Temperature sensitive powders

[Malxwal]

Looking for peoples experience of N540/N550 in terms of temperature sensitivity, also any other experience of Viht and RS powders in this respect.

My own experience of RS60 of late is that it was very temp sensitive, and so I'm now looking to change to something more stable in my 47, 22" barrel and sticking to 123 gr (mostly Scenars).

 

[VarmLR]

I don't know about double base Viht but I've always found N140 to also be very temp sensitive with a worrying tendency to spike quite alarmingly if anywhere near the upper end of what you might view as a moderate load in the low teens.  More recent experience with RS 62 shows probably a 3 to 4fps increase per degree which is also I guess on the sensitive side.

[Malxwal]

RS62 was one that was looking good for a trial in the 47. I also had a good load of N140 and 123 Amax, seemed to be fine in excessive temperatures the other day ( NE Scotland, but it was up above 20, so we were all near naked). I will have to try some behind the Scenars. Always looking for a wee bit extra poke, so the N540 piqued my gaze.

My 308 for some reason detested N140 behind any one of five different bullets, a bit odd, so I moved to Varget, of which I have one tub left.

 

[Catch-22]

I use N140 in my 6.5x47 and under a 123g Scenar. I'm pushing them at around 2930pfs from a 24" barrel. Wickedly Accurate and very temp stable.

I have gone up to around 2980fps but started to get pressure signs so backed down to 2930fps.

One thing I did find re pressure spikes was down to using a CCI250 primer - they would make my fps ES/SD go mental, just no consistency. As soon as I switched to a Murum KVB-223M (the Magnum SR primer, not the standard SR primer) both the ES & SD went into single digits. No pressure spikes and a slight improvement in accuracy too. 

[Malxwal]

Interesting, what sort of charge weight are you at for that ? going by Quikload, the N540 offers little advantage over N140, so perhaps worth doing a load work up with what N140 I have left.

[TJC]

I’ve done quite a lot of testing with N550 and found it to be a fraction over 1 FPS change per degree F change when DA hasn’t changed materially. It’s not quite linear at the extreme end of temp ranges but in the 40-90F range it’s quite consistent. 

[Catch-22]

2 hours ago, Malxwal said:

Interesting, what sort of charge weight are you at for that ? going by Quikload, the N540 offers little advantage over N140, so perhaps worth doing a load work up with what N140 I have left.

My charge was 38.3gn N140 under a 123g Scenar to achieve 2930fps. No pressure but upping to 38.6gn started to show signs and 38.8gn was just a bit of a no no. 

I am aware that the loads are pokey, but 38.3gn was consistent and showed no flux in temperature despite shooting in temps ranging from 8 to 22 degrees C. Haven't shot this load in higher temps yet though.

i did have a happy freebore, allowing me to seat right at the shoulder/boat tail junction, so no compression of loads. Neck tension was around 0.02". 

One thing to note is the higher energy N540 and N550 are generally considered to be barrel burners. If you look at their energy rating (right around 4000-4500 joules) and the consequential heat they provide,  they're right on the upper end of the powder energy scale. N140 is a lot lower, around 3700 joules.

[TJC]

15 minutes ago, Catch-22 said:

 One thing to note is the higher energy N540 and N550 are generally considered to be barrel burners. If you look at their energy rating (right around 4000-4500 joules) and the consequential heat they provide,  they're right on the upper end of the powder energy scale. N140 is a lot lower, around 3700 joules.

Often heard about this barrel burning issue with the 500 series but I’ve yet to experience it. Might be worth noting that N140 is 3700 joules as you say but N550 is 3900, only a 5% difference. Not nearly as much as some assume. 

 

 

[Catch-22]

I guess that's true, it's all relative.

Personally I believe style of shooting probably has more to do with barrel life. You could have the coolest burning powder going but if you're machinegunning them down the barrel, getting it hot enough to cook eggs on, then  expect very short barrel life. 

[TJC]

30 minutes ago, Catch-22 said:

I guess that's true, it's all relative.

Personally I believe style of shooting probably has more to do with barrel life. You could have the coolest burning powder going but if you're machinegunning them down the barrel, getting it hot enough to cook eggs on, then  expect very short barrel life. 

So true ! 

[Malxwal]

Well, as for style of shooting, I'm purely doing medium range informal gong stuff, no fast strings etc. The 22" barrel limits velocity, so stick to the 123gr and accept the velocity, as long as the accuracy is there. The increased barrel burner effects are not a concern, hence I tried the RS60. Load development produced a fantastic grouping at between 40.1 and 40.7, but that went completely out the window when temps rose to above 20c (not something we have to worry about a lot up here, but still, I like an easy life).

Interesting about the Murom primers; locally can only get CCI or Federal, AFAIK. Its the CCI450 primers I use.