300 RUM Headspace ?

[Moman]

I just got my 300 RUM Sendero II and have been doing some break in work with it. I measured the new Rem brass at the shoulder with a Hornady LNL gauge with the "E" insert. The shoulders measured 4.466 for the most part with a few coming in at 4.467. Occassionally when chambering a round, I can feel the bolt being a little hard to close, not real bad, just a little resistance and I'm sure this is the 4.467 brass. Once fired brass is measuring 4.464, .002 under. I'm thinking that the chamber is just a min spec and probably in the range of 4.466-4.467 and after firing, the brass is settling down to 4.464. I figure that I will bump the shoulders on the new brass back to 4.464 for a little clearance, but I wanted to see if anyone else has had this issue. Also, this is not a bullet into the lands issure as there is plenty of freebore.

[J E Custom]

Originally Posted by Moman

I just got my 300 RUM Sendero II and have been doing some break in work with it. I measured the new Rem brass at the shoulder with a Hornady LNL gauge with the "E" insert. The shoulders measured 4.466 for the most part with a few coming in at 4.467. Occassionally when chambering a round, I can feel the bolt being a little hard to close, not real bad, just a little resistance and I'm sure this is the 4.467 brass. Once fired brass is measuring 4.464, .002 under. I'm thinking that the chamber is just a min spec and probably in the range of 4.466-4.467 and after firing, the brass is settling down to 4.464. I figure that I will bump the shoulders on the new brass back to 4.464 for a little clearance, but I wanted to see if anyone else has had this issue. Also, this is not a bullet into the lands issure as there is plenty of freebore.

The brass will expand differently depending on the toughness of the brass (Spring back)

I would recomend sizing only enough to close the bolt with a little effort (To lose and you will work the brass to much and the life will be short.

The reason to neck size only is to make the brass last and consistant load performance
if the case fits the chamber tight it will shoot well and last longer.

I wouldn't worry about a tight chamber ,lots of guys would kill for one.

J E CUSTOM

[Moman]

JE, thanks for the reply. I'll have to admit, I was pretty excited when I measured the first couple fireformed pieces. It's got a real nice chamber in it, a little much freebore, but I figured it would. I have always been a partial FL sizer, usually going about .001-.002. Today I played around with my sizing die and set it to push the shoulders back .001 to 4.465 and they feed into the chamber quite a bit better. I feel a little better having a bit of room for a hunting rifle. I didn't expect that much spring back, I'll see what they come out at with the new shoulder sizing. Anyway, the gun really shows some promise. I did a good break in and thoroughly cleaned between each round for the first ten. Very small amount of copper fouling and the first three shot .5 Worked on three shot groups yesterday and it opened up a bit to .75 but should come around. Trying some 200 AB's tomorrow.