ventliner wear, slow vs fast powders

[rkrobson]

Curious to know if those of you who have used a fast buring powder, say vv110 and then used vv120 or vv130, and achieved comparable velocities with the same bullet, was there a noticable difference in ventliner wear, thanks, Ray

[jims]

I saw more wear with faster powders, especially like the now disfavored LilGun etc.

[ewc]

x 2

Lil'Gun wore a new factory vent in 6 shots for me. I should have been giving that a thought as to why.

Hopefully, I'm a better reloader today from that experience and the help of this board.

[Richard]

I believe the longevity of a vent liner depends on the intensity (pressure) of the load versus the powder burning rate. Its the high pressure that wears out the vent liner. IMHO
Richard

[edge]

IMO, it is high pressure and high volume!

If you shoot a bushing and a fouled BP, then you will have less wear. IMO, imagine the barrel is one volume, and the area behind the vent liner to the primer is another.

The pressure wants to equalize. If the area behind the vent liner/bushing is small, then less gas needs to rush through the liner to equalize the pressure!
The corollary is that the smaller the volume behind the liner the faster the pressure will rise...so more primer bulge occurs!

edge.

[rbinar]

Jun 7, 2010 20:18:33 GMT -5 edge said:

IMO, it is high pressure and high volume!

If you shoot a bushing and a fouled BP, then you will have less wear. IMO, imagine the barrel is one volume, and the area behind the vent liner to the primer is another.

The pressure wants to equalize. If the area behind the vent liner/bushing is small, then less gas needs to rush through the liner to equalize the pressure!
The corollary is that the smaller the volume behind the liner the faster the pressure will rise...so more primer bulge occurs!

edge.

You may note that on the last page on rifle construction my web site makes a comment about the inner volume of the breech plug.

The plug shown is shorter (1.6" versus 1.875" for stock) and the vent is recessed. That means the primer to powder channel is only .75" Also there is only one drill diameter (5/32") (there are two drilled diameters in a stock plug) to make the area behind the vent much smaller than a stock plug. This system works well if care is taken with the fit. Normally there's good vent wear and little chance of primer bludges with even a moderaterly stiff load.

Mark's comment above came up when I mentioned never needing to clean my breech plug. What happened was I'm so dumb that I couldn't tell the metal of the plug from the hardened primer crud (a mistake many have made). It was Mark who figured out what was happening. He also figured this lengthed vent life.

[edge]

Good to see you back, you have been missed

edge.

[mike.dawson]

Oh my goodness, welcome BACK!!

Mike

[153]

WELCOME BACK RB. Glad to see you on the board again. Hope all is well.

[ewc]

Good to have you back RB- you've been missed around here.

[deadon]

Welcome back Sir.

[DBinNY]

Amen to that. Welcome back RB.

[Jon]

Welcome back I hope all is well. You have been missed more than you know.
Jon

[edge]

Back to the original thread

There is another phenomenon that I believe takes place partially independent of the pressure.

When the primer is fired, it propels primer crud ( most likely mainly carbon) along with the flame through the BP, and through the vent liner.

IMO, as this progresses it slows and cools when it contacts any surface. When it cools onto the inside of the vent liner it makes a protective barrier for the vent ID.

The main charge is ignited and sends hot gases back through the VL eroding the carbon crud and sometimes some VL metal.

Under certain conditions the primer crud deposited essentially equals that removed during the second pulse. When this happens the VL will last nearly indefinitely since there is no metal wear!
Under some conditions the carbon crud will actually build up and the VL restriction will be reduced, and can get to the point of interfering with ignition!

edge.

[artjr338wm]

RB welcome back as well.
Edge am I wrong to extrapolate your comment to the conclusion of you can actually clean your drill bushing breach plug to well and the removal of ALL carbon deposits will actually lead to more wear on your drill bushing insert VS if you have left it in a condition of being slightly carbon fouled indefinitely?

RB FWIW, your drill bushing modified breach plug has 700+ shots on it and it is still going strong with a flash hole opening BTW .0315 and .032"

Thanks,
Arthur.

[edge]

Possibly.

I once had a drill bushing that started @ 0.024 and started getting very low velocities with Lil'Gun. When I cleaned the bushing the hole was reduced to about 0.013 IIRC.

You can have too much of a good thing

edge.

[rkrobson]

Thanks for input, there is definitely something to the breech plug phenomena, the reason I ask is I have an Ultimate that has a plug 1.595 oto in length, with a primer hole of .055 for 1.3 and a flash hole of .042 for .295. These do not generate excessive pressure at the nipple(using 45 win mag case) and the plugs last a very long time, mostly shot with 4 Pyro pellets and 3.5 T-7 mag pellets. I have shot several pounds of vv120 (not recommended)with owners knowledge, very accurate, and it takes about 5 grains les than a comparable load did in my Savage. Just some food for thought, Ray

[jims]

RB: Nice to hear from you. I got a nice deer with your .40 last year.

[dave d.]

:)ray its probably the shorter flame path and larger vent hole that is giving you higher velocitys in the ultimate.