Determining safe max pressures

[dubber123]

I need to determine a safe pressure at which I can operate a gun project of mine. Here are my thoughts:

The .45 Super, is accepted as being safe in "Good quality" 1911 style auto pistols. My take on it is, you beef up your spring rate, maybe add a buffer, and blast away, no barrel changes. Measuring my 1911, the breech end of the barrel is as thin as .097", and only 4-1/2" away, at the muzzle, it is only .065" The 45 Super is rated at 28,500 Psi.

On my project, the breech end gives me .102" of steel around the case, and at no point is there less than .100" all the way to the muzzle.

Not taking into account action strength, why could my barrels not be safe at the 28,500 Psi of the .45 Super. I have from a little bit more steel, to quite a bit more steel, depending on where you check? Thanks.

[dubber123]

Anybody care to poke a hole in my theory?

[S.R.Custom]

The steel in the barrel is not the issue; the chamber walls of my SBH .44 Magnum are only .095" thick. (But this ignores the differences in steel alloy strength & hardening between the two guns.)

It's the cases you have to worry about, specifically where they hang unsupported over the feed ramp. How do you know when you've gone too far in loading intensity? Blowing the grip panels off the gun when the case ruptures is a sure sign...

There's more to this .45 Super thing than a stiffer spring. You need to look into this a little deeper.

[KYCaster]

Aaahhhhh, but Supermag, he didn't say that his project is a 45 Super. He's asking if his unnamed project is safe because the 45 Super is considered safe.

Check this site, you might find the answer you're looking for.

http://web.ics.purdue.edu/~ssanty/cgi-bin/eightball.cgi


Glad I could help. :drinks:

Jerry

[runfiverun]

case and steel strength do have a lot to do with max pressure..
knowing paul he is trying for 50k with a 45 colt semi-auto thing.....lol

[dubber123]

KYCaster is on to it, I am only comparing pressures and wall thicknes of barrels. I also don't need to go to the 28,500 Psi, just trying to get a handle on the safe operating range of this, and determine what I should proof it at. The brass is fully supported, no feed ramp on my project.

As far as the .45 Super, I really do think it is mostly just a spring swap. The Super brass is thicker over the ramp. It is about 6,000 Psi more than a +P .45 ACP. I couldn't find any info that suggested the need for swapping out the barrel in a 1911. I could be wrong and just have missed it.

Thanks for the comments, (even you, Lamar). Keep them coming.

[Bret4207]

There's also the chamber cut to be factored in. It's my understanding that you can cut the chamber in a way to provide the least resistance to the bullets start, freebore so to speak. That will cut pressure and you can go to a maximum sized bore and shallow lands to cut pressure too. There is also the type of steel used in the barrel to consider, but the case will remain the weak part. Powder burn rate can affect pressure and the pressure curve too.

50K in an 1911? Way out of my league or interest area.

[Boerrancher]

I have not had a case rupture in a 1911, but in my younger years when I tried to make a Magnum out of everything, I did have some buldges big enough that I couldn't iron them out in the resizing die.

Paul, If I were you, I would start out at the upper end of the 45 acp loads and work my way up. If you start seeing signs of high pressure quit. Use new brass for your testing, as you don't want your first sign of high pressure to be a cracked or broken case.

Best wishes from the Boer Ranch,

Joe

[dubber123]

Well, I have been pretty vague, (and Lamar throwing the 50K thing in didn't help)!, but to clear things up I am NOT building a 45 Super! I used it because it is the best example of a thin barreled gun operating around the pressures I desire to use in my project.

The other reason I chose it, was the Super case along with a stiff recoil spring is all that is supposed to be required for safe use in any 1911. This tells me the designer of the cartridge didn't require any special barrel steel or anything, just a run of the mill 1911 barrel.

I am trying to figure a safe operating range for my double rifle project. I have more steel than a typical 1911 barrel, no unsupported brass, and couldn't see why the pressure limit should be any different.

