My .223 Rem F-TR rifles are chambered with long (0.169" or 0.220") freebores for the 90+ gr .224" bullets. Both reamer prints list the freebore diameter at 0.2242" (within their tolerances). The freebore in these rifles is tight enough that it will stop a bullet moving out toward "touching" the lands when using a Hornady OAL gauge. In fact, you have to push pretty hard on the stick before the bullet starts moving again within the freebore, until you finally feel them "touching" the lands. In my experience, the barrels I've had cut with these tight freebore reamers have been stupidly accurate. 5 shot groups fired using my F-TR setup (i.e. bipod) and tuned loads are routinely at around 0.25 MOA at 115 yd, and on occasion will be as low as in the mid/upper 0.1s. I'm fairly convinced that by far the limiting source of error in terms of precision of these rifles is me.
My .308 Rem F-TR rifles also have long freebores, but according to the reamer prints the freebore diameters are all 0.3085" (within their tolerances). When using the Hornady OAL gauge, the bullets slide completely freely through the freebore until touching the lands. There is literally almost no resistance until they touch the lands, which makes is very easy to measure and is noticeably different from the .223s. Tuned loads in several of these rifles shoot almost as well my two .223s, with 0.25 MOA groups not uncommon, and occasionally a tick better. If I had to compare the two different calibers/freebore diameters directly, I'd say the innate precision between the two is so close the difference is not worth discussion. In fairness, I do feel the .223s have a touch better precision in practice, but that's likely due to the markedly lower recoil. They're just a bit easier to shoot, rather than necessarily being inherently more accurate/precise.
Along this line, I've had several conversations with Dave Kiff at PTG regarding tight freebores, their effect on alignment of the bullet with a chambered round, and ultimately, precision. My impression was that Dave also seems to think there may be some benefit in terms of innate precision to having the tight freebore, although proving there is a difference that is statistically significant may not be such an easy row to hoe. How many groups would one actually have to fire to reliably demonstrate some rather small difference such as 0.25 MOA versus something like 0.20 MOA? I can also imagine that any precision difference between a tight versus slightly looser freebore might also depend largely on the bullet used. It might be very obvious with some, not at all obvious with others. My gut feeling tells me that a freebore diameter difference of 2-3 ten thousands such as my rifles have is not typically going to generate results that have an "in your face" obvious difference in precision, at least, not with the bullets I've been using. Perhaps stretching out the distance might also make it a little easier to reliably detect a difference, but out to 600 yd, I can't say with any certainty that I can currently tell the difference.
