Magazines Across Seven Decades

The Ruger .22’s magazine, and the way the pistol holds it, changed three times in seventy years, and every change was made for a mechanical reason: capacity and hold-open with the Mark II, the magazine disconnect with the Mark III, and a new release with the Mark IV. The magazines look alike, and the question “will this magazine work in that pistol” is the most common practical question the family generates. This volume answers it from Ruger’s manuals, which are specific on most combinations and silent on some. Where they are silent, this volume says so and does not guess.

6.1 The short answer

For the two pistols documented in these volumes:

• The Mark III (steel frame). Ruger: “The M10MKIII is the only magazine that should be used in RUGER® MARK III pistols because it is designed to correctly function the bolt stop and magazine disconnect.”¹
• The Mark IV (steel or aluminium frame). Ruger: “The RUGER® MARK IV pistol uses the same 10-shot magazine as the RUGER® MARK III pistol.”²
• So one magazine serves both — provided the Mark IV is a steel- or aluminium-frame model and not a 22/45. If the Mark IV documented here turns out to be a 22/45, it takes a different magazine altogether (§6.6). Its configuration is not yet recorded (Volume 7).

6.2 The magazine families, by Ruger’s own descriptions

Standard and Mark I — nine rounds, fixed base. The Mark I manual gives the first generation as “9-shot, magazine fed.” The Mark II manual later identifies the first-generation magazine for the purpose of telling owners not to use it: “the 9-shot, AMC pistol magazine (identified by its brightly plated non-removable bottom).”³⁴ It is held by the heel catch at the base of the grip, as the 1946 patent drew it.⁵

Mark II — ten rounds, removable base, the silver eagle. “The 10-shot magazine (Part M-10) for the RUGER® MARK II Standard, Target, Government Target, and Competition Model pistols is readily identified by the removable plastic bottom decorated with a silver ‘eagle’. The M-10 is the only magazine which should be used in these RUGER® MARK II pistols because it is designed to correctly function the bolt stop.”⁴ The Mark II was the first generation with a last-round hold-open, which the magazine follower operates (Volume 3); the nine-round magazine was not designed to do that, which is why Ruger excluded it.

Mark III — ten rounds, the interlock. “The 10-shot magazine (Part M10MKIII) for the RUGER® MARK III pistol is different from all other Ruger rimfire pistols. In addition to the familiar removable plastic bottom decorated with a silver ‘eagle,’ the M10MKIII magazine has a trigger interlock window and protrusion.”¹

Mark IV — the Mark III’s magazine. The Mark IV manual states that the steel- and aluminium-frame Mark IV “uses the same 10-shot magazine as the RUGER® MARK III pistol,” and Ruger’s launch release said the Mark IV “is compatible with a variety of Mark III aftermarket accessories including sights, scope bases and magazines.”²⁶ Ruger’s 2019 anniversary release describes the Mark IV as shipping with “two nickel-Teflon® coated, 10-round magazines.”⁷

The 22/45 branch — its own magazine at every generation. AP-10 (Mark II 22/45), AP10MKIII (Mark III 22/45), and a Mark IV 22/45 magazine that the Mark IV manual says fits only the Mark IV 22/45 (§6.6).⁴¹²

6.3 The compatibility table

Each cell gives what Ruger’s manuals say, and cites the manual. “Silent” means no Ruger document consulted addresses the combination; it does not mean the combination works or fails.

Table 1 — The compatibility table

Magazine ↓ / Pistol →	Standard / Mark I	Mark II	Mark III	Mark IV (steel/aluminium)
9-round “AMC” (Standard/Mark I)	Correct magazine3	”Should not be used”4	Not the M10MKIII; Ruger says only the M10MKIII should be used1	Not a Mark IV magazine; Ruger says use only magazines designed for the Mark IV2
M-10 (Mark II)	Silent	Correct magazine4	Not the M10MKIII (no interlock window or protrusion)1	Not a Mark IV magazine2
M10MKIII (Mark III)	Silent	Silent	Correct magazine1	Same magazine as the Mark IV’s2
Mark IV (steel/aluminium)	Silent	Silent	Same magazine as the Mark III’s2	Correct magazine2
Any 22/45 magazine	—	“Not interchangeable” (AP-10)4	“Not interchangeable” (AP10MKIII)1	Mark IV manual: 22/45 magazines for 22/45 pistols only2

The pattern is simple once the mechanism is in view. Ruger’s instruction is always to use the magazine designed for the generation, because each generation asks the magazine to do something the previous one did not: operate the hold-open from the Mark II, operate the disconnect from the Mark III. Ruger has never published a statement that a newer magazine is safe or functional in an older pistol, and none is made here. Whether a later magazine functions in an earlier steel-frame pistol is a question Ruger does not answer; any such combination should be treated as untested until the feed and the hold-open have been checked with the pistol unloaded and pointed safely.

