Throat Erosion

[Kodiak99317]

I have been keeping a very close eye on the amount of throat erosion on my 6/250 Imp. I’m shooting 105 Lapua bullets set to just touch the lands with 37.1g of H-4350 at approx. 3070 fps and after 730 rounds down range, my seating depth has grown .029” longer. Not a big problem since I can chase the lands for another 3000 rounds approx. if need be or until the barrel goes south.

I know my old smith told me back when he shot Silhouette, using W748, after one year, he had to move the seating depth some .080” to maintain the “just touch” mark and the following year, he switched to N202 and after another year, he only had to move the depth of the bullets out another .008”.

I’m using H-4350 since I’m in Canada and Higginson carries it so no worries about running short, same reason I use Lapua 105’s, easy of getting more. I did not want to use components that I can not get easily in Canada.

I read on one forum that H-4350 was a real barrel burner, something was in a post like "If you want to burn up your barrel, use 4350 for 1000 rounds." Is this statement true about H-4350, being a barrel burner?

How does H-4350 compare to the Viht powders,i.e., N-150 or N-550 or N160), or say Varget regarding throat erosion?

Finally, does jumping them reduce the erosion any vs "just touching"?

No sense trashing a good shooting barrel too soon eh!

Measured again at 911 rounds,Sept 2) and it is at .034" back... should get 4200 rounds or so with some luck and still have .100" of bullet hold, if the barrel still shots after that many.

 

[sewwhat89]

The folks I have talked with mention that in some calibers like .243 WW and 6.5-284, you can burn a barrel out faster with H4350 than if you used H4831sc. The strongest statement I have heard about burning out a barrel was concerning N500 series powders. All I have seen concerning them is they may or may not shoot good and get you the performance that you are looking for, but they will roast your throat quicker than other powders. I don't want to perpetuate any myths, so if you know contrary, speak up.

 

[M700]

Am very interested in this subject. I use H4350 pretty much exclusively in my .25-06 and also in several other rifles...

Not that I was expecting great barrel life from the .25-06 anyway...

 

[JER]

H4350 has been widely reported to give poor barrel life in 6 mm cartridges. In 6.5 mm cartridges, such as 6.5X55 and 260 Rem, barrel life averages 3000 to 3500 rounds.

Forum member Joesr has made some very interesting discoveries/developments to get 3000 + rounds of accurate barrel life from a 243 Win and his 243 Win-based 6 Competition Match cartridge by using H1000, not exceeding 3000 fps with 105 grain-class bullets, and keeping the throat smooth using JB or similar products.

His reasoning and experience is enough to sway me and my next barrel is going to be in 243 Win. If it doesn't pan out, I'll still have all my 260 Rem brass and dies.

Do a search under his member name.

 

[Silverfox]

I don't pretend to know much about which powders accellerate throat erosion, but I have been favorably impressed with the performance I get using N-540 in my .17 Remington using 30 gr. projectiles. N-540 also seems to be extremely well suited to the 25 gr. V-Max bullet in my .17 Remington that has a stainless steel super match grade Pac-Nor barrel with a 1 in 9" twist and three grooves. I guess I will probably be able to report some actual "first-hand experience" with throat erosion in my Pac-Nor barrel down the road a wee bit. I have ordered one of the bore scopes James Phillips has offered for sale over at the Benchrest.com Board. It is a rigid 17" bore scope that can be used for my two .17 Remington rifles.

Anyway, I thought I'd share some information directly from the Vihtavuori Lapua Web site concerning the 500 series powders:

N500 series

Adding nitroglycerol to the traditional single base powder makes possible in addition to geometry and coating a third controlled variable of ballistic properties: energy content. Vihtavuori calls powders that have nitroglycerol added,maximum 25%) high energy NC-powders, which form N500 series.

Adding nitroglycerol to the high energy N500 series is done by impregnation. After that, the grains are coated with a new type of chemical which results in very progressive burning characteristics.

The composition of a typical high energy powder is as follows:

* nitrocellulose * nitroglycerol

* coating agent * stabilizer

* flame reducing agent * wear reducing agent

Geometrically the powders in the N500 series are equal to the N100 series. Although these new powders have a higher energy content, they do not cause greater wear to the gun. This is because the surface of the powder has been treated with an agent designed to reduce barrel wear. N500 series powders work well at different temperatures, even better than the traditional N100 and N300 series. Temperature sensitivity naturally depends very much on the weapon and on the cartridge. The manufacturing technique employed permits a very high bulk density, which in turn makes it possible to use a bigger charge in a certain limited loading volume.

The words "flame reducing agent" and "wear reducing agent" caught my eye, but I don't know if the "flame reducing agent" is intended to reduce throat erosion??? I would believe that the "wear reducing agent" should help reduce throat erosion, but that doesn't keep the temperature down.

 

[paulT]

Silverfox, was myself interested in finding out if the use of vit n165 with lapua 90 and 105 scenars would prolong barrel life versus the use of hotter faster propellents such as varget or n150 etc, accuracy in my factory Blaser Lrs2 rifle with 243 match barrel is exellent with 48.6 vit n165 molly 90 scenars, seated into lands,one three shot group measured 0.362 out to out measurement at 200y and that was prone with bypod, i know ill have to repeat loading at range on bench etc to confirm accuracy but my gut feeling is that its a good load for my rifle, also noted exellent groups using vit n540 with molly 155 scenars in my 308 barrel, the vit series of powders are exellent, wonder if they will give away the secret recipe they use for the lapua factory ammo its extreamly consistant, regards paul T.