Good points about the leade into the rifling, and the burn rates of the powder. I assume, (theres that word again), that the cast lead slugs on my project will ease into the bore better than the typical jacketed bullet used in a .45 Super. I also assume the powder chosen for a 5" pistol would peak pressure faster than powder chosen for my 24" barrels.

I really do want your feedback, I just wanted to clear this up a bit. The chamber reamer is on the way, so I need to figure this out pretty soon. Thanks.

[BeeMan]

Dubber,

There is a booklet on building single shot actions that is a collection of articles from Home Shop Machinist(?). It does a pretty good job of explaining the strength of materials issues and what are known as hoop stress calculations, along with quite a bit more detail. You also need to understand and abide by safety margins in your design and the author deals with this as well.

I've done a bit of design work around this and validated my results by cross checking various commercial designs. I used traditional hoop stress calculations and created some spreadsheets to do the number crunching on nominal, design margins, and overpressure conditions. I don't have the time lay it all out here, but search for the book and understand it before you pop the first primer. I think I got my copy from Brownells.

Last, do a search for VarmintAl. He has a web site that explains brass deformation. pressure and other relevant factors, with actual numbers and images from Finite Element Analysis.

BeeMan

[dubber123]

Thanks, I will look for the book. I have the big Brownells catalog, maybe it's in there. The first few, (or quite a few) will be fired on the end of a long string. The liners come out easy, so I would think I should be able to re-check barrel dimensions, and measure brass before and after firing.

I planned on testing with a proof load of a known Psi., and then dropping down well below that # for regular use loads. Believe it or not, I did try and research this quite a bit before getting into it. (It's been in the works for about a year). Information was pretty sketchy.

[S.R.Custom]

I am trying to figure a safe operating range for my double rifle project. I have more steel than a typical 1911 barrel, no unsupported brass, and couldn't see why the pressure limit should be any different.

Comparing double rifles to semi-automatic handguns is like comparing apples to asparagus. But let me give you a hint at what you're looking at...

With a fully supported chamber, your big unknown is the steel itself. What kind of steel are we talking about? Has it been heat treated? To what standard? 120kpsi? Or only 40kpsi? And that's just the barrel. High pressure loads put added sheer stress on pivot pins, lock-up latches, etc.

Then we have to ask, what kind of steel is the action made from?

Here's why this is important... as part of the 'action' strength, there's the whole force per area thing. ( Pressure is measured in PSI, or pounds per square inch.) As an example, if you rechamber & rebore from .223 Rem to 300 WinMag --and assuming equal pressure levels of the cartridges, say, 50Kpsi-- the locking bits of the action will see a total pressure increase from 5,550psi of the original chambering to 10,330psi of the new one, even though the pressures of the cartridges are the same.

In other words, going bigger and hotter is going to increase stress on the action by A LOT. Whether your particular action can handle the pressures in question is unknown. At what pressure was the gun originally proofed at? If we knew that, we could go from there in figuring what is safe for your project.

In being cagey with your data, we can't help you, as there are too may variables. And in asking the question the way you did, I suspect you don't know what all those variables are.

[bigdog454]

Cartridge brass has a strength of around 65,000 psi befor it flows, as Beeman has said check out the book he recommended it gives a lot of info. You'll have to deal with the strength of the barrel and how it's been heat treated, what kind of steel, thickness, module of elasticity etc. then you'll have to deal with the strength of the action, and frame. These are considerations that the gun designer have had to deal with and then they recommend a max pressure that the gun function with safely. When yu start to exceed safely recommend pressures your pressing your luck. in the best case you'll only damage the gun.

[dubber123]

Supermag, not being cagey at all. As far as comparisons go, my barrel thickness Vs. pressure was and is a valid one. Everything I find on the Super indicates no special requirements for a 1911, indicating nothing special is required in the way of steel for operating at the 28,500 Psi. given to that cartridge.

