hypothetical situation

[fiver]

it's winter and well you know it's winter.
so let's discuss a little situation I'm running through my head. [stop laughing]

lets discuss a low neck tension low friction bullet situation we all could face if we so chose.
here is the scenario.
a rifle that has seen a number of jacketed rounds through it.
the bullet is sleek and streamlined, it's also lightly coated with a glossy powder and cooked making it even more slippery.
slippery like it's hard to hold onto slick.
the neck tension is about .001 under the diameter of the bullet.

which direction would you go with.
A. the powder speed
B. the distance to the lands
C. assuming you could reach them

lets say the cartridge is the 30-06 or the 308 since it seems to be getting as much discussion as about anything lately.

 

[popper]

Well not 308 but RD in Marlin 336 30/30 < 2 thous., using veggie oil TL (can't get much more slippery). LeverE at full throttle. Worked great! IIRC I was taper crimp then with hard alloy. Wipe a spirepoint jax (168 Amax) with just a TINY dab on your finger, then try to pick up by the nose with your other hand. No cooking needed. I stopped doing that, heck of a time trying to seat a bullet you can't hang on to.

 

[Ian]

Well, since all you left us to work with is the static inertia of the bullet, I'd go with the fastest-burning, most easy to ignite uniformly powder that would work for the desired velocity within the pressure limits of the system.

Such as...

My pet .308 load using slippery PC bullets and a pretty big, empty space out in front of the bullet. Who woulda thunk that a 70% case load of RX7 under a 174-grain cast bullet would get 2550 fps from a 22" barrel? I AM running almost two thousandths of neck tension though.

 

[fiver]

it's all about the slippery 'no' friction run to the muzzle.

 

[Spindrift]

Low neck tension, slippery bullet (and winter temp) would affect the powder burn of slower powders. As Ian said, the fastest powder that could satisfy your velocity requirements. I would probably try Viht N110 first (I love it!).

Chosen COL would depend upon bullet design. With a bore rider, I would seat to the lands- if possible. With a self-aligning bullet, I would also seat to the lands if I could- while retaining a decent (one calibre-length) bullet grip in the neck. Otherwise, the self-aligning bullet gets to jump. A crimp might be helpful.

 

[Will]

In that situation I would hope that I could close the bolt and get the bullet to jam fit in the ball seat area. I would most likely use 4350 or 4831 powder.

 

[Bret4207]

Low neck tension sounds like fast powder time to me.

 

[JWFilips]

Fast Powder and On the lands for me

 

[Bret4207]

Yes, by all means, seated as far out as practical. Missed that earlier.

 

[fiver]

okay so we all went with a jam fit and a fast powder.
everybody but Will [who cheated off my XCB tests... LOL]

the next question is why?
if we have the fast powder all ignited by the primer before the pressure is high enough to fully engrave the bullet what do we gain?
the second part of that is,,,,, since we don't have a start stop situation staring us in the face would any of you choose one of the super slow ball powders like H-110 or AA-1680?
we ain't talking over the top speeds here unless you wish to base your answers on that premise.

 

[Intheshop]

Lost me first on the powder coat..... then low(.001) tension. Ain't doin either here.

 

[Ian]

It was hypothetical.

More food for thought. My observations have been that jumping or jamming with PC doesn't make nearly as much difference to shot start initiation pressure as with regular lubed cast unless a really tough alloy and/or seriously oversized PC bullet is used. Since my most successful PC loads have been with softer alloy like straight wheelweights at 12-13 bhn or even softer alloy bumped back up with tin, have been sized to about halfway between jax and normal cast, then playing with seating depth has little effect on initial pressure. The primer drives the powder column and bullet out of the case easily either way.

What kicked my butt was switching to PC, undersized bullets in my BLK carbine with carbine length gas system. Had to go up nearly a grain of RX-7 to get my function and velocity back because there wasn't any way to get back all of that engraving resistance lost with the small, soft, slippery bullet that would go up the barrel several inches with just the primer.

When I have time I'll model something in Quickload to show the difference that initial resistance makes to the shape of the burn curve.

 

[fiver]

it might even show the engraving bump in the predicted pressure line from a normal start.

 

[Mitty38]

Ok you guys are a little out of my league but I am understanding a little here. I'll play.
Do not think I would want to go as slow as h110 with that.How about some H335, or some IMR3031 in a starting load, with a magnum primer to help make up for the cold weather temperature sensitivity. Then seat with the longest oal as I can get away with.
If I am way out there just tell me to shut up.

 

[Will]

H110 is actually pretty fast compared to H335 or IMR 3031.
I can’t imagine H110 or AA1680 being safe in this application. And I’ve never had luck getting either powder to shoot without some compression.

 

[Bret4207]

My choice was because you said the situation was one where a slower powder that likes some resistance to get a clean burn would have been difficult to get burning right. No mention of crimp, a skinny, slippery bullet and you may not be able to get it into the throat. To me that says use a faster, easy to ignite powder. It's not a case where we have much choice, or at least I didn't read it that way. I'm not a fan of depending on "obturation" to mash a bullet up a couple thou to fit the throat, but sometimes that's your only option. That's the way I read this scenario.

I've never worked with the super slow powders at all, but I suppose a case full seated to the bullet base might keep the bullet from moving back. How it would burn is beyond my experience.

 

[JWFilips]

I never liked slow powders with seated in the land bullets ( however my experience with them is with jacketed bullets back in the 1980's) Easy for me to begin my load with a cast rammed in there but Jacketed alway scared me! I backed off 2 thousands when working up a load. My casts are soft and PC coated and I only shoot low node so I guess my info does not pertain to much here!

 

[Brad]

Faster and slower are relative terms. With PC and a worn throat I would go maybe 1 or 2 faster on burn rate chart than “normal”. Instead of RE 19 maybe RE 15. Would consider RE 7 too.
Would I want to go to 2400? Not unless I wanted to stick in the 1700 FPS range tops.

The slick bullet and worn throat won’t give the resistance needed for a good ignition with slower powder. I would worry about inconsistent velocities with slower powders.

 

[JWFilips]

My pick would be Re 7 also

 

[Ian]

I interpreted the question same way Bret did. Jamming the bullet as much as posdible to create a load for the powder to work against from the outset allows the use of more heavily-deterred powders, and vice versa.

Mitty, think about H110 for a minute. Not just where it is in the burn scale (which really only means relative burn rate once it is lit), but the pressure required to MAKE it burn. AA1680 is another hard to light but fast powder. Hard to light means it takes lots of pressure and hot ignition in a tight space in order to defeat the deterrent coating and get it going past the smolder point.

This is why you wouldn't simply advance from Alliant 2400 to H110 to 4198 in your .30-'06 when working up velocity. Different kinds of powders have vastly different purposes, applications, and overall characteristics. The point here is to investigate the differences and exploit them to uour advantage.