Ponderings on Hollow-Base Boolits

[Bigslug]

My most recent advance into this art has been picking up pin gauges to check throat diameters in various revolvers and to begin contemplation on things such as reaming/polishing and fire-lapping to bring things to the ideal dimensions.

On thing that struck me as odd was the .449" throats in the Webley MKVI - smaller than the bore by a bit, but no leading with the 265 gr. HBRN RCBS slugs I'd been sizing to .452". Seems that the Minie ball base is working some positive magic - although it's possible these things are so slow that the forces involved aren't sufficient to cause a problem.

Of course the ideal situation is to work the gun so chamber and forcing cone dimensions are correct, and then alloy and size the slugs to match. There are many reasons why one would not want to modify the gun, so I got to thinking of how a hollow based boolit could be used in some circumstances to solve fit problems in situations where the gun cannot be adjusted.

One obvious problem is that the hollow base takes weight away from the boolit. My thought then was go with a front end something like LBT's LFN/WFN profile, and couple that with something like MP Molds hollow-base pins in the back. If a Keith were used as the starting point, the lead taken from the hollow-base would simply migrate to fill in the step caused by the SWC nose. Weight would be retained, and the bore would be sealed. The boolit would be front-heavy, and might enjoy some badminton-birdy drag in the base cavity - both of which might contribute to long range accuracy.

I THINK there's something to this concept, but as the only HB's I've shot are trundling out at a lazy 700fps, I cannot say my experience transfers over to the likes of .357's and .44's. Your thoughts?

[Piedmont]

I didn't realize until the last year or so how many factory loads use hollow base bullets. Like the factory 246 gr. RN .44 Spl, the .45 Colt traditional conical 250-255 gr. (hollow base or cupped, depending on manufacturer), and I am fairly certain the 158 gr. RN .38 spl., and of course the HB WC .38 load. All of these have a reputation for shooting well.

Phil Sharpe said these raise pressures and there is no need for them anymore (said that after WWII).

But is seems to me if one is content with not pushing for magnum velocities there is a great deal to recommend them. Chief among its virtues is the ability to fit a variety of cylinder throat and groove dimensions. The pliable bullet swages and obturates to meet the situation, doesn't lead, and shoots well.

I don't own any of the Mihec hollow base molds but with the capability of making multiple HB bullets per cast, perhaps there will be a resurgence. But these are not high velocity bullets.

I don't understand the comment in the original post that the HB takes away weight from the bullet. It is just a redistribution. I was reading an old Brian Pearce article a couple of weeks back and he said the HB reduced case capacity in the .45 Colt. I thought about it a bit and realized he was wrong. There was still the same amount of weight in the case, just more on the edges further down.

BTW, Keith had at least one hollow base version of his semi wadcutters. They were discontinued, presumably due to low demand.

[Piedmont]

How did I forget the .22 LR?

[MT Chambers]

Not to mention Airgun Pellets, which in some cases are driven to 1200 fps, with up to 4000 psi air pressure, and still most accurate at closer ranges.

[MtGun44]

I think they are far more forgiving of dimensional mismatch than solid base. I have
had two people that I know with .45 Colt revolvers that were not very accurate and
with the factory Rem or WW lead (which has a HB) they shot far better.
I also have a Trapdoor with a very worn and oversized bore which was throwing
everything solid based sideways, but went to 4" at 100 with HB 405 from Lee.

I think there is a pressure limit at the muzzle to avoid blowing the skirt out
and upsetting the boolit, but other than that they seem to have their place,
esp in a revolver with oversized throats or a very oversized diam barrel
rifle. I just bought a HB mold for my .50-70 Rolling Block to see if it
will help the accuracy - an oversized bore and I think the originals were
HB, - but not sure.

Bill

[Bigslug]

Phil Sharpe said these raise pressures and there is no need for them anymore (said that after WWII). . .But is seems to me if one is content with not pushing for magnum velocities there is a great deal to recommend them.

This is actually one of my major questions. If the alloy is chosen for the velocities in question, AND the load is correctly worked up for the boolit design, why not drive HB's as hard as anything else?


I don't own any of the Mihec hollow base molds but with the capability of making multiple HB bullets per cast, perhaps there will be a resurgence.

The MP .455 Webley mold is a darn close copy of my 1-hole RCBS (or both are darn close copies of the original pre-Hague Convention slug). At any rate, I ordered Miha's 4-cavity brass mold to speed production. It's NICE. Not done enough casting with either type yet to know if I prefer MP's sliding pin system to NOE's tilters, but they both do a good job.



I don't understand the comment in the original post that the HB takes away weight from the bullet. It is just a redistribution.

I meant that for a given configuration, a boolit with a hollow point or base will weigh less, and that given the space in the cartridge case and chamber that we have to work with, shape of the slug needs to be factored in to obtaining desired weight. A .44 with a Keith nose profile given a hollow base that that has been lengthened to retain the 250-255 grains of the original might be too long to fit in the cylinder, while going to a more filled out LFN/WFN nose might keep that weight range possible.

Of course we get into other variables like location of the crimp groove, but as a generalization, that's what I was thinking.

[Piedmont]

A .44 with a Keith nose profile given a hollow base that that has been lengthened to retain the 250-255 grains of the original might be too long to fit in the cylinder, while going to a more filled out LFN/WFN nose might keep that weight range possible.



