top of page

100-Round Case Gauge FAQs

- My ammunition fits in my gun but doesn't fit in your gauge. What gives?

In a nutshell: it's better to reject a few good rounds than let a bad one through.

In detail:

Our gauges are reamed with minimum-spec SAAMI chambering reamers. The way SAAMI specifications work, a maximum-spec round will fit into a minimum-spec chamber. However, most manufacturers ream their chambers with SAAMI maximum-size chambering reamers so that as the reamers wear down, the chambers are still 'in spec' until the reamer wears out.  Some manufacturers start even larger in the name of reliability (these are often the same ones referred to as having "acceptable combat accuracy" in reviews and cursed by reloaders for bulging brass)

Thus, given variances in brass and reloading dies and your chamber, rounds that are beyond SAAMI maximum ammunition size may well fit in your chamber.

Since we don't know what size your chamber is, we make the gauge holes to the minimum size so anything that fits the gauge should fit your chamber, even if it gets a bit dirty.

If a few rounds don't fit the gauge, toss that into the 'practice' pile or 'check with barrel' pile. In addition, if you load lead and coated-lead bullets, they are often .001" or more over the nominal bore size. This isn't a problem in-use as the softer lead conforms to the leade and rifling fairly easily, but in a tighter gauge they may stick.
  Also try washing out your gauge (see below)


Pressing cases lightly into the gauge is acceptable once you determine this ammunition also fits your chamber. The 40XL gauge is designed with a bit more room for lead and coated-lead rounds and is the suggested alternative to the 40L.

A few of our customers that load oversize lead bullets instead of dropping the loaded rounds in bullet-first where they will stick, drop them in the gauge base-first (this works best with .40 and .45 ACP). This doesn't check the bullet itself at all, but verifies the case is not bulged, which is usually what causes 40 caliber 'death jams'.

For 9x19 loaders that have oversize chambers and want a gauge that rejects less rounds, we have a few "9L" gauges that are reamed oversize.  They will pass a lot more ammunition, but as they are over SAAMI spec in size it is possible a round will pass that will not fit in any SAAMI-spec 9x19 chamber.

Troubleshooting ammunition that doesn't fit the gauge.

We often see the same reasons for ammunition not fitting the gauge and here's how to identify and fix them--

(As an aside, we have measured several commercial gauges to be quite a bit over SAAMI minimum specifications. Just because a round passes one of these gauges and not ours is not necessarily an indication our gauge is out of spec.)

  • Washing out your gauge--  Dust and residue from manufacturing, testing and shipping can occasionally creep in new gauges and used ones can gather dirt and lube and so on.  Fill a small pan with warm to hot water and a bit of dish soap.  Submerge the gauge in the water for a few minutes, pull it up and down to flush water through the holes and then rinse and dry (it will dry much faster if you rinse in hot water).  You can use soft brushes and cleaners that are safe for aluminum, but try just a water rinse first.

Testing your gauge and ammo--


First, get some new factory ammunition (not even factory-reloads) and try dropping that into the gauge. It should 'plunk' nicely in to every hole. Every gauge is tested before shipping with factory ammunition so this will verify if the gauge is still in-spec.

If all your ammunition sticks out about the same amount, it is often OAL or crimp. Take a Sharpie or other ink marker and mark up a few of your rounds that don't fit, all over the front half of the case and bullet, drop them into the gauge and give them a light push. Push them back out and examine them carefully to see where the ink has rubbed or scraped off.

If you see a mark on the bullet where it starts to taper down, your bullet OAL is too long for the gauge/chamber.

Solution: Load shorter so the bullet is within SAAMI specs or get an XL gauge if your barrel permits it.


If you see a mark right at the mouth of the brass, you have insufficient crimp or your brass is too long.

Solution: Measure and trim brass as necessary, increase crimp if needed.

If a lot of your ammunition sticks out more or less random amounts, it could be insufficiently-resized brass, slightly oversize bullets or dirt and dust in the gauge.

First try rinsing out the gauge with water and a cloth or compressed air and try again. A soft cleaning brush can also be used, but metal brushes should be avoided as they can scratch the holes.  Gun cleaning solvents that do not attack aluminum may also be used carefully.

If this doesn't improve things, take some re-sized unprimed brass and drop the empty brass into the gauge to verify your brass is being sized sufficiently. It should drop in and out easily, if not, check your dies and reloading setup. Brass fired in oversize and unsupported chambers will often appear to have a 'belt' at the base where the reloading dies can't reach and will not fit the gauge or your barrel. Roll-sizing the brass can repair this but beware of overworking the brass.

