N500 series of Vihtavuori and throat erosion ?

[TC]

Hi guys,

Consensus seems to be of the view that VV's N500 series of powders erode throats severely.

I'm curious to understand to what extent is this purely a function of Nitroglycerine being added to Single Based Powders vs shooters/reloaders trying to pump an already high energy powder for every extra fps velocity gain that they can ?

Has anyone got any experience of throat erosion/barrel wear with these powders both at the high end of the curve when it comes to velocity/pressure and vs a more tame load. I suppose what I'm asking is if the relationship on barrel wear/pressure is linear and if not how much does pushing it for that extra 25/50fps really impact barrel life ?

Any thoughts on the above and how the N series really compares in this area vs similar burn rate powders ?? Thx

 

[rminut]

This is probably an excellent for the ballistics sections, since it is internal ballistics, and Brian Litz might answer directly with some engineering data observations.

You bring up the point that most shooters do not want mention, they are pushing the load beyond the max. I first heard of VV540 burning barrels out faster from service rifle shooters. After talking and reading I found out some of those people were pushing the heaviest bullets available over 100fps faster than a regularly used max load. Since most of us don't have an Oehler 43 or other true pressure transducer methods to load test, we just base pressure off of primer indicators, and to me, the double based powders just show the signs differently, which means people are pushing far harder than they think.
I used MR2000 in my 6BR and get over 150fps more velocity than the regular Varget standard load, well I could not get close to that velocity from Varget so why should I compare the barrel life to Varget. Velocity comes at a price. I backed my load down 4 tenths from what I could use and still get far more velocity than Varget will ever produce and my barrel shoots just fine after 1100 rounds of MR2000. If I pushed it to the max I doubt I could say that, but I would be at fault for thinking that.
You also have to take into account that most people are using the heaviest bullet in the cartridge AND trying using a double based powder to get the most velocity. There is additional wear from heavier bullets.
No, it's not a linear equation when it comes to velocity and pressure and barrel wear. A 25/50fps increase doesn't really show up on the target, most people are pushing stuff to over 100fps compared to a single based, which could show up on the target, but it has to come at a price.
I say use them, but don't get velocity greedy.

 

[barefooter56]

TC,
I used N550 in my Palma rifle for years. It was a hot load (3030 fps because that's what she liked). I didn't notice much throat erosion ( Kreiger barrel 1-13 tr, ) at all really. .010 after 2 years was about it.What I did notice was that the load got hotter after the second year then was over pressure by the 4th year. It was confirmed by VhitaVouri that as these powders age the nitro does move closer to the the surface of the powder kernel and change the burn rate. Answer is to retest your load every year and reduce load if necessary to prevent over pressure and to stay on your velocity accuracy node. Very good powder though IMHO.

 

[Brians356]

Slightly off topic, but I notice 1 pound N540 at the local S.W. store priced at $43.00 vs $28 to $30 for most other powders. Has it always been that pricey?

 

[spclark]

It was confirmed by VhitaVouri that as these powders age the nitro does move closer to the the surface of the powder kernel and change the burn rate.

Hmmm... thanks for that comment.

I've had a stash of a few pounds of both N540 & N550 on hand dating from 2008 I believe. Been trying (not awfully hard) to sell it off but will cease further efforts in the interests of safety. Hate to let it go to waste but don't want anyone getting hurt either.

 

[Patch700]

It is my go to powder instead of h4350. .. I personally haven't noticed any worse throat erosion with it as compared to h4350 or RL17 .

Having said that I do believe there is a greater chance of having premature throat erosion when used in continuous rapid fire strings or on a busy day on a prairie dog town.

When I was doing a lot of shooting with the 6.5x300 I was using H870 as opposed to H5010 and the same scenario was noticed with the H870 , it was hard on the throats as compared to other powders of equal burn rate but if the rate of fire was controlled it wasn't as drastic as some might say.. It unlike any of the VV 500 series powders was a filthy powder.

The price factor for VV powder in my area is worth it to me as the availability of powders such as H4350 etc are so rare that when quantities do come in the prices are through the roof.... So if I have to pay more for a better product I'm OK with that.

 

[40X Guy]

Wow! That's very interesting and explains why and what happened to me last year as far as the Vihtavouri 5XX series changing burn rate with age. I had a .220 Swift 8 twist rifle built and used N550 dated around 2011 and discovered a load that shot bugholes at 40.7 grains. Ran out of that powder and I had a container of N550 dated 2008 that I switched to and used the same 40.7 charge. Velocity was 100 fps faster and bolt lift was very hard! Actually loosened the primer pockets in the 2 cases I shot! Ended up knocking it down to 39.8 to achieve the same results. The stuff is great powder but i had no clue at the time about why this happened.


As to OP's question, I can't help there as this rifle is a varmint rifle and I only have about 120 rounds thru it and throat etc. looks good as new as viewed thru borescope.

Frank

 

[Brians356]

What other powders, from other makers, are similar to N500 series, and likely to become faster as it ages?

 

[Patch700]

What other powders, from other makers, are similar to N500 series, and likely to become faster as it ages?

Double based ones... However I haven't seen a pattern with those types of powders having their burn rates alter dramatically over time... I have some kegs of double based ball powders that are early 90's vintage and although I always use cautiously they seem to be on part with their original burn rated. (They are still temp unstable too lol)

Any powder given enough time and how it's been stored can have its burn rate altered.

 

[barefooter56]

spclark,
It dosent have to go to waste. Just retest every year by dropping a couple grains and working back up. That "fertilizer" aint cheap my friend! Never has been. Even a Rolls Royce will have its quirks.lol !