Given the scarcity of smokeless rifle cartridge propellant, I think a lot of us have been motivated to try different things. Over the course of the last two years I managed to get a few pounds of Shooters World Precision Rifle powder. Having sat on this powder for some time I recently had a chance to try it with something I hadn’t planned on: the .224 Valkyrie. I have a Palma match coming up at the end of May and decided to give SWP a try in order to preserve my other propellants and to see how it would do.
Quickload predicted excellent muzzle velocity and safe pressures in my Starline cases, that averaged 32 grains of H2O capacity after being fired but not resized. A load of 24 grains under a 90 grain Sierra MatchKing bullet was predicted to give 2700 fps from a 26″ barrel with the rounds loaded at 2.36″ OAL for single round feeding during the Palma match, and 24.5 grains should give 2750 fps at 96% fill and almost 100% propellant burn. Not bad!
All loaded up and ready to go, I benched the 26″ rifle that I built. It has no gas system and I run it as a straight-pull bolt action using a side charge upper receiver and bolt carrier. A 3D printed handle helps work the action.
Right out of the gate, two things were apparent: This ammo has excellent accuracy, but velocity is well below prediction. The 24 grain load ran 2609 fps average and the 24.5 grain load ran at 2650. However this ammo was shooting 1/3 minute groups without trying very hard. I turned to Gordons Reloading Tool because it has a feature that will tune a powder based on real world results. In this case GRT predicted that 24.9 grains of SWP would result in 2694 fps at the same ambient temperature as the previous shooting session. So with the new ammo loaded up, off to the range.
Match rifle with 26″ 224 Valkyrie barrel for upcoming 1000 yard Palma match. Bench target on left was shot at 200 yards. Reduced MR Target was shot prone with a sling at 300 yards. Shoot-n-See is about the width of the 10 ring and the SNS 9 ring is about the width of the X ring of the reduced MR target.
In this case the ambient temperature was about 10 degrees warmer than the last shooting session, and GRT provides a field to account for this difference. The updated prediction was 2700 fps, for a difference of 6 fps. Shooting the ammo on a Lab Radar gave 2715 fps which is close enough in my books! Best of all, the accuracy remained excellent.
I shot on MR targets that were reduced to shoot from 600 yards down to 300 yards, which is the maximum distance at my rifle club. I shot many more X’s than 10’s and I think I’m ready for the Palma match. While the velocity is nothing to write home about for a 1000 yard match, I think the accuracy will play a more important roll, and the velocity is sufficient that all I need to do is make good wind calls in order to shoot well. I’ll report with range results after the match at the end of May.
I conducted a brief study of case capacity and its effect on muzzle velocity this weekend. Such studies are easy because spending time at the rifle range is fun. They are also difficult because time is limited and it takes a lot of trigger time to get statistically significant results.
This study is not rigorous in that insufficient data was collected to prove any correlation between muzzle velocity and case capacity for a given brand of case, but enough data was collected to show a link over several brands of cases. The difficulty here is that there is more to muzzle velocity variation than case volume, but if the variation in capacity is great enough, we see the effects clearly.
Starting with the case capacity in grains of H2O between a selection of new and once fired 308 Win brass from Lapua (once fired), Federal (once fired), SSA (new), Winchester (new), and Hornady (once fired).
SSA has the lowest capacity while Hornady and Winchester were about the same at the highest capacity. Approximately 2 grains of H2O capacity separate the lowest from the highest. We expect that all else being equal (i.e. the same powder charge and bullet weight etc.), the cases with the lowest capacity will exhibit the highest muzzle velocity and vice-versa. Here’s the results from the range session shooting off-hand with an M14 (shot pretty well, one 10-round string was 96-2x)
In this figure clear correlation between case volume and muzzle velocity is apparent. Obviously other factors influence muzzle velocity besides case volume as there is significant variation in muzzle velocity that does not correlate with case volume. For example, the SSA brass (grey dots) has lower muzzle velocity than the Federal brass (orange dots) even though it clearly has lower case volume, which generally correlates with higher muzzle velocity.
Given that the powder charges were thrown by an Autotrickler to 41.2 +/- 0.02 grains of H4895, the powder charge is the most consistent thing besides bullet weight at 168 grains for the Sierra Match King bullets used in this test. Notice also that for each 10-shot group except for the group shot with Hornady brass, the variation among the group does not correlate much at all with case volume. This is to be expected with sample sizes this small. Even so, the correlation among the data in general agrees with the prediction made by Quickload between 20 and 30 fps per grain of case volume, all else being equal.
The Hornady brass did show good correlation between case volume and muzzle velocity so let us consider it more closely.
This correlates with the prediction given by Quickload but is still too small a data sample to be taken as strong evidence. And there lies the problem as always with load development and accuracy: the difficulty with which we obtain meaningful results due to the constraints involved in gathering statistically significant data. Barrels heat up, fatigue sets in, Lab Radars fail to register a shot, and so on.
Ideally I would turn necks and be very careful about neck tension, flash holes, and the rest, and then shoot 50 to 100 rounds of each brand case. I’ve also found that correlation is stronger if the volume of the fired case is measured before resizing and compared with the muzzle velocity from the previously fired shot.
So take the data as it is, a point from which we can move forward, no more, no less, and an indication that what we expect is true, so now we have to be more careful to prove it.
In an upcoming article I will discuss strategies for using case volume measurements to inform load development for match shooting at 600 yards and beyond.
In this post I address the use cases for measuring case volume. Reloaders have gotten by for quite a while without measuring the volume of every case. Most reloaders never measure case volume. What are the reasons anyone would want to?
If you are interested in the Bison Armory Case Volumizer you can see them in our online store here.
