Miscellaneous Questions #22

This section contains brief discussions of various ballistics and shooting related topics as requested by correspondents. If you have a question you have been trying to find an answer to (keep 'em ballistics and shooting related--see your minister for the mysteries of life) email me by clicking here and I'll do my best to find the answer for you and if it is of general interest, publish it here. If you can contribute additional input to one of the answers I'd would appreciate hearing from you too.

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On this page:

How good are the polymer magazines for the M16?  
How can I start roll pins (split spring pins) straight without damaging them?  
What are the dimensions of large and small primers?

Q. How good are the polymer magazines for the M16?

A. While early polymer magazines left something to be desired as far as ruggedness and durability many current polymer magazines are very good.  However, the premier polymer magazines in use today are the Magpul brand "PMags" that are US Military approved and that are very popular among the troops and civilian shooters.  I have been using their Gen 2 magazine for several years and have not had a single problem or malfunction and I highly recommend them over other brands.  They are currently available in 10, 20, 30, and 40 round capacities.

There have been several generation of PMags and the data below explains the major differences in them

The GEN 1 PMag  was Magpul's first AR15/M4 compatible magazine.  It featured a polymer construction, easy to disassemble design with a flared floor plate, stainless steel spring, and an anti-tilt follower.  It came with a dust cover that could not be stored on the base of the magazine. It was available with or without a round count "window."

The GEN 2 PMag was Magpul's second design polymer AR15/M4 compatible magazine. It features an improved impact resistant polymer construction, easy to disassemble design with a flared floor plate, stainless steel spring, and an anti-tilt, self-lubricating follower for increased reliability.  The dust cover will snap onto the base of the magazine for storage.  It is available with or without a round count "window."

The GEN 2 MOE PMag is identical in form and function to the original Gen 2 PMAG except that the dust cover is now sold separately.  It is available with or without a round count "window."

The GEN 3 PMag is Magpul's latest polymer magazine for AR15/M4 compatible weapons. It incorporates new material technology and manufacturing processes for enhanced strength, durability, and reliability, especially in cold weather. Modified internal and external geometry also permits operation with a wide range of non Colt-spec platforms such as the HK 416 and MR556A1, M27 IAR, British SA-80, FN SCAR MK 16/16S, and others. A redesigned bolt catch notch in the rear of the magazine provides increased bolt catch clearance, while an over-travel stop on the spine helps ensure the magazine will not over-insert on compatible weapons.    It has constant-curve internal geometry for reliable feeding, and includes a dust cover.  The dust cover will not snap onto the base of the magazine. Low profile ribs and new aggressive front and rear texture provide better handling control, and a paint pen dot matrix has been added to the bottom side panel of the body to allow easy marking by the end user for identification. A new floor plate aids extraction and handling of the magazine while providing improved drop protection, and is slightly slimmer than before for better compatibility with tight double and triple magazine pouches.

PMags are also available in 7.62 NATO for the SR25/M110, MK 11 rifles, in 6.8SPC for the AR platform, and in a 5.56 x 45 design specifically for the HK 36.  See Magpul's website at www.magpul.com for more information.

Magpul also offers a magazine called the EMag (Export MAGazine). It is a lightweight 30-round 5.56x45 NATO polymer magazine that features a number of aesthetic and functional changes from the PMAG. While the EMAG remains 100% compatible with the AR15/M16 platform, its unique geometry is optimized for foreign-made weapons such as the British SA-80 (L85A1/A2, L86A1/A2, L22A1, L98A1/A2), HK 416, M27 IAR, and others.

EMAG features the same dust cover as the PMAG GEN M2 Dust Cover and can be stored on the magazine's floorplate to prevent possible loss.  It has large dual-sided windows with numerical indicators added to the body to identify 5, 15, and 25 loaded rounds.

Magpul also makes 20 rd AR magazines.  The Gen 1/2 were of the straight design and the current Gen 3 is a curved design which is also available in a 10 round configuration.

Note that the dust covers for the Gen 3 and the earlier magazines are different.  If you order replacement mag covers be sure to specify what generation magazine they are for.

Top View - Left to Right: Gen 1, Gen 2, Gen 3, and EMag


Side View - Left to Right: Gen 1, Gen 2, Gen 3, and EMag


Maglevel Window showing indicator


Baseplates  Left to Right: Gen 3, Gen 1,2, and EMag


Bolt catch clearance notch Left to Right: Gen 2 and earlier, Gen 3


Dust cover fitted and stowed on the base. (Gen 2).  Note that when fitted to the feed lips the cover depresses the top round to relieve stress on the feed lips.


20 Round Magazines - Left to Right: Gen 1/2, Gen 3


30 Round AR Magazines

  Gen I Gen I Maglevel Gen II Gen II Maglevel Gen II MOE Gen II MOE Maglevel Gen III Gen III Maglevel EMag
Weight oz
(Empty w/o dust cover)
 5.4 4.8 4.8 5.1 4.6
Dust Cover Y Y Y Y Optional Optional Y Y Y
Dust cover storage on base plate N Y Y Y Yes
Round count windows N Y N Y N Y N Y Y
Marking grid N N N N N N Y Y N


20 Round AR Magazines

  Gen 1/2 Gen 3 Gen 3-10
Weight oz
(Empty w/o dust cover)
3.4 4.2 n/a
Dust Cover Y   Y
Dust cover storage on base plate N N N
Round count windows N  N N
Marking grid N Y Y

Thanks to the folks at Magpul for the magazine samples.

Q. How can I start and drive in roll pins (split spring pins) straight without damaging them

A. To start the pins you can use what is called a roll pin holder which is steel punch with an appropriate sized hole in the end to support the pin.  Unfortunately, they are not cheap and if you don't normally need to insert split pins they may not be cost effective.  Brownells carries them.  However, you can easily make your own from a short section of 1/4 inch steel rod or even a small bolt by drilling an appropriate size hole.  The table below gives the proper hole size for several common roll pins.  Drill the hole about 1/8 to 1/4 inch deep depending on the length of the pin being used.

Starter hole sizes

Pin Drill #
1/16" 50
5/64" 44
3/32" 37
1/8" 29
5/32" 18

To finish seating the pins or to drive them out you should not use flat punches but rather a tipped roll pin punch that has a small dimple that sits in the hole of the roll pin to guide the punch.  These punches are also carried by Brownells.  Picture below.

Note tip

Q. What are the dimensions of large and small primers?

A. The chart below gives the nominal dimensions.  Note that these dimensions seem to vary a little bit depending on the source.

Primer Dimension
Type Height Min Height Max Diameter Min Diameter Max
Small Rifle 0.1150 0.1250 0.1746 0.1758
Small Pistol 0.1150 0.1250 0.1744 0.1756
Large Rifle 0.1230 0.1330 0.2105 0.2130
Large Pistol 0.1150 0.1250 0.2108 0.2120


Primer Pocket Dimensions
Type Depth Min Depth Max Diameter Min Diameter Max
Small Rifle 0.1180 0.1220 0.1730 0.1745
Small Pistol 0.1180 0.1220 0.1744 0.1758
Large Rifle 0.1250 0.1320 0.2085 0.2100
Large Pistol 0.1180 0.1240 0.2085 0.2100

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As far as I know all the information presented above is correct and I have attempted to ensure that it is. However, I am not responsible for any errors, omissions, or damages resulting from the use or misuse of this information, nor for you doing something stupid with it. (Don't you hate these disclaimers? So do I, but there are people out there who refuse to be responsible for their own actions and who will sue anybody to make a buck.)

Updated 2013-06-15