I have a Winchester Featherweight in the 270 WSM out of New Haven. I haven't tested a wide variety of ammo through it (cost) and I don't reload as of yet. I also don't have a chronograph so I can't help you there either. What I have found is mine seems to like the Federal 140gr Nosler Accubond round and I if I do my part, I can put all 4 rounds (gun capacity) in under an inch. The most I've ever done was nine rounds in under an inch in a consecutive string and the other three opened it up to 1 1/4". Of course, I did have my trigger adjusted down to around 2 lbs. and have since increased it to around 3 lbs. Regarding the chamber, I don't notice mine being excessively tight but I do remember the action being a little stiff when new which is mostly typical of any mass produced firearm. It's very smooth now but not sloppy by any means.
Mine also seems to prefer a somewhat clean barrel. I probably had over 100+ round through it with doing nothing more than using Hoppe's #9 solvent for cleaning after each outing unless I was going hunting. The groups started opening up to 3" or more and was causing me all kinds of frustrations especially after getting the aforementioned groupings. Last year, I bought some Butch's Bore Shine and couldn't believe how much copper residue the Hoppe's was leaving in. My groups shrunk back down to 1" and under after that. For whatever reason, it seems that it takes around 10-15 rounds to get the gun settled back in after cleaning it this way but even these groups aren't more than 1 1/2" to 1 3/4". In all honesty, it may be more of a situation of "me" settling in as I don't shoot it that often and usually only when checking it before deer season starts.
The only other round I've tested in it was the Winchester 130gr Ballistic Silvertip but it's been quite a few years back and I don't remember the actual grouping from them but I do know the Federal's shot much better. I've often thought of trying more variety but I have to catch myself and ask why since this load seems to do extremely well through it and since I don't reload, hard to justify spending $150-$200 in various ammo to find something that's going to give my 1/4" tighter group. After all, this isn't a benchrest rifle, it's a hunting rifle and other than decreasing the trigger pull is straight out of the box. I've only had a couple of deer run after being shot and that was only for 40 yards at the most, all others have dropped right in their tracks. The longest shot I"ve ever made was with this gun and it was just shy of 400 yards and she only ran for about 30 yards before dropping. I have been very pleased with this bullets performance and although pricey, I think it's worth your time to get a box or two and try it out.