12 Bore Schrifle project

Chris would love to see what kind of hole this will put through some plywood....then maybe a 2x10
So far I have 12 of them cast... They burn through the lead in my melting furnace like crazy so they take longer to cast than normal bullets because of that. But they heat up the mold really quick! So far I have just loaded the one as an experiment. There is no load data for a 775 grain bullet with lube grooves, fired from a 2 3/4" shell, but shotguns are among the most forgiving things to reload. I found a 1.75oz shot load using blue dot (which is faster than 300 MP) for a 3" shell and it was showing a max charge of 38 grains so I thought I would try 30 grains of slow magnum ball powder as a start and see where it goes. Obviously a shot charge doesn't have to press a bullet into rifling, which will increase pressure, so I went a little conservative. Plus the bolt action marlin seems to be a pretty stoutly built gun. I can't wait to get to the range and try this out! We'll see how bad the recoil is. Calculation shows that it will be right up there with my .416 Ruger but we'll see.
 
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finally got my brass cases in today... So I loaded one up. It reminds me of a massive .38 wadcutter
 
Eagerly awaiting the results.....
 
Eagerly awaiting the results.....
You and me both! But we are inundated with snow and 15 F temperatures and have been for the past 3 weeks :mad:. I am waiting for a nice day to get to the range.
 
Chris, out of curiosity have you discussed your project with the engineers at Marlin? If so, what were their thoughts?
 
Chris, out of curiosity have you discussed your project with the engineers at Marlin? If so, what were their thoughts?
I have not. Why do you ask?

Out of any liability, I can tell you that ANY manufacturer will tell you not to use ANY handloaded ammunition in their guns because they have no control over it. They're gonna shoot me down no matter how safe the load and project might be. It also has been about 20+ years since marlin manufactured this gun and the company has changed hands a number of times. I don't even know if anyone there would know more about it than you or me.
 
Like I said, curiosity. Many, many years ago I hunted deer up close in heavy cover with a 12 Ga. and slugs. But I don't recall them being as heavy as the ones you are proposing. If I remember correctly it was Winchester that offered the fastest slugs.
 
Like I said, curiosity. Many, many years ago I hunted deer up close in heavy cover with a 12 Ga. and slugs. But I don't recall them being as heavy as the ones you are proposing. If I remember correctly it was Winchester that offered the fastest slugs.

A standard slug is 437.5 grains and is booking along at about 1,600 fps. Mine weigh in a 775 grains and are designed like bullets with lubrication and lube grooves. I am only looking to get about 1,100-1,200 fps out of them but we will see where we land. I have started with the slowest pistol powders I have and may ultimately end up going with a rifle powder like Reloder 7.

The loads for the brass cases are 20 grains of blue dot as a starting load. The most conservative Max charge listed by Alliant for 2oz shot charge (875 grains) in a 3" shell was 33 grains. Owing to the fact that a shot charge doesn't need to press into rifling, I dramatically reduced my charges. ( I may only get like 500 fps with these loads but it's a good starting point.) A shot charge also has the powder pressed under the wad under some compression and in a plastic hull. My shells are tremendously more voluminous than a plastic shell due to the very thin brass walls. Even so... the walls taper a little so the 11 gauge over powder wad becomes wedged in about 1/8" above where the powder column ends. So there is an air gap there. You can actually hear the powder in my brass shells so they aren't compressed at all. The only other load was that plastic shell which was 30 grains of Alliant 300 MP. 300 MP is significantly slower than Blue Dot (even slower than H-110) as it is designed for maximum charges in heavy magnum revolvers. Even so... it is about 1.75x the charge used in a .410 shotshell. Given that a 12 gauge brass shell has an average of 3.5-4x the volume of a .410, I figured that a charge in the safe range for blue dot with a similar weight loads, should be more than safe for a significantly slower powder.

I had to use data for 3" hulls because it is so hard to cram 2 oz of shot into a 2.75" shell. However a 3" shell is still rated at the same pressures as a 2.75" hull. It just has larger shot capacity. This is why they are usually marginally slower than 2.75" shells. So, powder charge for shot loads should be similar to a slug charge given that most slugs have no need to be squished into rifling... Mine however does, so I significantly reduced the charge to start with. Because all the space in a shotshell is taken up by either wads or shot, case capacity has almost no effect on pressure for these shells (except for marginal differences in internal dimensions from different manufacturers). So a 3" shell should have the same space for combustion as a 2.75" shell of the same make, it just has more space for shot. In fact, there are 1-3/8 oz, 2.75" loads that have HIGHER max charges than 1-3/8 oz 3" charge weights... all just based on plastic or paper hull designs. So, to my way of thinking, you could effectively interchange the data between 2 3/4" hulls and 3" hulls and give them a margin for error.

I am not trying to make excuses here, I am just trying to effectively explain my reasoning for choosing the weights of powder that I did, and the reasons I believe they will be well within pressure maximums for a 12 gauge barrel and action.

The original paradox cordite load was a 750 grain bullet at 1,200 fps from a thin walled 12 bore paradox gun so that was what I was shooting for. (no pun intended.)

I am a nervous Nelly when it comes to making sure I don't blow guns up in my face and that is why I gave myself so much margin for safety with these initial loads.

