Which grain and cartridge type typically produces the best results in a 1:9 barrel at 100yds?

You could get hundreds of answers to this question, but what do you mean by 'cartridge type'?

1:9" barrels are supposedly the 'best of both worlds' when it comes to bullet weight (APPLIES TO .223 REM ONLY).

1:9" works well for everything from 35 grains all the way up to 70 grains and even higher in some cases.  The 1:12" barrels may work better for the lighter bullets, but can they still shoot the 69 gr. SMKs?  Probably not.  The only thing you will give up by not going to a 1:8" or 1:7" is the VLD bullets weighing 75-80 grains.

After browsing these boards for a several months now, it seems there are two types of ammo that "most" folks use.. the XM193 and the Q3131A.
IMO, I think the Lake City Federal XM193 is more accurate than the Winchester Q3131A at 100yds, I'm sure you'll get folks saying different but that is what I have determined with my RRA AR15 1:9. The XM193 is a bit louder than the Q3131A but it seems much more accurate.

Take it for what it's worth, I've shot 2 cases of each and I stand by it.

gilfrd

I've had great luck with 52 gr Sierra MK bullets with AA2230 or H4895 powder.
YMMV.

I have  a Bushmaster A1 20HBAR 1/9 That Groups the FEDERAL 69BTHP in litte Clovers at 100 yards Prone!!!

Also the Bushy A1 HBAR Shoots SANTA BARBRA SS109 Like MATCH GRADE!!

It seems that My Bushy A1 HBAR likes M855/SS109 and 69BTHP alot Better than M193!!


Now I also have a Bushy A1 Shorty 1/9 That likes the M855/SS109 over the M193 or Copies!

NOW BOTH BUSHMASTERS do shoot M193 very Tight just not as tight as the SS109 Bullet!

Also my Bushies like Q3131/Q3131A over XM193

With my Bushy 1:9 Vmatch 16", Federal 193 groups about 1 1/2 of the bench.  However 55 grain Vmax over 26.3 grains Varget, WW brass and primers, five shots into 5/8 inch.  So far hot or cold doesn't seem to matter.  The Varget seems little affected by outside tempture. Here in the desert 50 degree changes are common in one day.