bearing length vs. nose length?

[BD]

Anyone care to venture a theory here? I'm looking to put a little more boolit out in front of the case to fill up some throat, and gain a little case capacity at the same time. To do this without exposing a lube groove would require either a longer nose, (less bearing length), or a longer front drive band, (more bearing length). Which might be more accurate? And is there some relationship between bearing length and boolit length, or bearing length and nose length which should be respected?

Boolits of concern for this delema are .452 at about .780 in length.

BD

[felix]

Bill, if going custom, make it 80 percent bearing for typical barrel. ... felix

[theperfessor]

Felix -

Is that 80% the ratio of the bearing length to total length, or 80% of the bullet weight contained within the bearing length compared to the total weight of the boolit? And I'm curious where that figure came from, i.e. personal experience, a reference book, etc.

[felix]

Prof, that is length more so than weight. 80 percent would be too much for condoms by a long shot. The idea is to eliminate the slippage/stripping as much as is reasonable. This is why truncated cones shoot well, like Loverins. As a compromise, you can consider an engraving bore rider design for bores less than 40, for example. As the bore gets less and less, the bore rider portion can get longer and longer. No point having a bore rider not engraving in the nose portion when talking the ideal schema. This from experience, and talk on this board over the years. Look at Joe's 22 boolit carefully, as shown on the board today. ... felix

[45 2.1]

60% minimum of the length should be bearing. Much less than that and several design factors need looked at to maintain stability.

[Bass Ackward]

Man. So many factors here. Depends on what you want to do with it in so very many ways. More so because I suspect that you are using a handgun. More if a revolver, different if for an automatic.

What I am trying to say is that the more unsupported nose weight that you have, the stronger your front band is going to need to be over one that doesn't. That strength can come from lead in front of the drive band on such as a RNFP as opposed to a semi wadcutter. Or from hardness.

And besides the factors for launch, it has to fly at possibly a lower velocity if you want range.

If you want more of an idiot proof or flexible design for a revolver and you are not interested in range, and might want to shoot softer, then I go with Felix and 80%. That's my rifle goal as well.

If you have an automatic that needs to feed and doesn't potentially have misalignment issues on a few cylinders, then I go with Bobs 60% cause the lower velocity it will be more back heavy and easier to stabilize. In fact, many 45s have less than that, but require much more hardness.

But you have far to little information to offer much more than that.

[pdawg_shooter]

Go with a Loverin design and your problems are solved. They are the easiest to get to shoot good of any.

[BD]

This will be sized to .453 and shot from a 24 twist .450B barrel with fairly shallow grooves. Looking down the tube reminds me very much of a .45 acp barrel on a 1911. My objective is a 300 grainer @ 2,000 fps or so.

There is a couple of oddball design issues involved. The case has a slight taper, headspaces on the case mouth, and it's an AR platform. I had a lot of issues with boolits jumping forward upon chambering leading to erratic velocities, ( ES of near 200 fps in some cases and SDs of over 50). I addressed that issue by modifying a LEE 45-70 FCD so that it would crimp into a loob groove .1 back of the case mouth, leaving the case mouth at Spec diameter to headspace on. The rifle has a .2 throat @ .453 with no real ball seat beyond that.

The mold I started with was set up to an OAL of 2.10 with a .420 nose as I was thinking to get the nose all but engraved on the lands. This only gave me about 50% bearing length. The best I've gotten out of that boolit consistently is 2 .25" @ 100 yards. My current feeling is that using the nose profile on the lands is not that reliable in something that slams the cartridge in like the AR. There just may not be enough boolit in the throat to insure good alignment, and that I may need to move that "body crimp" back a bit and play with the case mouth diameter to help center things up.

Also, another guy in CA playing with this same cartridge mentioned that his 325 grainers show considerable evidence of "slugging up" when recovered from water. I'm thinking that a long front drive band, shorter nose and more bearing length may be the answer. Playing with Dan's software on the MM website it doesn't look like I'l be able to get 80% without the boolit being nearly a wadcutter. But 70% bearing length using a TC nose looks possible.

I'd like to get some of your opinions and put some more thought into this before I order another mold. $95 makes for expensive guessing!

BD

[felix]

I hear ya', Bill. You have the same chamber characteristic that I have in the Marlin 41 Mag lever gun: 0.20 freebore. A 260 grainer would be fine for this gun, but I don't want to shoot this much lead per shot. So, for the same reasons of money, I just shoot what I have on the bench and forget the optimum configuration for this particular gun. 70 percent is not bad, though. Go for it when the cash burns a hole in your pocket. ... felix

Bill, there is no reason not to have lube grooves on the bore riding nose. They don't have to be filled, but used to take weight off of the nose, a'la' Bob and John. The later Lyman target boolits are designed thisaway, and they do SHOOT! 225646 is my favorite in 14 twist. Your 24 twist should be fine, especially for a under 150 yards killing machine. ... felix

Does anyone have any Ranch Dog circa 300 grainers that have enough diameter to work in Bill's gun? If so, can you provide 50 or so? ... felix

[leftiye]

Or, maybe a loverin or similar design with a dry lube tumbled or dipped or sprayed on then lubed in the grooves that will be covered on a lubbersizer. I am working on a case to carry fully lubed loverins or similar seated way out and keep dirt off of them. Maybe a bandoleer with tubes in the loops.

