.375/.338 Lapua Magnum Improved - Load Data

[Rockfish Dave]

I'm starting this thread as a place to consolidate information on the case.

I'll be adding my information as I progress through load development. Please add any information you have as well.

Reamer Print for Single Feed (for most projectiles):

 

[Rockfish Dave]

These were provided by another 375-338 LMI owner:

 

[Rockfish Dave]

Steps of load development:

1. Load 10 each in 1gr increments to determine where pressure develops with each powder, with the magnito speed for velocity.
2. Next step will be finding a node with low ES.
3. Finally I'll play with seating depth/jump to lands to tune accuracy.

Here is what I plan on recording:

• Neck wall thickness
• Neck tension
• Bullet type and weight
• OAL of loaded rounds
• OAL of loaded rounds from ogive
• Jump to lands
• Powder (Type and weight)
• Primer
• Brass (Fire Forming or Fully Formed)
• Velocity
• Pressure signs or lack there of
• POI shift

Powders I'll test are:

• H-1000
• H-4831
• Retumbo
• H-4350

I'm going to stick with the 350gr SMK for testing.

 

[Rockfish Dave]

Kirby Allen's thread on his version of the 375-338 LMI:

http://www.longrangehunting.com/for...ess-load-development-velocity-results-120173/

 

[cowboywhorses]

Thanks Dave this will be one of my winter projects.

Looks to be a fun gun to play with.

Jeff

 

[Rockfish Dave]

Loaded the and fired the Retumo batch. I have issues with the seating die, so I was stuck with the Barnes 250gr TTSX or not shooting.

I used the load data from the Hogdon manual for a 338 Lapua Magnum firing 250 gr projectiles. Short version is it is way too light. The maximum charge listed only yielded a hair over 2400 fps.

 

[Rockfish Dave]

Given the extremely light load that the maximum Retumbo charge turned out to be, I am going to pull the bullets on the other lighter loads and start at the max and work up from there.

I'll stop at either 100% case capacity on the non-fire formed loads or 5 grains higher than the max.

Hopefully I can get another round done over the weekend. I'll be posting the detailed information to this thread once complete, but in the interim I'll continue to post updates.

* Side notes:

• The Barnes 250gr TTSX easily fit into the CIP length magazine and feed very smooth.
• The bolt release is a notched modified for a Seekins magazine & bottom metal (although I am running CIP Mags and bottom metal) and should allow me to eject all but the loaded brass VLD's without any issue.
• My headspace is .0055 so take that into account for the following:
  • The SMK's are 3.885" OAL touching the lands.
  • The Woodleigh Brass VLD's are 4.030" to the lands.
  • The Barnes 250gr TTSX are 3.665 OAL touching the lands.
  The above should help if you should decide to go with a shorter or longer length throat.

- Dave

 

[Rockfish Dave]

Specks for the rifle:

Defiance Deviant with 338LM CIP inlet
Bartlien Heavy Varmint with 8 flutes, 27" Stainless Steel Barrel: Gain twist starting at 1:11 and ending at 1:9.75
API Fat Bastard Muzzle Brake (I love it, but I cleared out shooters on either side)
Huber 2 stage trigger (1lb first stage and 2lb break)
Manners TF1 with CIP mini chassis
Bartlien Shop Services: Barrel chambering and muzzle brake installation

I have been so busy between family, work and being sick I figured might as well get busy shooting so I shot the loaded rounds rather than pulling and reloading.

I'll try to post up the targets when I get a chance, but best accuracy was with the H-1000 and H-4831. I was pleasantly surprised given the variation in charge weight and the fact that these were fire forming loads

Here are the initial fire forming loads and results for the Barnes TTSX 250gn none of the loads showed any signs of pressure:

---- ---- ---- ---- Retumbo
Series 1 Shots: 6
Min 2287 Max 2428
Avg 2345 S-D 48
ES 141

Series Shot Speed Charge Weight
1 1 2428 ft/sec 87 Clean Cold Bore
1 2 2358 ft/sec 86 Clean Cold Bore
1 3 2349 ft/sec 85 Clean Cold Bore
1 4 2287 ft/sec 84 Clean Cold Bore
1 5 2311 ft/sec 83 Clean Cold Bore
1 6 2337 ft/sec 82 Clean Cold Bore

---- ---- ---- ---- H-1000
Series 1 Shots: 5
Min 2282 Max 2428
Avg 2382 S-D 57
ES 146

Series Shot Speed Charge Weight
1 1 2401 ft/sec 88
1 2 2393 ft/sec 87
1 3 2428 ft/sec 86
1 4 2408 ft/sec 85
1 5 2282 ft/sec 84 Clean Cold Bore
1 6 2379 ft/sec 83 Clean Cold Bore

---- ---- ---- ---- 4831
Series 2 Shots: 7
Min 2374 Max 2529
Avg 2427 S-D 53
ES 155

