Nagging Question "Lube Grouve Locations ?"

[quicksylver]

Recently I was looking over some pictures I and others have posted on this and other sites.

Quite a few of them were pictures of different bullets side by side..

Some (mine) were of two bullets one NOE and the other Lyman both 299s'.

What I noticed was a striking difference in the location of the lower drive band and consequently
lube grouve...

Then I got to looking at other bullet designs..what caught my eye there was the size of the lube grouve just above the gas check...that's when I started to ask myself... ."why do those designs supply such a large amount of lube to a gas check ?"

My secondary thought was...."would it not be better to have a small lube grouve towards the back / just above the gas check ..with a wide drive band above that and a decent lube grouve (s) above that ?"

Seems to me that would place more weight towards the rear of the bullet and supply lube where it is most needed.....good things right?

Your thoughts...??

Lyman 311 334 Large lube area above gas check

Large and small lube area above gas check


PS... hope this is not out of the topic of "lube"

 

[Ian]

One of my pet peeves about NOE is that in an effort to offer customers the options for both plain-base and gas-check designs, the compromise doesn't work out well for either.

The Lyman 311299 in the photo above represents a good design. The space in front of the gas check is critical, this has been tested and proven. No space, meaning perfect gas check fit, doesn't shoot well, particularly at high velocity. Likewise, accuracy suffers when the space above the check is too great. You need about a fingernail thickness of lube in front of the check, and in front of that, a driving band of decent length, but not too long. 25% of caliber is a good, all-around length for a driving band on a rifle bullet.

 

[quicksylver]

Ian...Thanks for the reply.
Interesting

Would you say that all the lube above the gas check on the 311334 was more a matter of bullet design than a need for lube in that area ?

Would it be a better design for delivering effective lubrication if the lower driving band was moved back and the larger lube grouve was in front of that ?

 

[Eutectic]

One of my pet peeves about NOE is that in an effort to offer customers the options for both plain-base and gas-check designs, the compromise doesn't work out well for either.

Boy! Is this a true statement!!!!

Many NOE gascheck mold designs have a very narrow band above the gascheck shank because of this. Some of these shoot OK for me and others don't..... Also this trait may be gun specific! It is a flawed design technique to me because if there is ANY tendency for the base section to enter other than perfect during launch this is an Achilles Heel.....

Any cast bullet I design will have a short gascheck shank with nil groove above it. then a base (or first from bottom) band at least .100" wide. If plain base I like .125" wide base band to help gas cutting. I have proved these specs out quite a few times as I will modify bullets in my little jeweler's lathe to compare accuracy with different lengths.... In other words I like the lowest grease groove up farther on the body than a lot of designs offer.

Pete

 

[quicksylver]

Boy! Is this a true statement!!!!


Any cast bullet I design will have a short gascheck shank with nil groove above it. then a base (or first from bottom) band at least .100" wide. If plain base I like .125" wide base band to help gas cutting. I have proved these specs out quite a few times as I will modify bullets in my little jeweler's lathe to compare accuracy with different lengths.... In other words I like the lowest grease groove up farther on the body than a lot of designs offer.

Pete

If nothing else it seems to me it would get the lube where it is most needed.

 

[Ian]

The space above the check really doesn't have anything to do with lube. It has to do with how the gas check settles on the shank and how the alignment is handed from the rear band to the gas check as the rear end of the bullet goes into the rifle's throat. Having a little bit of "wiggle room" between check and rear band has proven beneficial to high-velocity .30-caliber shooting. My theory is that having the space helps prevent the base edge of the check from getting too squared-off. Square bases get trailing edge points from metal displaced by the lands (one of the big challenges of the Swedish Mauser with very wide lands) and these points can be irregular or break off unevenly, causing a lateral side-step at muzzle exit. If the check is crammed against the rear of the driving band in front of it, displaced metal has nowhere to go other than extrude the base of the bullet somewhat, and that also increases trailing edge points and the chance of the base getting out of square with the line of departure.

 

[RBHarter]

The shank overall is a bother with so many designs intended for the long necks . Great bullets that shoot great but you can only lube the top groove because the bottom groove and check are swinging in the case . 308 is a prime example .

