Uronen Precision (or Ase ja Osa) is a small Finnish family owned company.

I’ve been to see them a few times during the past years, and I’ve tested some of their rifles (AR-15s).

Their rifles are focused on match grade and competition rather than mass production. Each rifle is manufactured according to your specification.

They give an accuracy warranty to all .223 Remington rifles: rifle must meet or exceed 0.5 minute of angle accuracy on average at 100 meters, when high quality ammunition is used.

I’ve seen the old man himself go out to test a new rifle before delivery, so it’s a claim I’ve seen verified.

Picture below: Mr. Hannu Uronen is a very good competitive shooter, especially in handgun and rifle. He’s ranked Nr 3 in the World according to IPSC-Rating. Below he is shooting an Uronen Precision UR-15 .300 UP,  handloaded Sako brass, Sako bullet, Magtech primer and Hodgdon H110 powder.  Sight: Zeiss V8 1,1-8×30 ASV+ (1.5x on this stage) with Uronen Precision scope mount.

Anyway, the story behind the new caliber .300 Uronen Precision as told by Hannu below. (Unless you are fluent in his language you should not complain about his English):

.300 UP caliber creator Hannu Uronen found out, that he could shoot very relaxed and fast when using Open division pistol shooting major ammo. Or shooting military reservist action shooting matches, where only scoring is major for both rifle and pistol.

He was struggling to have the same performance with minor scoring in IPSC Rifle. .223 Remington caliber is used probably by 95% of competitors, it can only make minor power factor 150. Good rifle with good ammunition can be very accurate, recoil is very light, decent quality ammunition is cheap and so on, so there is no doubt that .223 is very easy choice.

The idea behind .300 UP started when Uronen Precision started to build rifles in caliber 300 AAC Blackout. Hannu did lots of testing with different barrel lengths, bullets, powders etc and got an idea of using major rifle for IPSC matches from testing. He did some comparing between .223 Rem and 300 BLK against the clock, and found out that even 300 BLK was usually little slower. However, he was able to get so many more points that hit factor became usually little higher with 300 BLK.

Hannu soon discovered, that even being ultimate all round cartridge for both supersonic and subsonic ammo, 300 BLK could be improved a lot for use with only supersonic ammunition. Long free bore, fast twist and short gas system needed for subsonic ammo, did not help with light supersonic bullets.

Shortly after this, Hannu got an idea to optimize 300 BLK for supersonic bullets only. First experiment was just to use slower twist rate, to reduce rotational speed of light bullets and even this improvement was noticeable. At this point, it was called “300 BLK Supersonic”.

However, there was much more to be done. Longer gas system to soften recoil, special “tight low friction rifling” with 12″ rifle twist and special chamber dimensions to accommodate modern plastic tipped bullets, as well as traditional match bullets. Also 300 BLK modest maximum pressure 3700 bar was raised to 4150 bar. This could be done, because .300 UP is only designed for AR-15 platform and bolt actions originally chambered for .223 Remington.

Even .300 UP uses 300 BLK brass, chamber and barrel dimensions are so different that there is no way .300 UP would pass 300 BLK CIP test. At this point, our caliber needed own name – that was the beginning of .300 UP

So to put it short: .300 UP is basically our version of 300-221; 221 Fireball case necked up to accommodate .308 caliber bullet. .300 UP is optimized for typical modern match bullets: Nosler Ballistic Tip, Sierra Matchking and Tipped Matchking, Hornady Match and SST, Sako OTM and similar.
Accuracy is on the same level with our .223 rifles, so 0.5 MOA 5 shot groups at 100 meters with match bullets are the norm. We have not been able to achieve the same with 300 BLK.

.300 UP also works very good with affordable bullets like Sako 120A and 143A (124gr FMJ). With these, accuracy of 1.0 MOA or better is the norm and hand loaded ammunition price (without case) is less than 0,30 euros per piece. So hand loaded .300 UP ammunition can be cheaper than affordable but decent quality .223 factory ammo like Topshot, Sellier & Bellot, Fiocchi or Geco.

Below – Left to right: .223 Rem, .300 UP with Sako 124gr 120A and last .300 UP with Sierra 155gr TMK

We have done all our testing with Sako brass because of the high quality but just like 300 BLK, you can make brass for .300 UP from .223 Remington brass.

.300 UP gives higher muzzle velocities compared to 300 AAC Blackout with same barrel length. This means, that .300 UP meets IPSC Rifle major power factor 320 with 155-160gr or heavier bullet (175gr or heavier for 300 BLK).
For lowered major power factor 280 120gr or heavier bullet can be used (130 gr for 300 BLK). Lowered power factor PF 280 basically means duplicating 7,62×39 ballistics.

Suitable powders for .300 UP major loads are (for example): Hodgdon Lilgun, Hodgdon H110, Winchester 296, Reload Swiss RS30 and Vihtavuori N110.

We still think that for many shooters, .223 Rem is the right way to go. It is very easy: rifles, ammunition and knowledge is widely spread everywhere.

Does this mean that we will reduce of making 300 BLK and/or .223/5.56 rifles ? Answer is absolutely NO! We believe, that .223 Rem / 5.56×45 will still be 90%+ of our production. Also for those who need to use subsonic ammunition from AR-15, 300 BLK is the way to go. We are especially proud of our Tactical Carbine 9.5″ 300 BLK

But for a sport shooter or a hunter, who is not afraid of hand loading his/her own ammo, is looking for something different, wants to have major scoring in IPSC rifle, .300 UP could be just the ticket giving that little extra advantage needed.

At this point, first internationally sanctioned rifle match (Mayday Rifle Level 3, Estonia) for .300 UP is over and the results look very promising: SAO winner Hannu Uronen and SAO 3rd Dagnis Maiberg used .300 UP (the 2 first .300 UP rifles made).”