Overall Length/Short Chamber

[sevenbridgesroad]

I'm having some issues with cratering and flattening primers even when using minimum loads.

I've been working up a load for a 338.06 with Nosler 210 grain partitions.

The Nosler load data indicates seating depth of 3.33 OAL. I also referenced Hodgdon for the same bullet and powder and the suggested seating depth is 3.25 OAL. I decided to strike in the middle and worked up a minimum load seated at 3.300. The cartridges chambered with no problem.

The primers cratered and slightly flattened.

I took my Sinclair OAL gauge and measured my COAL (which I should have done to start) and found that the OAL for my chamber with this bullet touching the rifling is 3.311, which is .03 shorter than SAAMI max length and .02 shorter than Nosler's suggested OAL of 3.33.

Should I be able to seat any bullet at SAAMI max OAL and still have it chamber safely in my rifle, no matter the length of the bullet (longer bullets would need to be seated deeper)?

Since I can't, and Nosler indicates I should be able to safely chamber at 3.33, are these indicators that the chamber is too short, and could be causing overpressure issues?

I should also mention that I've measured the headspacing and it is in spec.

Thanks.






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[TackDriver284]

Would you happen to have any pictures of the cratered primers to give us an idea?
Were you able to measure velocity when you fired them? Have you measured the necks of the loaded round, and the necks of the fired cases to determine if there is clearance within your chamber. Have you tried lower powder charges and work up from there? Virgin brass tends to give slightly more pressure than fireformed cases.

I would seat the bullet to the length that the magazine allows, then check the OAL so it seats .010" from the lands. I have seated as low as .005" from the lands in most of my rifles, as long as the magazine allows it, or seat shorter to fit the magazine and work up loads from that length and find a good node.

 

[sevenbridgesroad]

I'll get some pictures in a couple of days of the primers.

I can't seat the bullet to the maximum that the magazine allows as I would be .03 too long (would be seated way into the lands) That's why I'm asking the question as to whether this is an indicator that my chamber is to short, or not enough free bore. And if this is what is causing my overpressure signs.

Or, is it irrelevant and I just need to seat deeper? I've tried that also and it did relieve the problem but it didn't eliminate it.

I never thought about measuring my necks. I'll do that and report back in a few days. I've never experienced a sticky bolt.

I'm getting lower velocities while cratering/flattening primers with recommended starting loads.




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[gbflyer]

Seat them deeper. Your throat will grow with more rounds down the barrel. If it shoots well don’t mess with lengthening the throat.

 

[sevenbridgesroad]

It doesn't shoot well. I've been searching with different powders but I'm not getting the performance I need/want.

This is the load I'm currently working up per Hodgdon:

53.5 grains of BLC2 seated at 3.25. Per Hodgdon this should give me 2650 but I'm only getting 2537 with slightly flattened primers. When I run this up to 54 grains I get flattened primers but still rounded edges. Velocity is still only 2574.
I stop there.

I am getting better groups with BLC2 than anything else I've tried.

In full disclosure, I tried seating depth at 3.30 to relieve the pressure problem as Nosler states I should be able to seat to 3.33. However, this made the problem worse. Smashed primers at 54 grains and I cracked a case head at 54.5.

This is when I measured my chamber's OAL to find that with a 210 grain Nosler Partition my OAL touching the lands is 3.311. This is considerably short of SAAMI spec of 3.34 max OAL and shorter than what Nosler tested at of 3.33.

I'll measure my case necks to see if there is a difference between a resized unfired case and a fired case. The cases I'm using are twice fired, full length resized with no shoulder bump. Case length is 2.484, so they are not long.

I'm also going to make a dummy round at 3.33 to double check my measurements I got when I used my OAL gauge. Based on those measurements at 3.33 I shouldn't be able to chamber the round.

I could take it to a gunsmith to check it with Go /No Go gauges.





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[sevenbridgesroad]

Correction. Tackdriver said to measure the neck of a loaded round and a fired round. So that's what I'll do.

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[TackDriver284]

sevenbridgesroad, Sorry I misunderstood where you mentioned that the OAL length of the magazine is shorter than the OAL of the chamber. I would measure what the OAL length allows in the chamber and seat deeper .010" and start from there. Hopefully check other points I mentioned and see what the results are and some pictures of the fired cases / primers.

 

[seokladuckin]

Check case oal, to the shoulder.

You may be resizing too much from head to datum line of shoulder

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[PJGunner]

Check case oal, to the shoulder.

You may be resizing too much from head to datum line of shoulder

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This was my thought as well. Your rifle may headspace correctly, but if you're over sizing the brass in the FL die, you're creating a headspace problem. Proper set up of the FL die should cure the problem. I'll post how I set my die up.

This is how I set up my sizing die for bottleneck cartridges.

1. Take a once fired factory round and blacken the neck and shoulders with a Magic Marker or Sharpee pen. Some people like to smoke the neck and shoulder, but I find the Magic Marker/Sharpee pen a bit better.

2. Carefully lubricate the case.

3. Loosen the lock ring on the sizing die and back off about two turns from when the die is set to touch the shell holder.

4. Size the case. Note where the marks are on the case and turn the die down about a half a turn and size again. Turn down some more, and resize again. What you are looking for is the marks on the blackening just touching the shoulder.

5. Clean the lube from the case and try it in the rifle. It may chamber just a bit on the snug side. If so, turn the die down ever so slightly, lube and size again. Wipe off the lube and try in the rifle. If it slides in as easily as a factory round, you should be good to go. If not, usually one more very slight adjustment should fix the problem.

6. Tighten the locking ring for the die and you're done. You have just set your sizing die up for a custom fit to your specific rifle, rather than a generic one size fits all guns.

Paul B.

 

[sevenbridgesroad]

Below are pictures of my primers. The silver primers are CCI 200 and the gold one is Remington 9 1/2.

I measured the case neck of a loaded round and a fired round. The loaded round was .360 and the fired round was .367. .007 clearance.

I have not been bumping my shoulders back when FL resizing. The measurement to the shoulder on these rounds were 1.953. SAAMI is 1.948. I'm .005 over spec. I have some cases that measure 1.955 and they are snug.

Although the primers are flat but still round, and there is some cratering, I've never experienced a hard or sticky bolt.

What do you see in these photos?

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[Dr. Vette]

I don't see anything wrong with any of those primers, EXCEPT that your firing pin hole may be too large. This results in the primer flowing backward so it looks like cratering. I had this with a Weatherby Mark V in 300 wby (bought used) and had to have the firing pin bushed (i.e. busing added to make a smaller hole). Worked great.

You still have a LOT of round edge to those primers.
If you want to see flattening let me show you some Weatherby loads. :grin:

 

[desertcj]

The look of those primers isn't too concerning to me but, you cracked a case head!? Obviously, you shouldn't be jamming bullets into the lands, your barrel could have a short throat and it can easily be lengthened by a gunsmith. If you aren't seeing the results you want, try a different bullet. Sometimes, things just don't jive and you can fight it or accept it and move on.

 

[seokladuckin]

Firing pin problems.
Not that big of a deal.


Fire for effect

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[sevenbridgesroad]

Thanks for the feedback. I'll have my firing pin checked out.

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[TackDriver284]

Seems the cratering is due to the large firing pin hole, you can have it bushed by :
https://www.gretanrifles.com/

 

[Dr. Vette]

Seems the cratering is due to the large firing pin hole, you can have it bushed by :
https://www.gretanrifles.com/

That's who did mine.