My M4 Factory Full Length Mag will not accept 7 rounds

[Centuriator]

OK, guys...riddle me this. My M4 H20 with the full length mag tube will not take 7 rounds. I can only get 6 in the tube. I've been reading a bit about why and I'm, frankly, confused by what I've read.

 

Remove the retainer cap?

Cut off a four spring links?

Buy another spring?

Was gibt? As the Germans would say.

Your thoughts, suggestions?

[StrangerDanger]

You shouldn't have to trim any of the spring, the usual culprit is the ammunition itself. Try another brand of ammo to see if you can get seven rounds in her. Even though shells claim to be 2 3/4", many of them are not exactly within that spec.

 

Sometimes you can get a little extra room in the magazine tube by sliding the spring retainer out so it protrudes past the end of the magazine tube, then reinstall the magazine cap. The cap will press the spring retainer down as far as it needs. This may give you a fraction of an inch more room from where the retainer is currently set.

[NoTycoon]

I would cut the spring. They are often too long.

[Centuriator]

Thanks for the useful responses. Question re. the spring retainer. Can I remove that entirely and just let the magazine cap retain the spring? And in so doing, perhaps realize a bit more room in the tube? Or is there a purpose for the spring retainer beyond simply allowing you to disassemble without the spring popping out of the tube?

[NoTycoon]

Yes, you can remove the retainer. Just remember when removing the cap that the spring is not retained.

[Centuriator]

Yes, you can remove the retainer. Just remember when removing the cap that the spring is not retained.

 

Right, as is the case with my Mossberg and Remington shotguns. You have to remember to place your thumb on the spring and slowly unscrew then release the tension.

 

Thanks for confirming.

[NoTycoon]

If removing the retainer does not solve your problem, cut the spring. To determine how much to cut, compare the length of the compressed spring (length of tube less length of 6 full shells and the portion of the 7th shell that fit into the tube and width of follower) and the length of the uncompressed spring. Now, determine the compression factor as Compressed Length/Uncompressed Length.

 

Next, remove spring and cap. Insert, follower and seven shells. Measure down the cap end of the tube to the inside edge of the follower (where the spring will rest). This is the max space for the compressed spring. Finally, divide Max Space by the Compression factor to determine the Max Length of the uncompressed spring.

 

Cut spring to length.

[StrangerDanger]

No issues leaving the spring retainer out. It might buy you about 0.05" of extra length. I'm not sure if you're using a OEM or aftermarket spring. I've never had to cut the spring of a Carriercomp/Wolff spring.

 

When trimming the spring, the problem becomes the last round in the magazine tube is anemic and can cause failures to feed. So be really careful with this.

[Centuriator]

My M4 came with the factory 7 round magazine and, I assume, an OEM spring. Maybe I'll try another spring to see if that helps. I was using Federal 00 Buck and I could only get less than half the seventh shell in the tube, which surprised me.

[StrangerDanger]

I don't think you could cut enough spring to make up that difference. If you measure the length of each shell, you can get an idea of what 7 of them stacked would measure out to. Then compare it to say those Winchester or Federal Valuepack 2 3/4 shells that should fit.

[Centuriator]

Thanks for your help with this. I'll give everything a try. Because +1 matters.

 

Edited June 26, 2018 by Centuriator

[NoTycoon]

The M4 is a great gun, after you get the tube to hold 7, look up how to "ghost load" and you can load the gun with 9.