6.4 Why the Mark III magazine has a window

The Mark III was the first Ruger .22 that would not fire without a magazine. “Your RUGER® MARK III pistol is equipped with a magazine disconnect. This device prevents the trigger from being pulled if the magazine is removed from the pistol. You will not be able to use your pistol as a single loader or to fire the pistol with the magazine removed.”¹ A magazine disconnect needs a way of knowing that a magazine is present, and on the Mark III that is the job of the magazine’s trigger interlock window and protrusion — the feature Ruger names as the reason the M10MKIII is “different from all other Ruger rimfire pistols.”¹

What follows from this is stated by Ruger only in general terms: the M10MKIII is the only magazine that will “correctly function the bolt stop and magazine disconnect.”¹ The manual does not say what happens if an M-10 from a Mark II is inserted into a Mark III. The mechanical implication is that a magazine without the protrusion will not signal its presence and the disconnect will continue to block the trigger; that is an inference from Ruger’s description of the feature, and it is stated as one. It is also the reason that the Mark III takedown procedure requires an empty Mark III magazine to be inserted before the trigger can be pulled to release the hammer (Volume 4).

Two consequences for an owner are practical rather than mechanical:

• Spare magazines for a Mark III must be Mark III–pattern magazines (or the Mark IV magazine, which Ruger says is the same). A drawer of Mark II magazines will not substitute.
• A Mark III fitted with a kit that removes the disconnect — Volquartsen’s Mark II/III Accurizing and Competition kits do (Volume 7) — stops depending on the protrusion to fire. It still depends on the magazine to operate the hold-open, and Ruger’s instruction to use the M10MKIII is framed around both functions.

6.5 The Mark IV: same magazine, different release

The Mark IV kept the Mark III’s magazine and changed how it leaves the pistol. Ruger’s launch release: “The magazine drops free on release for faster reloads and a redesigned magazine disconnect safety prevents discharge when the magazine has been removed.”⁶ The mechanism is visible in the Mark IV parts list as a magazine assist, and in the manual’s warning that removing the right grip panel “will expose the magazine ejector. The magazine ejector is under spring tension and should be covered with your hand when removing the grip panel.”² The ejector pushes the magazine out when the button is pressed. Ruger’s Mark III documents make no drop-free claim for the Mark III, and none is made here.

The release button is in the same place on both: “a conveniently located push button magazine release on the left side of the frame” (Mark III spec sheet), “push-button magazine release on the left side of the frame” (Mark IV spec sheet).⁸⁹ Both put it behind the trigger guard where a 1911 shooter’s thumb falls, the change Keefe identified as the Mark III feature shooters “really liked.”¹⁰

6.6 The 22/45 exception, at every generation

The 22/45 has taken its own magazine at every generation, and the Mark IV added a further split inside the 22/45 line:

• Mark II: “The RUGER® 22/45 pistol uses a different 10-shot magazine (part AP-10) which is identified by its removable elongated plastic bottom. It is not interchangeable with the M-10 or AMC magazines.”⁴
• Mark III: the 22/45 “uses a different 10-shot magazine (Part AP10MKIII) which is identified by its removable elongated plastic bottom. The AP10MKIII magazine is distinguishable from earlier 22/45 magazines by the presence of the trigger interlock window and protrusion … the AP10MKIII is not interchangeable with the M10MKIII magazine.”¹
• Mark IV: “The RUGER® MARK IV 22/45 pistol uses MARK IV 22/45 pistol magazines only. MARK IV 22/45 pistol magazines are not compatible with the MARK III 22/45 pistol.”²

Keefe, handling the first Mark IVs in 2017, explained why the 22/45 and steel-frame Mark IV magazines look nearly identical and still do not interchange: “The magazine bodies for the Mark IV 22/45 and Hunter are the same, but they are not interchangeable due to the shape of their baseplates.”¹⁰ The baseplate is how each magazine meets its frame. It is the first thing to check on any Ruger .22 magazine of uncertain origin.