It won't be too long to fit the cylinder because only the hollow base is longer. But there is no more displacement, no more use of case capacity, because the same amount of weight is below the crimp as was there before. It is just shaped differently.

[303Guy]

My interest in the hollow base is in its perceived ability to swage down in the throat without base edge feathering or rifling drag on the base edge. That's for softer boolits that are fitted to an oversized throat.

[Harry O]

The 41 Long Colt that I use for CAS shooting has a 0.386"OD hollow-base bullet that is shot through a 0.400"ID groove diameter barrel. You can literally drop a clean dry bullet down the bore of the gun by gravity alone. I cast them out of approx 40:1 lead:tin and have never had any problem with leading. The velocity is low, approx 770-800fps with 20gr of black powder.

I tried a hollow-base bullet for a 44-40 Marlin with micro-groove rifling (this was before they started offering Ballard rifling in their CAS guns). The bore was way oversized for a 44-40. I think it was a standard .44 Magnum barrel. Leading was bad with standard CAS flat based 44-40 bullets. I got a Rapine hollow-base 44-40 mould. It still had problems with a 40:1 mixture, but hardening it up a little bit (approx Bhn 10) worked OK. Soft enough for the base to expand and hard enough to grip the rifling.

I think that there is a place for hollow-base bullets unless you have a machine shop and can build your guns to have exactly the correct dimensions (or have a gunsmith on retainer).

[45 2.1]

but other than that they seem to have their place,
esp in a revolver with oversized throats or a very oversized diam barrel
rifle. Bill

The other place you haven't mentioned is shot out barrels........ those that keyhole any you try in it.... like an old Colt 1917 with very faint rifling. With the HB RCBS it shot fairly small groups again (instead of keyhole patterns).


This is actually one of my major questions. If the alloy is chosen for the velocities in question, AND the load is correctly worked up for the boolit design, why not drive HB's as hard as anything else?


Very bad idea if it is anything other than a shallow cup shape with thicker sidewalls........ too much pressure will leave the skirt in the bore if it thin. Next shot will ring the barrel in all probability.

[beagle]

I got intrigued with hollow base bullets a while back and played with the Keith 358431 and also the 358395 in both the .38 Special and .357 Mag. I also played with the 429422 in both the .44 Special and .44 Magnum.

Casting can be difficult and you have to inspect the HB cavities very close and toss any with wrinkles in the cavity or around the base.

Accuracy was pretty good in the .38 Special and .44 Special at factory velocities. Attempting to use at Magnum velocities or close thereof produced dismal results.

My best accuracy was with fast burning powders like Bullseye. It seems that a fast bump is needed to expand the HB and get the benefits of the hollow base.

Based on my testing, I kinda gave up on HB bullets as there seemed to be no real advantage over a good plain based design in loads for the .38, .357 and the two .44s. Maybe in special cases it would be different. I've always wanted to try some HB bullets in the .45 Colt but never went to the expense of having one made. At one time, NEI cataloged a HB for the .45 Colt that was pretty close to a clone of the factory bullet./beagle

[MtGun44]

45 2.1 -

The worn rifling application is what was happening with my Trapdoor. Very worn barrel, oversized and very shallow
rifling. Lee 405 HB and 12 gr of Unique made it shoot again.

Bill

[Harry O]

Beagle is right about fast powder. The faster the better with hollow-base bullets. Even faster than Bullseye is Black Powder. That is what I use with the majority of my HB loads.

Also, there is a limit to how hard the bullet can be cast, as mentioned by 45 2.1. With my 44-40 Marlin, I cast several hardness hollow-base bullets. The hardest was about Bhn 18, air dropped. It ended up leading as bad as the dead soft flat-base bullets. It was not expanding at all. In addition, it was almost impossible to get the skirt to fill out properly with the antimony in the mix. The best for that one was was about Bhn 10, with very little antimony, as mentioned earlier.

[Bigslug]

Beagle is right about fast powder. The faster the better with hollow-base bullets.

This is the puzzle I've just cracked open. I'm working with two 1917 dated Webleys, one in the original .455, the other modified for .45ACP. Both guns have .449" throats. I was able to shoot both into an evidence collecting trap. The original ammo gun gets Titegroup and flares the RCBS hollow base out to about .452". The ACP gun has a charge of Trail Boss to fill the larger-than-needed space for the low speeds required. The boolit for this one came out about .447". Got to slug that bore down from the muzzle and push it back out before it goes through the cylinder to get a better idea of what's really happening here.

[jethunter]

I don't have a lot of experience with the HB bullets, i shoot them in 455 webley and a bit in wad cutter 44 and 45.

The 455 - 265 gr HB is the traditional "webley" bullet, but i can consistantly get better groups out of about any RN or SWC flat base bullet providing it is very soft - like BHN 11 or less. That's been consistant in more than 1/2 dozen webley revolvers.

I can't say I noticed better accuracy with the 44 and 45 WC HB bullets used in 45 S&W and 44 Russian/Special. possibly a bit better at lower velocities.

[lwknight]

One of the hollow base bullets greatest forte's is the flechette effect. Granted that they tend to forgive mismatches but they also work great for popcorn fart loads.

Low velocity loads can fail to stabilize solid bullets where H.B. will make very accurate plinkers or
my favorite , the 100 grain 38spl rat thumper with 2.0 grains bullseye.

You don't even need ear protection and it will not shoot a hole in the barn wall.