After coming to the conclusion that my 375 RUM had a tight necked chamber(this rifle was a prototype of a custom shop 700 ABG for Remington for the release of the RUM line back in 2001), I acquired an outside neck turner. Why it was made that way I have no clue, and the gun dealer told me nothing about it when I purchased it.

Here are a few numbers. Interesting factoid before I get started. My Swift manual has a neck diameter of .578 for the 375 RUM... Neck diameter before turning with a bullet seated was .411 for a thickness of .0180, and would not chamber. After turning it was .400 on the mark with a seated bullet, and the bolt closes with slight pressure. BTW I got those numbers by measuring a round with a seated bullet because I do not have a micrometer with the ball on the end specifically for this purpose

If I do the math right, that means that now my neck thickness is .0125. Is that too thin? I know that when you neck turn for uniformity you turn till the thinnest side just barely gets touched by the cutter, but I did have to go just a hair past that point by cutting, loading a dummy, and chambering in the rifle several times till it finally chambered.

I just want to make sure the brass is not going to seperate or something like that before I go for the trial by fire(no pun intended,well... maybe).

I guess as soon as I knew that something was wrong the first time I tried to chamber a round I could have just cast the chamber and measure the cast, but hindsight is 20/20, huh. Besides the fact that RUM ammo is not really available around the world, I would really be up a creek without a paddle even if I went on a trip in the states with missing custom ammo since factory stuff would not chamber either.

Maybe sending the rifle to a smith to get a reamer run through the barrel again to give me a normal neck diameter would be a good thing.

Thanks for the input. I do know that a lot of you folks dislike Remingtons immensely, but for the record I got this rifle last year before I started frequenting this forum, so please cut me a little slack here about not having a CRF. Also, my next rifle will be a CZ550 in 450 Rigby or 470 Mbogo, no more Remingtons for me.

Easy way to confirm your suspicions would be to throw $30 at a 'smith and have him cast the chamber and some of the throat/bore. If it is so tight, you'd stand a chance of a high pressure "situation". Not to mention the hassle of having to turn all your cases. The 'smith could open up the neck easily.

Yup.

I doubt VERY much that Rem. or any other arms company put a gun on the street with a tight neck. The liabilities would be tremendous, and without marking the barrel as such would be suicide, I would be willing to bet that the problem is somewhere else.

B, if that were the case, then why would the round not chamber without neck turning, and then chamber after the turning? Everything else I did as far as case prep, bullet seating depth, same brand of bullet, sizing methods, measured OAL and case length were all the same from one to the next. Not one dimension beides the neck diameter of a loaded round changed. I measured everything twice before turning and after.

If you need to turn some brass from 100% of the neck area you need to have someone look at your chamber. Neck-turning 100% of the neck will very likely reduce the ability of the neck to provide enough tension to hold the bullet under recoil...the ones in the magazine.

If you are the original owner I would take it to a Remington Repair Center and have them do the diagnosis and make any changes.

Unfortunately, I am not the original owner. This was a demo , had less than 75 rounds through it.

I would still take it to the nearest REmington Repair Center and have their 'smith take a look at it.

It is hard to determine from your post as to what the problem may be..perhaps the shoulder is not getting set back enough and that is your problem...

A too tight neck in a factory rifles would be extremely unusual, more likely they are all over size..

Did it accept factory ammo would be my first question and how far in did it accept your reloads would be my second question...Miking everything is going to solve nothing until you have your chamber specs and that requires a cerrosafe chamber casting..

Many times it is necessary to trim your shell holder so that the case will go deeper into the die..some folks cut the die bottom but its better to cut the shell holder..

Atkinson, it looks like getting the chamber cast is going to happen here in the near future. When I try to chamber an unturned round, I run into problems about 1/4" to 1/8" before the bolt handle clears the channel on the side of the action for the bolt to close. It was not a matter of how far the bolt was able to close, I could not get it to the end of the stroke to try to close it.

What a pain in the rear, I have had this rifle since the beginning of January, and I still have not been able to get a full day's shooting out of the thing(revert to comments in opening post about CZ550 purchase...).