.300WM Christensen Arms Load Development

[lancetkenyon]

Starting load development on a Christensen Arms rifle. Last year, I cleaned it thoroughly and mounted a scope on it. It was having issues with a flier or two out of every 5 shots. It went back to Christensen Arms and a new barrel was spun on, and a test target was returned with the rifle giving it a clean bill of health.

Fast forward a couple months, and shot some rounds getting it re-sighted in. It is still sub-par for accuracy, and also has a mean cold bore deviation. So before it gets wrapped around a tree or run over with a truck, I figured I could work up a load for it and see what it can do.

I have always wanted to get behind a Christensen Arms rifle, and this thing is a beauty. 8lbs 8oz. including mount and scope. It would be a dream to carry around the elk canyons. With the brake, I am hoping it does not kick like a mule.

I cleaned it and stripped the barrel completely. tore it apart and reassembled torqueing everything to spec.





I was given about 100 pieces of once fired brass. 50+ of HSM headstamp, and 40+ Winchester headstamp. I weighed the brass, and found a 20+ grain difference in brass weight. HSM was 262.6 to 265.5. Winchester was 241.8 to 244.7. So I won't be using all of the brass due to the big variation. I also have 20 unfired HSM rounds with 185 HVLDs, and 8 Winchester rounds with the same bullet. I will use them as foulers and sighters.

I also noted the HSM had signs of pressure with flattened and cratered primers.





The Winchester did not show quite the same pressure signs, but still a bit.



Upon checking the loaded virgin rounds and once fired brass, I found a bid discrepancy in headsapcing, which can cause pressure.

Winchester factory loaded rounds, most within .003".



HSM factory loaded rounds, most within .002".



Once fired brass before resizing.



And resized with .003" bump.



Owner wants to shoot 185-190 Berger HVLD, so I went and grabbed a box for load development





Checking the chamber and throat depth, the 190 Bergers are touching the lands at 2.8725" CBTO & 3.555" COAL.





I resized and bumped shoulders back .0025", and tumbled them.



I trimmed them all to minimum length of 2.610"









Chamfered inside and out





Uniformed the primer pockets and deburred the flash holes (which I didn't show)





Then annealed the whole batch (I slightly over annealed that one as you can see with the orange flame change, but my camera was being slow.)





Sorted them into the two headstamps for loading

[lancetkenyon]

Then primed them all with CCI 250 Mag primers

 

 

 

I wanted to try some of the 212 ELD-X in the rifle too, so I loaded the Winchester brass up with those and worked up a ladder test set of rounds.

 

Here is the seating depth with the 212 ELD-X touching the lands

 

CBTO

 

 

COAL

 

 

My load data

 

 

Starting charge weight

 

 

Marking the primers to know what charge weight is what in case I dump them over (I did this once. It sucked)

 

 

Top charge weight. It started to compress at this point, so I stopped for now

 

 

My 212 ELD-X ladder test ready to shoot

 

 

Powder for both will be the H1000

 

 

 

Load records

 

 

My starting charge weight due to the significantly heavier brass content which equates to less case space and more pressure

 

 

Ending charge weight due to a compressed load with the 190 HVLD at seating depth. Seating depth will be tested after a ladder test and charge weight testing. So I don't want too compressed of a load for when I start seating bullets deeper in the case.

 

 

 

Ladder test ready to shoot

 

 

I was hoping to go shoot the ladder tests, but the rain this weekend put a damper on that.

 

Here is all the data accumulated so far on the loads.

 

 

 

[Kingzero]

Nice job so far. I would love to shoot a Christensen arms rifle but wonder if the cost is worth it. Especially since my Tikka 7mag is 8.5lbs ready to hunt.

 

I had been working on load development for a friends 7wsm and all his once fired HSM brass looked the same as those 300's.

[lancetkenyon]

How was the headspacing between factory unfired and once fired brass before resizing? These are .0200"+ difference. That is a lot from other rifles I have worked on.

[Big Browns]

WOW Lance, you are definitely a wealth of information! I can't wait to see how it shoots!

[Kingzero]

Well it wasn't that much. I just went to check my notes and couldn't find them. I asked my wife if she knew where my yellow notebook was and she said she stuck it inside a white binder. Unfortunately it was a white binder on top of a stack of stuff to be thrown out.....which was 2 weeks ago. It had all the chamber measurements, factory and fired brass measurements and load info and results for 2 different powders......bummer.

 

 

EDIT: Just measured one of the factory rounds and a fired case and the difference is 0.012

[Cell4soul]

Subscribed. Curios to see how this rifle shoots with load development.