If the brass is being sized correctly, try marking up a few bullets on loaded rounds that don't fit as above with an ink marker and press them lightly into the gauge (often this will push the round all the way into the gauge). Remove them and inspect them carefully and if you see scrape marks in different locations on different bullets, it is likely the bullet is slightly large or out of round. This is quite common with lead and coated/plated lead bullets and not usually a problem except in gauging. If this ammunition works well in your firearm, you can live with pressing them slightly into the gauge or get an XL gauge designed for lead and coated lead bullets and use that. If you have access to an accurate micrometer, measuring the bullets at several places will also often show size changes.

If just one or two holes seem to be bad (ammunition that this hole rejects fits all the others), it could be dirty or damaged.

Clean it and inspect it carefully for dings in the rim area or debris in the hole. There will be tiny variations from one hole to the next, but they should not cause any issues like this.  We can repair some gauges depending on the nature of the damage.

If you still have questions, please contact us for assistance.  We can examine some dummy rounds of your ammunition if needed.

- What is this "Leade" you mention?

Leade is the taper at the front of the chamber that transitions the bullet from the chamber area into the rifling. It is also often called the "throat" Rifling lands are smaller than the bullet so they can bite into it and make it spin. The leade is where the lands taper down to meet the bullet. Leade is specified along with other chamber dimensions by SAAMI (see example below from .40S&W). Often the maximum OAL of a particular bullet is determined by where that bullet profile intersects the leade. This is important if you load your ammunition over SAAMI lengths. Without a correspondingly opened-up leade (also sometimes called barrel throating, which is not to be confused with chamber throating which takes place at the other end of the chamber), your slide can be slamming the bullet into the rifling (or worse, back into the case) every time a long round is chambered.


Most of our gauges have the first part of the leade reamed in by the chambering reamer and so will catch some over-spec rounds (Exceptions include the .40L and 40XL).







100-Round Case Gauge FAQs

- Ammo fits the gauge but jams in my pistol and it is hard to extract loaded rounds.  What's up with that?

Most commonly your OAL is longer than your chamber allows, so your bullet is getting jammed into the rifling and possibly set back further into the case.  This is sub-optimal in pistols, so here's one way to check the maximum OAL your chamber allows for a particular bullet.  Usually this is not the OAL shown in your loading manual, since that's going to be a one-size-fits-all number and likely measured with a different bullet than you are using.

First unload your pistol and field strip it.  Clean the barrel and chamber, set all the other parts aside.  Grab a few of the bullets that you want to use and some calipers.

100-Round Gauge FAQ- OAL

Then search through your cleaned, fired (but not yet resized) brass for a case that fits the barrel chamber-- it stops solidly on the case mouth when pushed in and can be picked back out with your fingers.  Now check that case also allows you to push a bullet into the unsized case with some drag but not too much force (it shouldn't take a lot of tries to find one, but you may have to try a few). 

Seat your bullet by hand about 1/8" into the case so the fired-case plus bullet "round" is too long.  Push this round into your chamber until the brass seats on the case mouth.  

Carefully extract the round and measure the OAL (don't squeeze too hard with your calipers or it will shorten).  Pull the bullet back out and repeat a few times with a few bullets to get a baseline measurement.  This baseline is your absolute-maximum chamber length with that bullet (1.1325" in the picture below).  We suggest making your target OAL at least 0.010" shorter than the baseline to allow for variations in bullet, temperature, seating and dirt.  If the baseline number is much longer than your desired OAL, you can load to that; your chamber has room to spare for that load.  


Mark the piece of brass and stash it somewhere handy so you can use it again if you change bullets or barrels.

Check Box FAQs
50 Round Gauge Spacing

- Why is my gauge shorter than a loaded round?

The gauges are not OAL-length for several reasons, the main one being maximum OAL varies depending on the bullet profile, so we would have to pick one and it would be wrong for other bullets.

The reason for that is OAL is governed by two things--

  1. The maximum length that fits and feeds through magazines and action

  2. Where the bullet profile intersects the chamber leade.

This second number is what determines the max-OAL in many cases-- bullets with more of a cylindrical shape will hit the chamber leade and stop before a more tapered bullet does (see discussion of 'leade', above). This intersection is difficult to measure with calipers so the load books do the work and give reloaders an overall-length value to use.

For example: Hodgdon lists the OAL for a loaded 9x19 115gr Speer Gold Dot at 1.125" but a 147gr Hornady XTP OAL at 1.100". The 147gr Hornady is a truncated-cone design with a long .355 cylindrical section whereas the 115 Gold Dot is more rounded and can be loaded longer.

Our regular-size gauges (all but the L and XL) have the first section of the chamber leade reamed in so they will reject over-long rounds where the bullet profile won't fit a SAAMI chamber. The L and XL are designed for use in combination with firearms with extended leades.

