Thanks, Ed,
Been meaning to order those gas seals. They are on the way now, and more.
Including more of the plastic over shot disks, for over 10 grains of Blue Dot with RL-17.
They also work well for roll crimped squirrel loads of 1.75 ounces of 7.5 shot in 3.5" Federal plastic hulls. Can see the load through the plastic: from 3.25-oz. slug to light shot load.

I'll start over with 160 grains of RL-17 with gas seals, waxed card wads, and no Dacron fluff ... with and without the 10 grains of Blue Dot ... and go from there, with the RMC brass.

Now, please convene the "12GaFH Think Tank" and assign a BC number for the 1085-grain Nohbozo Brass Darwin.

I think .150 is a little low, but Ok for conservative estimates for now. I had hoped the 209's would work better with Rl-17 alone, but it seems you will need the starter powder or CCI-35's. I continue to have no problems with them in my gun.-Rob

I have a question included in an observation concerning case friction against the walls of the chamber.

Givens...

Given...That the case walls are not uniform linear thickness from end to base...

Given...That the thinner walls at the front(hole end) of the case grip the chamber walls before and/or tighter that the walls at the base end...

Given...That the base end of the case begins to move rearward before the front end does and contacts the bolt/frame while the front end is locked against the case wall...

Given...that when this happens the case stretches, usually near the junction of the case wall and the "case head" thick section of the base which usually leads to incipient head seperation...

Question...

Wouldn't/shouldn't there be some kind of "reduction/adjustment" in the actual rough figures for the amount of psi that is transfered/absorbed by the chamber wall???

Maybe by using only the front 1/3"??? circumferential area of the case OD....or???

Or...does it really matter except for arguement/discussion purposes???

Once the pressure gets above the yield point of the case metal, the brass has to move TO somewhere and FROM somewhere...either being "removed" from casehead/case wall junction when the case moves rearward or from the case walls toward the case front as the pressure "irons" the brass.

I my experience with a tightly fitted chamber/bolt the brass moves toward the front, lengthening the case and/or thickening the neck wall.

I've done several tests projects to see how this works by using a SAAMI minimum chamber and a tight bolt/case fit in a Savage LA 308 Win, Lapua benchrest prepped brass, Redding bushing neck die, adjusted for "0" shoulder setback, Hornady 150gr SP bullets, Fed 205M primers and Varget powder, and a 50KPSI pressure load for the whole testing procedure.(keeping all the parameters as "scientifically uniform" as I could)...then re-adjusting the headspace out(relatively quickly done with the Savage nut system) by 0.002" (or as close as I could get) and using Redding Custom shell holders to keep the shoulder relation as close to the same as possible.

The cases always stretched more with the first 3-4 shots per case, always at the front end for the tight fitting...up to about 0.006" "headspace". The amount of reloads per case was highest with the tight fit,(no surprise there), then dropped off quickly as the headspace approached 0.012".

With my lack of measuring equipment I couldn't really determine the where or how tightly the case was gripping the chamber...only that there was an effect and this effect has been borne out by many, many benchresters and target shooter.

I have always wondered how or if any studies were conducted concerning this and if those studies were published somewhere...??? Probably of little use for the average shooter, but it has niggled me for 25-30 odd years.

Most all of the parameters are known or can be adjusted and calculated relatively simply.

Whenever I come across the "how much can it stand" or "you CAN'T do that because..." questions and myriad answers or when I'm messing about with a new toy and working up loads, this "how the he** do I calculate that" nagging question always pops into my mind.

I've wanted to ask this question, but this thread is the first time the opportunity and relevance presented itself. I asked the same question of one other forum but all I got for the most part was the usual non-descriptive naysayer and/or mindless "what the he**???" rhetoric.

Not trying to muddy the waters but would like some cogent responses or observations.

Any thoughts???

Thanks

Luck on your projects.

With too much heaspace cases will thin just ahead of the end of
the corner radius faster and case stil llengthens.
A good fitted chamber where more brass flows forward
making case longer with added firings, lasts longer. When I figure
amount of the case that grips the walls I measure the part of the
case body ahead of the corner radius. I tested in my 458 different
headspaces and when it was sloppy. like 8-14 thousands case life was
only a third as long and I shot them till they showed thinning,but tightening
headspace cases lasted forever. And in either situation the cases are
still taking part of the reward thrust.Only when sloppy, cases thin
faster doing it.

