300 WSM neck tension, problems found

S

SteveS

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Back in November I started a thread on neck tension for magnum rounds because I was having problems with bullet pullout under recoil. I've found a couple different problems with equipment and set up.

In the original thread (under general discussion) I reported an outside sized neck diameter of .3345 or so when sizing without the expander button. Al Nyhus reported getting about .006" more restriction with his Redding dies.

I contacted Redding and the helpful fellow there stated that they had problems with their early 300WSM sizing dies and had changed the design to size the neck down further. Redding replaced my die at no cost, great customer support for 10 year old dies. My original die had an "S3" design code rolled into it, the new one is "OR". The new die, without the button, sizes down to the size Al was reporting. I believe his dies must be of the later design. The sizer button remains the same size at .3065. With the smaller restriction I'm getting more springback in the necks (my theory) and the final sized internal diameter I believe is now .306 vs. .3065 with the original die. This is an increase of 33% in bullet to neck interference, .002 vs. .0015.

I also found a set up error. I was sizing the shoulders down to almost .010" under the chamber size resulting in a lot of slop. I'm wondering if the combination of a slight bullet slip and the case propelling .010" deeper into the chamber than it should caused the bullet to jam in the lands and pull out. My loads are further than .010" off the lands so I don't think the sizing problem could cause the bullet pullout by itself.

I've pulled all my old loads and resized all my cases with the proper set up. I plan to fire them with jammed bullets to try and blow the shoulders forward where they should be. Then I can resize at the proper length and better neck tension. Hopefully the better sizing fit will get rid of a few random fliers and improve the velocity spreads.

Thanks for the advice on the original thread, maybe this info can help someone else avoid the same problems.

Steve Sanders
 
SteveS said:
I also found a set up error. I was sizing the shoulders down to almost .010" under the chamber size resulting in a lot of slop. I'm wondering if the combination of a slight bullet slip and the case propelling .010" deeper into the chamber than it should caused the bullet to jam in the lands and pull out. My loads are further than .010" off the lands so I don't think the sizing problem could cause the bullet pullout by itself.

I've pulled all my old loads and resized all my cases with the proper set up. I plan to fire them with jammed bullets to try and blow the shoulders forward where they should be. Then I can resize at the proper length and better neck tension. Hopefully the better sizing fit will get rid of a few random fliers and improve the velocity spreads.

Thanks for the advice on the original thread, maybe this info can help someone else avoid the same problems.

Steve Sanders
Click to expand...

You'll have to please refresh us (me at least) regarding "bullet pullout," I have no idea what you're talking about, but it is my opinion that you've created a large problem with the .010 shoulder setback.

They will absolutely not "blow forward."

You cannot blow shoulders forward unless you've a rimmed or belted case. You can blow them forward a little bit in your case because ten thou is a huge gap, well beyond the sorting criteria ("field gage") for even the US military, the extractor will probably stop forward movement of the case at 5 thou!

If you fire them as they are they'll stretch backward somewhat, the rear of the cases will stretch back erratically to (sometimes) (eventually) stop against the boltface. In 1-3 firings. They will end up somewhat approximating your chamber length..........

But the correct fix is to make brass that fits properly.

I realize you probably don't believe me. I realize that if you ask 10,000 people they'll all say "the shoulders will blow forward."

In the end, when you've cured your fliers you can decide whether or not I was correct in my assessment and post your results here. :)

opinions vary

al
 
Al,

I had a bullet jam in the lands and pull out of the case when I opened the bolt. I had taken a shot, loaded another round and when I opened the bolt again the bullet was stuck in the lands and pulled out.

I've read that this technique will not blow the shoulders forward because the blow of the firing pin will push the case forward. Wouldn't a hard seat into the lands hold the case in place?

The only other technique I know of is to expand the neck first to create a false shoulder when necked back down to 30 cal. I was hoping I could avoid that but maybe not.


Thanks

Steve
 
Last edited by a moderator:
Steve, glad to hear you tracked the problem down.

When refiring your cases, consider a light bit of 3-In-One oil on the cases to help them form to the chamber a bit better. This reduces the friction between the case and the chamber so the case doesn't 'stick' to the chamber wall when fired. As an aside, the last bunch of 300WSM cases I got (new Winchester stuff) measured .011 shorter from base-to-datum than fired cases did from the factory chamber. While you obviously don't want to have that much clearance every firing, initial firing of the cases with that clearance isn't a big deal. With new cases, there's plenty of flexibility in the brass due to factory annealing to let them conform to the chamber. Since your cases have been fired a few times, I'd suggest annealing the shoulder/neck area just so it's a bit easier to get them to f-form correctly on the first refiring. A good tool to measure base-to-datum (the Hornady Lock and Load, for example) is essential for setting up your dies correctly to get the shoulder 'bump' where you want it to be. Between .001 and .002 is a good 'bump back' shoulder dimension on resized brass.

Good shootin'. -Al
 
Al,

I use the RCBS Precision Case Micrometer, it can be used to measure both the shoulder datum and the distance to the lands.

I've never done annealing, but maybe this is a good time to learn.

Thanks

Steve
 
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