start load for VV N 540 and 7mm08

[NZVarminter]

N540 is not listed in the VV manual for the 7mm 08 yet it looks to be a suitable powder. Anyone got a start load for it with 120-140g bullet weights?

Thanks

Grant

 

[Ratwhiskers]

Grant.

I was looking at N540 for my 7-08 last year till I discovered that it was a harsh double based powder that with top loads will trash the throat in your barrel. I moved to it's next of kin N140 and have never looked back.
Quickload gives me 42grains for a 120 v-max
Lapua brass
Fed' 210 std primers
@2980av f/ps
24" Border 5R barrel
3 shots give me a point to point of .253" @ 100yrds
I can also substitute the v-max for a 130SMK and get the same point of aim at 2800av f/ps with the same load.
Hope this helps mate.

 

[NZVarminter]

so what exactly is the story with these double base powders?

Do they give more velocity for same weight, but at the expence of throat erosion????

 

[Ratwhiskers]

Grant.

I'll try and find the post on the other forum and stick it in here, but yes you have the general idea mate. They are supposed to give added energy in the same volume with roughly the same burn rates as their little sibbling. The only problem is that to do this they use nitro glycarin as the extra kick and as you know that is a vigerous explosive Re; Throat Errosion . I spoke to my gunsmith about this and he advised me to stay well clear of the stuff unless I could afford his services every couple of years to screw in a new barrel. Powders of this kind seem to be used in heavy calibres or small cases wanting to chuck bigger pills just that bit faster to make up for the loss in volume.

 

[Ratwhiskers]

Here we go..... Found it.... It states that they use a reduced amount and a special additive.... But I really like my barrel, and for the few extra clicks it takes me to hit things at 600yrds l'm not going to spoil the pipe....
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....We are happy to be able to supply reloading powder for all quality concerned shooters like you.

Bore and throat erosion is really dependent on powder composition. The important parameter is flame temperature, which is unfortunately immeasurable quantity. Based on thermodynamic calculation, and long experience it is well known fact that higher energy content (i.e. heat of explosion) leads to higher flame temperature and higher throat erosion.

Easiest method to improve ballistic performance is to add nitroglycerol in powder composition. These powders are called double base powders. As you have heard, these powders tend to cause more barrel and throat erosion compared to single base powders. This difference is clear but it is, however impossible to quantify as for example as numbers of rounds to reach same erosion level.

All Vihtavuori N100 (N105...), N300 (N310...) powders, 3N37 and 3N38 are single base powders. These products are made with best available raw materials and manufacturing methods to get maximal performance you can get without using more erosive double base composition. Therefore, these Vihtavuori products cause less erosion than most of other competing powders. Especially high nitroglycerol contents (and thus erosion) are used in spherical powders (ball powders) and some US products.

Among Vihtavuori product line we have only five types we call N500 (N530 ... N570) which are by composition double base powders. N500 rifle powders contain small amount of nitroglycerol to add a bit more performance required mainly for extremely long distances. Even with these products we have added a special additive as well kept nitroglycerol content rather low in order to minimize the barrel erosion effect.

So, my opinion and advice is to keep barrel and throat erosion on minimum by using only single base powders like Vihtavuori N100, N300 and 3N.

Best Regards,

Mikko Vuoristo
EURENCO Vihtavuori Oy