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View Full Version : 308 PMAG Chop/Pin to 10 rds: How To


FMJBT
06-26-2012, 10:32 PM
After some searching, I wasn't able to find much infoonline for converting the 20 round 308 Pmag to a 10 rounder by shortening the body of the mag. I dissasembled some of the blocked 10/20's I had and experimented until I found the right length for holding 10 rounds. Unfortunately the ribs on the 308 mag do not line up with where it has to be cut, like the 5.56 20 round mag does. Because of this, the base plate will have to be pinned or screwed in place to hold the magazine together. Not a big deal, it's easier than it looks.

Tools/Materials you will need:

-Drill, either hand held or a drill press (I used a DeWalt cordless electric)
-Drill bit. The diameter of the drill bit should match the diameter of the material used to pin the mag base plate to the body. I used 1/16" stainless weld wire, so I went with a 1/16" drill bit.
-Hand held clamp (Not required, but it makes the job easier)
-Ruler
-Fine tip permanent marker
-Hacksaw
-Wire cutter/Pliers
-Large file or coarse sandpaper
-Wire or screws to pin the base plate

Procedure:

1) Disassemble mag into base components. If pinned already, the pin will need to be either pulled out or driven entirely into the mag to facilitate removal of the base plate from the body:
http://farm9.staticflickr.com/8161/7452712180_2c9a3f89bf_c.jpg

2) The body will need to be cut 1/8" above the top of the middle rib. Mark the cut off line with a fine tip permanent marker as shown:
http://farm9.staticflickr.com/8154/7452710580_0e51007066_c.jpg

3) Carefully cut along the line with the hacksaw. I cut slightly below the line to leave a bit of extra material. You can always remove extra material, but adding material if you cut too much is not really an option.... After cutting, even up the edges using either a file or coarse sandpaper backed by a flat surface:
http://farm8.staticflickr.com/7130/7452708902_6d9187b091_c.jpg

4) Using clamps or tape to hold the base plate in place on the magazine body (spring and follwer NOT inserted), drill holes for attachment of plate. The front set of holes should be in line vertically with the rib the runs down the forward edge of the magazine and about 1/8" below the upper edge of the base plate. The rear set of holes will be at the rear most edge of the base plate, again about 1/8" below the upper edge and 1/8" from the rear edge. After drilling, test fit pin material to ensure it passes through the base plate and magazine body:
http://farm9.staticflickr.com/8153/7452707442_c9f7aa7805_c.jpg

5) Trim magazine spring as shown:
http://farm9.staticflickr.com/8018/7452705954_ba9e039251_c.jpg

6) Bend lower portion of mag spring to match the section of spring that was cut off:
http://farm8.staticflickr.com/7255/7452704050_2925270ed2_c.jpg

FMJBT
06-26-2012, 10:33 PM
7) Re-install mag spring base onto the mag spring. Install follower, spring/base into magazine body. Install magazine base plate and insert pins or screws to hold in place. If using pins, leave them long to make it easier to pass them through both sides of the mag and base plate:
http://farm9.staticflickr.com/8006/7452702410_fd1859d07e_c.jpg

8) Test fit 10 rounds into magazine to check capacity and integrity of the pins or screws (Better to blow apart now than later at the range). Ensure the magazine will NOT take an 11th round. (If 11 rounds do somehow fit into the mag, disassemble and remove more material from the magazine body. The holes will need to be re-drilled in the mag body if further trimming is done):
http://farm8.staticflickr.com/7109/7452699338_f7f3394152_c.jpg

9) If everything seems good at this point, cut the pins to length and file off the rough edges. At this point I superglue the pins in place as well as filling up the small gap between the magazine body and base plate. The pins alone should be able to hold, but I like the peace of mind from having the whole thing glued together:
http://farm9.staticflickr.com/8160/7452697818_a89fb6a456_c.jpg

10) Go do some shooting from a bipod without balancing on the base of the magazine!
http://farm9.staticflickr.com/8001/7452696504_5632949b12_c.jpg

Jpach
06-27-2012, 10:30 AM
Not a bad idea. I like it. I have a super easy way of converting them to 10 rounders (pin and epoxy a thick trimmed section of plastic coat hanger into the hole thingy on the bottom of the follower), but I find the 308 PMAGs to be just a tad too long. Your method solves this problem quite well.

BTW, is it you who uses 190 SMKs in your 16"?

FMJBT
06-27-2012, 11:26 AM
Not a bad idea. I like it. I have a super easy way of converting them to 10 rounders (pin and epoxy a thick trimmed section of plastic coat hanger into the hole thingy on the bottom of the follower), but I find the 308 PMAGs to be just a tad too long. Your method solves this problem quite well.