I think RE-17 will do ok with good seals and no fluff. When using
BPI columne if powder room needed leave out cork. And nitro cards/wads
can be used instead of cork if needed. Load I laid out here knowing how
long BPI column is you can get 180gr of RE17 without cork with
a 1040gr slug I had measured, with slug out about a 1/3 its length
in RMC case .Ed

I’m sure that I am wrong about some of this, but concerning Foobars post. I believe P.O. Ackley mentioned in one book about a proper wildcat chamber and cartridge. I believe he would unscrew the barrel one turn and shoot the cartridge in a falling block rifle and the block would be free to move, as in the cartridge would not press back against the block meaning that the case friction held the case in the chamber? I may be off, it’s been a long time since I read that. Someone that has his books may be able to check me on that?

Foobars quote,
“Wouldn't/shouldn't there be some kind of "reduction/adjustment" in the actual rough figures for the amount of psi that is transfered/absorbed by the chamber wall???”

I think the problem with this is that every chamber is different, and the brass isn’t exactly the same measurement either. So, that to build this into a standard equation may not be the safest way, because what is true for one rifle may not be true for another. For example, a rough chamber will have more friction than a smooth chamber. Maybe they just keep this as a safety margin built into action design since there are too many variables to actually rate this for every situation? Not sure.

I’m wondering if the brass is actually moving rearward first? Would it not be moving out first? Since the powder directly above the primer goes off first would the case not begin expanding outward then forward until the neck meets the chamber neck? I think it would move forward second because the case head is the thickest part of the case and it would take more energy to make the case expand rearward, towards the case head? This is all thrown out the window for a match chamber on a tight action. In that case, the only way for the case to more is forwards towards the neck. Everything is happening in such small increments of time that maybe it’s hard to verify?

This is a pet peeve of mine because there is next to nothing written about this, or maybe it just is difficult to spot? And it is something that Is very interesting to me also.

Hope this is okay being off topic.

Hope to see pics of Rob's double soon! Also hope chambering my barrel didn't delay progress on the double!

Ed, you beat my post. Would that load be the same in bmg brass? The 180 grain with 1040 slug?

RIP, are you gonna run any aluminum darwins with re 17???

Ackleys test involve low pressure 30-30
and the rearward thrust was less than
what the brass would hold.So brass
and the head of the case stayed in
chamber. It held it all ok.
Boy and friends used old 30-30 barrel
bolted to a table, set a 10 lb steel block
against a case in chamber and had
hole for a pin to hit primer. Tap with hmmmer
it would fire safely and block wouldn't
hardly move. Case took all the thrust.

That 180 wasn't a load I've shot just a
statement of what it will hold with
the BPI seals and flexseal.With long BMG based
case in NEF you could go 20-30 gr more than
top load in RMC case with 1080 gr slug.Ed

Thats all true, but Paul mauser put three locking lugs on the back of the Mauser for a reason. I've always been taught to rough up my chambers with 400 grit emery cloth to maximize a cases ability to grip the chamber walls and I would also expect about 1/3 of the theoretical rearward case thrust is distributed radially in an ideal situation as a gausian distribution of peak pressures. In other words at the point of ignition, case thrust is linear, at some point in the pressure curve, the pressure is high enough to case the brass case to expand radiualy and grip the chamber walls orthogonally reducing linear thrust along the axis of the bore. However, once peak pressures have ceased and the brass case springs back, then the majority of the pressures will be exerted linearly again. For example,I'll bet Ackleys experiment comes out differently with a .300 RUM at 63KPSI and a very peaky pressure curve. for example, because case head or bolt thrust will be much higher. Its absolutely true that in a gun with excessive headspace that the point of failure is at the point where the thickest case head internal brass ends at the juncture of the case wall. On firing the brass case sticks to the chamber walls and the case head stretches back till it contacts the bolt and locking lug system. Eventually it fails at that point. In a zero headspace gun, that stretching does not happen and the brass flows forewards again from radial pressures. Interestingly Almost all the Kasboomed guns i've examined failed from some sort of hoop strength failure, not locking lug failure. With nthat said, I have seen set- back locking lugs on some soft Mausers when high pressure loads were chambered in them ( i.e early .300 wby magnums). I suspect the math needed to calculate this will be reasonably complex, but undoubtably exists somewhere. Nevertheless, I'm with Ed in that the simple calculations we generally use to calculate bolt thrust are over estimates because they dont take into account the cases wall gripping effect that reduces the theoretical bolt thrust. This is probably a good thing as overestimation is better than under estimation. My belief is that case wall grip is probably a very good phenomenom in low pressure cartridges with nice slow pressure curves as we are trying to create and probably the reason why the NEF survives the 12GaFH 8000 ft-lb loads it does.-Rob