In the past, measuring case volume was a slow task. Typically the reloader would weigh a case, fill it with water, then re-weigh the case to measure the weight of the water that filled the case. Obviously not the most desirable method. With the new Bison Armory case volumizer, the task is simplified to the point that it takes only minutes to accurately measure the volume of 100 or more cases.
Prior to this, there was not much point in discussing the reasons for measuring case volume. The cost in terms of time and effort were simply not worth the resulting information. Now that cases are easily measured with the Bison Case Volumizer (BCV), the question of why becomes interesting.
Checking for bad cases
Split case necks and other defects are real. Are you hunting? Shooting in a match? Going to a training class? The BCV easily detects any case with split neck or other compromise to its structure. A volumized case is one you can rely on.
Pushing the limits
Bison Armory does not advise pushing muzzle velocity to the limits, but we know some reloaders will do this. Suppose you are reloading all Winchester cases and a Starline case sneaks in. If you are pushing velocity to its maximum safe limits, a case with lower capacity than expected, like you might get from one from another brand sneaking into your batch unknown, could cause catastrophe. The BCV will detect these cases. In addition, suppose a new lot from the same manufacturer happens to be low. Manufacturing tolerances will vary somewhat even for the best manufacturers. The BCV when used properly and within its limitations, will alert the reloader to these sort of situations.
Long range accuracy
At 500 yards and beyond, variation in muzzle velocity starts to have a significant effect on accuracy. I shoot long range matches in F-Class and Service Rifle categories. Pushing the 223 Rem to 1000 yards is a lot of fun with the right bullets, but how much does variation in case volume affect long range accuracy? Quickload is a handy tool for cursory investigations into this question.
We can start with the common question of how much does variation in powder charge affect velocity and hence vertical dispersion at long range. For the 223 Rem with my personal load of 22.2 grains of H4895 in a Winchester case behind a 90 grain Sierra MatchKing bullet, we find a nominal muzzle velocity of 2550 fps. Quickload says +/- 0.1 grains of H4895 will result in +/- 10 fps out the muzzle. For my pet 223 long range load, that means the following vertical dispersion at distance:
Distance (yards)
Velocity Low/High (fps)
Drop Low/High (in)
Drop Low/High (moa)
600
1718 / 1734
86.9 / 85.2
13.8 / 13.6
700
1601 / 1617
134.6 / 132
18.4 / 18
800
1492 / 1506
195.8 / 192.1
23.4 / 22.9
900
1390 / 1404
272.8 / 267.6
28.9 / 28.4
1000
1298 / 1310
367.7 / 360.7
35.1 / 34.4
Now we know why long range shooters spend $1000 on an Autotrickler powder measure in order to throw charges quickly to +/- 0.02 grains. 1.7 inches at 600 yards and 7.0 inches at 1000 yards will lose you some X’s and 10’s.
What about case volume variation? Quickload tells us that variation of +/- 0.25 grains of powder will result in a muzzle velocity spread of 20 to 30 fps in the 223 Rem and variation of +/- 0.5 grains in the 260 Rem will see about 20 to 30 fps variation as well, depending on bullet, powder, and powder charge etc. As a fraction of case volume the variation is about the same.
Note: The velocity change for 223 Rem from +/- 0.25 grains of case volume is about the same as for +/- 0.1 grains of charge weight. So if you care about charge weight variation you probably ought to at least be interested in case volume variation.
I have verified this through experiment. Admittedly not a huge numbers on the surface, but how will this affect my performance in a match? With a low muzzle velocity of 2546 and a high of 2563 (difference of only 18 fps) we get the following trajectory table using Hornady’s ballistics calculator:
Distance (yards)
Velocity Low (fps)
Velocity High (fps)
Drop Low (in)
Drop High (in)
Diff (in)
Drop Low (moa)
Drop High (moa)
Diff (moa)
500
1847
1861
50.6
49.9
0.7
9.7
9.5
0.2
600
1723
1736
86.3
85
1.3
13.7
13.5
0.2
700
1606
1619
133.7
131.7
2.0
18.2
18
0.2
800
1497
1508
194.6
191.6
3.0
23.2
22.9
0.3
900
1395
1406
271
266.9
4.1
28.7
28.3
0.4
1000
1302
1312
365.3
359.7
5.6
34.9
34.4
0.5
The X-ring of the MR target is 3 inches and the 10 ring radius is 6 inches. At 500 yards the 0.7 in difference between high and low is pretty small but could cost an X or a 10 on shots that the shooter puts at the outside of the ring. At 600 yards the variation almost doubles and can start costing X’s and points.
For 800 to 1000 yards we shoot at the NRA LR target with an X-Ring that is 5 inches in radius and a 10-Ring that is double with a 10 inch radius. It is clear that the difference of 3, 4.1, and 5.6 inches between the low and high velocity values at 800, 900, and 1000 yards respectively can cost a lot of X’s and points. At 1000 yards in particular, the vertical dispersion is slightly larger than the width between rings.
Volume variation in Winchester 223 brass
I measured the volume of 98 Winchester 223 Rem brass cases and got the following results
The low value was 30.31 grains H2O and the high value was 30.73 for an extreme spread of 0.41 grains with a mean of 30.56, a median of 30.57, and a standard deviation of 0.09 gr H2O. Pretty good results actually. I’ve seen outliers with much bigger deviations. This is good brass. An outlier will definitely cost points during a match.
Once measured, what do you do with the cases? My personal approach is to omit any outliers and then split the rest at the mean or median to use for a 20 round match plus sighting shots. In this situation they are effectively the same. In this way I assure that my ammunition for a 20 round match will exhibit minimal vertical dispersion at long range, having in this instance a variation in case volume of +/- 0.1 grains H2O
In the next article I will compare measuring case volume by water weight using an FX-120i scale with the results from the Bison Armory Case Volumizer.
