As I understand it, 223 ar15s won’t cycle with any subsonic 223 ammo that one can obtain without a permit from the energy department (:) ). Given the limits of a 1-7 twist, the stuff we can handload is generally limited to 70 grains which just does not generate sufficient pressures to cycle an ar15 when kept in the 1000fps range.

However, I was just wandering through the brownell’s web site and noted that they had a titanium bolt carrier that “Requires substantially less gas pressure than standard bolt, so an adjustable gas block is recommended [when usign conventional 223 ammo]" This got me thinking that if one were to combine a lightweight bolt carrier, light weight buffer and bigger gas port plus adjustable gas block, one might be able to get an ar15 to cycle with subsonics. Of course, there would still be the problem of getting the same gun to work with conventional supersonic ammo without having to swap out a larger number of parts, but one problem at a time, and the brownells description seemed to indicate that the piece could cycle with this carrier with a gas block turned way down.  

Anyone tried rebuilding an ar15 to cycle with available 223 subsonics?

Factory AR15s already cycle ammo designed to cycle stadard ARs.  Just use cycling subsonic and pay the price for it or get a .22lr kit... no need to reinvent the wheel.

removing the weights in the buffer would be less expensive than a super-lightweight bolt carrier –– good idea.

who makes the 90g subsonic? are there round nosed 90g 223 bullets available for handloading that will stabilize in a 1-7 twist?

thanks

What on earth are you talking about? [>:/]

Just get a .22 conversion and shoot cheap subsonics all you want.

the best way to do this would be a shorter than pistol length gas system and an 8 - 12" barrel.  you would also want to use a case shorter than .223, like a .222 or even shorter, so you can actually load the 90 grainers to mag length and have them gripped by the case neck, or I guess you could just load them all backwards.

it would work and it would be crazy quiet, and the 90gr pills are super long and unstable, so they would have a pretty good wound track all things considered.

I am doing the exact same thing right now in .30 cal with a 300 whisper.  8" barrel, shorter than pistol gas tube, and 170 -220 gr projos.

If you don't mind setting up a specialty gun then set it up with a pistol length gas system on a 16" barrel.  It can be done and don't get overzealous with getting the heaviest bullets you can find.

In reality though, get a .300 Whisper and call it a day.

it sounds like what is needed is a source of round nosed, flat based 223 bullets that are as heavy as possible while still being stable in a 1-7 twist at ~1000fps. No one seems to make such bullets for handloaders.

recall there is someway to make jacketed bullets yourself, perhaps using fired 22lr cases?