I hope that makes sense...

Now... if you ran the data in quickload and tell me that I am going to be running 30,000psi... I will definitely rethink my approach. I do appreciate your concern.
 
Like I said, curiosity. Many, many years ago I hunted deer up close in heavy cover with a 12 Ga. and slugs. But I don't recall them being as heavy as the ones you are proposing. If I remember correctly it was Winchester that offered the fastest slugs.
Actually I just found some load data for the Dixie Triball load. pressure tested by Dixie Slugs. It is 3x .600 round balls for a total 975 grains. His load data was 28-29 grains Alliant Blue Dot in Cheddite hulls.
 
I just looked at Quickload. It doesn't have any loads for shotguns. It seems to me that most rifles perform better when loaded close to or at their maximum. There are also ramifications from using charges below the minimum recommended load. BTW I am concerned about your safety, but at the same time see that you have done enough research and enough thinking about the project to warrant continuing with it. The "wildcatters" of the past did much the same as you are doing. Now some of their ideas are standard offerings.
 
Gonna put one heck of a hole in anything you hit with that cannon. Interested in how she shoots...
Bruce
 
I just looked at Quickload. It doesn't have any loads for shotguns. It seems to me that most rifles perform better when loaded close to or at their maximum. There are also ramifications from using charges below the minimum recommended load. BTW I am concerned about your safety, but at the same time see that you have done enough research and enough thinking about the project to warrant continuing with it. The "wildcatters" of the past did much the same as you are doing. Now some of their ideas are standard offerings.
Thanks for checking anyway. I can see concerns about reducing load data too much if I had a whole lot of empty space in the case. I made sure I filled in the case with wadding so I wouldn't get detonation issues. I will let you know if it looks like a nerf dart going downrange or if I get it stuck in the barrel. Although I doubt that 20 grains of blue dot won't push that load clear of the barrel at least...
 
So I took it to the range today to chronograph...

5 loads of 20.0 grains blue dot

Vel avg. 455 fps

1 load of 30.0 grains 300Mp

Velocity: 647 fps.

All felt like powder puff loads with a lot of unburnt powder. About half of them hangfired. I am pretty sure this is due to the very low powder charge. The primer has the oomph to push everything a little ways out of the shell before the powder has a chance to burn and you get rounds that hang for about a tenth of a second then light off with more the sound of a rocket than a gun. Pressure was barely sufficient to seal the case as every load had powder around the outside of the case and spit debris back in my face a bit before pressure built to the point that it sealed and drove the bullet from the barrel.

Big bores are a whole other ball game with the struggle being trying to build pressure, not keep it down...

I guess we're going up in powder charge a bit...
 
So I will ultimately have to give up the idea of using the brass casings. They have far too large ID and require a heavy crimp just to hold the slug in place and get proper ignition (without the crimp the round kind of just -pfffftBOOM-s, even with fast powder like Unique). The problem is that the crimp never fully opens back up and crimping so heavily has caused a few of them to split at the neck on firing after only one loading. So I ordered a bunch of cheddite 3" hulls and a BPI roll crimper. Gonna try and build some modern looking paradox loads that are similar to the ballistics of the original kynoch loads except mine will be 775 grains instead of 735. still going to be shooting for 1,200 fps. Apparently you can get that with PSI as low as 6,000 in a 12 bore. Gotta love them huge pushing surfaces. up around 9,000psi, with blue dot, you can easily get 1,450 fps and 3,600ft-lbs. not quite up there with my .375 H&H but with that much weight and diameter, it's gotta have one heckuva punch!

I will keep updating this periodically as I finish load development and start stock modifications.
 
Why did you cut it off so short?
 
Why did you cut it off so short?
To make it light and handy for the thick Adirondack woods. It has zero effect on the ballistics because it is 12 gauge and only makes easier to point and carry. Recoil with the load approximating the original Explora or Paradox loads is pretty mild.
 
chris,
with the low pressures of black powder, we need to anneal the brass cases more than for smokeless in order to get good case obturation.
of course any case annealing is actually partial annealing, as a full anneal would make the brass way too soft.
it would also help the crimp to flatten out on firing, as well as minimize case splitting.
this does not however solve the wall thickness issue.
on the cast boolits website are sometimes seen threads about mostly 20 gauge single shots with rifled barels.
bruce.
 
chris,
with the low pressures of black powder, we need to anneal the brass cases more than for smokeless in order to get good case obturation.
of course any case annealing is actually partial annealing, as a full anneal would make the brass way too soft.
it would also help the crimp to flatten out on firing, as well as minimize case splitting.
this does not however solve the wall thickness issue.
on the cast boolits website are sometimes seen threads about mostly 20 gauge single shots with rifled barels.
bruce.

Thanks! I just got my BPI roll crimper and made up some shells yesterday. They don't look as cool but they are infinitely easier to load. I haven't shot any yet but we'll see how the point of impact shift from a properly loaded heavy bullet. I have relegated the brass shells to heavy buckshot loads. I can fit the appropriate charge of blue dot under 15 pellets of 00 buck in a 2.5" shell because their interior volume is so large.
 
Have you considered a veggie or wool wad on top of the powder?
 

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