depth of lube grooves?

[runfiverun]

okay here is the question.

if your lands are .004 tall and you are trying to get higher velocity.
what depth would you want your lube grooves to be.
.003 just under your land height so you have lead to steel contact?
.004 so it is just touching the lead.
or would you want .005 so that the boolit is actually riding on the lube.
and only touching the lands on the sides.?

lets hear it and why?

[leftiye]

I think that most lube grooves are from .015" and on up. Those shallow lube grooves that you describe might not carry sufficient lube. Remember that the barrel generally doesn't touch anywhere in the area of the lube grooves.

[MtGun44]

lube is forced out to lube and seal between the boolit and bore.
It is consumed as the boolit travels down the bore, so you need a lot
available for a long barrel, like a rifle. Think of the groove as a storage
tank full of lube, and also as a lube applicator. You want plenty of lube
and well applied. The boolit is guided by the bands, sealed and lubed
by the grooves.

Bill

[crabo]

Is there a disadvantage to too much lube and how would you tell if it is a problem?

[Bass Ackward]

Depth depends on how much your bullet carries and where it is located vs your bore condition as to how much you need.

The advantage of lube grooves deeper than the rifling height is that it allows the hydraulic pressure to equalize and thus have the lube flow to where it is being consumed 360 degrees. That means that your bullet can carry less and still do what is needed. That also means that you can have more of your bullets weight in drive band width resulting in a stronger bullet. Obviously, if lube is trapped between two rifling and not being used while another space is empty, then you have a lube starved situation.

If the quantity of lube is too great in that section and the hydraulic pressure gets too high because of a high spot down the bore, then the bullet is going to size down and allow the lube to squeeze out either forward or back. Back is not good as that then allows hot gas to replace that volume and now that section is starved if it isn't cut too.

[BABore]

Is there a disadvantage to too much lube and how would you tell if it is a problem?

Yes you can have too much lube in some cases. It usually shows up as either a cold bbl, first shot flyer where the excess lube has congealed in the bbl, or a lube purge flyer during a string.

For every velocity there is both a quantity and quality of lube that is required. In most every case, in my guns, best accuracy is obtained at the point where the lube is almost completely used up. Usually where you just start seeing a light grey wash. Additional velocity will open groups and can start to cause light leading. Less velocity may also open groups slightly and you may encounter a lube purge flyer on occasion although I usually see the cold first shot thing going on.

You need to have an arsenal of lubes available to you and be able to read the signs. I've pretty much settled on two lubes for HV pistol and rifle loads from 1,600 to 2,500+ fps. They are a custom lube outlined by 357Maximum, and LBT Blue or Blue soft. The LBT is for the most demanding conditions. IMO most of the commercial rifle molds like Lee, Lyman, and RCBS don't have enough capacity. If I'm going to use one of them at above 2,000 fps I'll reach for LBT lube. It will usually get you upwards of 2,200-2,300 fps before their limited capacity bites you. Not much you can do after that. Your bbl condition also has a great bearing on this break point. IMO you treat lubes like you do powders. It's another variable that must be tested for every load.

[runfiverun]

ba's second paragraph above.
would explain why i have to shoot a couple then move on target[a given]. and after about 15 shots the group will shift down and to the left just slightly.
the group also tightens up. and i can shoot untill the bbl is too hot to continue.
i have always attributed this to the lube in the bbl coming up to temp and working with the boolit's lube to the end of the bbl.
i haven't cleaned this bbl for going on 2 years now and the results are repeatable hot or cold weather.and this is the only load this rifle will ever see at this point.
but got a new one to play with and i am trying to just put a picture together.
step by step manual if you will.

[Bass Ackward]

For every velocity there is both a quantity and quality of lube that is required. In most every case, in my guns, best accuracy is obtained at the point where the lube is almost completely used up. Usually where you just start seeing a light grey wash. Additional velocity will open groups and can start to cause light leading. Less velocity may also open groups slightly and you may encounter a lube purge flyer on occasion although I usually see the cold first shot thing going on.


Me too. Best accuracy occurs just before leading begins.

[leftiye]

Sounds like maybe less of a gooder lube might be the way to go? Maybe a lube that coats very thinly, doesn't lump up or get real hard (maybe just plain doesn't get hard?) made of a primo oil like jojoba, or bullplate lube (speed green) with Carnauba?

[crabo]

The LBT molds have very shallow, rounded lube grooves. Quite different than the idea of square based lube grooves that are towted on the SWC design. Veral's lube and boolits have some very good reviews. There might be something to the idea of a less amount of a very good lube.

[BABore]

Sounds like maybe less of a gooder lube might be the way to go? Maybe a lube that coats very thinly, doesn't lump up or get real hard (maybe just plain doesn't get hard?) made of a primo oil like jojoba, or bullplate lube (speed green) with Carnauba?

The boolit's lube groove or capacity dictates the quantity. Unless your dealing with a Loverin-style, or multiple lube groove boolit, your stuck with it. It is what it is! Now you must adjust your lube's slickies to match your velocity. Most lubes have just plain too much slickness. It's a real fine line when your dealing with top end accuracy. Lube problems are seldom encountered at normal (Lyman) book speeds. They come about when your pushing the envelope with HV pistol or rifle loads. This is not to say that low end loads can't stand some testing or tweaking too, cause they can. Bottom line is don't marry yourself to any one lube. Speed Green, FLWFL, LBT, Carnuba Red, and the like are all good lubes and may have their places, but any one of them is not the answer to every load. It's no difference than saying you use Unique for all your pistol loads and that's as good as it can get. If your easily satisfied, fine, stick with one lube for all your needs. If you want to squeeze that group down to the best it can be, don't stop tweaking.

[leftiye]

BAB, Understood, but what if - you could have any lube groove size that you wanted? Say you could make your own molds for instance.

[BABore]

BAB, Understood, but what if - you could have any lube groove size that you wanted? Say you could make your own molds for instance.


I do just that.

You error on the side of caution. Make the lube grooves wide enough and deep enough to give a more than adequate supply. That gives you the option of using a simplier lube (less slickies) should the high end stuff prove to be too much. Should you skimp on the capacity, then your trapped by ONLY being able to use that same high end lube, or you are velocity challenged because of it. You also have to pay attention to the width & depth of lube grooves, where they are positioned, and the adjoining band size. Picture a 45 colt Keith-style boolit with a 0.075 long base band and wide deep lube groove. How will it react when kicked in the pants hard? Lots to consider.

A good way to start is to select a bunch of boolits that typically provide adequate lubrication at the velocity your shooting for. Calculate the lube volumn in cubic inches. Calculate the square inches of bearing surface from the full diameter bands. Then do a ratio. You'll find a set of values to establish a baseline. Now select some known lube starved boolits and compare the values. This should start to paint you a picture on what is needed. Be aware that bore ride noses don't have the same lubrication needs as full diameter noses.

Hope this helps some.