.375H&H Viht N540 reloading: early results

[zambezi]

Sako factory ammo [478D] in .375H&H throwing a 270gr Barnes TSX bullet leaves the muzzle of my rifle at a chrono'd 2600fps. I used that round to very good effect in Namibia in November 2019 with some shots out to 240m. All shots were one-and-done.

So my reloading target is to equal or better that load [for less money than the £5.50 per-cartridge asking price at UK RFD counters]. After some research, the Viht N540 powder looked a good match to the 270gr Barnes TSX bullets. I have started with some very conservative loadings and had some very accurate and useful loads already. I will work up toward the target MV with care and small increments.

There are 5 test shots on the sheet below. All shots taken from bench rest at 100m. The first two on the lower target are 65gr N540 with a cartridge length of 2.996 ogive. Mean MV was 2325fps. The three shots taken on the top left target are at charge weights of 65.5gr, 66gr and 66.5gr. The respective MVs were 2356fps, 2355fps and 2388fps. Cases all extracted easily, primers clean, bolt face unmarked.




I do not think that the Sako factory ammo MV of 2600fps is a random choice. At that speed, the terminal velocity at 220m is still sufficient for full Barnes TSX deformation/performance. Most of my shots in Namibia were in the 150-240m range. So 2600fps is the target to match...

 

[CarlW]

I agree that you should seek to raise the velocity a good bit more. However, in the meantime, nice shooting! Nothing wrong with those groups.

 

[alberta boy]

Great shooting , but your right , I'd try for higher velocities . From your description of the fired cases , you have a lot of room left to increase your loads safely . I've found the 375 H&H to be one of the easier cartridges to find accurate loads for , another reason why it's one of my favourites , keep us posted .

AB

 

[zambezi]

Round three of the .375 load development has thrown up a possible measurement issue. I am measuring MV using a Chrony F1 on a platform located 3m in front of the muzzle . I have used the same set up for all testing. On occasion, I have benefitted from simultaneous speed testing using a colleague's radar based chrono'. On those occasions, the two gave similar values. Further reason for hardware confidence: In 2019, Chrony F1 derived data was subsequently cross-verified by drop data at 250m [when I tested my 6.5x55mm].

The three separate days of .375 load development started at a charge weight of 65gr N540 and has risen to 69gr N540 and MV has not tracked in a linear fashion. The first batch at 65gr all returned MVs in the 2400fps range. Testing on two other days differed somewhat.

Today's test loads were 4 grains higher than the start load but appears to have delivered a negligible MV increase.

<day 1 < day 2 < day 3

The intra-day MV values appear to seem sane with respect to each other. So I now think that there is a test set up issue that is causing some variation in empirical measurement. I.e. something in the measurement methodology is changing between range days.

Today I had a number of "err" events as clouds blew in. Optical chronos can be susceptible to light changes IIRC. Also, re-reading the Chrony manual, the guidance is to ensure that the projectile passes in the lower third of the wire hoops. I.e. nearest the optical detector. The lay of the land on day 3's testing meant bullets flew nearer the reflectors than on the two previous outings. Perhaps that skewed the results a bit? Any wisdom out there?

< Maker states to fire bullets here

 

[Selous]

Hard to quantify the effect without another chronograph (magnetospeed or Labradar) present but I understand that light levels and passage of bullet in different regions can alter results. Another possibility is that you may have identified a wide node where variation in charge weight doesn’t cause much change in velocity. Does the SD and ES support low variation ie consistent velocity? What were the groups like in this velocity flat spot? I guess the only was to know is to retest

 

[Border]

See if you can borrow a Magnetospeed.

 

[Marcher]

69 gns is quite a lot of powder, and will produce a lot of blast. I know 3metres is a sensible distance to place the chrono, but could the blast be effecting it ?

 

[zambezi]

See if you can borrow a Magnetospeed.

I always shoot with a moderator fitted, so have not been able to fit one of these. Also, reports in my shooting club declare variable results

Hard to quantify the effect without another chronograph (magnetospeed or Labradar)

On the one day that I ran the Labradar and Chrony F1 in tandem, they agreed to within 6%.