[BD]

I don't think I'd need all the grooves lubed. I have 120 rounds of cast through the rifle right now without a scrub down and the bore is bright and shiny. Current boolit has one lube groove and the space just forward of the check is lubed, and that provides plenty of lube to coat the muzzle brake. If I go to a loverin I may need to reconfigure the body crimp die to crimp into the smaller grooves. As is, it would squash one drive band.

BD

[Bass Ackward]

I don't think I'd need all the grooves lubed. I have 120 rounds of cast through the rifle right now without a scrub down and the bore is bright and shiny. Current boolit has one lube groove and the space just forward of the check is lubed, and that provides plenty of lube to coat the muzzle brake. If I go to a loverin I may need to reconfigure the body crimp die to crimp into the smaller grooves. As is, it would squash one drive band.

BD

Well, you have hit on the very first secret to successful design and that is knowing your gun. Having tried different things even jacketed can give you incite as to where you need to go.

The problem for the bullet is 300 grains in 45 caliber. As you go up in caliber, weight needs to really increase for best results. LBT has a formula for determining a "rifle" bullet. And that is bearing length needs to be 2X bore diameter. In 45 caliber, that is tough to do below 400 grain so it tells you you must compromise on something.

The problem for the gun is the specifics that you mention. Again ideal is 80% which is easy to attain at 400 grains and I will go as low as 70%. But even these figures mean little to you. I avoid bore rides like the plague because I change mixes all the time. I don't need to be a slave to a mix or a mold temperature to produce a diameter that can't be corrected rationally by sizing.

From your description of your rifling, it sounds like your bands do need to be wide and maybe you still won't be able to get away from hard depending on the pressure level it takes to achieve your goal. Keep in mind that you can make the front band work for you even more by using a taper on the front band. This way it is there, but it can begin farther out so that you keep case capacity. Then start your truncated cone. Beyond that, the next trick is to minimize your lube groove width. The shorter this width, the wider your bands will be and the shorter the overall length will be. Then this will restrict you on lube quality you can get away with. Cause with short rifling, you can't tollerate fouling.

Since you don't have the bearing length, don't go too wild with a meplat either would be my suggestion even if it looks weird. Many people get caught up in appearance and let emotion get the best of them.

There is no free lunch. Everything affects everything else, and then your throat will elongate as the powder roughs it up and the next slug polishes it smooth. But without seeing for myself, my recommendation would be NOT to think custom until you slug and see what you have after about 500 rounds. Often, the whole landscape can change.

But I would start designing now. Design one and then print it out and set it aside. Come back in a week. Without looking at the be fores, start designing again. Then compare what you did the last time and see if you have any new ideas from week to week or if anything grows on you. Beg borrow and steal to shoot as much stuff as you can get your hands on to learn the gun.

Then when you are ready, and do your measurements of your slug, you will tweak the measurements on your best design "guess" and it will probably be a good representation of what you "THINK" you need. If it turns out looking like something already there, that's OK too, but it will fit. That's the difference.

[45 2.1]

This is something close to what you want I believe. It shoots very well out of my 4570s. Easy to redesign to the smaller 45 bore also. Hollow pointed it is quite nasty on critters etc.

[Bass Ackward]

I re-read your particulars and I see what you are trying to do. Good design challenge. Quite the dilemma.

I played around with what I thought might work and feel more comfortable with 315 grains for 2000 fps if you insist on touching. If you can accept less, then you have WAY more options. And I think it will present only minor finickiness.

This design is touching and will leave you about 45 grains of usable case capacity and get you 1900+ with the 5744 class 35k psi to 4198 class 39k psi. (This with 22" barrel estimate. If you have longer, jump for joy. Less, you have disappointment in your future. :grin:)

Since pressure is this high, hard is about your only option anyway, so use it to your advantage. I did NOT account for the fact that you might need to use your make shift crimp again in the first lube groove based upon your circumstances. But that can be played with to put the groove in the right spot and align it up some.

Real key for this is your "bore" diameter cause I am cutting weight by cheating to reach with a fat bore ride section that will butt-up. And if your throat lengthens any or the angle of the leade moderates some, then you will definitely need the make shift crimp because you will be jumping which I assume you were trying to prevent.

So why not jump from the beginning and build a stronger design to handle that? That should give you some food for thought.

[BD]

45 2.1, That is essentially the design I'm using now, except my lube groove is shallower and there's no crimp groove. The issue with it is that I'm feeling that I can't seat it forward enough and maintain any kind of decent crimp as the case mouth lands in the lube groove.

Bass, I think you may be right about going a little heavier. At 315 grains I could pretty much fill the throat, crimp the case and still have something that looks like a boolit. These cases are only 1.70 long. case capacity of H2O is 57 grains. Hornady produces factory brass with a case capacity of 60 grains of H2O. The factory brass uses small rifle primers and a load of LilGun under the Hornady 250 grain FTX will stay in an inch all day long. No such luck with cast. I've had better luck with cast using H110 and cut down .284 brass with the large rifle primers. So far I've had good luck with LilGun under condoms and H110 under boolits. I haven't been able to find any 296 or 5744 locally. I ran some loads with WC680, and it would work in a pinch, but velocities are all over the place and 3 moa is about all I could get.

I'm not sure that I need to fill the throat and touch the lands, I just have the feeling that I need more boolit in the throat on chambering than I'm getting now. I'm going to seat some way out and try them this weekend.

Thanks for all the help. I'll keep you posted
BD