Here's a problem for you maybe one of you guys have seen.

I have just purchased a new unfired weatherby ultrlight chambered for .300 winchester. I have also brought new winchester brass. I use redding dies and have no problem with them in two other 300 wins that I load for.I first of all neck sized the brass to make all the necks were round. I tried putting an empty case into the rifle and cannot close the bolt unless I actually cycle the bolt and hit the case fairly hard. Which is something I should not have to do.I then got out my full length die and am now actually touching the shell holder. I have also taken out the expander ball and done the same procedure. Still a bitch to close bolt with an empty case in. I am thinking there is something not quite right with this chamber. I am wondering if it needs some polishing or if a small base die would work. Once the cases are fire formed hopefully the problem will be solved till more shells are brought. Whats your opinion??

Three things-Chamber shoulder length too short,
due to tight chamber if bolt lugs are seated ok or 2 if brass works good in other 2 guns--
Tight chamber on the base or belt,but you should see scrubbing with magnifying glass.
And check belt with a H&H go and no/go gauges.
Or 3 the lug seating poor, giving tight chamber due to length to shoulder or belt being too short.Which you can check with black marker
on back of all lugs, working bolt with tight case. If not even, seat them in, thus gaining a little headspace.Ed

i had (well, still have sort of) a mark v 300wby w/ same problem. would not chamber my reloads period. bright ring just in front of belt where chamber was hitting the case measured .5127 or something like that. reamer specs in front of belt is .514", nom case is .513. tight chamber, right? took to local idiot alleged gunsmith who was a wby fac service cntr. told him the chamber was tight, needed cleaning up. he checked head space, chambered a fac round, charged me $46 for 1 hr work, told me my dies were bad. ammo from these worked in 2 other rifles, ammo from another guys dies woundn't work in this one. bought another set of dies. same thing. asked 2 retired gunsmiths both of whom said "sounds like a tight chamber; probably cut w/ a dull reamer." sent to mcgowen, they said "it seems to have a tight chamber; probably cut w/ a dull reamer." since was the 26" #2 contour & i had another 300wby i had it rebored/chambered for 340 mag.

it would seem yours is suffering same symptom. on mine, the scrubbing mentioned was noticeable w/ naked eye. if you live around fort worth, i can tell you where NOT to take it if you want it fixed.

i actually wrote a pretty hot letter to wby but never bothered mailing it. i got the rifle used; wasn't even trying to get it fixed under warranty, just fixed. for twice what this goober charged me i could have bought a reamer and fixed it myself and still had the reamer. as it was i wasted that $46 and the cost of a 2nd die set i didn't even need.

How much is the case expanding when fired?
Can a bullet drop back in the unsized neck? Does the die size it back to close to its unfired state especially just above the belt.

I`ve a tight chambered 270 win that will hold a bullet in the mouth of a fired case unless it`s turned and only seems to expand ~.001 for the majority of the case body - remember the brass has some spring back and this isn`t a measure of the chamber just a idea of the case/chamber relationship. The chamber in mine is custom and I doubt you`ll find one this tight in a factory rifle. Fired unsized cases chamber just fine.

I`d take a good look at the case just in front of the belt and see if the die isn`t failing to resize it enought at this point. I`ve read of this being a problem with some belted cased cartridges and regular dies. There is a collet type die available to help correct it but I don`t remember who makes it.

I'd smoke a case, just to see where the contact is taking place.

I just got a 7mag back from the gunsmith, and I can't chamber Wby headstamp brass because the belt hits. The 'smith headspaced it on the shoulder, which is fine, but my Wby (i.e. Norma) has a bit larger belt (about 6 thou) than the domestic makers. FWIW, Dutch.

The brass I am putting in the rifle is still unfired (virgin brass) it has only been resized. I think that the chamber is too short.

Take a case, blacken thoroughly with a black marker, force chamber it, and examine the case.

Where is it rubbing (as evidenced by the removal of the black)?

3 possibilities immediately come to mind

1) belt/head-bad chambering job (belt groove to shallow) as mentioned above
2) shoulder/head-bad chambering job (reamer not run deep enough) as mentioned above
3) head/mouth (maybe with partially collapsed shoulder)-bad chambering job, neck too short OR brass too long

The fact that it chambers in your buddies' rifles only indicated that their chambers are cut larger...

Cut a few thousands off the top of your shell holder,( file )then try it, maybe you will need to cut off some more until it works, then you have custom fitted dies for your rifle, or a ruined $5.00 shell holder at the worst scenario...

If that does not work then you may need to take a cast of your chamber and may need to outside neck ream...

I suspect the first option will work, thats a common cure...