I am going from a larger cartridge, to a much smaller one, which is in my favor as far as action strength. ( the opposite of your example). I am not concerned with action strength. I am quite sure, even if I am TOTALLY wrong, all I would do is wear the locking lugs, (all 3 of them) prematurely.

There is a fellow on here with MUCH experience in hotrodding shotgun actions, and in consulting with him, due to the MUCH smaller case head, (among other factors), said he would feel safe running the action to 35,000 Psi. Well beyond my self imposed limits.

My question dealt with barrel strength. Period. My blanks are current production 416 stainless. There is a heat treat code on them, and no, I don't know what it means. I am confident it is at least the equal of most if not all 1911 barrel steels.

I didn't mention my project specifically, as when you mention making a rifle out of a shotgun, many people get their panties in a twist immediately, and assume you are trying to kill yourself. I also wanted to see who could read, and understand, and who was just skimming. The proof testing on the end of a long string will have to suffice I guess.

[Wayne Smith]

Wasn't it Askins that tested the Springfield barrel/action by turning down the breach area of the barrel and firing it until it failed? If I remember right he had it about as thick as a piece of notebook paper before it failed. Granted, this was with thick military brass, but still, indicates that chamber pressure is not as critical as we may think.

I'm no expert but in a double rifle isn't the pressure of the case head against the action the limiting factor? This is what stretches the action after repeated firings and ruins the gun. I believe it is a function of the recoil pressure and the size of the casehead, but that is probably very oversimplified and maybe straight wrong!

[Ricochet]

Hatcher reported that experiment somewhere in his Notebook.

[mtgrs737]

Scanning through this thread I see nothing about the very small contact surface between the barrel and slide locking lugs being brought up. The 1911 locking lugs will wear faster with more violent loads, however most of us will not shoot that many to find out what the wear progression is, My HK full size USP is rated for 45 super ammo. 45 super brass is stronger in the webb area and you can get it from Starline.

[dubber123]

Wayne, the Askins test would have been an interesting read! Yes, overpressure loads will eventually loosen a double, (rifle or shotgun). The locking areas can get peened, and the pivot point can loosen, increasing headspace. All very expensive to fix.

Going from the large 12 ga. case head, to the much smaller .50-90 case head, allows me to run higher pressures than the 12 ga., without the action "feeling" any more stress. The fellow with all the shotgun action experience on here crunched the #'s for me, and came up with 35,000 Psi. I have no intention of going anywhere near that, so the action isn't in question, at least to me.

[dubber123]

Scanning through this thread I see nothing about the very small contact surface between the barrel and slide locking lugs being brought up. The 1911 locking lugs will wear faster with more violent loads, however most of us will not shoot that many to find out what the wear progression is, My HK full size USP is rated for 45 super ammo. 45 super brass is stronger in the webb area and you can get it from Starline.

Contrary to popular belief, and rampant speculation, we aren't really talking about the .45 Super.[smilie=1:

[S.R.Custom]

There is a fellow on here with MUCH experience in hotrodding shotgun actions, and in consulting with him, due to the MUCH smaller case head, (among other factors), said he would feel safe running the action to 35,000 Psi.

I assume you mean 35kpsi in your proposed cartridge. As long as the total pressure on the breach face did not exceed the total design pressure of the parent gun, I'd say yes, the action might be good for that. (I'd still need to know the design and proof test pressure of the shotgun in question before I could agree with certainty.)


My blanks are current production 416 stainless. There is a heat treat code on them, and no, I don't know what it means.

Now we're getting somewhere. It shouldn't be too much of a problem to call the MFR and get the needed info. With that knowledge --and the finish dimensions of your new barrel-- you could calculate the pressure capability of your barrel. The MFR may even be willing to calculate that for you.


I didn't mention my project specifically, as when you mention making a rifle out of a shotgun, many people get their panties in a twist immediately, and assume you are trying to kill yourself.

