Solve this mystery

[WTNUT]

I know I am going to feel like an idiot when we figure this out, but at times it is best to stop where you are at, step back from the reloading bench and take bite of humble pie.

Facts:

1. Have a new custom built 7MM Mag, bolt action.
2. Used the Hornady O.A.L. Gauge to find the length at which the 180 grain berger VLDs were touching the lands.
3. Next, plan was to use the Berger recommendation of backing of .010, .050 and .090 and loading 6 rounds at each length. I loaded 5. The plan was use a conservative load that has historically shot well for me in 7MM Mag with that bullet to primarily test seating depth. I picked 68.5 grains of Retumbo. Not by most accurate load historically, but conservative and safe for a new gun.
4. I used new Nosler brass. I did not resize them. I did use a Wilson expanding mandrel before priming. I primed the brass then loaded powder and seated bullets to the depths noted above.
5. The custom maker had sent a load and I noted it was shot on the lands per records. So at .010 off, I did not attempt to chamber any rounds.
6. Went to my range, and none of the rounds would chamber.
7. Came home and double, triple and quadruple checked the OAL with Hornady gauge. Got the same reading.
8. Took one of the loaded rounds that was loaded to .090 off the lands and seated the bullet a few hundreds deeper. Still did not chamber.
9. I got the box of new brass out to see if it would chamber. Every one I tried did chamber.
10. I pulled the bullet out of the .090 off round I had seated deeper to test.
11. I used a Redding Premium Die set that I had lying around and resized the brass with the full length resizing die and the reseated the bullet.
12. Shazam the round would chamber at .010 off, .050 and .090 off.

So tell me what the heck happened. Were all 15 of the new Nosler brass pieces that I selected originally off? Did the Mandrel do something? I can not figure out why those rounds will not chamber.


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[LaHunter]

Hard to know for sure, but a possibility may be that the expander mandrel could have had enough resistance to change the geometry of the shoulder of the brass, given the lists of facts that you listed.

 

[Geewhiz]

Sounds like the brass needed sent through a resizing die

 

[JFK]

Does the OD of the neck pre and post mandrel sizing vary by a lot?

 

[Couescrazy33]

Full length size your new brass. Then make a dummy round to desired specs. Then try chambering

 

[WTNUT]

Sounds like the brass needed sent through a resizing die

Then why did all the other brass in the same new box chamber ? It was not loaded, just the brass.


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[WTNUT]

Does the OD of the neck pre and post mandrel sizing vary by a lot?

I did not check, but will. It had to have something to do with the mandrel process - seems to me.


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[WTNUT]

Full length size your new brass. Then make a dummy round to desired specs. Then try chambering

That is what I did and it chambered. I must have not made that clear.


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[WTNUT]

I will check tomorrow based on some of these suggestions. I walked away earlier before I became frustrated. I am also going to check the diameter of the mandrel. I want to make sure it is the right size. I will run the mandrel through new brass that chambers then see if it chambers after the mandrel.


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[WTNUT]

Could not wait until tomorrow.

Took one new brass confirmed it would chamber. Then ran the mandrel through it and it chambered.

Next I pulled a bullet on one of the 15 rounds I loaded originally that would not chamber. I confirmed it would not chamber after the bullet was pulled.

Then I only ran it through a redding neck resizing die. After that it would chamber.

The mandrel is the correct size, but it was the first time I had used that mandrel when I loaded the first 15 rounds. Something seems to have had to happen with the mandrel that changed the neck of the case the first time. Maybe not enough lube at first. Not sure.


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[A382DWDZQ]

What is the outer diameter of the neck on a mandrel expanded case, and then what is it on the neck sized case?

 

[Vern400]

If the bullet seating force is too high, you can cause a case swell near the shoulder. I guess you could do the same with the mandrel. If the sizing die is squeezing the neck way down, and the mandrel is opening it way up, could be a problem. Lube it up!

