6mm cm
- Thread starter bedrock
- Start date
Hi coyote i ran the numbers on teh 105 hybrids they are an option to look at. I MAY have access to a large quantity of 115 dtac so i am still going with the 115 and most like the matrix bullets.
Longshot.
There has been several reports of guys getting in excess of 3,000 rounds down a barrel the shoulder angle and powder choice seem to have a hugh affect on barrel life.
Longshot.
There has been several reports of guys getting in excess of 3,000 rounds down a barrel the shoulder angle and powder choice seem to have a hugh affect on barrel life.
Shoulder angle making a big difference to barrel life? Now I've heard it all.
Powder choice making a difference I can believe but it is going to take some serious convincing to make me believe that a few degrees difference in the shoulder angle is really going to make a difference in the barrel life. YMMV.Shoulder angle making a big difference to barrel life? Now I've heard it all.
Don't take my word for it research it yourself.
cheers
Trevor
ok for a less flippent remark
"Mark"
One of the biggest culprits that contribute to barrel wear is throat erosion. Upon firing, the explosion of the primer forces the bullet into the throat of the chamber where contact with the lands is made. Of course, now there is a mixture of burning and unburned powder in the case and in the throat. As pressure builds, the bullet is forced into the rifling and up the barrel. Depending on the angle of the shoulder of the cartridge case, there is a concentration of hot gasses and abrasive unburned powder at the point of these angles convergance.
To explain, looking at the case of the old .300 H&H, you see a long tapered shoulder. If you draw lines following to the point where these angles converge, you see the turbulence point is well into the throat, possibly into the rifling. A different example is the .284 Winchester. With its 35 degree shoulder, the lines converge in the case neck. The 30-06 and .308 case lines converge just outside the case mouth, in the chamber throat. With these different cartridge designs also come different amounts of abuse of the rifles throat. Even with advancements in quality of steels, not much is going to stop this bombarded area from eroding. Stainless steel will help some, but not dramatically, perhaps 15 to 20 percent. A notible reason for competitive shooters using stainless, is because a stainless barrel's accuracy seems to fall off all at once. With a chrome moly barrel, it will shoot great, then start to tease you with throwing shots out every so often. This gives symptoms of something else wrong, hence the need to keep good records.
What throat erosion looks like is a dry mud puddle, with surface cracks in the steel. Advanced cases of this malady will cause copper fouling and high pressure signs. The copper fouling is sometimes deposited evenly in the length of the barrel, deposited there by hot gasses and powder traveling up the barrel during firing. This could almost be described as a copper plasma coating.
remarks from the designer of the 6mmSLR
The .243 Win is a bear on the throats of barrels in part because of its case design (i.e. short neck and 20˚ shoulder angle) which has a tendency to put the focus of the hot gasses right up in the barrel (i.e. people call it a "barrel burner" for that reason). Both the 6CM and the 6 Super LR have longer necks (6CM only slightly longer, and 6 Super LR a lot longer) and steeper shoulder angles than the .243 Win. (6CM 31˚ and 6 Super LR 30˚) which changes the focus of the gasses and the efficiency of the cases. Running slower burning powders can help as well (H4831SC, H1000, etc. that provide more push further down the barrel than back at the chamber).
http://www.gunsmiths.com/articledetail.php?id=95
http://262neck.webs.com/theriflescartridges.htm
A long case-neck is desirable - not just to hold the bullet in alignment but also to keep the 'turbulence-point' within the case neck. The turbulence-point is the point where the shoulder angles would intersect if extended. Most accurate cartridges exhibit this characteristic.
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