204Ruger

Just bought a plum crazy lower and a custom upper in 204 with ER Shaw barrel.
The rig came with Magpul 223 plastic magazines. They will not function at all, a round is either
not picked up at all or the round is at such an angle that the bolt jams on it and dents it
in the middle. I tried my DPMS 20 round magazines with no more than 10 204 rounds and they work
90% of the time, but I have to really slam the magazine it and be forceful on the charging to get a round picked up at times. When a round is picked up from the magazine, the gun runs perfect.
I am using Hornady 32 gr V-Max factory ammo.
What is the best magazine for the 204 in an AR?
Also, does anyone make a magazine specifically for the 204 round? I have seen mention of Bushmaster
and Remington making them, but cannot find them for sale anywhere.
Thanks

I have a Bushy .204 and the 5 round mag that came with it is marked .204, and has worked flawlessly with 32g and 40gr factory Vmax.
Tried a PMAG marked 5.56x45 30 rd mag using a LULA loader and when loading (forget the number of rounds) and made a severe dent in the case. Called Magpul and was told that due to the follower the .204 would NOT work. Never tried the PMAG in the Bushy.
I have been trying to find a hi-cap mag that will work, but have not been able to find a definite yes on a mag that will work.
I don't know if the .204 5 round mag is available from Bushmaster.
Stopped in the showroom of another AR manufacturer who also makes a .204 AR and was told the 5.56 mag should work, but I am once bit twice shy.
Did order a 5.56 AR today that comes with a 30 round mag. Will test the .204 in the mag when I get the AR.
Will let you know if the mag works with the .204 round, and if you find a mag that does work please let me know.
Wish I could help you more.

The Bushmaster .223 or 5.56 mag will work perfectly for the .204. I contacted Bushmaster before making the purchase. Ran 20 shots through works just fine!

just realized my post is completely useless to you. different lower hahahaha...

FWIW, you may want to use a digital caliper and take measurements of the mag well opening on that lower. It almost sounds like the manufacturing tolerances are on the tight side and causing too much resistence/interferance with the insertion of the magazine. Find a friend with a Bushy, DPMS or Colt to compare yours to and see it it's just a tight mag well. JMO

I took some measurements on the mag wells: DPMS front = .892 middle = .956 mag release indent = .987
The Plum Crazy measurements were: front = .901 middle = .927 indent = .968
So, the plum crazy lower is a little tighter.
When I load the PMAG with 204, after I get 3 rounds in it, it is obvious they expand the magazine, there is no or little spring pressure, the top round is at a very tilted angle (bullet up) and they do not work. 223 rounds seem to load in the PMAG OK. When 204 rounds are in the PMAG, the indents on the inside of the magazine that are on the 223 case neck, are positioned way back on the 204 case shoulder because it is so much higher on the case. I think that is the problem. I have read a lot of blogs about this and the recommendations seem to be go with the C-Products steel mags, with anti-tilt follower and load only
half a magazine. I ordered 2 and will see if they work. I also plan to put the 204 upper on the DPMS lower
and see if that works better than the Plum Crazy lower. The DPMS lower has a timney trigger and that will be better for Yote shooting anyhow.
Also, I have looked for AR-15 magazine specs and even a diagram that named the parts of the magazine but could not find anything. I was looking for magazine body specs and 'names' of the different body parts.
Anyone have a link for such?
Thanks to all that gave advice.

I received the C-Products, straight, 20 round, stainless 5.56 mags with the anti-tilt follower.
They work much better than the Magpul (which don't work at all!) PMAGS with the 204 cases.

There is still a problem with not stripping a round from the magazine some times. I still plan to
put the 204 upper on my DPMS lower sometime and try that. Maybe the magazines are not seating
well in the plum crazy lower?

I don't know if this is your problem. On any semi auto with a detachable magazine you have to make sure the mag pushes up all rounds properly after the round on top is stripped off. If this is not happening, it will explain feeding/jamming problems. Some ways to do this is using a Lula type loader while noticing equal pressure while loading/unloading. Another is to manually strip of the top round and seeing if the next round is pushed into the proper position.
I also notice I have to be careful while loading a mag to see if the .204 round is pushed all the way back in the mag, to include the round under the round on top of it. I believe this is due to the long overall length of the .204 cartridge.
I have also heard that a properly fitting mag will drop when empty by just pushing the mag release. This enables you to drop the mag while holding another to insert. So there has to be some free play.

HTH, or eliminates variables.

I have a bushmaster with the factory mag and a 20 rnd mag wich is not stamped 204 and the cutout on top is alot different the factory 5rnd mag stamped 204 is more open on top, having said that the 20rnd mag works fine. I also bought some cheap plastic mags stamped 223 only to find that the shoulder guide inside the mag was setback for the 223 wich made it slide against the body of the 204 causing the mag to bulge and break. i would check that before buying any standard mag

I have had trouble with any plastic mags due to expansion of the sides of the magazine. I went to a METAL Charles Daily brand and now all is well with the world. JME

Just from personal experience but neither my boss nor I have had any issues with the PMAGs from MAGPUL in either of our 223's or 204's. I interchange them depending on what upper I am using with a DPMS lower. He bought two different colors of the PMAG's to keep his caliber obvious. I have both the 20 and 30 round ones but don't care for the 30 round due to the length sticking out of the mag well when moving around. I do like the look and feel of the plastic mags over the louder, colder, metal ones but that is simply my personal preferences.

I have a rock river lower and it feeds excellent no matter what mag I use or how full. I did smooth out edges of feed bumps on all my mags as cases were getting nicked. Other n that no issues

Made some small mods to pmag and works flawless with .204 . Need a file or solder gun about two mins of work.

drahtman wrote:Just bought a plum crazy lower and a custom upper in 204 with ER Shaw barrel.
The rig came with Magpul 223 plastic magazines. They will not function at all, a round is either
not picked up at all or the round is at such an angle that the bolt jams on it and dents it
in the middle. I tried my DPMS 20 round magazines with no more than 10 204 rounds and they work
90% of the time, but I have to really slam the magazine it and be forceful on the charging to get a round picked up at times. When a round is picked up from the magazine, the gun runs perfect.
I am using Hornady 32 gr V-Max factory ammo.
What is the best magazine for the 204 in an AR?
Also, does anyone make a magazine specifically for the 204 round? I have seen mention of Bushmaster
and Remington making them, but cannot find them for sale anywhere.
Thanks

Isn't the Plum Crazy lower a composite polymer?

I had the same problem and I saw a post on the PredatorMaster forum about how to fix the problem.

You have to file or grind out the ridge for the first 3 or 4 inches and they work fine after that.

I hope this helps you. I was ready to get rid of my new Pmags.

Jimmy