I picked up an Interarms MK10 in 243. It will shoot an inch or better with everything I have tried. Here is the question or problem. With factory rounds and reloads the primer backs out. At first I thought the loads were hot but the factory rounds do the same thing. I cannot rechamber a fired case without a huge effort. Now, I just read one of the Ackley handbooks and there was a part about oiling cases. On a whim today at the range I wiped down the cases of a factory round and a handload with oil and fired them. They were a little tougher to extract but the primers didn't back out. I couldn't rechamber them either. The hand loads are not max. Could the chamber be out of round, be oversized, or have excessive headspace? Is this just a problem with the .243 round?My Sako '06 chambers a fired case like a new case. The shoulder doesn't even move. I have not yet full length resized. Back to the .243, I have been using the lee collet die, and after neck sizing most rounds will chamber with a little effort. If it is tough and I rotate the case a little it will chamber. Any input would be greatly appreciated. Thanks.

It sounds like you've answered your own question. If it chambers more easily when turned a little bit, the chamber (or just the neck, it sounds like) must be eccentric.

The chamber may be rough, though, as it sound liek unless you oil them they are sticking to the chamber walls and allowing the primer to back out.

Have you had the head space checked?

Don

I don't believe I can answer my own question as the whole deal confuses the hell out of me. I'm sure this one will be a learning experience but I would rather learn from others mistakes than my own. I have not had the rifle headspaced but it and a chamber cast are scheduled soon. There are enough variables though, that I would trust the ARL members to give some exceptional insight into the problem. That was the reason for the post. The vast majority of off the cuff answers given here, when researched, tend to prove themselves true, hence the post. Also Don, I am still working on getting up to Prescot and getting those pictures of the Magnum actions for you. Thanks for the reply.

I forgot to add that the only thing that chambers easily this far is a factory round because I have yet to full length resize for it handloading. Regards........

Carnivore,
First have the rifle checked for excessive headspace. If it checks ok, have the gunsmith check if it is bearing on the lugs at the bolt head and not on the third lug at the back of the bolt.

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Gerard Schultz
GS Custom Bullets

Carnivore. First off, let me mention that oiling cases is not a good idea. The case has to grip the walls of the chamber, ans oiled cases don't do that too well.
Now you said your rifle was a Mark 10. Do you mean one that is marked Mark X? (correctly called Mark 10. Most people don't)
Regarding the hard chambering of the fired rounds, try this. The Mark X is a 98 Mauser type rifle with the claw extractor. Take the fired round and partially plce it is the camber, but pushing down on the base just enough for the extractor to pass over the rim as it would if being fed from the magazine. It would be easier to show you than explain it, so I hope you get the idea.
That may be part of the problem, although the two Mark X's I had did not give me that problem.
Wish you lived a little closer. I'd like to take a look at it. Could be a number of reasons, including headspacing, improper sizing, and even a poorly done chamber is not out of the question. One of my Mark X's had a chamber so tight, I had to alter a shellholder and base of the resizing die to load for it. Sure was accurate though.
If you get down Tucson way, bring it down and look me up. Maybe we can figure it out.
Paul B.

Primers backing out is indicative of excessive headspace. Difficulty in chambering fired round is indicative of a chamber that is out of round or one in which the reamer has chattered. Careful inspection of a fired case should tell the tale. Regards, Bill.

Carnivore,

If you need a gunsmith, e-mail me and I can recommend a good one in Glendale area. Have seen quite a bit of his work, pretty good.

1894, I know what you are talking about and I am not doing that. I open the floor plate for room and slip the brass under the extractor. If the headspace was off the barrel would simply have to be faced correct? If the chamber was sloppy or out of round can it be cleaned up? It is not rough as far as I can tell. I will be going to a gunsmith today with fired and unfired reloads and factory stuff. Everyone, thanks for taking the time to reply.

Ok, I guess I learn something new every day. I bought the rifle used, and got an excellent deal. Whatever! I never even thought to check to see if the bolt matched the reciever. The smith I took it to checked the factory and handloaded fired unfired, and oiled rounds. Yes, it was way excessive head space. Where did it come from? The bolt. The non matching bolt! So after the cost of the work it wasn't such a deal after all, but damn does it shoot!! I got a one hole clover with factory Rem 100gr psps. The handloaded Sierra 75 gr, and Hornady 70gr vmax did the same, on the same day! Thanks again for the replys.