Distance from Bullet base to lube groove

[MSD MIke]

I would be interested in thoughts about what affect the distance of the bullet base to the lube groove has on bullet performance. As an example the Lyman 358311 has a greater distance than does a lee 358-150-1r. Does it make no difference or is one more suitable for certain things than the other?

Thanks
Mike

[longbow]

It'll certainly make a difference in case volume if a boolit is seated deeper or shallower. Less volume = higher pressure for same weight boolit with same powder charge. In this case the 358311 is 160 grs. vs the Lee 150 gr. It may also have a different nose shape (longer) so may require deeper seating.

For many guns OAL is the limiting factor so boolit seating has to accommodate feeding, cylinder length, chamber/throat, etc. Different weights and nose shapes may require different seating depth to function and that will affect pressure. All same weight boolits are not created equal and some guns have longer throats or cylinders so can tolerate boolits seated out which gains powder room at safe pressure.

You may see some group buys for boolits designed specifically for long cylinder revolvers or single shots where longer heavier boolits can be used effectively or same weight boolit seated out for greater powder capacity. Many boolits in group buys now have multiple crimp grooves to allow use in several different gun designs so where the boolit can be seated further out there is a benefit.

Longbow

[Guesser]

I experimented some years ago, using two obsolete Ideal molds. #357443 and 357446. 43 has a narrower base band than 46, What I found to my satisfaction was that 46, with the wide band needed to be pushed harder to get acceptable accuracy from my guns. For my use I limited the 357446 to near full power loads in 357. The 357443 would shoot accurately from the same gun at 38 Special levels as well as full power 357 loads. Just me playing around a long time ago. I sold off the 357446 mould and still use the 357443 in Special and Magnum rounds. Move along....nothing scientific to be seen here; keep moving....

[Harter66]

Typically a heavier/thicker plain base will manage higher pressures but 9mm and 357 mag designs seem to work fine in 38s . Many of the NOE designs for gc are available pb which gives things like the 312-230 almost a quater of an inch of base band .

Aside from pressure bearing and bearing surface I don't know that the base thickness makes a big deal.

[John Boy]

I shoot both these Ideal bullets loaded with black powder or smokeless with accurcy. IMO, the size of the base is immaterial, it is the overall design of the bullet that counts:
182734Ideal 31947 - 210gr
182735Dr Hudson design, Ideal 319273 - 185gr

[JSnover]

Does it make no difference or is one more suitable for certain things than the other?

Thanks
Mike
No difference. The size, shape and number of grooves, maybe, since they affect weight distribution but that probably only matters with deep, wide grooves vs. narrow/shallow ones. In the end all you really care about is getting enough lube on the boolit and most of them have all the grooves they need.

[tazman]

That distance is one of the things I look for. I get better accuracy when the bottom driving band is longer to the first lube groove. Not certain why but it works for me.

[longbow]

Sorry, I misread and was thinking base to crimp groove. DUH! Crimp groove, lube groove... they both have "groove" in them. I get easier to confuse as I get older.

I like a thicker base band myself at least 0.100". I seem to get less gas cutting with a relatively thick base band than a thin base band. That of course depends on pressure and likely burn rate of powder to an extent but given a choice I look for a fairly thick base band.

[wv109323]

Where the lube groove is (and the size of the groove) affects where the Center of Gravity of the bullet is located. Does that make a difference? My answer would be it depend on a lot more factors than just plain CG. Rockets, Missiles,Bombs and arrows are all stabilized on the rear of the body.
The H&G 68 and Nozler 185 JHP have a CG to the rear of the bullet. Many claim the rearward CG helps accuracy.
A bullet is stabilized by the rotation. But the bullet also yawls in its flight. The nose lifts ever so slightly so it does not fly perfectly straight. That yawl needs to be stabilized from the rear of the bullet.
Also the thickness of the base to lube groove affects strength (along with alloy strength). While in the barrel that area is under extreme pressure usually 10,000 to 50,000 psi. If that area has any flex then the exit from the muzzle is not equal around the bullet base circumference. It would be the same as a bad crown on the barrel just on the bullet and not the barrel.
I know I have a .360-158 SWC mold that has a deep grease groove then has two crimp grooves on the front of the bullet toward the nose. The nose has a larger meplate than most. It has a forward CG. I can not get that bullet to be accurate at .38 Spec. velocities. I can not hold 10 rounds on a 24" X 24" paper at 50 yards. That is from a S&W model 14.
With all that said, there is no reason a bullet profile should be inaccurate due to science or past history.

[GWM]

The 358311 is a long lived design that has seen a lot of variation from different cherries. The lenght of the base band has varied a lot back and forth over the years. I have one 358311 of the longest base band variety and that is probably my most accurate boolit. However I would not say for certain that longer is better. If I knew what actually causes accuracy it would be great. There is a lot of variables and the balance is probably what does it.

[Bent Ramrod]

On a revolver boolit, yes; where a wide base would help seal the throat and forcing cone as the boolit moves forward. Probably not, on any rifle boolit. The Kephart rifle boolit was designed with a fat base and lands for the smokeless .30 calibers, but worked no better than any other plain base boolit. "Better," for hotter loads, meant gas check designs, on whatever base the boolit had.

[popper]

A thicker base drive band will take the pressure better. Filling the base lube groove fully will increase the 'strength' of a thin base drive band. Movement of the CG doesn't make much difference if the CP is in the right place.