I have had this olympic arms rifle that I was told was built for the Army marksmanship unit in the early 90s. The lower has a williams set trigger, weighted A2 stock and looks standard otherwise.  The upper is very unique.  Looks like it started off as an A2 but the carry handle was machined of and a weaver rail was screwed onto the top. It has a standard upper witha forward assist. The most unique part in my opinion is the barrel. It has a 24in 1/10 heavy barrel thats fluted under a free float tube. Then the barrel is .750 the rest of the lenght. It is marked SUM 5.56 and also has an MH stamped. It has a low profile gas block that looks like it was made from a standard front site. Anyone has any information on this set up I would love to hear it. I have pics but can't get them to load.
https://www.amazon.com/photos/shared/1XO2D_d5TXSbcgjVAYu1Mw.nfgFA-jJrXhO4-oW84ygxH

Ultramatch?

search that term and you should probably find the same or similar.

I know the S U M stands for stainless ultra match but all the barrels I have seen in pictures are not 1 inch under the free float tube and fluted. I have tried multiple searches on here and other sites and have found nothing so far.

https://web.archive.org/web/20090322155505/http://www.olyarms.com/index.php?page=shop.product_details&flypage=shop.flypage&product_id=29&category_id=6&manufacturer_id=0&option=com_virtuemart&Itemid=37&vmcchk=1&Itemid=37

Your rifle is older than that one^ the olyarms website is archived on waybackmachine

But I get results just doing Google searches. https://forums.brianenos.com/topic/5581-olympic-arms-ultra-match-barrels/

Thats way more than I could find. Greatly appreciated.  I was able to load a link to.some pics of the rifle and what the barrel looks like underneath the tube. Thats a hefty price tag for back then.

Not for the Army Marksmanship Unit.  

S U M was "Schuetzen (Gun Works) Ultra Match."

Crane and the Navy Team were the true National Match M16 pioneers in the 70s and 80s.  They were never successful as there were no good bullets to handle winds past 300 yards comparable to the 7.62.

USAMU had its own crash program going, command-directed by Colonel Mac Johnson.  The Custom Gun Shop was picking the brains of guys like Bill Wylde and others to develop an M16 to beat the Marines with their M14s.

1993 and 94 marked the first years the Army's M16 and ammo program started beating the Marine Team at Camp Perry.  By 1999 the Marines were also shooting the M16.

Thanks, that's awesome piece of history. Definitely need to read up more on the subject.  I plan on putting a decent piece of glass on it and maybe working on some hand loads. Just need to figure out a recipe for that 24in barrel in a 1/10 twist.

If the barrel is in fact 1:10 twist I’d load some 69 grain Sierra Match King with TAC power and CCI 450 and see how it shoots.   Sierra recommends a minimum 1:10 twist with 69 grain SMK.  If the barrel is a 1:12 twist then some Sierra 52 HP or 55 grain bullets.

My Sierra loading manual list 25.3 grains of Varget with Remington 71/2 primers as their accuracy load with 69 grain SMK.




https://www.sierrabullets.com/product/22-cal-5-56mm-69-gr-hpbt-matchking/

My local gun club 600-yard reduced course record was established in the early 90's by a guy shooting a rig virtually identical to your rifle, except his had a 1:9 twist SOG barrel. 200-16X with iron sights.

Olympic Arms made excellent barrels. It may have been owned by someone in the U.S. Army Marksmanship unit, but it wasn't government property, or you wouldn't be in possession of it. The CMP doesn't sell AR-15's to the general public.

I have an Oly SUM barrel in 6x45 that I had Adco cut and turn to an A1 profile.  It shoots fantastic and I will never part with it.

Thanks for finding that. I have an Ultramatch rifle as well but mine is slightly newer than OP. I have the coat of arms logo and the raised upper but my upper doesn't look chopped/modded.

I'm planning on filing an eForm 1 for it, hopefully that will help with the model number. Why would I make an Ultramatch into an SBR? I'm making a Stargate SG-1 'Carter Special' and it turns out that's the correct upper receiver: https://imgur.com/a/obmzhri