[300RUM]

How was the headspacing between factory unfired and once fired brass before resizing? These are .0200"+ difference. That is a lot from other rifles I have worked on.

That would make me want to put headspace gauges in the chamber to see if it was a little long.

[Eagle mountain ranch]

All I can say is I wish I had the spare time you have. Great work looks like you are on top of it. If I was your buddy I wouldn't be worried. Nice work ...

[CraigK]

Nice write up as always, can't wait to see what's to come. On a side note, how do you like that scale? I keep wanting to get one just haven't yet.

[lancetkenyon]

The Gempro 250 is great. A single kernel weighs about .02 grains. And it reads it.

[L Cazador]

Lance great job of covering all the basics to set up for some good ammo. One thing you didn't mention was neck thickness and neck thickness variations which can really spoil a lot of good brass prep. Did you check for this? By the way it's not unusual to see a difference of .020" of case headspace between new or factory brass and fired brass. I just did some Lapua 6.5 brass Creedmore and it was under by .010". That's why you must fireform first and then work up a load. All new brass and factory ammo is made to fit all firearms, that's why it's undersized.

[el diablo]

Lance great job of covering all the basics to set up for some good ammo. One thing you didn't mention was neck thickness and neck thickness variations which can really spoil a lot of good brass prep. Did you check for this? By the way it's not unusual to see a difference of .020" of case headspace between new or factory brass and fired brass. I just did some Lapua 6.5 brass Creedmore and it was under by .010". That's why you must fireform first and then work up a load. All new brass and factory ammo is made to fit all firearms, that's why it's undersized.

their is always that one guy LOL^^^^

[300RUM]

Lance great job of covering all the basics to set up for some good ammo. One thing you didn't mention was neck thickness and neck thickness variations which can really spoil a lot of good brass prep. Did you check for this? By the way it's not unusual to see a difference of .020" of case headspace between new or factory brass and fired brass. I just did some Lapua 6.5 brass Creedmore and it was under by .010". That's why you must fireform first and then work up a load. All new brass and factory ammo is made to fit all firearms, that's why it's undersized.

Factory ammo and brass does have to be undersized to fit in a minimum chamber. Say the go gauge, used to measure the minimum chamber, is zero. The brass goes in 0.010 short. When it is fired it comes out 0.010 long. The no go gauge is typically 0.004 longer than the go gauge. A field gauge is typically 0.010 longer than the go gauge. Say the brass that Kingzero mentioned above that grew 0.012 when fired started out 0.010 short. It would be 0.002 long, right between a go and no go gauge. Unless the brass Lance is working with, that grew 0.020, started out over 0.016 short it seems the chamber may over the no go gauge and possibly close to the field gauge range. As a disclaimer I have never chambered a barrel for a belted cartridge but I expect the tolerances for headspace would be similar to the non-belted cartridges I have worked with.

[Coues Sniper]

I had a 300 RUM from Christensen Arms, and I about lost my mind trying to get it dialed where I wanted it. It would shoot like a dream for several strings, and then go to absolute garbage, and then back again, without much ryhme or reason as to why. I checked EVERYTHIING over a period of a couple years, and couldn't get it figured. Tried different combinations of bullets, powders, primers, COAL's, on and on, same issues no matter what I did. Sent it to Christensen several times, and it always shot perfectly for them, of course. Took it to several smiths. By the end, the only original part on the rifle was the trigger, and the barrel. I had swapped every other piece of the rifle out, even the brake. Finally took it to a new smith, and asked him to try and build a load for it. He had same issues. He had it shooting ragged holes with a certain load, and then the next day would shoot it to verify, and it would be a different poi and garbage groups. Finally I asked him to just rebarrel it. He finally gave me a piece of information that made sense to me - he explained that since Christensen mills down their barrels before they wrap them (mine was milled from a Krieger Match Grade barrel, they make their own barrels now I believe), it causes the barrel to expand slightly from the heat. When they cool, they go back down, however, they don't return to the exact same diameter. Now, this wouldn't be THAT big of a deal, except they don't mill down the ends, so since the barrel didn't expand at those locations, the barrel is slightly smaller there. He verified this by measuring the barrel in the middle, and the ends. He explained that this is the opposite of what you would want and can cause inconsistency with harmonics. At any rate, he rebarrled it with a Proof Research barrel in 300 Norma, and it shoots incredible - no fliers or garbage groups.

 

As a side note, even if it wasn't for the above, I'd never deal with Christensen again. I just didn't like the way they dealt with me. And in full disclosure, I do have a 6.5x284 from them that I haven't had any issues with. My smith said it depends on the rifle, and that the issue I explained above doesn't affect the smaller diameter calibers as much.

 

Hope that helps.