Series Shot Speed Charge Weight
2 1 2529 ft/sec 85
2 2 2461 ft/sec 84
2 3 2421 ft/sec 83
2 4 2418 ft/sec 82
2 5 2414 ft/sec 81
2 6 2374 ft/sec 80
2 7 2374 ft/sec 79


---- ---- ---- ---- H4350
Series 3 Shots: 4
Min 3146 Max 3229
Avg 3192 S-D 41
ES 83

Series Shot Speed Charge Weight
3 1 3227 ft/sec 99
3 2 3229 ft/sec 98
3 3 3168 ft/sec 97
3 4 3146 ft/sec 96

 

[Rockfish Dave]

For the Barnes 250 TTSX it looks like my data supports Kirby's results; H-4350 is the go to powder. Since these are fire forming loads I'll revisit it with fire formed brass, but at around 3200 fps what is not to like!

Re-cap:

---- ---- ---- ---- H4350
Series 3 Shots: 4
Min 3146 Max 3229
Avg 3192 S-D 41
ES 83

Speed - Charge Weight
3227 ft/sec - 99 gr.
3229 ft/sec - 98 gr.
3168 ft/sec - 97 gr.
3146 ft/sec - 96 gr.

I'm loading up the 350gr SMK's with H-1000, H-4831, and Retumbo since these powders were way too slow for the 250gr TTSX and I am betting the H-4350 will be too fast.

I have the seating die at .020 off the lands.

 

[Rockfish Dave]

350SMK Fire forming results. None of the following showed any signs of pressure.

---- ---- RETUMBO

Speed Charge Weight Density
2600 ft/sec 98 Compressed
2565 ft/sec 97 Compressed
2568 ft/sec 96 Compressed
2534 ft/sec 95 Compressed
2513 ft/sec 94 Compressed
2465 ft/sec 93 Compressed

---- ---- H-1000

Speed Charge Weight Density
2616 ft/sec 98 Compressed
2627 ft/sec 97 Compressed
2590 ft/sec 96 Compressed
2593 ft/sec 95
2548 ft/sec 94
2523 ft/sec 93

---- ---- H-4831

Speed Charge Weight Density
2639 ft/sec 93 Compressed
2613 ft/sec 92
2575 ft/sec 91
2522 ft/sec 90
2466 ft/sec 89
2483 ft/sec 88

Looks like I will be exploring the H4831 for 350SMK fire forming loads...

 

[benchracer]

I have been following this thread with great interest as I am considering a build for this same chambering. Based on my own experiments with my H&H and based on what Kirby had to say in the thread you referenced, it looks to me like you should have quite a ways to go before you run out of throttle.

If my understanding of the data you have posted so far is correct, you are only doing fireforming work at this time. What are you getting for case capacity after fireforming?

Kirby's writings and my own research with QL confirm your findings that Retumbo and H1000 are too slow. Likewise, Magpro and 7828 SSC were shown to be excellent powders for the 350 SMK. QL also indicated Norma MRP (currently available) and VV N560 are top choices. Do you have plans to test any of those powders when fireforming is complete?

I look forward to learning more as your load work with your rifle progresses.

 

[Rockfish Dave]

Thanks for the input. I only have these powders on hand and want to see this through to completion so that anyone else can use this information for their load decisions.

I'll be taking this barrel off and putting on the second barrel to break in, picking up where I left off on the first barrel during the break in process with the H-4831. I'll take the loads up to 98 grains if the case capacity will allow it. (I annotated when I could feel the bullet base crunch powder as compressed even though I could still shake the round and feel/hear it moving).

Last I will prep the fireformed cases to finish off the break in. Hopefully I can run all the powders to see what the max loads and velocities land for the four powders with the 350 SMK's.

Ultimately I will be sending these off to be Melonited so my last step will be for the final fire formed load data and expect it will be a little hotter than a normal twist, non Melonited barrel.

Ultimately I will finish testing and posting the load results for the various projectiles when finished. I still need to go through my notes for all the information to give a more complete picture.

 

[AfricaBob]

Dave please would you provide some insites into your 375-338 LI the following questions:
a) Why did you design the 375-338 LI wdith a 35 degree angle?
b) Who made the dies for you?

 

[Rockfish Dave]

Dave please would you provide some insites into your 375-338 LI the following questions:
a) Why did you design the 375-338 LI wdith a 35 degree angle?
b) Who made the dies for you?

Bob,


I went with 35 degree shoulders because that is what others have done. in reading and talking with those who have 35 degree shoulders, in addition to personal experiance, no one has feeding issues like I have heard about with the 40 degree shoulders (no personal expirience with 40 degree shoulders though).

I would like the slightly increased case capcity though for the 350 gr projectiles that a 40 degree shoulder would afford.

The dies were made by whidden gun works and they provided 3 stems to load everything from my 350gr brass solids to the 250gr barnes ttsx. I would buy them agaiin.

Also whidden makes hydro forming dies. I have gone to hydro forming cases to skip fire forming. It's a personal choice, but works for me.