408 Cheytac loads

[232593]

I did not see a .408 reloading thread so figured I’d make one.

I did a pressure test with RL25 with 420 grain Parker Productions (Formerly known as RMB) this weekend. I loaded them .025 off the lands

At 134 grains I saw pressure signs start to show on the brass. No heavy bolt lift.

From what I have observed with Retumbo and these bullets they seem to like the 2850 range. So I will test the 128-129 grain charge next time I get to the range.

I used Peterson Brass & FED215 primers.

Rifle was a factory Desert Tech HTI 29” 1:13 barrel.

 

[232593]

When I acquire them, I will test the powders you recommended @Dogtown and post data here.

 

[232593]

@Dogtown do you have a recommendation on a starting charge of N570 with a 425 grain CEB Laser?

 

[Dogtown]

Not really - I haven't owned a .408CT since 2010

 

[Dogtown]

Here's a back of the envelope calculation from QL

 

[232593]

View attachment 8189571

Here's a back of the envelope calculation from QL

Thank you. I appreciate that.

Have you ever used it before? How large are the granules?

Looks like it’s quite a bit slower than Retumbo. I get 2856 with 130 grains.

 

[Dogtown]

I have lots of experience with N570. The granules are BIG compared to most other powders in that class. It’s slower than Retumbo but a tad faster than RL33.

 

[232593]

Thank you. You noticed any unusual humidity or temperature sensitivity with it?

 

[Dogtown]

Nope. It's a very popular powder for a reason.

 

[232593]

View attachment 8189571

Here's a back of the envelope calculation from QL

Provided the CEB Lasers get to me on time I’m planning on doing a pressure/Satterly test starting at 134 grains of N570 and working up in .5 grain increments with the bullet seated .025 off the lands. I’m thinking I’ll find my node at the 2830-2860 mark. My plan sound reasonable? Any advice or recommendations you have would be appreciated.

I have a DT HTI with 29” factory barrel.

 

[Dogtown]

A velocity derivative-based load development method is only viable when the per-charge samples are >=5, otherwise you're undersampling noise and will draw an inaccurate conclusion. It would be one thing if every shot at a specific charge weight will be the same velocity, but it won't. And you won't know the variation in velocity without shooting a decent amount of samples.

If you haven't shot this combo of cartridge/bullet/powder, then I'd suggest doing a pressure ladder first. It will give you a safe pressure window to work in first before wasting components testing different charge weights with 3-5 shots.

1. load single shots from 138gr - 147gr in 1gr increments (138, 139....147).
2. shoot each in order, checking for pressure signs. Stop when you see telltale signs and choose a range of charge weights to test for consistency.
3. you don't have to check velocity on each of these shots, but it does give you an idea of what to expect. It will also help you cull the lower velocity safe loads as "I'm never going to shoot that slow."

So let's say you saw pressure at 145gr of N570 and 142gr was the minimum acceptable velocity. Now it's time to load some strings from 142-145 with 0.5gr increments (with .408CT 1gr increments may be a better choice) and test those for:

a) do they group or scatter?
b) is the shot-to-shot velocity consistent or all over the place?

You can also track the POI shift over each load (like an OCW test). With big expensive magnums, I tend to do coarse 3-shot tests initially just to get a feel for how the load evolves, looking for hints of a trend towards a consistent load. Usually I find a window, for example in your case it may be that you get group scattering at 142.5gr and 144.5gr, with decent groups in between. Then I would load 5-shot strings from 143-144 in either 0.5gr or 1gr increments and test those. Again, just looking for consistency in this case - precision can be tuned with seating depth after the above is done.

 

[Dogtown]

Just to add on pressure signs, when I was shooting .408CT & .375CT looking at primer flattening wasn't the most reliable pressure sign. Even mild loads started to flatten primers (for me at least). Ejector swipe and heavy bolt lift were much more reliable pressure signs to avoid.

 

[232593]

For #3, I plan on recording the velocities of each shot with my chronograph and posting here. Hope to have some data to post on Saturday.

So 138 grains is a good starting charge weight then?

 

[Dogtown]

Yeah, based on what I'm seeing in QL with a COAL of 4.515". You're above 95% case fill and still under 53000psi. Of course that's using some assumptions and actual load data would be better, but.....408CT

 

[232593]

Just to add on pressure signs, when I was shooting .408CT & .375CT looking at primer flattening wasn't the most reliable pressure sign. Even mild loads started to flatten primers (for me at least). Ejector swipe and heavy bolt lift were much more reliable pressure signs to avoid.

Were you running an HTI when you were doing those tests? Reason I ask is the way those bolts are made, bolt lift is very different than regular rifles.

 

[Dogtown]

Nope, my first gen SRS is what replaced my .408Windrunner back in late 2008.

 

[Dogtown]

The heavy bolt lift on my SRSs I have still tends to be fairly noticeable, especially that last 10 degrees. If I get high pressure, sometimes the initial bolt lift is fine, but then it gets near the top to unlock and that's when it gets sticky. A traditional action tends to have heavy lift through the entire rotation of the bolt.