But if you had mentioned the original purpose, the panty-twist responses could be immediately rejected as invalid. (If they say it can't be done, then they obviously don't know what they're talking about.) The difficulty with posing the problem the way you did is that the only valid answer you could hope to get was "it depends," and you can get that from any 8-ball.

Actually, I'd like to hear more about the project...

[dubber123]

Thanks, Supermag, now we're getting along neighbor-like! They are Pedersoli blanks, so I don't know how much success I would have in getting any pertinent info.

Yes, the calculations were done based on my conversion cartridge. At 30,000 Psi, they came in slightly lower than the SAAMI pressure for a 12 ga. 2-3/4". 35,000 Psi. pretty well evened out the stress the gun would feel. This leaves ALL of the safety margin built into the action by the manufacturer.

I worded it the way I did, as I don't know everything about these blanks, other than the 416 stainless construction, the heat treat code, and the word "Carpenter" on them. I liked comparing them to the .45 Super, as they have basically identical wall thickness, and I have to assume of the vast array of 1911's built, by many manufactures, over such a long period of time, not all can have super strong barrel steels.

Being designed for a 18,000 Psi cartridge, (the 45 ACP), I doubted ANY of them have anything special about them, barrel material wise. The Super is considered safe in them all. I don't know if this explains my thought process any better. The much slower powder I will use I wouldn't think to be a negative as far as safety either.

[S.R.Custom]

Thanks, Supermag, now we're getting along neighbor-like!

A hand injury from back in the day has me typing as succinctly as possible. It sometimes (frequently?) comes across as a bit rude.


They are Pedersoli blanks, so I don't know how much success I would have in getting any pertinent info.

Then you can only assume with certainty the qualities of the base material.

http://www.onlinemetals.com/alloycat.cfm?alloy=416


... Being designed for a 18,000 Psi cartridge, (the 45 ACP), I doubted ANY of them have anything special about them, barrel material wise.

They will be heat treated, at the very least for wear properties. This heat treatment no doubt is figured into the final strength of the material for pressure containment purposes. To what degree, I don't know, as I'm not a 1911 guru.

I understand your logic, and it may be valid. In the thicknesses you're talking about, though, I'd be inclined to nail down the physical qualities of the material in question, or assume the worst possible scenario.

[dubber123]

.

I understand your logic, and it may be valid. In the thicknesses you're talking about, though, I'd be inclined to nail down the physical qualities of the material in question, or assume the worst possible scenario.[/QUOTE]


"assume the worst possible scenario" You sure we AREN'T neighbors? [smilie=1:

Actually, by dumb luck or otherwise, my ideas seem to pan out. None the less, maybe I'll tie on another few feet of string for the proof firing.

I checked out the metal link provided, and they list 416 stainless, in ANNEALED condition, which I assume means no heat treatment at all, (I.E natural state), and they list it as rated for 39,900 Psi yield strength. If this info is correct, I should be OK. Makes me feel a little better at least! Thanks for that link Supermag.

[S.R.Custom]

You sure we AREN'T neighbors? [smilie=1:


We may have been at one time; I used to live in Shoreham. ;)



I checked out the metal link provided, and they list 416 stainless, in ANNEALED condition, which I assume means no heat treatment at all, (I.E natural state), and they list it as rated for 39,900 Psi yield strength. If this info is correct, I should be OK. Makes me feel a little better at least!

Not so fast... yield strength is more a description of the property of the material than it is a measurement. There has to be a thickness component in the equation. I'm just a dumb architect, so I don't know the process for calculating the pressure containment capability of materials. (I can only tell you how tall you can make a column of the stuff before it buckles.) You should probably quiz your engineer brother in law on this. Or maybe we're lucky enough to have one lurking here? (Engineer, that is.)


Actually, by dumb luck or otherwise, my ideas seem to pan out.