 

[popper]

I'm not a 'greaser' but I'll try to present some logic. Some tolerance is needed on the length of the shank - base gets hit with pressure, Pb needs a place to move - there is 'some' space under the GC. Lots of lube above the GC means you 'lube' the case neck when fired - what does that do to neck tension? Does a lube have enough 'body' to prevent Pb from filling the mouth to throat space? IMO, mould 'copies' were for specific alloys & lubes and the design may not apply to other uses. If we assume the most demanding need for lube is at the chamber end - does the bore-rider section need lube? I guess one reason for coating or T/L - L.G.s aren't part of the equatio.

 

[Eutectic]

.012"- .015" shank above a crimped on sized gascheck show no impingement issues for me. This includes fired samples as I'm a 'stickler' for multi-faceted testing procedures! This said I don't have 'Swede' experience....... I see a Norwegian every day in the mirror if that counts??

I have shot NO CLEARENCE as well...... In the majority of tests I didn't get any accuracy degradation even though extrusion damage was clearly visible on fired samples?? So maybe 30-35% shot worse. Just another example with cast bullets why everything needs a Physical Test!

If the last step of bullet prep is a swaging operation they can be tight like a half jacket without trouble for me. A tidbit probably no one cares about.

I use mostly Hornady gaschecks annealed dead soft. I shoot a lot of .22 & .25 caliber and here gaschecks are thinner material.... .35 caliber are as well. These are less critical than a nice thick .30cal Hornady..

Testing trumps assumption for me more times than I care to admit!

Pete

 

[Ian]

Funny thing about testing is the devil is in the details when two people compare notes. 99% of my tests were done with Hornady checks straight from the box, and maybe 5% of those tests done with 6.5mm checks with the remainder being 30-cal.

What I found with 30-caliber is that anything more than .010" clearance to the bottom of the front band proved sufficient for accuracy. I was doing this test concurrently with Joe and in addition I used two different bullet styles to test the effect of varying the check to band spacing. Check shape, thickness, and state of anneal are variables which can affect a lot of things. Filing the shank down for a full contact with the rear band degraded accuracy reliably with two different 30-cal bullet designs pushed over 2200 fps. Squaring and sharpening the bases of seated checks also degraded accuracy, not sure why. I wasn't able to recover bullets well enough during that phase of testing to determine of the trailing edge extrusions were even or not, but the purely empirical data suggested an ideal range of gap. I find your results with the checks swaged to an almost "half jacket" interesting, all I can say is the rest of your system must be very much squared away and the trailing edge extrusions quite uniform.....if such is the case and they don't break off, then all is well. When wiggling a bullet through a loose neck, a lot of "fudge factor" is needed regarding the trailing edge and extrusion should be minimized.

The Swedish Mauser will eat your lunch with metal displacement and launch alignment. Getting neck clearance to nearly nothing is a good start, but even then the bullet base will get mangled. Without a precisely metered amount of buffer behind the bullet I never was able to get decent velocity without destabilizing the bullet.

 

[fiver]

the long shank is also an unsupported area of the boolit.
on a 30 cal the shank is 284-5 in diameter a long shank it isn't gonna touch steel.
well it probably is after you put 40-k of pressure on it while the front half is trying to cram into the hole.
hopefully it's straight.
I personally prefer a single lube groove right above the rear drive band [and like Pete] a pretty fixed distance from the check mouth to the rear drive band.
just enough to let displaced metal roll into the space.
I'm still kicking back and forth on whether to fill the space with lube.
on one hand the lube provides some strength right there, on the other it is more lube that can get blown out and around the case.

I think if I were dealing with a long shank I would lube just that part of the boolit and shoot it against one not lubed there at all and see what I got.

 

[quicksylver]

Does all of this maybe suggest why I get better accuracy out of 30 cals with the Lee 160 Tl as opposed to the Lee 155 ?
Or are there other stronger variations taking affect
Both are sized .310 and lubed with BR and BLL.
I am showing different checks but when all are prepped the same the 160TL has the edge.

