I am planning on putting together an AR15 carbine, using a Bushmaster 16" "light" profile barrel.  I have obtained a Colt AR15 carrier, but it's a late type with the entire rear lower section milled away.  As such, it is obviously lighter than the older "full circle rear" types, which themselves are lighter than M16 carriers.  

It occurs to me that there must be some optimal dynamic relationship between gas port size, bolt carrier mass, and buffer mass, for the system to function within its intended limits.  Clearly, the idiotic design changes by Colt had nothing to do with increasing reliability of the rifle, but to make it more difficult to convert AR15's to full auto.

Since these later carriers are so much lighter, should I use an "H" buffer in the tube, to at least partly make up for the loss of mass in the carrier?  Did Colt make heavier buffers to go in these later AR15's, or perhaps slightly decrease gas port size?  Or, do they just bottom out harder at their rearmost travel?

Am I totally over-analyzing it, and should quit worrying about it and just slap it together?

Thanks in advance for insights & comments,

Ted

You are over analyzing....

Put the 9mm buffer in it and forget it.   The 9mm buffer is similar weight to the rifle buffer, but for carbine length tube.

It is a semi-auto, so rate of fire control and bolt bounce are not applicable here.


EDIT- the link saved a while back does not work as it should.

I've never had any problems with any of my Sporter carriers.

Quoted: Am I totally over-analyzing it, and should quit worrying about it and just slap it together? Ted

Yes.  .

I have had no problems with Colt 'shaved' carriers in any builds.

Thanks for the input guys.

However, consider this--When Eugene Stoner designed the AR15, he did so with the aim of making it as light as possible.  So, if that whole area of steel that's missing from the new style AR15 carrier is "unnecessary," why wouldn't Stoner have left it off?  That's an appreciable chunk of steel in such a lightly constructed rifle.  He could easily have left a little area that was just enough to trip the autosear.   It just makes me wonder.

Were the original AR15 buffers lighter?  I think they may have been.  Maybe that had somethng to do with it.

At any rate, the reason I want to use the Colt carrier vs. a Bushmaster or other copy is that as much as I hate Colt and their policies, I still trust the steel and specs of the bolt/carrier groups, which in my opinion are the most important part of the system.

Ted

Quoted: Am I totally over-analyzing it, and should quit worrying about it and just slap it together? Ted

NO.

You are not.

Gas pressure is very different between rifle and carbine.

here.... this is a similar thread.

www.ar15.com/forums/topic.html?b=3&f=12&t=204788

have a good one.

Stainless

Quoted: Thanks for the input guys. However, consider this--....

However consider this,  several of those guys posting have done this and/or seen this setup before.  You're theorizing - they've done it.  Listen to them.

If stoner left that section of metal off what would trip the auto sear?

The lighter the carrier and buffer the more felt recoil and faster the cyclic rate.  It will still function just fine though.  If you have NO buffer yet buy an H, H2 or 9mm buffer.  More weight in the rear will make the foreend feel lighter anyway as well as slow down the cyclic rate (non issue for you) and reduce felt recoil.  If you already have a buffer you can just run it and it will work.

What's an "H2" buffer?

Quoted: At any rate, the reason I want to use the Colt carrier vs. a Bushmaster or other copy is that as much as I hate Colt and their policies, I still trust the steel and specs of the bolt/carrier groups, which in my opinion are the most important part of the system. Ted

Something else to consider. Colt has for a while put PLASTIC buffers in their MT's. The 16" flat top with standard stock will have a shaved bolt carrier and plastic buffer, and I've not heard of any problems with that combo.

Whats an H2 buffer?  Its heavier than an H buffer but not as heavy as an H3 buffer.