I used to rely on it quite a bit myself, but my lifelong education has taught me the stuff is finite in quantity...

http://images.despair.com/products/demotivators/trouble.jpg

[dubber123]

Not so fast... yield strength is more a description of the property of the material than it is a measurement. There has to be a thickness component in the equation.
[Quote]


I kind of thought so too... Maybe the site wasn't so usefull after all...[smilie=1:

I'm not sure without knowing the exact properties of this steel I will ever know. I will probably just do it like they did 100 years ago: Load it well past your proposed operating level, fire it remotely, and if nothing stretches, cracks, or goes flying, load down and continue on.

[S.R.Custom]

Well, that works too. I was just trying to save you from having to buy string. :mrgreen:

[leftiye]

Otra vez people. Repeat after me... The force that stretches a break action rifle or shotgun isn't pressure against the standing breech. It is the tendency or desire of the barrel to depart downrange. And, yes, as stated the action can be stretched.

Dubber, I'd help if I could, but I can't with the lack of info being given here. Concept to worry about - it will not just be how thick your barrel is that you must worry about. It will be the tensile strength of the steel per square inch multiplied by the lengthwise section of one side of the cylinder wall - as compared to the total area of the inside of the cylinder per inch multiplied by the pressure applied. I have it (the formula) somewhere, but don't remember where, and I can't remember what it is exactly. Very interesting thread, would be more interesting if we could get down to cases (not brass ones, pun not intended).)

P.S. Rifle barrel blanks are NOT generally heat treated, except maybe (hopefully) to be stress relieved. I believe (and may be wrrrr..., but I doubt it) that this limits the tensile strength to that of mild steel or about 60,000 Lbs/psi. BIG difference between this and the 225,000 psig. yield strength of 4140 chrome moly in other appliations where it is HTed to Rc of 45.

[dubber123]

Leftiye, I know my lack of barrel specifics makes this whole thread a moot point. Assuming that 1911 barrels weren't of super twice cryogenically treated double heat treated Titatium coated wonder steel, and having them be coincidentally the same thickness as my blanks was as close as I could come to a planned Psi range. If they are safe, I figured mine would be too..

I understand what you are saying about the barrels wanting to move forward, but didn't some crafty fella have some saying about: " For every action, there is an equal and opposite reaction"? If my calculated breech thrust is within the normal range for the gun, the forward thrust should be no more, correct?

Supermag, I'm not buying string, I'm gonna borrow it....

[S.R.Custom]

Hee hee, look what I found--

http://www.engineersedge.com/calculators/shell_internal_pres_pop.htm


Caveat: There's some serious math behind this. Who knows if the author got it all punched into the spreadsheet correctly. (But if he did, how cool is that?) Anyway, it's worth what you paid for it.

[dubber123]

Ok, my heads swimming, about the only thing I can get a grasp on is the Radius...

Also, which variable given is for the cylinder material? Obviously steel will contain pressure better than PVC pipe.

[S.R.Custom]

Let's use the .44 Mag SBH as an example, ignoring the effect of the cartridge case-

P= maximum anticipated pressure (max load). Let's say 35,000 psi

R=radius of the chamber. 0.23"

S= yield strength of the material. Assuming the use of 4140 Pre-heat treat, roasted and quenched to 100,000 psi

E= 1 (We have no joints.)

Punch it all in, and I get 0.102" as a wall thickness for the SBH.


Which is pretty close, considering the actual wall thickness of the chamber wall (at its thinnest) of my SBHs runs about .095". (I suspect that Ruger actually heat treats to 120Kpsi or more, because as anyone who has ever reamed one out will tell you, those cylinders are harder than the hinges on the gates of Hell.)

[BeeMan]

Dubber,

Another source to research is Machinery's Handbook.

I don't know, but what Supermag linked is likely the thin wall calculation. Machinery's explains the difference between equations for thin wall and thick wall vessels. Of course a barrel is machined from stock and has no weld so the joint efficiency at the linked calculator doesn't apply.