6.7 Loading, handling and cleaning

Both current manuals give the same loading instruction and the same caution about the follower button on the left side of the magazine: “When using the follower button, have it under control. When loading or handling the magazine, do not pull the button down and then release it suddenly. The rim of the cartridge hitting the magazine lips may set off a sensitive primer and cause the cartridge case to discharge, burst violently, and result in injury.”¹² Cartridges should “lie parallel and evenly in the magazine,” ten or fewer.¹

The magazine is also named first in both manuals’ malfunction diagnosis: “Most failures of a cartridge to feed or to chamber are caused by a damaged magazine, improper gun handling or defective ammunition,” and the manuals ask the owner to check “that the magazine spring tension is adequate” and that “the magazine lips … are free of nicks and burrs and are not deformed.”¹ Disassembly for cleaning is the five-step procedure in Volume 4 §4.9; the manuals’ warning is that the retaining plunger and spring “will fly out with considerable force” if not contained, and their closing line is that “damaged, non-standard or improperly assembled magazines should not be used.”¹²

6.8 Buying magazines for the pistols documented here

The owner’s inventory, as recorded in September 2026, lists additional magazines for the Mark III as a planned purchase (“Need more Magazines”), not yet made. On Ruger’s statements:

• The correct magazine is the Mark III-pattern ten-round magazine, Ruger part M10MKIII in the Mark III manual’s nomenclature, or the Mark IV steel/aluminium-frame magazine, which the Mark IV manual says is the same magazine.¹²
• If the Mark IV documented here is confirmed as a steel- or aluminium-frame model, the same magazines serve both pistols. If it is a 22/45, it needs Mark IV 22/45 magazines, which will not serve the Mark III.²
• Ruger’s manuals ask for “GENUINE RUGER® FACTORY magazines” in the Mark IV and name only Ruger parts for the Mark III.¹² Aftermarket magazines were not evaluated for this dive.
• Ruger’s current catalogue part number and price for the magazine were not verified for this volume, so none is printed. The only Ruger price found is the recall page’s valuation of a free thank-you magazine at “$29.95” in 2017.¹¹

References

Footnotes

1. Sturm, Ruger & Co., Instruction Manual for Ruger Mark III … Autoloading Pistols, © 2015, pp. 12, 15, 17, 21–22, 27, https://ruger-docs.s3.amazonaws.com/_manuals/markIII.pdf , consulted 2026-09-19. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷

2. Sturm, Ruger & Co., Instruction Manual for Ruger Mark IV … Autoloading Pistols, code PM1179, © 2026, pp. 12, 15, 23, 25–26, https://www.ruger.com/dataProcess/manual/fetch.php/ms/40160/manual_40160.pdf , consulted 2026-09-19. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶

3. Sturm, Ruger & Co., Instruction Manual for Ruger Mark I Target Model and Standard Model Automatic Pistols, code A-7-81, https://ruger-docs.s3.amazonaws.com/_manuals/markI.pdf (scanned; OCR), consulted 2026-09-19. ↩ ↩²

4. Sturm, Ruger & Co., Instruction Manual for Ruger Mark II Autoloading Pistols, code AP & KAP 1/03 C R8, “Magazines,” https://ruger-docs.s3.amazonaws.com/_manuals/markII.pdf , consulted 2026-09-19. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

5. W. B. Ruger, US Patent 2,655,839, “Blowback Autoloading Pistol,” filed 5 November 1946, issued 20 October 1953, https://patents.google.com/patent/US2655839A/en , consulted 2026-09-19. ↩

6. Sturm, Ruger & Co., “Ruger Perfects Rimfire — Again: Introducing the One-Button Takedown Mark IV,” 22 September 2016, https://ruger.com/news/2016-09-22.html , consulted 2026-09-19. ↩ ↩²

7. Sturm, Ruger & Co., “Ruger Commemorates 70th Anniversary with Limited Edition Mark IV,” 26 April 2019, https://ruger.com/news/2019-04-26b.html , consulted 2026-09-19. ↩

8. Sturm, Ruger & Co., spec sheet, Mark III Target model 10101, as archived 14 January 2016, http://web.archive.org/web/20160114101901/http://www.ruger.com:80/products/markIIITarget/specSheets/10101.html?buy=1 , consulted 2026-09-19. ↩

9. Sturm, Ruger & Co., spec sheet, Mark IV Target model 40101, https://ruger.com/products/markIVTarget/specSheets/40101.html , consulted 2026-09-19. ↩

10. Mark A. Keefe IV, “Mark IV: The Ruger Evolution,” American Rifleman, 20 March 2017, https://www.americanrifleman.org/articles/2017/3/20/mark-iv-the-ruger-evolution/ , consulted 2026-09-19. ↩ ↩²

11. Sturm, Ruger & Co., “Mark IV™ Recall” page, https://ruger.com/dataProcess/markIVRecall/ , consulted 2026-09-19. ↩