I decided to do a little temp stability testing today. TL;DR all 3 are temp stable.
I recently finished developing loads for my PRS gas gun in 6mm Creedmoor and N160, N555, & H4350 all gave good results with 108 ELDMs. H4350 & N555 both showed excellent velocity consistency over 20 shot samples. N160 was not quite as good as the others but was still more than acceptable. N555 and N160 showed the best dispersion results but H4350 wasn't very far behind. The best overall performer has been N555 and it's less expensive than H4350 to boot. So the only question left is temp stability since I live in Kansas and 30-40 degree swings over the course of a day or from day to day are not uncommon.
Vihtavouri lists both N160 & N555 as temp stable so I decided to see how they stack up with H4350 since that is kinda the gold standard for the Creedmoor case.
I loaded 15 rounds of each powder, froze 5, heated 5, and left 5 of each at room temperature. I would have liked larger samples but felt that 5 shot averages would be good enough since all 3 powders had shown consistent velocity during my earlier testing. I also wanted to try to test all 3 at the same temperatures or at least as close as I could get and decided that would be easier to do with smaller strings.
Test protocol: All rounds were loaded in a single session with components from the same lots.
The frozen rounds were put in a plastic bag in the freezer at -2° for 4 hours and then put in a cooler with ice for the trip to the range. The temp in the cooler was measured at 15° at firing time. Each 5 shot sample was fired less than a minute after being pulled from the cooler and the rifle was allowed to cool for several minutes in between samples.
The heated rounds were put in the dehydrator for 4 hours with it set at 115°. I wrapped them in a towel on the dash and ran the defrost every few minutes to keep them warm on the trip out and while waiting to be fired. The temperature of each sample was measured at 105° right before being pulled out for firing. Each sample was fired within a minute of being removed just like the frozen test rounds.
The room temperature rounds had been in a 68° house prior to the trip to the range and were kept in the pickup cab prior to being fired. The temp in the ammo box was measured at 76° probably due to the defrost being run. These were also fired immediately upon removal.
The test was fired by my Seekins SP10 with a 22" barrel and load data was as follows.
Starline SRP Brass
CCI 450 Primers
108 ELDM
2.200" Base to Ogive
40.0 gr H4350 (AVG 2846.4, SD 5.5, ES 24.7)
41.0 gr N555 (AVG 2840.4, SD 6.4, ES 24.3)
41.5 gr N160 (AVG 2865.2, SD 9.9, ES 43.5)
The only difference between the samples was the powder used. Listed after each powder is it's velocity performance over a 20 shot sample from my previous testing.
Ambient conditions this afternoon were mostly cloudy, 56°, and high humidity.
Results: Keep in mind these are 5 shot samples so the SDs aren't all that useful. I think the averages at least are in the ballpark of a larger sample but I would expect them to change up or down a few fps if the sample size was increased.
H4350 -
Cold 15° AVG 2854.3 SD 6.1 ES 15.6
Middle 76° AVG 2867.0 SD 4.9 ES 13.6
Hot 105° AVG 2864.8 SD 6.7 ES 17.9
This is pretty much what I've been told to expect from H4350 and is excellent.
N160 -
Cold 15° AVG 2822.0 SD 8.6 ES 24.4
Middle 76° AVG 2849.5 SD 10.0 ES 31.2
Hot 105° AVG 2850.1 SD 18.1 ES 48.8
This is also very good with a less than 30 fps increase over 90°. My earlier testing showed N160 to not be as consistent from a velocity standpoint as H4350 & N555 at least in my gun and that was also the case here. Having said that it has still shown good velocity performance and excellent dispersion so I wouldn't hesitate to recommend giving it a try. It's also the most affordable of the 3 at around $300 for an 8 pounder.
N555 -
Cold 15° AVG 2840.4 SD 9.6 ES 23.5
Middle 76° AVG 2847.2 SD 2.0 ES 5.7
Hot 105° AVG 2832.3 SD 3.3 ES 9.1
This is the most interesting result with the hot rounds being the slowest but still excellent results. It has also been on a par with H4350 when it comes to velocity consistency and even better with dispersion in my gun.
I'd say all 3 propellants are what I would call "temp stable" with H4350 & N555 being outstanding and N160 being very good.