If this works, here are the appropriate equations. I'm sorry but you'll have have to look it upto understand the variables and units. I'm a lousy typist and would not want to make an error typing out what is in a readily available text.

Lames
s = p(R2 + r2) / (R2 - r2)

radial at chamber ID
s = ((pa2)/(b2-a2))(1-(b2/a2))

Radial at barrel OD
s = ((pa2)/(b2-a2))(1-(b2/b2))

Tensile at chamber ID
s = ((pa2)/(b2-a2))(1+(b2/a2))

Tensile at barrel OD
s = ((pa2)/(b2-a2))(1+(b2/b2))

Use at your own risk due to risk of typos and nonstandard use of terms. I highly recommend a spreadsheet or at least showing every step on paper if you use a calculator.

BeeMan

[dubber123]

Thank you both, Beemans formula has likely given me a permanent headache. Using Supermags link, this thing should blow up the first shot, no question.

Supermag found me some excellent links. One of which I believe is to the supplier of the blanks. I need to have mine Rockwell tested, and when I do I can use their chart to determine actual yield strength. They may be 100,000 Psi blanks. I will see about getting them tested this weekend.

[Cap'n Morgan]

Save yourself the headache and build a simple proof setup, using the barrel in question. 8 grains of Bullseye behind a 230 grain bullet will generate 41.000 psi - that's roughly twice the SAAMI max load. If the barrel survives that, it will stand up to anything you can throw at it.

[dubber123]

Save yourself the headache and build a simple proof setup, using the barrel in question. 8 grains of Bullseye behind a 230 grain bullet will generate 41.000 psi - that's roughly twice the SAAMI max load. If the barrel survives that, it will stand up to anything you can throw at it.

Read back through, we aren't talking about .45's.... :D

[Cap'n Morgan]

Read back through, we aren't talking about .45's.... :D

No problemo. If you have the cartridge specs and max testing pressure (e.g. max pressure +50%), Quickload will come up with a suitable load.

Oh, and please use a lanyard...:wink:

[BeeMan]

Dubber,

Time for some additions and corrections -

The booklet is 'Building a Single-shot, Falling-block Rifle Action' by Walter Mueller

http://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=13833&title=BUILDING%20A%20SINGLE%20SHOT%20RIFLE%20ACTIO N

On the formulas, the formatting did not copy and paste as intended. The numeral 2 was supposed to be indicating the value was squared.

s = stress (I don't know how to generate the appropriate engineering symbol on this contraption)
p = internal pressure
a = internal radius (chamber ID divided by 2)
b = external radius (barrel shank OD divided by 2, use minor diameter if under threads)
r = selected radius

Hope this helps with the headache:coffee:

BeeMan

[felix]

Hopefully, the newer guns are using the steel developed for the Ruger 454. The steel knows how to stretch significantly more than the usual run of gun steel, including 4140 that Ruger typically uses. The bonus is that Ruger and the steel company released this steel formulation to the gun public for anyone to use. ... felix

[JIMinPHX]

In a 1911, you can reduce stress on the brass by delaying the unlock time with a modification to the firing pin stop (yes, that's right, the firing pin stop). That does not address the issue of stress in the chamber/barrel. If you aren't the guy that made the barrel, then you don't know the material & heat treat that was used. You are navigating in uncharted waters.

To do that project correctly, you need a whole lot of test equipment & you need to do destructive testing on a representative sample of equivalent mechanical systems so that you can calculate your safety margins. I don't think that it is a good idea to just work it up higher & hope that it is going to be OK in the long run just because it survived a higher pressure proof load once. The working pressure needs to be far enough below the yield pressure of the system so that significant metal fatigue is not set up with each progressive shot. That ratio of yield pressure to distortion pressure varies with alloy & heat treat. You don't know what you are dealing with & you don't know what the test parameters need to be. You are feeling your way around in the dark & I would not encourage you to continue.

