Several years ago(2004) I reloaded 30 rds 6.5x55 in SB cases for a hunting trip, 160gr round nose. I had decided to shoot a few last week but could not get them to chamber (very tight bolt) without excessive force. Initial thought was that maybe I had the OAL wrong. I double checked against my dummy rd but OAL was the same, double checked dummy rd and its good. Broke down one bullet, seated a 129gr. SP but had same results. Final outcome is that it seems to be the case shoulder on all rounds. I have heard of actions stretching but I have never had brass stretch without being shot??? Any thoughts?? As a last resort, I can pull bullets, powder and primer then run brass thru the die again.

Did something change on the gun? Different bolt, different barrel, etc? Maybe the chamber is dirty and that's making the cases extra tight?

Seen people over crimp and cause a swelling of the shoulder. Case length OK?

Question is did they chamber right after you loaded them? They didn't grow over the years; they were made that way. Either not sized enough, or like Ram said, over crimped and budged neck/shoulder.
You said it is the shoulder; then you need to set your die down until it touches the shell holder, and the ram cams over some. If that does not work, then you need a shorter die. I have faced off many of them.

A little more info. 1. No changes in rifle and I do not crimp my rifle brass.
2. Rounds were reloaded using a Lee Loader (same thing I use on all my 6.5 Lapua brass.
3. Previously I had fired a total of 10 of the SB brass/160gr out of this 20 rd group without issues (that was 10 yrs ago). Rds have been sitting in an ammo can since then.
4. Found issue at range, had shot 10 rds Lapua brass prior to and 5 rds after. So, no issue with chamber.
5. I do not pick up range brass for the 6.5 (have never seen any)
6. I have 20 more in another box and at least 2 have the same issue.
Next step, mic the brass at intervals including OAL of brass.
One note. I originally loaded these rounds for a trip to Montana (6.5 was a backup for my Muzzleloader) for black bear.

Most likely; it is simple; brass does not spring back forever; at some point it will not chamber; and with a Lee loader, you can't set the shoulder back; they only neck size.
Check the case length but that won't be it.
Your only solution is to get a press and full length size the brass, bringing the shoulder back so it will chamber.
All this is common.

As with your second box of 20, some will chamber and some won't. They were always this way. When you fired the rounds several years ago you were simply lucky that you happened to put cartridges in the gun which would chamber and not those which would not.

Overall case length is fine, however, the necks on the S&B brass are shorter than the Lapua (I had just trimmed all my Lapua). Issue is definitely the shoulder. Once I started measuring the length of the shoulder, you could see it. Now, what to do. Bolt closes part of the way, do I force it down and shoot them or pull all bullets and powder and primer and scrap the brass. Or buy a die....Thanks for the help !

Have to agree with dpcd and stonecreek. A Lee die since it only neck sizes will let the brass grow until it can't be chambered.

While there isn't any danger of firing them I wouldn't use them hunting. So if they were mine I'd pull the bullets and save the powder. Primer is history.

If you have a press buy a set of FL dies. If that is all you load and are happy with the Lee I wouldn't spring for a press and dies.

So if you don't go the die route you could pitch the brass and start over. Privi brass is .28 each up to .90 or so for the better brass.

Or maybe ask someone here that has a set of dies to FL them for you. If they remove their decapping pin it would save your primer. Probably time to anneal the neck.

Thanks for the feedback from all of you. Think I will pull the bullets, save the powder and see if my RCBS die will help the issue, if not, scrap. I have been reloading off and on for 45 yrs and have never seen this issue. Of course, I usually don't keep loaded rounds for 10 plus years.

Just to verify. When you say Lee Loader you are talking about the little set that you use a mallet to drive the case into the die to size the neck.

Or are you talking about a lee die set used in a reloading press?

You say its he shoulder? use marker on the shoulder of the case and probably on the rear of the case, and close the bolt snug as you can.

run this thru the die and another in the chamber to find out where its too tight..

Also a chamber cast always helps..

An over size chamber in the rear as a rule will interfere with chambering as will a long neck or blown out shoulder..These things are easy to deal with if your a experienced reloader, if not the best route is a good gunsmith..European rifles were never intended for the reloader as a rule..Sometimes something as simple as fileing down the shell holder will solve these problems, sometimes rechambering to a larger case is the only option short of a rebarrel, but first you must identify the problem, not guess at it.

One thing Im pretty sure of is keeping loaded rounds around for 10 years is a non issue with your problem unless they were loaded for a different rifle then it could very well be the problem in which case you need to pull the bullet, dump the powder, take out the primer pin in your dies, and full length resize the cases without losing the primers, and check the OAL and perhaps trim the cases all to the same length..

Yes, Lee loader and mallet. Have been using this exclusively for this rifle since I bought it.

Yes, definitely the shoulder. Not sure why but will down load and resize.