I recently finished developing loads for my PRS gas gun in 6mm Creedmoor and N160, N555, & H4350 all gave good results with 108 ELDMs. H4350 & N555 both showed excellent velocity consistency over 20 shot samples. N160 was not quite as good as the others but was still more than acceptable. N555 and N160 showed the best dispersion results but H4350 wasn't very far behind. The best overall performer has been N555 and it's less expensive than H4350 to boot. So the only question left is temp stability since I live in Kansas and 30-40 degree swings over the course of a day or from day to day are not uncommon.
Vihtavouri lists both N160 & N555 as temp stable so I decided to see how they stack up with H4350 since that is kinda the gold standard for the Creedmoor case.
I loaded 15 rounds of each powder, froze 5, heated 5, and left 5 of each at room temperature. I would have liked larger samples but felt that 5 shot averages would be good enough since all 3 powders had shown consistent velocity during my earlier testing. I also wanted to try to test all 3 at the same temperatures or at least as close as I could get and decided that would be easier to do with smaller strings.
Test protocol: All rounds were loaded in a single session with components from the same lots.
The frozen rounds were put in a plastic bag in the freezer at -2° for 4 hours and then put in a cooler with ice for the trip to the range. The temp in the cooler was measured at 15° at firing time. Each 5 shot sample was fired less than a minute after being pulled from the cooler and the rifle was allowed to cool for several minutes in between samples.
The heated rounds were put in the dehydrator for 4 hours with it set at 115°. I wrapped them in a towel on the dash and ran the defrost every few minutes to keep them warm on the trip out and while waiting to be fired. The temperature of each sample was measured at 105° right before being pulled out for firing. Each sample was fired within a minute of being removed just like the frozen test rounds.
The room temperature rounds had been in a 68° house prior to the trip to the range and were kept in the pickup cab prior to being fired. The temp in the ammo box was measured at 76° probably due to the defrost being run. These were also fired immediately upon removal.
The test was fired by my Seekins SP10 with a 22" barrel and load data was as follows.
Starline SRP Brass
CCI 450 Primers
108 ELDM
2.200" Base to Ogive
40.0 gr H4350 (AVG 2846.4, SD 5.5, ES 24.7)
41.0 gr N555 (AVG 2840.4, SD 6.4, ES 24.3)
41.5 gr N160 (AVG 2865.2, SD 9.9, ES 43.5)
The only difference between the samples was the powder used. Listed after each powder is it's velocity performance over a 20 shot sample from my previous testing.
Ambient conditions this afternoon were mostly cloudy, 56°, and high humidity.
Results: Keep in mind these are 5 shot samples so the SDs aren't all that useful. I think the averages at least are in the ballpark of a larger sample but I would expect them to change up or down a few fps if the sample size was increased.
H4350 -
Cold 15° AVG 2854.3 SD 6.1 ES 15.6
Middle 76° AVG 2867.0 SD 4.9 ES 13.6
Hot 105° AVG 2864.8 SD 6.7 ES 17.9
This is pretty much what I've been told to expect from H4350 and is excellent.
N160 -
Cold 15° AVG 2822.0 SD 8.6 ES 24.4
Middle 76° AVG 2849.5 SD 10.0 ES 31.2
Hot 105° AVG 2850.1 SD 18.1 ES 48.8
This is also very good with a less than 30 fps increase over 90°. My earlier testing showed N160 to not be as consistent from a velocity standpoint as H4350 & N555 at least in my gun and that was also the case here. Having said that it has still shown good velocity performance and excellent dispersion so I wouldn't hesitate to recommend giving it a try. It's also the most affordable of the 3 at around $300 for an 8 pounder.
N555 -
Cold 15° AVG 2840.4 SD 9.6 ES 23.5
Middle 76° AVG 2847.2 SD 2.0 ES 5.7
Hot 105° AVG 2832.3 SD 3.3 ES 9.1
This is the most interesting result with the hot rounds being the slowest but still excellent results. It has also been on a par with H4350 when it comes to velocity consistency and even better with dispersion in my gun.
I'd say all 3 propellants are what I would call "temp stable" with H4350 & N555 being outstanding and N160 being very good.
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