Sorry for the negative opinion,
Jim

[dubber123]

Ok guys, I just had my barrel blanks hardness tested. The number is 27 on the Rockwell "C" scale. Twice. Using one of Supermags links to the Kalyani Carpenter steel site, 416 stainless steel at that Rockwell comes out to about 104,370 Psi yield strength.

[S.R.Custom]

Ah, I can feel the joy from here. :-D

[dubber123]

Ah, I can feel the joy from here. :-D

You have no idea... Many thanks!:-D :drinks:

[leftiye]

So Beeman how about running the numbers for Dubber's barrels through the formula for us ? Please!

[dubber123]

So Beeman how about running the numbers for Dubber's barrels through the formula for us ? Please!

With that yield strength, at .100" wall thickness, it will contain 30,700 Psi. An operating load will of course be quite a bit lower, to give you a safety buffer zone.

I have to decide if I will be happy with a 25% buffer zone, or if I think I need 50%..

[dubber123]

Proofing at 33,800 Psi. http://i254.photobucket.com/albums/hh83/dubber123/IMG_3081.jpg Load was a 450 gr. boolit, 81 grains of Varget. THIS WAS MY PROOF LOAD, NOT LOAD DATA! (Liability Disclaimer)

[dubber123]

http://i254.photobucket.com/albums/hh83/dubber123/IMG_3093.jpg Cases fell from the chambers, and fall right back in. It doesn't look like it is even breathing hard... Other than the recoil....

[leftiye]

In those lower pressures (though 33,000 may be a bit high for this), often the only real pressure signs you'll get is moderate case expansion in front of the case head. If fired like that , or with your normal loads, neck sized only - eventually cases would stick. The pressures in effect don't completely rely on the barrel for support, only on the cases. Check your barrel for bulges, that's where you would find failures first at those pressures. Is BELL making brass again? (Ackley did tests to see where unsupported brass failed, and didn't get case head separation failure until about 35,000 psi.)

[BD]

Never mind, I found it down in special projects.

BD

[dubber123]

Thus far, the barrels look the same as when I put them in. The liners push in and out with hand pressure, so they are easy to inspect. I have 50-60 rounds fired.

[S.R.Custom]

... The pressures in effect don't completely rely on the barrel for support, only on the cases.

Yes, the cartridge cases add some strength to the system, but because they are but a mere .015" or so thick at their thinnest , they are ignored. For the pressures in question to be able to rely "only on the cases" for support, the cases would have to be more than a quarter inch thick. And that's assuming modern cartridge brass specifications.

Dubber, done any target work yet? How far down range can you keep both rounds on a pie plate? An interesting aspect of your setup is that you can 'index' the barrels inside the shotgun tubes. Which is, I assume, the purpose of the Sharpie markings on the cases...?

[dubber123]

Yes, the cartridge cases add some strength to the system, but because they are but a mere .015" or so thick at their thinnest , they are ignored. For the pressures in question to be able to rely "only on the cases" for support, the cases would have to be more than a quarter inch thick. And that's assuming modern cartridge brass specifications.

Dubber, done any target work yet? How far down range can you keep both rounds on a pie plate?


Pie plate?, 25 yds. Maybe! :roll: I dunno. I just fired 2 with 60 gr. W-748., 500 gr. boolit, 20 yds. both within an inch or so , (shooting at a snow bank. I'm loading 2 more with 62 grs. I may hang up a target for these. I'm nervous I may run out of adjustment. Time for "plan B" then.

Actually the Sharpie marks on the case was to keep the proof loads seperate. There are marks on the liners and shotgun barrels. The elliptical on the muzzle definately works, I just don't know if I have enough.

[S.R.Custom]

Also-- do you get any torque effect rotation of the barrels?

[dubber123]

Also-- do you get any torque effect rotation of the barrels?


The barrels do not move at all when fired. Push the liners back 1/2", and they slide out with your fingers. I assume the case is gripping the chamber, and the breech face, preventing rotation.