Another possibility is that you may have identified a wide node where variation in charge weight doesn’t cause much change in velocity

Worth bearing in mind! I am returning to the range where I have the greatest control over firing position-to-chrony set up and will retest the first batch weight vs higher charge weights. If the 65gr N540 load delivers a repeatable 2400fps, but slight charge weight increases do not deliver a linear increase in MV, then your wide node hypotheses might hold true.

On the upside, I still have some charge weight wiggle room at higher values per Viht tables and case performance so far.

 

[zambezi]

69 gns is quite a lot of powder, and will produce a lot of blast. I know 3metres is a sensible distance to place the chrono, but could the blast be effecting it ?

Perhaps, but I don't think so. I have at least one set of tests where Chrony F1 results were validated by an independent Labradar measurement. Also, 69gr N540 is not horrible to shoot, and does not cause case over-pressure signs. And the Viht tables cite 73.4gr as the max load in N540 using my preferred projectile:

 

[zambezi]

CORRECTION. I have re-read the Chrony manual and the statement below is slightly off.

the guidance is to ensure that the projectile passes in the lower third of the wire hoops. I.e. nearest the optical detector. The lay of the land on day 3's testing meant bullets flew nearer the reflectors than on the two previous outings. Perhaps that skewed the results a bit? Any wisdom out there?

< Maker states to fire bullets here

Quoting from the Chrony F1 manual we see that centrality of projectile passage is key and that the optimum height is 10-15cm above sensors:




In practical terms, I now see that sweet spot aligns to the brass ferrules on the diffuser uprights:

 

[Border]

I have the cheaper Magnetospeed Sporter. It can't be used with a moderator. What I do is load a ladder with 5 or 6 cartridges, take the mod off, fit the magnetospeed and fire one of each increment just into the backstop without aiming. This way I get a ballpark figure on what the powder steps give velocity wise and can check for pressure signs.
All being well I then refit the moderator and shoot at paper to check poi and potential groups. I had an optical chronograph before and really like the simplicity of the MS.

 

[Selous]

My Chrony F1 in now semi retired after the Labradar arrived but I used to align the horizontal cross hair with the brass connectors. Judging by your photo and measurements this looks about right for optimal function. The trouble with optical chronos is that correlation with Labradar or magnetospeed in one day may not mean correlation on another day.

 

[Colonel]

From what I have read RL-15 is the most accurate powder for 375H&H. On the Barnes website they show a 270 with RL-15 start at 67.5 for 2494fps and a max of 75.5 for 2725fps. The website al shows for the 270gr bullet Big game powder, starts at 76gr for 2641fps to max of 84.5 for 2841fps.

 

[Outback]

I have replaced my F1 with a Competition Electronics Prochrono Digital Chrornograph which seems a much better piece of kit . On your reloading I would have started at 69 grains and loaded three rounds in half grain steps up to book max weight loading to book COAL which you would have been able to get your base to ogive length of your first round if you prefer , this is how I have always reloaded with great results .

 

[Vortex2019]

From what I have tested, RL-15 is good on a wide range of projectiles.

I currently use speer 235gr, with 74gr of RL-15 giving me 2850fps. 2MOA elevation at 200yd and 5MOA at 300yd.

In the past I have also loaded up 300gr DGS with 65gr RL-15 and that gives 2350 fps

Both loads giving MOA accuracy at 100. The 235gr giving good groups out to 300.

 

[palmer_mike]

For what it’s worth, Kynamco load a 270gn SN round for this chambering that has a MV of 2650fps.
Most Kynamco loads are derived from historic MV’s so that older rifles with regulated sights will shoot as expected at the sight graduations......

 

[Odders]

Top tip to ensure your Shooting Chrony keeps on working. Replace the lower metal rods supporting the "sun screens" with suitable diameter wooden dowel.
(Nope - didn't break mine but a mate did for his by clipping one of the metal rods & breaking the unit where it seated)

 

[scrumbag]

For what it’s worth, Kynamco load a 270gn SN round for this chambering that has a MV of 2650fps.
Most Kynamco loads are derived from historic MV’s so that older rifles with regulated sights will shoot as expected at the sight graduations......

Not sure you can still get cordite

 

[palmer_mike]

Not sure you can still get cordite

We don’t use cordite at Kynamco these days......

 

[Cranhill]

I used 300grs SPRN with 82grs N160