Load workup / validation with123gr ELD-M and BM8208

[EigerWand]

Hi, I'm setting up a new "standard load" for hunting, with my Sako Vixen based Grendel . This is for hunting mostly smaller deer like Sika, Fallow and Red Deer hinds, plus of course goats and the occasional pig. With only a 16" barrel, I hadn't been very impressed with the knockdown power of factory SST and reloads using 120gr NBT were very accurate but penetrated too far on the goats, with mediocre results. A box of factory ELD-M performed fairly well, with good expansion and wound cavity like I was expecting. So, I've worked up a load to give a fairly good velocity , but leaving a wide margin of safety ...


Load Development Grendel ELD-M 123gr


Seating
Ejection port clearance limits my cartridge overall length to tip of bullet (COAL) and has to be less than 2.250" for my gun. This is a hunting rifle, so rounds need to feed from the magazine and eject cleanly if I don't fire them. There is plenty of clearance to the lands and the magazine will hold longer rounds if needed. With the Grendel having a small cartridge capacity and a long bullet (1.2405 - 1.2440") and velocity being a performance limiting factor (trajectory and terminal velocity for expansion), I decided to simply seat the bullets out as far as I could.

Powder weight
I'm using BM8208, made by ADI in Australia and sold under a similar name in the USA. For a 123gr projectile at 2.250" COAL, the manufacturer gives a starting load of 25.5gr and max 28.5gr, noting that is a compressed load. It happens that I'm using the same brass (Lapua), case length and primers (Federal 205M) as listed in the ADI manual. Differences are that I'm using the ELD-M, which is probably longer than the Sierra HPBT quoted, and my twist is 1:8 instead of 1:9.

I've noticed that, for me, compressed loads make the COAL longer. Presumably the press springs a bit or the bullet moves back out in the neck after seating. I can overcome it by screwing down the seating die but it doesn't seem a good thing to do if I want consistent loading. So, here are the COAL to tip for rounds loaded with powder weights across the indicated range.

Fig 1 COAL.jpg
Fig 1 COAL at tip for a range of powder charges

This is just for one round at each powder weight. It looks as if the powder is being significantly compressed above about 27.5 gr. Measurements of Case Base to Ogive (CBTO) showed a similar trend but with a wider range, up to +/-0.001", between loaded rounds with the same powder weight.



Powder weight ladder
My plan was to test loads from the lowest to the highest listed and, if safe and satisfactory, my goal was to use 27.5 gr. That would give me a full grain clearance if I could show that 28.5gr was safe. I had already loaded 20 rounds at 26.5 gr to test function, grouping and terminal ballistic performance in goat hunting and that was satisfactory.
I loaded two each at 25.5 and 26.0 gr to complete the low end.
I loaded 5 each at 26.5 and 27.5 to give an indication of grouping (as best you can with only 5 shots).
I loaded 3 each at 27.0, 27.9, 28.3 and 28.5gr to give an indication of change in point of impact.
Set up a borrowed Chrony F1, put on safety glasses and started shooting !

For each round fired, I checked:

• Ease of extraction - possibly some smoothness of bolt lift at 28.3 and 28.5gr but it could have been imagination
• Primer flattening - no differences across the range of powder weights
• Base for brass marking - none
• Case base diameter expansion - 0.000" to 0.002" with no trend with powder weight (see below)
• Obvious body/neck splits - none

Fig 2 base exp.jpg
Fig 2 Case Base Expansion

I used calipers which measure to the nearest 0.0005". Where two cases gave the same measured expansion, these are shown with small offsets of 0.03gr for clarity. Perhaps in future I should wait for the cases to cool back to ambient temperature before measuring post firing.

Velocity
Unfortunately it started to get dark as I shot, so a lot of the higher weight charges didn't give a reading. For some reason I did get a single measurement at 28.5gr. Measurements for a later batch of 10 loaded at 27.5gr for sighting in are also shown. Interestingly, in both series there was one shot with much lower velocity. Both these were good shots right in the middle of the 100m groups. The difference of 56fps, at 300yd, would predict a drop of 2" low, which is pretty hard to even notice in a hunting situation. At 600 yd, it would be 0.2 mRad (5") below the group centre, which is starting to be of interest. The middle part of the powder weight range shows an increase of about 70fps for a full grain of powder. The average velocity for 27.5 gr was 2380fps with this Chrony on the day.

