgun brass of appropriate size in regard to the size bottle neck cartridge to be measured. I then slip it over the case mouth of the bottle neck case, square it up nicely to get a consistent measurement, then measure head to shoulder datum with a dial caliper. Pretty simple process, and as long as I take several measurements, and make sure it is squared up, I get a good clean measurement, it functions very accurately for me.

And I also check to see just exactly how much head space I have with the brass chambered, then by fitting pre-measured, or confirmed feeler gauges into the bolt face, then chamber the once fired brass, adding thicker feeler gauges until I've found zero. It sure helps know how much shoulder bump is needed, or not needed.

There are other ways to do the same thing that I've tried, but the piece of brass thing just seemed so simple and works great for me.

GS

 

[horseman1]

Gamestalker, thanks for that idea. I got motivated to make something to check the shoulder setback on my 223 and 30-30 reloads. A trip to ACE Hardware (with some brass cases in my pocket) should do the trick. Gotta love that place... You can still find Strike Anywhere matches, some Craftsman hand tools that still say Made in USA and real copper Chore Boys .

[edit] and Dad's Rootbeer!

 

[Slamfire]

Gene Barnett made for me this reamer cut gage (on right) from a barrel stub. Both of the cases in these gages are once fired range pickups, and as you can see, the Wilson gage swallows them, but the reamer cut gage shows just how ballooned these cases are.



Frank White at Compass Lake Engineering will create these reamer cut gages, I paid him $35.00 for a 223 Rem. He used the exact same reamer he was using in chambering a match barrel, but, he offered other options.

Compass Lake Engineering:
719 White Drive
Alford FL 32420

Proper sizing of cases for gas gun mechanisms is important for function and safety. The first, function, you will encounter many threads where a new gas gunner is having extraction/ejection problems in his rifle. Upon further questioning, almost always the shooter is using brass fired in a different rifle. Then comes the questions of whether the brass was full length sized, and often it is, and gaged, but the sizing die is a standard sizing die. The usual cure is full length sizing with a small base die, because a standard sizing die would not reduce the case enough and upon unlock, the fired case is dragging against the walls of the chamber.

Most gas gun mechanisms have enough inertia to “crunch fit” a slightly long, or slightly fat case to the chamber. Both of these problems can be cured with small base dies and sizing to gage minimum. In most mechanisms, all a crunch fit case does is cause a failure to extract. However, for shooters of Garands/M1a’s, Mini 14’s, M1 carbines, a crunch fit case may reveal a hidden and perhaps the most dangerous design deficiency in this mechanism. All Garand type mechanisms have had, and will continue to have, out of battery slamfires. The Garand mechanism, like most semi auto rifle mechanisms, does not keep the firing pin positively retracted and relies almost exclusively on primer insensitivity to prevent cartridge ignition after a firing pin rebounds off the primer.

As can be seen in this M1 carbine receiver, nothing is holding the free floating firing pin as the bolt travels forward. Only at the final moment does the firing pin hit anything, and that bridge does not function well as a firing pin block. In the M1 carbine manual it is called a firing pin retraction cam, and that is its primary purpose: to pull the firing pin out of the primer during extraction. It only comes into effect during cam down and does not work well, if at all, in preventing incidental contact between the firing pin and primer.







This is a case, from an eight round clip, chambered in a Garand. Notice the nice deep pot mark



The highest risk of an out of battery slamfire occurs when a long or fat case is chambered and the bolt has to “crunch fit” the case to the chamber. In the Garand mechanism it is possible for the firing pin to rebound off the primer without the lugs being in engagement.

I tested this in all matching examples of these Garand receivers. The firing pin tang is just touching the receiver bridge, the tip is fully extended around 0.064”, and the lugs are not in engagement. If a fat or long case caused the bolt to stop, slow down, that firing pin is rebounding off the back of the primer at the highest forward velocity in the bolt travel.







SAI M1a, same condition as the Garands above



Other, later mechanisms use certain design features that prevent firing pin contact with the primer until after the mechanism is locked. But, the Garand mechanism was an early semi auto rifle. It was also never intended to be fired with anything but new military ammunition of minimum dimensions with relatively insensitive military primers. For this mechanism, reducing the case below chamber dimensions reduces the risk of an out of battery slamfire. You want the bolt to close on the case without any chambering resistance. This is why small base sizing and using case gages is important. Also, using the least sensitive primer you can find, the "mil spec" primers by CCI (#34) and Tula will also reduce the risk. Unfortunately because primers all vary in sensitivity, and you don't know the sensitivity of each individual primers, you may, unwittingly , have a particularly sensitive primer in your case. If you have done your part by correctly resizing, then it is more likely than not that you will have an inbattery than an out of battery slamfire.

Still, despite everything you do, you can still have an out of battery slamfire in the Garand mechanism. Based on a 1963 test on factory new M14's, with three HRA and three SA M14's each to be fired to 6,000 rounds, one SA M14 fired out of battery with military ammunition.

* USATECOM Project No. 8F-3002-04, Comparison Test of Rifles, 7.62 mm, M14, Manufactured by Springfield Armory and Harrington and Richardson Arms Company, July 1963

At round 5271 a Springfield Armory M14 went off out of battery, with military ammunition. The report states:

“One rifle fired when the bolt was in the unlocked position causing breakage for the firing pin, extractor, bolt roller, ejector, and stock. The magazine split, causing the magazine floor-plate spring and 12 rounds of ammunition to be ejected against the bench rest from which the rifle was being fired. The case ruptured and several pieces of brass were found in the area. A broken part of piece of brass perforated a cardboard box with was position between the gunner and the proof director. The cardboard box was used as a brass catcher. Not all the broken pieces were found. Although no one was physically injured this is a seriously unsafe condition.”

So, six rifles were tested, five completed the test firing 6000 rounds each, one slamfired out of battery at round 5271, for a total round count of 35, 271. Therefore the probability of an out of battery slamfire with mil spec primers is 1:35,000.