107gr SMK with 8208 XBR, a New Look

[LRRPF52]

I decided to do some testing with the 107gr SMK after seeing Bryan Litz's evaluated BC data for it. Comparing it next to a 123gr AMAX, the 107gr SMK has a much longer boat tail. The Litz data I have states that it has a G1 BC of .461, and a .230 G7 BC.

The numbers look very nice actually, so I'm going to run a ladder and see where I'm at. Looking at Hodgdon's data in Volume I, they show a max load of 29.8C, and it definitely compresses once you get to 29.8gr of 8208.

I'm using a COL of 2.245".
Lapua 2x brass
Rem 7 1/2

We'll see how it does from the Lilja barrel.








Lilja 318 17.6" Wasp profile (very light) barrel fired on 17MAY2016, 64˚F
28.5 2562fps
28.8 2579
29.1 2624
29.4 2626
29.7 2655
30.0 2658

This was with a 2009-2010 lot of 8208XBR if I recall correctly. From what I've seen, I won't load much over 29gr under the 107gr SMK. Notice the large jump from 28.8gr to 29.1gr? That's a 45fps increase for .3gr, which is a potential departure from the trend if it duplicates. Small cases get dicey when loaded to max fill with faster powders.

[BluntForceTrauma]

Excited about this project, Paul, been wanting to see what XBR does with the 107. Cool photos, too!

[1911man]

This is a combo I've been looking to play with too but have been focused on my creedmoor since it's competition season for me. I look forward to seeing your data.

[bwaites]

28.5 of XBR gave me sub .25 groups in my 28" Grendel. The very first group I shot with it was sub .25. I took 50 rounds to the range after I discovered it, and had 10 straight sub 1" 5 shot groups, and all but 3 were sub .5 inch. I honestly didn't want to quit shooting it, it was one of those days that was sort of magic. It's a light bullet that flies like a 123.

I need to go back to it.

[AZ. Old Guy]

What a clean setup you have. I'm envious.

[Fredman]

I clean my bench off, and the night shift comes in and makes a mess again.

[LRRPF52]

Hodgdon's published max load is 29.8C (compressed), and that limit is based on case fill, as the pressure had not yet hit 50ksi, but is close at 49,300psi.

I loaded up:

28.5gr
28.8
29.1
29.4
29.7
30.0

Just re-measured the 30.0gr COL to see if it grew. If it did, it was only .002", as it is 2.247". Meplat condition is highly variable on BTHP's unless you personally uniform them with the trimmer, which I have, but think is pointless for my needs since I'm not competing in 1000yd bench rest.

Sierra lists the BC for this bullet at .406 to .420 looking at speeds from 2300-3350fps. I suspect they are using a form factor comparison. Litz goes into way more detail when analyzing BC, and lists it at:

G1: .461
G7: .230

The 123gr AMAX seems to be .468 for G1, and maybe .233 for G7.

The 107gr SMK flies faster than a 123gr, by about 170fps. If the BC's are roughly the same, that's a huge advantage for the 107 SMK.

I need to try CFE again with it. Last time I shot it with CFE, my mv's were all over the place, couldn't make heads from tails, which was either the changing lighting conditions, or inconsistent burn with a slow powder behind a lighter bullet. We'll see this time.

[Heinz57grendel]

This is my go to load and by far my favorite bullet. 107 smk lapua case 29.3 gr of 8208 with a cci 450 primer. Shoots .5 moa consistently

[Macht]

I load those with 28.0 gr of 8208 in Hornady brass with a CCI 450. It's my most accurate handload. Dunno why, but my loads are always lighter than anyone else's. If I push any further I get ejector smears though.

[Klem]

29.8/8208 with a 107SMK, 57.4mm OAL - Quickload predicts a peak pressure of 56,900lbs and 102.7% case fill.

107SMK
28.5/8208
CCI450
56.8mm OAL
Taper crimped
Lapua cases

[LRRPF52]

Hodgdon's piezoelectric system measured 29.8gr under the 107gr SMK at 49,300psi. I'm referencing Volume I of the 6.5 Grendel Reloading Handbooks, page 50.

The 123gr SMK on top of 28.5C gr of 8208 produced 50,000psi on their system. This is another example of how off QL is with this cartridge unless you calibrate it. JASmith has done a lot of tweaking of QL to get more accurate pressure representations, but it is way off, and checked against a pressure trace system as well.

The 102.7% case fill seems right though. It definitely is a compressed load.

[Klem]

Hodgdon's piezoelectric system measured 29.8gr under the 107gr SMK at 49,300psi. I'm referencing Volume I of the 6.5 Grendel Reloading Handbooks, page 50.

The 123gr SMK on top of 28.5C gr of 8208 produced 50,000psi on their system. This is another example of how off QL is with this cartridge unless you calibrate it. JASmith has done a lot of tweaking of QL to get more accurate pressure representations, but it is way off, and checked against a pressure trace system as well.

The 102.7% case fill seems right though. It definitely is a compressed load.

Agreed...I have come to the conclusion that QL is conservative to an unreasonable degree. All the warnings and disclaimers alone annoy me as I wade through them all looking for output. But I still use it as a benchmark and it is useful for doing what-if's. No doubt a piezo pressure measuring device used to interpolate (not extrapolate) is more accurate than a computer simulation prediction.

I have loaded heavier than 28.5 with no pressure signs on the cases. 28.5 is my most accurate load. Also, the 107SMK is the most accurate bullet I have used. Pity it's not a dedicated hunting round.

[JASmith]

I still use QuickLoad a lot but have learned to accept that its best use is for relative pressure predictions.

Run QL against published pressure and velocity data and you'll see it both over- and under-predicts pressures.

Before doing that, however, read this discussion: Understanding SAAMI Pressure Standards. You will feel better about QL "inaccuracy" afterwords.

I need to check my notes this evening, but I think my tests of this powder and bullet suggest that a typo may be present in the published data.

[kmon]

Agree with JASmith about quickloads, sometimes it predicts too high pressure like in the Grendel and too low in the 6.5-284 Norma as two examples in the opposite ends of the spectrum. There are also cartridges that it is amazingly close to even being spot on. It is a tool that doesn't take all possible variables into account but overall is still useful.

That link is to an interesting read and informative. It is also a much better read than the pressure information on the SAAMI website. http://saami.org/index.cfm

[Klem]

Interesting article.

Eliminating the high-end tail of a Normal Curve is the technical justification for being conservative. Also bearing in mind that the SAAMI peak pressure upper limit for calibres is far less than manufacturer pressure proofing. Going a little over SAAMI according to Quickload or bullet/powder manufacturer tables is not likely to cause anything more dramatic than shortening your brass life.