I feel your humble pie pain.
I recently developed loads for a friend's new Howa 308. It had a very tight chamber and headspace at the extreme low end of the spec.
I had to adjust a sizing die I've been using for 30 years on multiple rifles. I had to screw it down to a strong cam - over height or empty cases wouldn't load. Plus, it had a sticky bolt. The bolt would raise just fine but darn if it would pull back! It didn't matter whether it was an empty case, or whether it had been fired! Don't know how many times I had to pull back while slamming the rifle butt down on the bench.
I got it shooting pretty good, but I am strictly not impressed.

I thought a blind pig could reload for any 308 until that happened.

 

[rayporter]

is the barrel marked with a neck diameter??

 

[TaperPin]

If it’s tight enough to give resistance like that the first thing I’d check is a carbon buildup in the chamber neck. Smoking the case/bullet or covering it with sharpie will show where it’s making contact.

 

[Weldor]

Get a Sinclair chamber length gage they are about 8 bucks and try that. That will tell you the astual chamber length, check against your brass sizing and total length. Most of my chambers are long and nowhere near SAAMI specs. No trimming required and no carbon ring once you set it up right.

 

[Harvey_NW]

7mm Mag is known to have sloppy and sometimes interfering tolerances, that's why Peterson makes a long version. I've had 7mm Rem Mag cases that grew .012" first firing. My guess is that your chamber is cut on the lower end of headspace tolerance, and those cases that wouldn't chamber just needed to be bumped. Without a headspace gauge (highly recommend getting at least the cheap Hornady one) you can't rule that out.

If the neck area of the chamber is in fact tight enough to cause chambering issues due to variance in brass thickness of that lot, you will likely have pressure issues and need to turn all the necks of the brass down. If it comes down to that I highly suggest getting whatever you can back out of that Nosler brass and investing it into something better. Nosler brass is absolute junk, and has always gave me nothing but a headache.

 

[wind gypsy]

7mm Mag is known to have sloppy and sometimes interfering tolerances, that's why Peterson makes a long version. I've had 7mm Rem Mag cases that grew .012" first firing. My guess is that your chamber is cut on the lower end of headspace tolerance, and those cases that wouldn't chamber just needed to be bumped. Without a headspace gauge (highly recommend getting at least the cheap Hornady one) you can't rule that out.

If the neck area of the chamber is in fact tight enough to cause chambering issues due to variance in brass thickness of that lot, you will likely have pressure issues and need to turn all the necks of the brass down. If it comes down to that I highly suggest getting whatever you can back out of that Nosler brass and investing it into something better. Nosler brass is absolute junk, and has always gave me nothing but a headache.
View attachment 696385

wouldn’t the fact that belted mags typically have a sloppy shoulder fit on virgin brass make them less likely to have such issues?

It’s a head scratcher. Only thing I can think of is the virgin brass is in poor form or mandrel opening or bullet seating process is bulging shoulders.

 

[Harvey_NW]

wouldn’t the fact that belted mags typically have a sloppy shoulder fit on virgin brass make them less likely to have such issues?

In a SAAMI chamber yes, but if the gunsmith tried to get cute and cut a chamber with tighter headspace I could see the dimensions interfering where some of the cases will chamber and some are tight by the variance in the brass size.

It’s a head scratcher. Only thing I can think of is the virgin brass is in poor form or mandrel opening or bullet seating process is bulging shoulders.

We are talking about Nosler, lol. Definitely possible, I was just saying without the tools and measuring all the dimensions that changed after sizing it's hard to really narrow down what it was. It is my understanding you can bump the shoulder a thou or two in a neck sizing die which could have fixed it, instead of being only a neck size issue.

 

[WTNUT]

What is the outer diameter of the neck on a mandrel expanded case, and then what is it on the neck sized case?

Outside diameter of the loaded shells that did not chamber with bullet still seated was .320 when measured with calipers and .322 when measured with a mic. A new brass out of the box measures .310 with calipers and .312 with a mic. After using the mandrel the new brass measures .312 with calipers and .313 with mic.

Going to load a few later today and see if they chamber. Going to resize the brass that did not chamber after I pull powder and bullets.


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[WTNUT]

If it’s tight enough to give resistance like that the first thing I’d check is a carbon buildup in the chamber neck. Smoking the case/bullet or covering it with sharpie will show where it’s making contact.

Thanks do not think that is it here. It is brand new built custom rifle only fired 8 times thus far.


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