M4 in 7.62x39. Do I need heavier buffer/spring for proper function

I’ve been tol that my M4 in 7.62x39 won’t operate/cycle properly if I used a 5.56 buffer/spring. Especially in third position on the safety. If true what should I use.

Good question Sarge.

What does that mean? Select Fire?

There is some “Black Art” here, 7.62 x 39, with the multiple variety of loads, barrels (riffling twist and type), it’s more than just the length, so things are going to be different. You could possible need a stronger spring, but you may need to adjust the gas too. I would prepare for these possibilities. What works for someone else, with $6 Red Army Standard " Elite " 7.62x39 123gr FMJ, and the same barrel on our build is only a place to start.

Your Mileage May Vary.


ok bill. lets assume that a person is putting a three position saftey in the last position and it fires and cycles fine in the 2nd position. How ever in the third position it fails to pick up a new cartrige an goes into battery in chamber without being cocked either.using a mil spec 3oz buffer an M4 carbine spring and using tula or wolf 7.62x39 123gr fmj. this person wants this lower working so it can be squirriled away in case of the SHTF scenerio. what then is your advice?

Copied from AR15.com

This question will get A LOT of emotional responses…

  1. The safety will not go into the third position if it is from a semi-auto parts kit.
  1. There is no specific safety besides using a semi parts kit (including the semi safety) for a semi-auto AR. Use FA or burst parts kits if you have a registered lower/etc.
  1. If you put an auto safety in your semi-auto gun, well… probably the best advice is DO NOT DO THIS.
  1. People will say you can put a safety that rotates to the third
    position with no problems. Will these people giving advice be at your
    trial or help pay lawyers fees or visit you in prison?
  1. Do as you please. You have been duly warned.


Ok warnings all noted. However the issue still remains about function. Does anyone have any help here. Warning noted but if TSHF I don’t honestly believe at that point anyone is gonna care about legalitys. They’re gonna get out that hidden lower and do whatever it takes to protect Fam an survive. Btw- let clarify a legal point you can have ALL the m16 parts in your gun an per judicial standing as of this date that IS NOT ILLEGAL until you drill 3rd hole and place the auto sear in it–fact. Thanks for your reply bill but this issue still needs addressing.

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