12GaFH Double rifle( Dos Diablos is very appropriate) progress. Its been going slowly. I made the 4140 Quarter rib over again as I didnt like the way it fit. (10 hrs). Then cut out the upper and lower ribs from some 1" 4140 tubing ( 6hrs). The ribs had to be exactly the same width as the quarter rib .730 and it was a gigantic PIA. Not so easy to do, but it worked out. Then came the front sight 4 hrs to get the dimensions right. Again has to be .730 to match the ribs.This one is made from Aluminum and will be used for regulating the gun. Sling mount also had to be made as it too is needed for regulating. Now I have to make a new extractor.Dimensioned it out today and wrote a profiling pgrm to make atest extractor tomorrow. Now you know why double rifles are expensive!!!! Bottom picture is just the parts placed on the gun so you can see what its gonna look like. I used a reject piece of rib for visual effect. The actual pieces are much nicer. The Quarter Rib covers the remaining piece of rib from the zabala monoblock perfectly. God alone knows how long that would take if you tried it by hand. Again all parts for this gun are being made by CNC so that in theory its reproducible.-Rob

name's Baby!

Dos Diablos.
Givin' you a devil of a time.

Hey Rob, see that's all bad karma. You should have named the double something like two holy angels or something and it would have gone together easier!

It's looking great. Can't wait to see finished pictures of it.

On a second thought, I think I may start a little bit lighter than the 220 grains of H50bmg, not scared at all you know, just want to conserve powder....

http://www.youtube.com/watch?v...-4sc&feature=related

Saiga from hell?
or this...

http://www.youtube.com/watch?v=bhDPoVm74To&NR=1

TBMFDRTKOBE. . . or
The Big Heavy Double Rifle That Kills on Both Ends?

My only concern is that Will is going to think it is too heavy for it's caliber?

Looks great Rob! Congratulations!

Rusty- Thanks,but Too heavy for caliber? I dont think so! Maybe way too light! I'd pay money to see Will fire a right- left with it!
Boomie- That saiga was actually quite impressive and decently controllable.
New extractor pgrm ran perfectly and by 3:00 it was fit to the gun! At least one thing went off correctly! Now I can chamber and headspace the beast!Getting close to regulation time.-Rob

Next 12GaFH experiment for me:
hotter 209 primers
BPI Gas Seals
RL-17 powder in RMC brass.
Will be trying these along with the CCI-209 primer as a control:
CCI-209M
Win. W209
Fed. 209A
Rem. 209 Premier STS

To see if any of these burns the RL-17 more completely, higher velocity, without resorting to the Blue Dot starter again.

Rob:
Looking very nice matey. I'm surprised at the amount of gap that you have between the barrels. Is the gap really ment to be that wide? It certainly makes it different that for sure.

Gibs the barrels are taper turned from 1.1o- .970 at the muzzels. This was done to make the barrels fit the forearm. The result is a .730 gap between the barrels which has to be filled by a .730 rib which in turn means the quarter rib and front sight need to be .730. Once regulated, this gap may change slightly. Every decision you make on a double rifle has consequences you will need to consider later. The single best decision I made was to design a quarter rib that covers the old Zabala rib remanant on the monoblock. This way the final gun will have no obvious mating points and will look extremely professional. I have to take my hat off to the old world craftsmen who builtthese things by hand. The amount of work I've put in so far with CNC equipment is a hell of a lot and I can onlyimagine what it took those guys.-Rob

Rob:
Well matey all I can say is so far its looking very professional. I understand that the donor unit was a 10G frame or have I got that wrong? Not that thats an issue since it can only make for a stronger finished unit. I'll say this much tho, from the bizz end its rather intimidating!

Be very keen to see how it go's regards the regulating. I'm like the rest of the guys here - cant wait to hear how the first shoot go's!

Here is picture of my 4bore falling block with
the block to be the breech setting in the hole.
Breach needs trough on the top yet, but
it is set for exact width and height and the
bottom recess and link hookup is done now since
the picture was taken..Ed

Ed- Did you find a good wire EDM shop to profile those pieces for you?-Rob

I'm doing the rest with my equipment.
Got trigger, hammer all set and mounted.
Got breach block done, linkage and lever.
Coming toether ok.Ed.

ED- Seriously, wire EDM is cheap and accurate and will save you an enourmous amount of time. You have some curves in that block that will be difficult to do right with a saw, milling machine and grinder. save yourself alot of grief.-Rob

Ed - still the Mad Max of "get it done" guys ...

Gonna file the interior of the slot by hand Ed ..??

LOLOLOLOLOLOLOLOL

The hole for the breach block was done and had square corners
and the steel I had for breach fit perfectly with
one side milled for width. Getting a good hole for the breach was
my only holdup.