Additional reasons to make the gauges shorter than a specific OAL value are:

  • Detecting under-length (and arguably more dangerous) 'short' rounds would be more difficult. By placing our gauge on a smooth flat surface under-length rounds will stick out less than longer ones.

  • Reduced material cost and weight for lower cost to you

  • Poking rounds out is easier

  • Decreases wear on the gauge if you load it on a flat surface as that takes the impact of rounds dropping in and provides consistent light insertion force lifting it up.

  • Easier to swipe a marker across the base of ammunition without marking up the gauge when it's on a surface.



- What ammunition boxes work best?

We designed the gauges to work with the most common square 100-round boxes, including Dillon & MTM. Berry's most recent boxes also work very well. Boxes with slanted tops and special latches do not work as well. We suggest 100-round boxes, although some dextrous people can make two 50-round boxes work.





- What is the difference between the silver and black gauges?

The black gauges are anodized for longer life and appearance. The silver gauges are only surface-treated and are therefore slightly more accurate, but will wear out somewhat sooner (you should still get tens of thousands of rounds or more out of either). The black gauges have 1/4" accessory mounting holes while the silver ones mostly do not. Some gauges are not available in black for manufacturing reasons

- Why does my gauge have two holes in the front?

These are used in manufacturing and can also be used to mount accessories onto the gauges or attach them to fixtures for commercial users.  If you do use the holes, take care not to bottom screws in the holes to avoid deforming the gauge bores.

Note that many silver-finish gauges do not have these holes.

- What is the difference between the .40, .40L and 40XL?

The 40 gauge is designed only for SAAMI ammunition.  Some .40s have slightly larger leade areas, but do not depend on that.

The 40L gauge has been discontinued as of mid-2016.

The 40XL is designed with a long-leade and a bit more bullet area than our old 40L gauge, so coated-lead, plated and lead bullets drop in and out more easily.  This is the one to get if you load coated or lead bullets on a regular basis.  You will however have to verify OAL yourself.

- Can I use a 40 gauge to check 10mm?

Sort of.  The 10mm is .150" longer than the .40, but all but the last part is identical enough for gauging.  If you don't mind not-checking the extractor groove and rim as seen below, you can just drop them in.  You can also flip them backwards into the gauge to check the rim area, but be aware the .40 chamber is smaller than the rim spec for the 10mm so it might cause rounds to stick that are actually in-spec.

- Which 9x19 gauge should I get? 9x19? 9 Match? 9 Supermatch?

Since 9x19 has been made for more than a hundred years in a vast number of countries, specifications and dimensions for it are all over the map. The 9 Supermatch gauges are made at or below the SAAMI minimum chamber spec and will reject a surprising amount of ammunition. This is good if you only want the very best ammunition for your tight-chambered custom gun or extra reliability for a big match, but can be annoying if you have a looser-chambered production gun.  The 9 Supermatch is only made occasionally in small quantities so is often unavailable for periods of time.

Most users will be happier with the regular 9x19 which is made a few thousandths of an inch larger.  Several of our national-champion team members use regular 9x19 gauges for all their match ammunition.  We consider all our regular gauges to be 'match grade'.


- Why is there no chamber step in my older .38SC gauge? Can I use it for .38 Super?

[As of mid-2016, .38 SC gauges are now made with a 'Nonte' style chamber, so the following does not apply.  If you have an older .38 SC gauge and want to exchange it for one with a stepped chamber, please contact us]

This is a weird leftover from the early days of the .38 Super cartridge. It was originally designed to headspace on the rim like revolver rounds of the day and SAAMI has never updated their specification to match what most modern gun builders use for chambers (that is probably a can of worms they don't want to open with a bunch of old guns around). Since there are no SAAMI specifications for .38 Super Comp or TJ or .38 Super Nonte (the most common headspace-on-the-case-mouth variants) as of yet, we had to go with the SAAMI reamer to avoid a huge mess of which custom specification and brass and gun builder is correct.

This means rounds will change where they sit in the gauge depending how much bullet crimp you use, so you'll have to determine with a few known-good rounds where the good ones should sit and compare others to that to check case length. Case bulges, most cracks and rim problems are still caught as well.

The .38 SC gauge can be used for .38 Super but it will not check for oversize rims and case length since the rim recess is not reamed.  We make a .38 Super gauge which is a better choice.  That will work for Supercomp rounds as well although obviously won't check the rim size.


- How can I clean or disinfect my gauge?

Soap and hot water works well as does isopropl alcohol and gun cleaning solvents that are safe for aluminum.  You can use any cleaner that is safe for aluminum on the gauge.  If you use bleach or other harsh chemicals please check on a small area first to make sure it doesn't discolor.  Avoid scraping the holes with metal brushes and scrapers as this can scratch and distort them.

