I have a 7mm mag with chambering issues. It handles factory loads well but hand loads seem to be the issue when locking the bolt down it really gets tight even with just brass and no bullets Chamber is clean with no obstructions. My brass is tumbled clean and trimmed to 2.49" as RCBS manual calls for 2.5" max and appears to be in pristeen condition. I've used an old set of RCBS dies previously with the same problem so I recently bought a new set of Hornedy dies hoping they would cure my ills to no avail. Again, no problem with factory loads. I'm open for and would appreciate any ideas as I'm about done.
Check your shell holder and your dies for built up dried lube or crud.
How many times has the brass been fired and resized? Were they fired in your gun?
Possibly you aren't adjusting the resizing die correctly. Try a few variations of over-camming, adjusting the die just a tiny bit each time.
Inspect the brass after you try to chamber it, are there new scratches or marks on it? Blacken one with a dry-erase marker or a non-permanent felt tip marker and chamber it to see if you can determine where it's hitting.
Belted magnums often develop a bulge just above the belt that is difficult to resize and makes chambering difficult.
What jwdurf said about swelling just in front of the belt, is a problem with most all belted mags. I don't recall the name now, but there is a collet die that addresses this issue, it return the brass to factory/SAAMI spec. It is supposed to increase the life of the brass also.
Take a fired(from your rifle)unsized case and see if it chambers smoothly. If it does, your sizing operation isn't set properly.
If your belted magnum shows "bulging" above the belt you have a chamber issue. However, the "bulge" most see is nothing more than an optical illusion. I have 5 rifles chambered in belted magnums, 3 savage, 1 ruger and 1 custom 1917 Winchester. None of them bulge above the belt.
Ahhhhh, the Larry Willis belted magnum collet die. A $100 solution to a problem that 99 out of 100 times doesn't exist.
Over-camming. Raise the ram and set the die down until it touches the shell holder, then turn it down a touch more so that when you raise and lower the ram it cams gently against the shell holder. This is the adjustment I'm suggesting playing with a bit. And by a bit I mean a 16th of a turn or less at a time. Do not adjust it too tightly against the shell holder.
Also do check and be sure the shell holder is clean, inside top and bottom. A couple of thousandths of an inch of crud can cause a mile of grief.
I'm curious to see the outcome of this problem. I have two model 110 Savage in 7mm Rem Mag. One eats anything I feed it. The other has the exact problem as the OP states.
I have a 7 mag barrel that I pulled off of a 110 that wouldn't chamber no matter how my die was set up. I put a polishing wheel on my dremel, added a little polishing rouge and ran it through the chamber a few times. Cleaned the chamber out real good. After that it chambered rounds like a hot knife through butter.
Wonder how he's sizing? If he's partial or neck sizing, the case need's a bit more sizing. Belted mag case's last longer with partial sizinf but, if your not getting in quite far enough, your gonna start pushing against the neck. If he's neck sizing, every now and then he need's to FL size as the case has grown to much. Doesn't sound like crud in the chamber as I think he said factory case's chamber fine.
With the die screwed down to the shell holder the case should be returned to spec. But direction's say down to the shoulder and a bit more to over cam. Partial sizing does not get to over cam and it work's well. If there was a build up of lube in the die, the die would over size or maybe dent the case. Shoot cleaner into the case and clean it good, eliminate that possibility. Check length after re-sizing. If he's partial sizing, screw the die down maybe another 1/8th turn and try again. Keep doing that until the case quit's rubbing on the shoulder. I'm guessing this problem is with an MTY case, if not, check the seating depth of the bullet. A bullet into the lands can easily stop the action from working. One being right on the edge of missing the lands can chamber and not leave much of a mark on the bullet, seat the bullet a eight turn at a time until the resistance is gone! The problem is either the case is not being sized enough, the shoulder at the body is buldged a bit after seating the bullet or if the bullet is seated when this happen's, buldged at the shoulder or bullet hitting the lands.
7 Rem mag RCBS dies need a lot of cam over in the press otherwise the shoulder won't get pushed back
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