BTW, is it you who uses 190 SMKs in your 16"?

Yeah, with the shorter bipods especially, the 20 round mags are just a bit longer than I like. Stepping away from the rifle, it will rest on the magazine base and isn't very stable. A good wind will knock the rifle right over if you're not holding it. Shooting at uphill angles gets to be a pain too. I normally dig out a small hole under the mag for clearance. That gets old real quick :)

I load up 190 SMKs for all my 308's. I was worried the 16" Rainier Barrel would have a hard time stabilizing them due to the 1-11" twist rate, but it seems to do pretty well with them. I haven't shot any groups @ 100 yards with it, but the long range performance is pretty impressive. I need to get out and shoot some groups with it if for no other reason than to establish a baseline so I can work out bullet drop at various ranges.

HK Dave
06-27-2012, 1:12 PM
http://midwestpx.com/index.php?cPath=15_87&osCsid=7t1pj8atchnitr4uf06qm5p5r4

So that's how these guys do it.

Thanks for the "How-To". Gonna save me a few bucks and do it this way. :D

HK Dave
06-27-2012, 1:16 PM
Anyone know a tutorial to make stubby ar15 pmags?

FMJBT
06-27-2012, 3:15 PM
Anyone know a tutorial to make stubby ar15 pmags?

There used to be a tutorial on here, it was a "Sticky" for a while. The 5.56 pmags are even easier than the 308. You trim the mag along the bottom of the uppermost rib on the 20 round mags. Trim enough off of the rib so that the base plate will slide over it. The rib now becomes the lip for attaching the base plate. It's still a good idea to pin or glue the base plate on because the rib doesn't work quite as well to secure the base plate as the original lip does.

G38xOC
06-27-2012, 9:19 PM
how did u know how much to cut on spring ?

FMJBT
06-27-2012, 9:29 PM
how did u know how much to cut on spring ?

Guessed. I went with rough percentage of how much of the magazine body was removed and removed a similar amount from the spring. The spring probably doesn't even need to be cut at all. I did it mostly to relieve some of the spring pressure off the base plate since it is only held in by the two pins going through thin plastic. It also makes the magazine a bit easier to load, and reduces the potential for the spring coils binding up in the shortened mag body.

motorwerks
06-27-2012, 10:04 PM
I did pretty much the same thing but I used roll pins. It works pretty good.

G38xOC
06-27-2012, 10:08 PM
that was good guess ! looks great !

HK Dave
06-28-2012, 7:42 AM
Take a 20rd. Pmag body.
Cut at the red line, straight across the bottom of the top rib, I use a fine tooth Hacksaw.

http://i19.photobucket.com/albums/b193/hylander7/Firearms/Smithing/Pmag%20%20Mod/Picture126.jpg

You should now have this:

http://i19.photobucket.com/albums/b193/hylander7/Firearms/Smithing/Pmag%20%20Mod/Picture107.jpg

Next useing a flat coarse file, file the bottom of the mag body where you just made the cut,
File flat until you can just start to fit the floor plate. Now use a fine flat file to smooth it out and just enough so the floor plate will slide on snug. You want that rib to be the same thickness as the groove in the floor plate where it mated with the mag bottom before you made your cut

http://i19.photobucket.com/albums/b193/hylander7/Firearms/Smithing/Pmag%20%20Mod/Picture107-1.jpg

Remove two coils from the spring.
I have tried them with the springs unmodified and then with the springs modified by removing two coils.
Either way they function 100% .

Now just re-assemble the Mag as normal and Bam you have a 10 round Mag.

http://i19.photobucket.com/albums/b193/hylander7/Firearms/Smithing/Pmag%20%20Mod/Picture111.jpg

http://i19.photobucket.com/albums/b193/hylander7/Firearms/Smithing/Pmag%20%20Mod/Picture110.jpg

Note:
Sometimes a particular Mag may be able to load an 11th round in, if this happens you will need to replace
your 20rd. follower with a 30rd. follower.
If you need a 30 rd. follower you will only be able to load 8 rds.
Just file the bottom tails of the follower until you can load 10 rds.
Just remove a little at a time, Fit and file, fit and file.
Or you can epoxy a spent 9mm casing on the bottom of the follower and it will limit the mag to 10rds.

http://i19.photobucket.com/albums/b193/hylander7/Firearms/Smithing/Pmag%20%20Mod/Picture119.jpg

Remove two coils from the spring.
I have tried them with the springs unmodified and then with the springs modified by removing two coils.
Either way they function 100% .

Nice! Thank you!

Looks like it's time to order up some LR20s and and some 20 Round PMAGS.

HK Dave
06-28-2012, 7:42 AM
Err rebuild kits that is.