- Will you make me a gauge in XYZ caliber?

Maybe. We almost never make one-offs because they are very time consuming and costly. However, if you want something we don't currently make, drop us a line and if enough people do that, we'll probably put together a production run.

- What size ammo boxes work with the 50-round gauges?

"Medium" or Mid-size size ammo trays work well.  These are commonly available OEM.  Click here for some more information


This USPSA/IDPA box only measures 8.75" long and that's way shorter than the USPSA box!

Check that you have removed the IDPA plate from your box. If the text on the inside doesn't say 'USPSA', then it is not in USPSA configuration. (Make sure the IDPA plate is installed tight and flush with the side wall for IDPA use.)

This box only measures 6" wide but the tolerance in the rules says I can have +1/16" What gives?

Tolerance is just that. It means boxes that are a bit bigger than the spec are tolerated, but boxes that are right at the spec are also legal. Do not depend on tolerance to get your pistol to fit or you will be unhappy when you run into a box that is made with little to no tolerance.

Note that as of 2022, most of our boxes are now made to the +1/16" spec.  

Why does my gun not fit this box while it does fit in the other box at my club?

These boxes are designed to be close to the minimum-size at room temperature so there will be no question that a pistol that fits this box will fit any other legal box.  Wooden boxes can also warp and change dimensions with humidity and temperature changes. We calculate this box will expand or contract approximately 0.010" in length (a bit less in width and height) if it's temperature is raised or lowered about 120 degrees F/ 50'C.

I'm running a major match and have no box, can I use one of yours?

Yes!  In 2017 USPSA and DNROI approved our boxes for match use.  If you have one already, you'll want to check it's actually within the specifications and not a tiny bit small.  Our official "match" boxes are at the maximum-allowable size, size-checked and have a bottom plate with the appropriate rules laser-engraved in to avoid arguments at the chrono station.

.22 Basepad FAQs

I lost the set screw or wrench from my +1, +2 or +3 basepad. What do I need?

The set screw is #4-40 x 3/16" or so long (1/8" or 1/4" will also work depending on the pad)
Once you get the screw, poke the wrench up through the hole from the bottom, place the set screw onto the wrench and back the screw down into the hole. The holes are not threaded all the way through so the screw can't be lost while the magazine is assembled.

The wrench is a .050". This is usually the smallest one in sets of wrenches, but check the label before buying a set

Centerfire Basepad FAQs

What magazine is the CZ SF1 pad designed for?

The CZ SF1 pad is designed for the Mec-Gar MGCZ7517 It's the latest one with the blue follower and the best one available for competition.  Other mags may or may not work depending on the tube length. SP01 tubes will work but will stick out a lot. Older CZ75 mags may not seat.  The "BX" basepad will let older CZ magazines seat properly. 

What is the difference between the CZ SF1 and SF2 and SF3 pads?

The CZ SF2 pad is designed for the CZ Shadow 2 which has a slightly shorter frame height.  It covers the 'gap' between the frame and pad better than the SF1 pad on a Shadow 2 and also blocks over-inserting the magazine and jamming things up if that's a problem for you.  SF2 pads will probably work on a Shadow or SP01 but you should check to verify they seat properly before taking them to Nationals.  The SF3 pad has a cut for the 'toe' on newer factory basepad retainer plates.

What about the brass basepads?


They are cool.  You should get some.  They won the USPSA Nationals in Production, so how can you expect to win without them?

OK, for some specifics, they are just under 2 oz more than our aluminum basepads in both the TF and CZ versions which by no coincidence whatsoever is the amount of weight allowed added by the new USPSA Production rules (they are not-allowed for IPSC so if you shoot outside the USA or the US IPSC matches; pick up some of our aluminum pads for that).  Size-wise, the brass TF pad is the same as the TF-LF1 pad, but with the back corners trimmed a bit.   The brass CZ pads are closest to the SF2 CZ pad but should work on most SP01s and Shadows as well as Shadow 2's.  If they are just a bit shy from seating in your gun, you can sand down the top of the pads a bit without hurting anything.


If they get dull and tarnished, you can run them in your brass tumbler for a while to make them shiny.  Alternatively, you can use brass-black or careful heating to give them a darker or old gold look.

Will the Tanfoglio TF-LF pads fit my large-frame Tanfoglio with a magwell?

Not without some modifications. You will probably have to trim the rear corners of the basepad to clear the magwell.  We do have a TF-LF-MW basepad sometimes that will clear the magwell.

What is the BX pad for?

The BX pad fits a large number of 9mm and .40 cal pistols such as the CZ 75, Beretta, XD, Taurus and others.  Some magazines will require the Shockbottle retainer plate as well.

.22 Basepad FAQs
Centerfire Basepad FAQs
bottom of page