The slot for trigger and hammer-- and the linkage and lever recess,
I'm doing with my vertical mill.The slot in bottom of breach block
for linkage did with the mill.Ed

Good day at the Range! Shot 10 rds of 12GaFH and had a blast. My record of zero misfires with CCi-35 primers remains intact! Those Brass Darwins were quite accurate at 50 yrds too! used the 240gr H50BMG load.-Rob

Rob ....DO YOU OWN A FRIGGIN' CAMERA ...?? Or are you going to tease us year after year ...??

You know we're a simple lot round here ...we need constant visual stimulation ...

Got a quick question for you gurus on the 12 gafh. I got my reloading components from Rob this week and loaded up a couple of rounds. I haven't had a chance to try them out yet, but found something weird. The little plastic overshot card that is the divider between the blue dot and the h50bmg was very tight in the bmg case. I thought I had it tamped all the way down and loaded the powder on top, but, when I had finished loading them I shook the cartridge and could hear powder moving. I know for sure that the bullet is sitting on the powder so I know that that isn't moving, so it has to be the blue dot. I am sure there is not much room in there, but, should I pull the cartridge apart and try to reset the plastic disc? Thanks for the help. I hope to be able to take it out next weekend and shoot it some. No brake yet though, it should be a nice shove!

That is weird.
Why are you using starter powder if you are using Rob's case?
Did you have the primer pockets converted to 209?

The RMC brass is so thick walled that all the standard 12Ga wads and discs fit perfectly, like they do in a plastic 12Ga hull.

Thin-walled 12ga brass like the MagTech cowboy stuff requires wads and cards that are bigger than standard 12ga: 11Ga.

15 grains of Blue Dot fills the shallow hemispherical base of the RMC 3.5" brass, which is shaped much like a 50BMG case internally.

I used a rubber mallet to tamp the loads down in the RMC cases.
There is no way they could be loose,
because there was no air space possible between the Blue Dot and the plastic overshot disc.
The disc is resting snuggly on top of the Blue Dot before the H50BMG is poured in.

Maybe the Nohbozo base is deeper internally, and not fillable to it's top
(where it curves out to maximum case inside diameter before starting the long taper to case mouth)
by a mere 15 grains of Blue Dot?

When you press the overshot plastic disc down onto the Blue dot, you may have some air space left even when the disc is in as tight as you can get it.

That cannot happen with RMC 3.5" brass.
Hopefully the 3.85" RMC brass will have the same shallow hemispherical base profile.

I do not think you need to disassemble the loads if that is all that is happening.
There is a little air space between any primer and the powder to be ignited.

I do not think you will have a detonation problem with 15 grains of Blue Dot powering off the slow H50BMG.
Might not be as uniform as it could be.

Matt- Doubt its the Blue dot your hearing. You probably didnt tamp the disc covering the blue dot down far enough and when you seated the Bullet on top of the H50BMG it pushed the starter disc down and left a little air space in the H50BMG powder column below the bullet. Thats what you hear moving. You'll have no issues shooting it that way though.
RIP those are AC-DC cases with 209 primer adapters.-Rob

A little while ago we discussed bullet making for the 12GFH and what metals would be suitable to use for Mold made bullets. One of the options was a Zinc alloy of some type (Rip's idea IIRC) or just plain Lead since other metals had issues - even pure copper (not easy to smelt).

Well I may have found an answer:
Bismuth 90%
Tin 5%
Copper 5%

This is a Lead free replacement for Fishing Sinkers that handle like Lead. In other word's you can use all the same gear that you would normaly use to make DIY Lead sinkers/bullets/shot. But its a tad lighter and Stronger/tuffer than lead .
The Bismuth an Tin I can get in ingot's and the copper I can get in powder form. Using the powder copper allows me to add the copper into the smelted BismuthTin mix just prior to pouring (so i have been told). The Alloy is also availabe in precast sinkers as well as a solder (has flux in it tho). I have yet to find any of the alloy sinkers here in Oz, but I have found a Local supplier of Bismuth an Tin ingots not very far from my home plus another where I can get hobby amounts of copper powder.

So all I need now is a good Mold made to the specs I'd like and a Layman Pro smelter and I should be off an running on making suitable bullets ( I hope).

The nice thing about Bismuth is that its completely inert, has no nasty side effects when smelting, same goes for Tin. The only thing I can find out that may be an issue is that it will need a sealant of some kind to the alloy if its going to be stored for long periods to stop it oxydising. Not hard to over come.

Ohh one other thing, this alloy will expand slightly on solidifying, could be a handy feature.

