It's either me or maybe.............. this year....!?

[Poper]

Dang! Another first for me!!!!

I am working up loads for my Mauser M18 in .243 Win. (Love the rifle and have a nice 85 gr. load.)
So, I want to use an Enduron powder with a 100 gr. Speer BTSP. I go to my 2019 Hodgdon manual and look up IMR4955. (I have 2 lbs.) and the powder charges are 43.1 - 46.9.
My routine for hunting loads is to start 2.5 grains below maximum and load six rounds of each load in 1/2 grain increments to the maximum powder charge. So, six rounds each of 45.0, 45.5, 46.0, 46.5, 46.9. Seat to overall length of 2.700" (fits easily into the magazine and is off the lands about .030" with that bullet as measured by the RCBS Precision Mic.)
I go to the range this morning to set the final zero on my Winchester 1885 and then fire the test loads in the M18 over the chronograph. 1885 simple, easy. Three round clover leaf 2" dead-center-high at 100 yards; back down 2 clicks - done!

Now the reason I load six rounds of each of the powder charges in my test loads is very simple: 1) The barrel is clean and unfouled. 2) I fire one of each powder charge at the center bull of my 5-bull Redfield sight-in target to foul the barrel and to verify none of the powder charge steps are too hot. If as I am firing the progressively hotter charges I get a sudden jump in recoil, chrono'd velocity and/or a sticky bolt lift, then stop right there and fire no more of that charge weight.

Round number one of my test loads (45.0 gr.) recoils a lot more than expected!
Check chrono..... 3158 fps!! Ugh!
Uhoh, sticky bolt lift! Very sticky!
Doh! Smoke rolls out of the chamber as the case comes out!
Double DOH!! Primer is missing from the case!! Find primer on the magazine follower.
I STOP RIGHT THERE! ONE AND DONE!!

So I get home and go straight to the loading bench and dig out my 2019 Hodgdon manual and check the load data again. Yes. The notes on the loading card and the book match.
I check the 2018 Manual... Ditto. Same numbers. I check the 2017 Hodgdon manual... All three agree.
Ok, then..... Maybe I made a mistake in my weighing of the charges?
I pulled each of the test ladder bullets in succession and weigh each one. They all weigh exactly what they should.
So.... Maybe I grabbed Magnum primers instead of LR primers? (It just happens that I opened a new 100 pack of primers for this batch of test loads.) Nope. The pack was where I remembered placing it (where I routinely place the opened one) and only 30 primers were missing from it and it is labeled CCI-200 Large Rifle Primers.

So I check all the rest of the recipe and the only difference I can discern as a possibility is the case: I used Nosler 2x fired cases in lieu of Winchester cases. Noslers weighed in 7.74 grains (empty) heavier. Winchester weighed 164.88 grains and the Nosler at 172.72 grains. Is this enough to make this kind of difference in the .243 or is there something else I should be looking for?

Again, in 30+ years of handloading, this is a first for me.

 

[FROGO207]

You used different bullets, barrel, and different propellant. This can add up to higher pressures than the factory found with their setup. I would email the propellant manufacturer and report your findings. They might have something printed wrong or your rifle will not safely use that load and need to back down. I would not think that 7ish grains less volume would cause a starting load to act that way in that large a case.

 

[PWC]

I like your troubleshooting process, watching...

 

[Poper]

You used different bullets, barrel, and different propellant. This can add up to higher pressures than the factory found with their setup. I would email the propellant manufacturer and report your findings. They might have something printed wrong or your rifle will not safely use that load and need to back down. I would not think that 7ish grains less volume would cause a starting load to act that way in that large a case.

Different barrel, yes. Same bullets (probably different lot number) same propellant (IMR4955).
I have IMR4831 loads for the same 100 grain bullet that work fine with a good accuracy node about .5 grain shy of maximum, so I think the rifle is ok. I need to have a smith look at it after this blown primer because one of the plunder ejector's is stuck back behind the face of the bolt. The other one works fine, though.
I contacted the Hodgdon via their website. I am interested to see their reply.

 

[243winxb]

Possibles - Scale off. Brass difference. Tight chamber neck. Rounds loaded neck diameter larger then .276" Tight barrel diameter. A 10% hotter batch of IMR 4955.

The new powder is double based. Contains Nitroglycerin. Should not be an issue, unless there is a recall.

 

[tlf65]

Did you check the length of your brass before loading it, back in the dark ages about 1968 I managed to break the firing pin in a Winchester model 70, 22-250 using over length brass.

 

[edwardware]

Again, in 30+ years of handloading, this is a first for me.

In 30 years you've never had a mid- or lower level manual recipe show up with high pressure sign in your rifle? Really?

Happens to me on a regular basis. My manuals are noted with lower DNE values for individual rifles. My M77 .270 DNE charge of H4831 under a 150gr bullet is the Start charge in several manuals. . .

This is why we start low, and that's before reducing case capacity, etc.

 

[Poper]

In 30 years you've never had a mid- or lower level manual recipe show up with high pressure sign in your rifle? Really?

Happens to me on a regular basis. My manuals are noted with lower DNE values for individual rifles. My M77 .270 DNE charge of H4831 under a 150gr bullet is the Start charge in several manuals. . .

This is why we start low, and that's before reducing case capacity, etc.

Maybe a overly flattened primer or a sticky bolt where brass flowed into an ejector hole, but this is the first time I have EVER had a mid-level powder charge blow the primer completely out of the brass and blew an ejector out of the face of the bolt. - Yes, really. - In a number of different rifles in a variety of chamberings.
This casehead has expanded enough that it is sticky being rechambered in the rifle.

 

[Bfh_auto]

In the future. Run one load in 10% increments from the start of the charge to the rifle's max.
If you do this at 300 plus. Half your load workup is done.