Blew a Primer _ Analysis

[Pdvdh]

Received 2 boxes of 8x68S cartridge cases. One box of RWS brass, and one box of Norma brass.

After necking it down, fire forming with Cream of Wheat, trimming to length, and outside neck turning, I thought I'd provide a table containing some of the pertinent specifications of these 8x68S cases, comparing them to the Hornady 375 Ruger cases. 'elkaholic' and I have been using the Hornady 375 Ruger case to form the 30/375 S.I. casings for about 5yrs. I'm now swapping parent cartridge cases, switching from the Hornady 375 Ruger case to the 8x68S cases. There's a bit more case preparation work involved with the 8x68S brass, but I believe the benefits will be worth it. More consistent brass and stronger case heads, yielding longer case life while realizing higher MV. I'll be surprised if I can't get an extra 75-100fps MV (200gr bullets) using the RWS cases.

Below is information on the three brands of cartridge casings. You'll see the 8x68 cases have a rebated rim (smaller OD than the case web), and the OD of the extractor recess, case web, and case rim are all smaller than the Hornady 375 Ruger brass.

No problems so far. Next I'll be firing some full pressure loads in the Norma brass to identify a maximum RL26 powder charge, while monitoring case rim and primer pocket expansion, any brass flow into the bolt face recesses, and any other signs of pressure. After learning where the Norma brass pressures out, it'll be on to the RWS brass. Time to burn rubber...

Any questions - ask.

 

[elkaholic]

Will be watching! Jace is working on this as well. Looking forward to some useful info.....rich

 

[shawnb]

What action are you using paul?

 

[elkaholic]

Both Paul and I have BAT HR's

 

[Pdvdh]

Pics are nice.
From left to right:
1) Parent RWS 8x68S case in virgin form, straight out of the RWS box,
2) Parent RWS case showing case neck trimmed back to a 2.605" length to case head, case neck sized down for entry into .337" chamber neck, and the case shoulder set back for firm contact against the shoulder in my 30/375 S.I. chamber. This is the case fully prepped for Cream of Wheat loading and fire forming,
3) COW fire formed RWS case, with the case neck length trimmed back a second time for desired overall case length, and the case neck outside neck turned for proper OD and clearance with bullet seated in my chamber. I also annealed the case shoulder after fire forming, which is visible on this case, extending down about 1/3" into the case body from the body/shoulder junction.

Poof! Magic! High quality RWS 30/375 S.I. cartridge casings.

A close look and comparison will reveal the COW-fired case web has expanded about 0.012" to conform my chamber diameter. It will expand more toward the case head with the first full pressure load firing a 200gr bullet. Off to the races... pedal to the metal... (OMG!!!) maybe this weekend...

 

[RockyMtnMT]

Nice looking cartridge.

Steve

 

[shawnb]

When trimmed to 2.605 what was the case length after fireform?

 

[Pdvdh]

When trimmed to 2.605 what was the case length after fireform?

Most cartridges measured 2.602" - 2.605". That's no typo! Some cases lost no case length. Only two of 19 cases lost more than 0.005", with the maximum reduction on those being ~ 0.007".

There's a lengthy explanation involved on how I minimize case length shrinkage during COW fire forming. "elkaholic" and I discussed my method on the phone for a good while this past Monday. He was experiencing up to 0.045" loss of overall case length copying my method with other lubricants. We think the difference is the super slick oil I use, which Rich didn't have available for use.

Here's a link to a Thread I created two months ago wherein I shared my improved COW fire forming methods. I think the case lubricant I use was identified in that Thread. I now have additional positive experiences COW fire forming brass. Enough to state with extreme confidence, that lubing the casings prior to COW fire forming is a tremendous advantage. Here's the link to that thread:
https://www.longrangehunting.com/threads/a-i-fire-forming-tip-of-the-day.194793/

If you're planning to COW fire form some brass soon, and want to get the process from the horse's mouth (me) after reading that Thread, send me a PM with your phone number and I can further share my experience. I just received another 20 RWS 8x68S casings yesterday, so I'll be COW fire forming again soon. Possibly this weekend. This will either cast my success 100% in concrete, or... otherwise. But I expect the same results - very minimal loss in case length during COW fire forming, and much better (fully formed shoulders) formed cases at lower COW fire form case pressure.

At 2.605" case length prior to COW fire forming, the case neck contacts the 'step-down' shoulder in my chamber. This is where the chamber transitions from case neck diameter into the 'lead' section that's in contact with the bearing surface of the seated bullets. In my chamber, that transition goes from 0.337" down to 0.3085". So, there is one additional case prep step that the center case in the above photo doesn't show. Before I could chamber the 2.605" length case, I had to cone the leading nose of the case neck inward with a 7mm RM Body Die. Then the case neck would clear the 'step-down' shoulder and I could close the bolt on the prepped cases. After fire forming, the end of the case neck remained coned inward - conformed to the 'step-down' shoulder in my chamber. I expected more case shrinkage, but experienced hardly any. So I then trimmed the cases to final length, which removed that cone on the nose end of the case necks. Enough information... for now...

Not sure how many have the interest. PM if you want additional detail! Beyond what's been provided here and in the Thread linked above. Cheers!

 

[elkaholic]

Good stuff Paul! I have some majic oil on the way

 

[Oldcappj7]

I'm going to lay in the weeds until Rich duplicates this non-shrink feat with this snake 'ol as well. It sounds like it's figured out though.
I do have 95 of these trimmed to 2.6 and full of COW that I would like to not have shrunk back .040 or so. So I'm anxious to have this all be successful. Thanks Paul.

Jace

 

[Pdvdh]

I'm going to lay in the weeds until Rich duplicates this non-shrink feat with this snake 'ol as well. Thanks Paul.

Jace

Good idea Jace! Rich and I have joked about the Midas touch versus the magic lube. All in jest.

 

[shawnb]

Lots of good info. So for the ones like me who use bullets to fireform (coyote hunting, foulers, etc) whats the thoughts on that? I usually crush fit the casing and jam the bullets hard.
Should i leave some unique on the casing?

 

[elkaholic]

Lots of good info. So for the ones like me who use bullets to fireform (coyote hunting, foulers, etc) whats the thoughts on that? I usually crush fit the casing and jam the bullets hard.
Should i leave some unique on the casing?

It seems the only oil so far that works is what "Phorwath" uses!

 

[Pdvdh]

Lots of good info. So for the ones like me who use bullets to fireform (coyote hunting, foulers, etc) whats the thoughts on that? I usually crush fit the casing and jam the bullets hard.
Should I leave some unique on the casing?

With COW fire forming, my lube will enable the case to fully form to the chamber at the lower COW case forming pressures, with very little case length reduction. Sometimes no loss of case length.

However I would not fire full pressure maximum loads with a bullet. If you're experiencing significant case length loss and want to see if some Hornady Unique case lube will reduce the overall case length loss while firing a bullet, I'd reduce the powder charge by 10% and see what the case length measures compared to a casing fire formed without any lube. And then, of course, please post the results?

I'll try the same thing with my magic oil lube if I fire form with bullets in the future. But have no plans in sight. I normally use COW, rather than bullets.

Be careful when playing with fire...