Fig 3 MV by Pwdr Wt.jpg
Fig 3 MV for ladder of powder charges

Predicted effect on trajectory
The average MV for 5 shots at 26.5gr was 2307fps and for 10 shots at 27.5gr it was 2382 fps.
This is similar to about 2 or 3 inches of barrel length so you'd expect it to be quite significant.
The predicted drop (Strelok)
Range__26.5gr___27.5gr
300 yd___1.9 _____1.7 mRad
300m____2.2_____2.1 mRad
500m____5.3_____5.0 mRad

Grouping
All groups were under 1 MOA (29mm at 100m). The most informative were those shot at 26.5 and 27.5gr, as they had 5 shots each. Further 5 shot groups shot another day with 26.5 and 27.5 gr for sighting in are also shown. These show the variation in size between 5 shot groups and start to give an indication of the underlying precision. There was no obvious trend for better grouping as with any change in powder charge weight; all charges were satisfactory.

Fig 4 group size.jpg
Fig 4 Grouping for a range of powder weights

Photos of the groups
1cm grid, shot at 100m. 3 squares = 1 MOA approx.
For the loads with 5 shots, I put them on two different targets because that was the way I had laid the rounds out in the plastic storage box. I didn't even know they were the same load till I did the tally up at the end. I had to estimate the group sizes from the grid rather than measure it directly with the ruler. So, C & D are one group with 26.5 gr and F & G are one group with 27.5 gr. Also shown are other 5 shot groups with those powder weights, shot while sighting in.

Fig 5 255 and 26gr gps.jpg
Fig 5. Targets for 25.5 and 26.0 gr

Fig 6 265 gps.jpg
Fig 6. Targets for 26.5 gr

Fig 7 27gr gp.jpg
Fig 7. Target for 27.0 gr

Fig 8 275gr gps.jpg
Fig 8. Targets for 27.5 gr

Fig 9 279 to 285gr gps.jpg
Fig 9. Targets for 27.9, 28.2 and 29.5 gr

[

[EigerWand]

Mean Point of Impact
I've plotted this as vertical and horizontal movement to see whether there was a stationary "node" where changes in powder charge made little difference to point of impact.

Fig 10 mpi elev.jpg
Fig 10 Mean point of impact elevation

Fig 11a Horizontal MPI.jpg
Fig 11 MPI horizontal

The grid here is 1cm so we can see that the largest difference between mean point of impact across the entire range of powder weights was < 20mm, which is comparable to the group sizes I got. There was no "node". I could afford to load a whole grain of powder over or under weight and the shot would go to the same MPI.

Test at 600 yards
This is 544m. Strelok predicts that, for MV 2380 fps and G7 BC 0.255, the elevation should require a come up of 5.7 mRad.

Target 1
Shots 2, 3, 4 & 5 had 5.7 mRad elevation.
Windage was 0.5 Right, perhaps not quite enough.
The grid squares are 1 MOA (0.29 mRad).

Fig 12 600yd T1.jpg
Fig 12 600 yd target 1

Target 2
Elevations:
Shot 1. 5.7
Shot 2. 5.7
Shot 3. 5.6
Shot 4. 5.7
Shot 5 5.8
Windage varied from 0.6 to 1.0 mRad.

Fig 13 600yd T2.jpg
Fig 13 600 yd target 2

So, it appears that 5.7 was pretty well the correct elevation on the day.

Conclusions:
* The maximum uncompressed load was 27.5gr BM 8208
* Loads up to 28.5 gr were safe.
* Powder charges from 26.5 to 28.5 gr shot to the same point of impact.
* MV increased by about 70 fps for 1.0 gr increase on powder, comparable to increasing barrel length by 2-3".
* Loads at 26.5 and 27.5 gr grouped similarly, about 20mm@100m (0.7 MOA).
* MV for 27.5 gr was an average of 2380 fps with sd 21 fps but with a couple of apparently low velocity shots (50-70 fps slower).
* The nominal MV of 2380 fps was confirmed by shooting at 600 yd, where point of impact matched Strelok's predicted elevation within 0.1 mRad. No correction of MV, BC or click adjustment was needed.

[Lemonaid]

Thanks for sharing, very thorough and well detailed write up and will be helpful to the community. What results did you get with the factory Eld M ammo for comparison (velocity and accuracy) ?

[EigerWand]

I only bought one box of black factory ammo so didn't do accuracy testing or velocity.
Here's what I got during sighting in:

Hrnd Blk 123 Factry ELDM and NBT w suppr 450w.jpg

There are also groups with the previous load of 120gr Nosler Ballistic tips with and without suppressor.

I couldn't really say my hand loads are more accurate than factory because I've made a few mods so the stock fits me better since the and changed scope. By the look of it, I must have been using a moa scope at the time because it's a MOA grid target. That would be the VX-1 3-9x40, a good solid scope.