 

[Ian]

It suggests why, but to extrapolate conclusions is about as thin as the ice upon which I base my own opinions of gas check clearance. Even in my own testing with bullets cast from the same mould, to modify the gap involved shortening the bullet ever so slightly or shortening the check, either of which introduce their own variables. One might say of the examples above that the shallower grooves of the TL bullet might help alignment and concentricity by "riding the bore" as compared to the bullet with deeper grooves. Who is to say for certain? Sometimes, to say empirically "bullet A shot better for me in my 'system' than bullet B under the same conditions" will have to suffice.

 

[quicksylver]

Ian...I am familiar with that ice.....I usually just shrug my shoulders, accept the results and walk away...never really knowing WTHH.....

That's why we're lucky to have people like you on this site...at least someone like me can get a plausible explanation of what's happening..

My conclusions so far are:
1. a large area of lube above the gas check is more a function of bullet design than need for lube in that area;
2. it naturally follows that that space just gets filled with lube 'cause there is no way around not doing so.
3. a large lube area there can actually hamper accuracy in a round where the bullet base sticks below the case neck..

 

[fiver]

nevermind that the lee 155 just has the lube grooves and drive bands in the wrong place.
look at it, the lube groove should be in the front half of that drive band.
everything should be sucked back.
the COG is all wrong.

 

[Ian]

Ian...I am familiar with that ice.....I usually just shrug my shoulders, accept the results and walk away...never really knowing WTHH.....

Drives us nuts sometimes, doesn't it? Lust for answers has led me to stretch the breadth of conclusions farther than they should be and commit other errors of the scientific method, but, sometimes repeated experience will leave us with some definite prejudices that hold true for a lot of different gun systems...at our house. Maybe not at anyone else's. All I can do is throw my experience and opinion out there, such as it is, and let everyone else mull it over for themselves. When considering a .30-caliber bullet, I personally will never pick one with a gas check shank that doesn't fit my concept of "right", which is a pretty narrow specification.

I would generally agree with your conclusions #1 and #2, but for #3 might add that a large space above the gas check might hamper accuracy whether the bullet is all in the neck or not.

 

[freebullet]

I shoot checkless more than anything else even with gc designs so, I'm fond of bullets without a bunch of empty space/shank at the back. In your examples I'd go with the lyman & lee 160 designs.

 

[Bret4207]

I am of the opinion that we haven't really figured out exactly how lube functions quite yet. I theory it's actually lubing the bullet. In practice it's depositing lube, functioning as a seal, supporting the grooves somewhat and probably a few things we haven't considered yet. Placement of the groove should affect things like propensity of a given design to lead a barrel, but we already know that's not true. Loverin designs should be lead free, but they can lead as bad as anything. In short, we don't know what we don't know! At least I don't.

Yes, I agree you need a space, someone said about a fingernails worth, above the GC so they can seat completely and uniformly.

My 2 cents and worth just what you paid for it.

 

[Eutectic]

I sense everyone's frustration in this thread! I have it as well! We have a complex multi-faceted situation going on and we basically are facing it blind! Ian is right in saying each of us have 'evidence' from personal experience of what works for us..... And even this at best, may not always be the case!

It's a lot like the favored quarterback in the Super Bowl having to play with a blindfold on

If we only had a method to photograph (in slow motion) the bullet's launch!! And watch C.O.R.E. in action..... Then we maybe could get a record of 'constants'...

It's like engineering in Braille.

I have two NOE molds for a modified RCBS .25 cal 85gr bullet. The bullet has two lube grooves... I only use the bottom one. The second mold I removed the bottom lube groove. The first had been shooting moa and always blew back lube on the neck of the case.... The second modified bullet now is even more accurate at the moment and no lube blows back?? I think the lube groove more forward seals in the throat prior to losing a perfect 'seal' to the rear in the 'jump' so to speak.... But do I know this for sure? Does the modified bullet shoot better because rearward seal is better or something else?

Braille may be good for reading but cast bullet experimenter's need a slow motion view to know what we think we know, so to speak!

Pete

 

[Brad]

Slow motion is possible but it isn't cheap. High speed cameras cost a bit.
If cost weren't an issue it would be interesting to have Tom cut two moulds that differ only in lower lube groove location or size for a fair compairison. Actually, he could cut a single 2 cav mould with the cavities being different.
Would be an interesting study.