Gibs- Nice alloy, but i dont see any advantages over Linotype. Linotype doesnt expand or contract at all. Melts at a decently low temp and gets really hard after a day or so. -Rob

Rob:
Well the thing is, I dont want to use lead at all. One its to heavy for what I'm after, 2 its rather poisnous. I'm after an easy quick safe clean way to make bullets that I can change the weight of for a given dimension/size till I find the right combo. The alloy above can have other metals added to it like:

ANTIMONY
CADMIUM
INDIUM
LEAD (if I really wanted to)
SILVER

Not all are really usable like Cadmium (nasty stuff) but I can mix an match as I need to get the perfect weight to size ratio.
So over all its a rather handy Alloy that can be tailored to my/our needs since even the Bismuth/tin/copper ratio's can be changed as well. You can even drop the copper and replace it with either one of the metals above or again change the Bismuth/tin mix. I'd say this alloy is like wonder metal. I cant wait to try it out.

As long as lead is available it will continue to be used...BUT...the environmentalists are going after lead like a lizard after ants...in any form..bullets, sinkers, shot, tire weights etc.

So if you want to keep shooting and "they" don't get the powder or primers first, you/me/we better have an environmentally friendly lead substitute for our use.

That mixture you came up looks better for bullets than Bismuth shot which seems to be a mix of 97% Bi and 3% tin.

I've been halfway expecting the bullet makers to come up with a core material for the cup and core bullets made of some mixture of Bi/SN/CU with some kind of catchy name to grab your ba*** and get around the BS. I would bet on the fact they are working and testing some right now.

You can tell the difference in the "phoney" lead tire weights by the shine and color...same with the sinkers. Might be something to start stocking up on for the future...I'm guessing ALL types of lead based products will be a thing of the past very soon.

Bismuth is still expensive for shotshells, more dense than steel but slightly less than lead, it should make a very good bullet.

Then there is always Titanium...powdered or as a mixture. As a core material it has many advantages and disadvantages.

I don't like mucking about with casting lead, but have thought about using Bismuth shot...except for the cost...in the larger calibers.

Gibs...Keep us posted on your progress...you never know you might come up with something to make your next million.

Who knows...maybe in the future bullets will be made of copper, bronze, copper covered Titanium or brass only...if there is a future.

Luck on your projects.

Foobar:
You hit the nail on the head my friend. In Parliment just last week in Q/A time, the issue of lead shot came up and weather or not it might get banned. It seems that on our fresh water lakes the amount of lead trace elements in the mud that the ducks sift through is getting rather high. Plus some animals that eat stones to help digest their food have been found to have eaten larger lead shot (00SG, 00 ect) and died as a result. So its only a matter of time that Lead again becomes a bad thing to use like it was in paints an all the drama that that caused. Another is like you I'm not keen on smelting lead in my barkyard shed with my son around (he'll want to watch an see how its done an I cant say I'd blame him for that). So a safe clean alternitive is needed thats as easy to use as lead. Yes Bismuth is not cheap, but then again what is these days, more so anything to do with firearms!

Gibs,
That is an excellent idea, but about 10 times the cost of lead and about 5 times the cost of Linotype and zinc,
from prices and alloy information found by tooling around at links here:
http://www.alchemycastings.com...products/fusible.htm

It is low-temperature-melting and expands a wee bit as it cools, should cast beautifully. About proper alloy for hardness and sheer strength desired: Let us know if you test it.

I do not fear toxicity from lead or zinc. I fear the toxicity of politicians and greenies.
Good idea to limit the waterfowl exposure.
A lot of projectile lead could be reclaimed from shooting berms and skeet ranges and recycled.
Interesting times we live in!
Muzzleloading roundballers will be using what alloy in the future?

Rob,
It makes sense that the Blue Dot (delicate flakes) would not make much noise, even if shaking around in some air space.

If compressing the load allows room for the H50BMG to rattle later, that suggests the plastic overshot disk was not seated firmly in contact with the Blue Dot initially
(there was air between the disk and the Blue Dot)
and/or
the disk was broken or tipped, in seating wad/slug after the H50BMG was poured in.
H50BMG grains and plastic disk fragments would be more likely to make audible noise with the shake.

RIP- If that disc tiped or broke, I sure hope there is enough blue dot to give good ignition. IF it doesnt go Boom immediately, I would hold on for two minutes or so before opening that action. Thats not a pretty picture.
Matt- Did you fire the NEF yet?-Rob

Does anyone know if Lee or Layman make custom mold's ? Or failing that anyone who does?

RIP- Found a source for pretty good custom molds. I make my own.-Rob

Brooks' Tru-Bore, maker of the Triple-Foster Darwin mould:

http://www.brooksmoulds.com/bullets.html