Load development - what would you do??

[nodakhunter]

Here's the story:

I started load development with a 245 Berger in a 300 Norma Improved (35º shoulder). This rifle is built on a BAT HR with a 27", 1:8 twist Rock Creek barrel. Shot a pressure ladder with RL33 and the round barely seated to fit in a CIP length Lapua magazine (I believe cartridge OAL is around 3.710" or so). This puts the boattail barely above the neck-shoulder junction and the bullet .025" off the lands in this chamber. Anyway, I ran it up to 94.8 grains of RL33, carefully watching for pressure signs and had none. I then shot a ladder at 700 yards and found two nodes - one from 90.8 to 92 grains, and the other from 94-94.8.

To test both nodes, I loaded up rounds in the middle of both nodes and shot for groups at 185 yards. The loads with 91.5 grains averaged around an inch to slightly over an inch (mostly horizontal dispersion), but the loads at 94.4 shot bugholes. Seeing this, I decided to pursue the 94.4 grain load and took it out to confirm zero and get velocities.

This load averaged 2999 fps over a Magnetospeed with an SD of 8.7 (good enough for me). I removed the Magnetospeed from the end of the barrel and went to finalize a zero, which is when the issue occurred. After not seeing any pressure signs at all with about 20 of these loads thru my gun, I got very faint ejector marks (only visible in bright sunlight) and the slightest hint of stiff bolt lift. Considering this is Lapua brass, the fact that there are ejector marks makes me think this load is too hot to continue shooting.

I'm reluctant to give up a fast and extremely accurate load, but safety is #1 in my book and I don't want to cause damage to my gun and especially to anyone that might be shooting it. So, where should I go from here? Should I try to tighten up the horizontal in the low node and play with that a bit? I'm thinking simply dropping down to 94 or 94.1 grains to try to run the high node wouldn't make that big of a difference in pressure.

Or, maybe I should send the gun to Shawn Carlock to have him work his +P magic on it and hit that node without any worries...

 

[Timnterra]

Did you try a seating depth test? You might be able to drop the pressure just enough by pushing the bullet back another 20 thou from the lands.

 

[Sockeye66]

Did you try a seating depth test? You might be able to drop the pressure just enough by pushing the bullet back another 20 thou from the lands.

Couldn't that potentially increase the pressure due to less case capacity?

 

[nodakhunter]

Did you try a seating depth test? You might be able to drop the pressure just enough by pushing the bullet back another 20 thou from the lands.

I did do a seating depth test back to .040" off the lands, and my best accuracy seemed to be in that .015-.025" range. My other thought about pushing that bullet back further into the case was that the boattail would have been below that neck-shoulder junction. I've never experienced them but have heard some nasty things about donuts appearing there.

 

[Rick Richard]

I have a 300 NMI and tried my best to get it to shoot in the lower nodes thinking I would preserve brass and barrel. Well, this gun just does not like the lower nodes. It shoots best at the top end. So that is where I shoot it. You just can't make it do something it just does not want to do in my opinion. Good luck.

 

[Timnterra]

Couldn't that potentially increase the pressure due to less case capacity?

That's really only a problem in straight walled cartridges with fast burning powder. In bottleneck rifle cartridges pressure increases as bullets approach the lands.

 

[Timnterra]

I did do a seating depth test back to .040" off the lands, and my best accuracy seemed to be in that .015-.025" range. My other thought about pushing that bullet back further into the case was that the boattail would have been below that neck-shoulder junction. I've never experienced them but have heard some nasty things about donuts appearing there.

Ive never had a problem with doughnuts. I have also just changed the way I set neck tension and I now use a neck sizing mandrel after full length sizing (without expander ball). Instead of bushing dies. This mandrel would prevent the possible formation of a doughnut. There is an interesting article/ video by Scott Saterlee talking about optimum seating depth. Optimum Meaning the most forgiving seating depth. He did lots of tests to determine where bullets would be seated and have the least effect from a growing throat so that seating depth would not have to be retested during a PRS season. He found the sweet spot to be between 50 and 65 thou off the lands for both Berger and eldm bullets. I used to seat everything at 20 thou off and leave it there but I've started working further out and found great results with lots of different bullets. It's worth a try.

