7400 casings getting stuck in chamber

[Coyote Jack]

I have a 7400 that I bought new about 35 years ago. It is cambered in .270 caliber and is used for deer and moose hunting only. If I were to take a guess I would say it has somewhere between 250 to 300 rounds through it. My problem is that the spent cartridges are getting stuck in the chamber and the extractor is ripping a piece of the cartridge off when the gas forces the bolt back. I have been told that this is caused by the chamber being pitted and when the bullet is fired the brass expands, gets caught by the pits and the extractor can't remove the spent casing because the bolt reacts so fast that the brass has not had a chance to relax back to normal size. I had the chamber re-polished and it made no difference. I guess what I am asking is, is there any way I can slow the bolt down just a little so that it does not try to extract the spent cartridge before the cartridge has a chance to relax? Other than this problem the rifle has worked very well and shoots very well with MOA accuracy most of the time.

Jack

[Mainspring]

There is no adjustment and probably not an easy way to slow the bolt down. A new Action Spring might help but just a few hundreds rounds fired is not much.

Usually it's not rust pits that cause an issue but the little raised rust bumps in the chamber. Cleaning the chamber to remove these bumps usually ends in success. Polishing a chamber can cause another issue, an oval shaped chamber that is larger in the middle than the entrance.

Looking at fired brass can tell a lot, it will show a reverse image of the chamber. Bumps in the chamber will be pits on the brass, pits in the chamber will be bumps on the brass, and looking at the scrape marks will tell you where that issue is located. The term "frosted" is used to describe the appearance that these issue cause.

[Coyote Jack]

Thanks for the reply. I know exactly where a spent casing is and I will be going there later this week. I will post a photo or two when I get it. It is still in the deer stand. lol

I was wondering if maybe using a spring out of an 1187 12 gauge might slow it down a bit.

Jack

[Coyote Jack]

As promised here are a few photos of a spent cartridge from about 3 weeks ago. It has been sitting on the window sill of my deer stand and has discolored a bit but it is typical of what things look like. I should add that I don't feel any bumps on the casing.

Jack

[Mainspring]

The last pic showing the primer seems to indicate high pressure, are these reloads? High pressure can cause the problem you are having, try a different make or type of factory ammo. If you are shooting reloads then check the data, if the data is fine the loads may still be too hot.

The body of the case looks much better than I expected. Usually a bit of rust in the chamber will be the bumps, the case will be the reverse and shows divots where the pits are. I'm not sure I see anything that indicates a chamber problem.

[Coyote Jack]

These are Federal Premium Vital Shock High Energy 140 grain Trophy Bonded Bear Claw. They are a hotter load than some with a muzzle velocity of 3100 fps. Looking at the primer of a live cartridge and a spent cartridge I do see that the primer has tried to come unseated after firing. Also the first 1/4 inch of the casing closest to the primer is deformed compared to the rest of the cartridge. You can see the difference in the color of the cartridge in the above photos. Both of those observations seam to back up your theory.

Jack

[Mainspring]

The two different colors on the case, after firing, is normal. Forward of the line is the chamber and rearward of the line is the part of the case that sticks out of the rear of barrel.

The primer shows high pressure two different ways. The "flattened" primer can be common but is an indication of high pressure. The ring around the firing pin indication is where high pressure pushed the firing pin rearward then started pushing the primer into the bolt face, this is not good.

I think that this rifle with this ammo is incompatible.

[Coyote Jack]

Thanks, I will pick up a box of slower bullets and see what happens.

Jack