New barrel problems, maybe?

[earl1704]

Question: is the chamber on my new barrel cut correct, to long, to short?
New Kreiger barrel 270 WSM
Once fired cases measured headspace: 1.7525 (shortest), 1.7620 (longest) trying to bump the shoulder back about 3 thousands. Settled on 1.7600 headspace.

When I put the case into a resizing die (RCBS) I have to put the die 'high' in the press to only bump back 3K. If I put the die high I cannot over cam the press and miss about an 1/8 of an inch on the bottom of the brass that does not get sized.
In my way of thinking the camber is to long.
Other info;
Plug gauge 2.1275, average fired case length 2.1190
Hornady #2740 bullet, 150 gr. SST, seating depth 2.2500, 'jammed in' is 2.2535 (average)
Am I looking at this correctly, or am I missing something?
I am not looking for 'book' specs. this is a custom barrel, I am trying to make a tight fit for accuracy. At 75 yards I get a 4" inch pattern.
At 300 yards I get anywhere from a 1/2 MOA to 8" spread depending on the day (same shooter).
Load; Winchester case, WLRM, 150 SST, H4350, 56.8. As the powder load increases pattern opens way up. That being said the 56.8 powder load only patterned a 1/2 MOA once.
Checked scope, changed scope, played with everything I could think of narrowing it down to the chamber....................yes, no other thoughts?

Earl

 

[ShtrRdy]

Did you push out the primer before measureing? That could make a big difference in your measurements.

I'm not too familiar with the 270 WSM but you'll need to take a look at the SAAMI drawing and figure out if the chamber dimensions make sense.

Can you measure the headspace measurement on a new piece of brass? Then compare that to the fired cases?

The fact that the fired cases are showing different headspace measurements sounds like the brass needs to be annealed. The case neck/shoulder sounds too hard.

 

[MagnumManiac]

Firstly, regardless of a 'long' or 'short' chamber, your accuracy issues sound like another issue entirely.
Stella accuracy is generally found with cases that have not yet been fireformed, yes, I'm talking unfired cases here. Making a case fit tightly with a chamber that may have a nominal size that the die cannot match is asking for trouble.

How do you know that the case is square to the centerline of the bolt/chamber after sizing?

Any eccentricity is forced to be worse in a tight chamber and close fitting case.
Some wiggle room is needed,you may need to buy a Redding body only die to bring the base of the case into spec, or a bump only die to bring the shoulder only into spec.
Personally, I use a body die to bring the case body AND shoulder into spec on difficult cases. Then size the neck separately, either with custom neck dies or mandrels.

Hope this helps.

Cheers.