 

[Timnterra]

Here's a podcast talking about seating depth.

MDS Episode #0014: Scott Satterlee and Hand Loading | Modern Day Sniper Podcast

You asked about hand loading, so we listened! We have a special guest on the podcast who needs no introduction in the precision shooting world, Mr. Scott Satterlee. Scott is a renowned handloading “tinkerer”, and we wanted to go straight to the source for the latest information regarding...

moderndaysniper.podbean.com

 

[Bob Wright]

I would also test seating depths at the lower node. The higher node is putting pressure on the edge of failure IMO.
if you're not satisfied, try another powder/primer/bullet.

 

[WeiserBucks]

Is this virgin or fire formed brass?

 

[MagnumManiac]

Drop the charge back to 90g and shoot another group string. If the node is wide enough it should make little difference to group size.
You could also seat a tad deeper, but as you do, I try not to seat the boat tail below the neck/shoulder juncture.

Cheers.

 

[lancetkenyon]

If you were on the first firing after initial fire forming brass, you are probably still finishing the final fire forming. I have found several times in various wildcat cases, that fire forming takes at least two firings. And even in 4 different .300NMIs. If this is the case, the less case forming still happening, the more pressure you will get. You need to re-chrono those and see where you are at.

 

[WahooYahoo]

The signs of pressure are like a growling dog. Better back off. I would explore your other node.
As an aside, without hi-jacking this thread... maybe someone can help me with this. I don't know where I heard it but it is accurate I my experience. I don't use it to find my load, but I check my found load against it and it's generally accurate. I find pressure, then reduce my load by 3% and there's the next flat spot. I ask because, 94.4gr - 3% is 91.57... the other node the OP found. In my load work-ups, this is proven to be right.

 

[Dragoon300]

Here's the story:

I started load development with a 245 Berger in a 300 Norma Improved (35º shoulder). This rifle is built on a BAT HR with a 27", 1:8 twist Rock Creek barrel. Shot a pressure ladder with RL33 and the round barely seated to fit in a CIP length Lapua magazine (I believe cartridge OAL is around 3.710" or so). This puts the boattail barely above the neck-shoulder junction and the bullet .025" off the lands in this chamber. Anyway, I ran it up to 94.8 grains of RL33, carefully watching for pressure signs and had none. I then shot a ladder at 700 yards and found two nodes - one from 90.8 to 92 grains, and the other from 94-94.8.

To test both nodes, I loaded up rounds in the middle of both nodes and shot for groups at 185 yards. The loads with 91.5 grains averaged around an inch to slightly over an inch (mostly horizontal dispersion), but the loads at 94.4 shot bugholes. Seeing this, I decided to pursue the 94.4 grain load and took it out to confirm zero and get velocities.

This load averaged 2999 fps over a Magnetospeed with an SD of 8.7 (good enough for me). I removed the Magnetospeed from the end of the barrel and went to finalize a zero, which is when the issue occurred. After not seeing any pressure signs at all with about 20 of these loads thru my gun, I got very faint ejector marks (only visible in bright sunlight) and the slightest hint of stiff bolt lift. Considering this is Lapua brass, the fact that there are ejector marks makes me think this load is too hot to continue shooting.

I'm reluctant to give up a fast and extremely accurate load, but safety is #1 in my book and I don't want to cause damage to my gun and especially to anyone that might be shooting it. So, where should I go from here? Should I try to tighten up the horizontal in the low node and play with that a bit? I'm thinking simply dropping down to 94 or 94.1 grains to try to run the high node wouldn't make that big of a difference in pressure.

Or, maybe I should send the gun to Shawn Carlock to have him work his +P magic on it and hit that node without any worries...

In my experience with a 338 Lapua and Lapua brass, the ejector marks you are getting are not a problem. If the load shoots well there, use it. I load 98 - 101 grains of RL33 with 300 gr Berger's and see about the same. The Lapua brass will take it, I've reloaded my cases five times without a problem. Your 300 NM with 245's running 3000 fps should work well.