 

[232593]

Yeah, based on what I'm seeing in QL with a COAL of 4.515". You're above 95% case fill and still under 53000psi. Of course that's using some assumptions and actual load data would be better, but.....408CT

View attachment 8192112

What do the numbers look like with a COAL of 4.590? That’s my COAL at .025” off the lands.

 

[Dogtown]

STOP! DON’T LOAD ANY FURTHER! That COAL is going to make it EXPLODE!

Actually it’s not going to make much of a difference on the low end

 

[232593]

I’m starting at 135 grains with that COAL. Think that will be ok?

 

[Dogtown]

Of course.

 

[232593]

Started at 135 grains of N570 and stopped at 139. No heavy bolt lift but some marking on the brass.

Looks like a potential node to start working at 137-138 grains of N570. Maybe I should try another test from 132-136 and see if there is anything in the 2800 range?




Retumbo seems to have a possible load in the 130-131 range it seems.

Thanks for the information @Dogtown

 

[Dogtown]

If those are single shots, you’re not looking at a node. You could run the same test five times and get different curves.

But if you’re seeing pressure marks on brass, then just avoid anything at and above that charge weight. If you like the velocity in a certain range, then start testing with 3-5 shot strings in 0.5-1.0 grain increments within that window. Don’t worry about groups so much, but note any obvious standouts (good and bad), and just look for consistent velocity.

 

[232593]

If those are single shots, you’re not looking at a node. You could run the same test five times and get different curves.

But if you’re seeing pressure marks on brass, then just avoid anything at and above that charge weight. If you like the velocity in a certain range, then start testing with 3-5 shot strings in 0.5-1.0 grain increments within that window. Don’t worry about groups so much, but note any obvious standouts (good and bad), and just look for consistent velocity.

With 130 grains of Retumbo I get 2907, with 131 grains I get 2902. So I’ll test a group if 3 at 130, 3 at 130.5, and 3 at 131.

For N570 137 gets me 2945 and 138 gets me. 2944. So 3 at 137, 3 at 137.5, and 3 at 138.

Could that work or am I missing something?

 

[Dogtown]

Yeah, you’ve got the right idea.

 

[232593]

Looks like my gun does not like N570 & 425 grain CEB lasers at speeds over 2900

 

[232593]

Maybe the 2830-2850 range will be better?

 

[232593]

So @Dogtown odd thing happened when I was testing Retumbo & N570. I would have two shots that would be really close to each other, velocity wise and then one that would be waaay off.

 

[Dogtown]

Looks pretty normal to me - I see that kind of behavior often in 3-shot groups during load development.

 

[232593]

Everything grouped less than an MOA but only one of them was about 1/2. Hopefully there is a velocity node at 2830-2850. So far it seems Retumbo is the superior powder.

 

[Dogtown]

Again, 3-shots is the absolute minimum for any kind of statistical analysis (you can create a line from two points, but you need three to create a curve from linear data). You might just try shooting a 5-shot group with that 1/2" group and see what the SD is like. It might be that you get four that are very close, with one outlier. In that case, your SD will drop with a 5-shot group vs the 3-shot group you got.

Use 3-shot groups to get a ballpark idea about stuff (charge weight, seating depth, etc). Use 5 or more shots to do the actual analysis. I know it sucks with big-bore components, but that's the price of admission.

 

[232593]

Looks like 133 grains of N570 is about the best I have to work with with that powder

I’m going to try seating them .005 off the lands next, maybe that will tighten that group up a bit more.

 

[232593]

@Dogtown when you ran .408 did you ever try RL50 with a 420 grain bullet? I’m thinking about pressure testing 420 grain RMBs and RL50 today. I almost have a single digit ES load finished with RL50 and the .375 ATIPs.

If I could get 1 powder type for .375, .408, and .50 BMG…

 

[232593]

Tested RL50 135-143 grains. No pressure signs so I think I’ll try 144-150 next time to get to 2850

 

[232593]

Again, 3-shots is the absolute minimum for any kind of statistical analysis (you can create a line from two points, but you need three to create a curve from linear data). You might just try shooting a 5-shot group with that 1/2" group and see what the SD is like. It might be that you get four that are very close, with one outlier. In that case, your SD will drop with a 5-shot group vs the 3-shot group you got.

Use 3-shot groups to get a ballpark idea about stuff (charge weight, seating depth, etc). Use 5 or more shots to do the actual analysis. I know it sucks with big-bore components, but that's the price of admission.

I took that 1/2” group and seated it .003” off the lands and it tightened up to about 1/4-1/3”. ES stayed about the same.

 

[Grubber]

I am just going to tag in on this thread, great stuff.

 

[232593]

I am just going to tag in on this thread, great stuff.

Do you run a .408?

 

[232593]

CEBs seem to do ok with 143.5 grains of RL50 behind a 425 grain CEB Laser .004” off the lands.

Problem is it grouped at only just under an inch. @Dogtown do you think seating them .025 might improve things or make it worse? Or would it be better to keep the same seating depth and drop the powder charge down .5-1 grain to get the bullet at that 2850 range all .408s seem to like?

 

[232593]

@Dogtown do you think STABAL HD would have any utility in .408?