Oversize chamber

[megasupermagnum]

I am trying to build a .410 shotgun, rifled slug gun using brass shells. To do this I am using 9.3x74R brass. I plan to trim to 2.5", and fire form. There is a number of sources on how to do this, however, my question pertains to the chamber.

I intend to shoot these hard, up to full power 45,000 psi levels. I plan to have a chamber reamer made, but it needs to be able to safely chamber and fire a .410 plastic shotgun shell to remain what is considered a shotgun by the DNR.

I'll post below what a Federal .410 plastic shotgun (labeld .410 shotgun) shell measures, followed by a 9.3x74R (labeled .410) sized approximately what it would measure for my purposes. My main concern is the case web, which measures .473" on a .410 plastic shell, and .463" on the 9.3x74R brass.

Now this will be built on a bolt action, and I do not ever intend on shooting plastic shells out of it besides just to test fire, or prove that it is a .410 shotgun to a DNR officer. Can I get away with a chamber that is .474" at the opening? If so, will .011" oversize cause any safety problems with 9.3x74R brass?

[Moleman-]

The base will take a pretty decent load to fireform up near the base, and around 1/8" in front of the rim will likely stay pretty close to what it is now. As long as you're sizing to .473" dia and not the smaller .463" every time the brass shouldn't be overworked. What action are you using?

[megasupermagnum]

As long as I can get away with it, I only intend to neck size just enough for the bullet using a .450" 44 magnum sizer. I would probably size no more than 1/2" down at the most. I will be using a Savage 110 action for this, and be using a 44 caliber barrel blank.

Here is another question for you. When trimmed to 2.5", just a small section of the original neck remains. 9.3x74R is meant for a .366" bullet. Would it be better to size down just a little bit and use a .357 bullet, or would it be better to expand and fit a 44 caliber bullet in there for fireforming. I believe I can make both ways work. I expanded one today, first with a tapered expander, then with a NOE .429" expander plug.

A third question. I am using brand new Hornady brass, that is presumably annealed. Should I anneal these again, or can I get away without it?

[EDG]

Have you ever fired a real .410 rifled slug load?
If you stick with the original rifled slug design they are a joke. I shot an armadillo at about 20 feet with one and the slug did not exit the armadillo. After the buzzards got through a week later the armadillo shell had the slug still laying in it mashed out to the diameter of a quarter.

[megasupermagnum]

Sure, my great uncle used to hunt deer with an old ward western bolt action .410. He hunted about 30 years with it with nothing but good results on our northern whitetail bucks until he lost his hand in a work accident.

I've never tried them on deer myself, although I have shot .410 slugs. Shooting water jugs, I didn't see much difference between them and a 357 magnum.

That's not all that related though, as what I am doing will be on par with a 444 marlin. I'm looking to shoot 300-350 grain bullets at about 2000 FPS.

[Moleman-]

If it were me, I'd start by annealing the case neck. Then expand with a well tapered and lubed .427" expander as deep as you can go until the case starts bulging excessively because of the case wall thickness. Run back through a sizer and trim to length on the long side. The cases will shrink in length a little as the cases expand. The more they have to expand the more shrinkage there will be. I do a similar thing for several wildcat cartridges including 30-06 cases to make a 44x1.8" which will launch a 265gr interlock at over 2300fps out of a 16" barrel. The only area that really fireforms is the area above the case head as it is usually the only area undersized before firing and takes a decent load to expand.

[megasupermagnum]

Ok, that sounds like a good plan Moleman. How much longer should the chamber be than the brass?

[Moleman-]

Are you going to headspace both off of the rim, the case mouth or one of each? 9.3x74R looks to have a .055" rim where 410 is listed at .060". Don't have any 9.3x74R to check but a box of Win super-X 3" #6 shot seems to have a rim .055"-.057" thick. If you were going to headspace it off of the rim, you'd need a lip on the chamber except on the bottom for feeding and where the extractor rotates. I would suspect that if the HS was on the tight side for 410 it would still close since the 410 rim isn't solid on most shells.

[AntiqueSledMan]

Hello megasupermagnum,

Why not use Magtech Brass Shells?

https://www.ballisticproducts.com/Ma...tinfo/3924165/

I would think if a Warden would check your ammo with a 9.3x74R head stamp he would issue a citation.

AntiqueSledMan.

[Wayne Smith]

If you go ahead with this fire form your brass with a couple layers of Scotch tape around the base, enough to just fit into the chamber. This centers the case and the fireform exists ahead of it, centering the fireformed case. Not my idea, came from reading Donnelly et al. After fireforming the case the tape can be removed as the fireformed case will be centered for all future shooting.

[GhostHawk]

To be honest I think you are skating around the edge of the rules here.

If a gamewarden ever looked down the barrel and saw rifling where he was expecting smoothbore I suspect you'd be in trouble.

Essentially, if I am reading this right, you want to make a rifled barrel with brass case that would shoot essentially a .44mag bullet. But still be able to chamber a .410 shot shell.

I think at the least you are breaking the spirit of the law. Maybe more, maybe no. Would depend on how the law is actually written, and interpretation by the officer.


That being said, I've watched my dad take more than his share of deer with a .410 pump shotgun and slugs. Trick is you have to get close.

All that being said, its your project, you decide. But I think your riding for a fall. And felt duty bound to warn you.

[AntiqueSledMan]

GhostHawk,

Minnesota does allow rifled barrels in the shotgun zone.
But to build a wildcat cartridge and call it a .410 shot shell
would be the question, my guess is any warden or judge
would see a rifle with a wildcat cartridge not a shotgun.

AntiqueSledMan.

[megasupermagnum]

Yes, absolutely no law against rifled barrels here. Rifled barrel shotguns have been used since they first came out a long time ago. Believe me when I say I've done a lot of time digging through the laws about shotguns. The scary thing is the only thing the DNR books say on the matter is a "shotgun shooting single projectile". I've called 13 individuals asking for a definition of a shotgun, including the warden in my hunting area. Not a single one of them has called me back. Most didn't even answer their phone. I talked to the warden a while, and he again said "shotgun shooting single projectile". I asked specifically, can I shoot brass shells. He said no problem. I asked if there was any reason I couldn't use 444 marlin brass. That got him stumbling. I asked again, what is the MN legal definition of a shotgun, remembering that rifled barrels are allowed. He had no answer, and said he would call me back. He never did.

The point being that the Minnesota DNR does not recognize what a shotgun is. Is it a smooth bore? No, rifled barrels are allowed. Is it the plastic case? No, brass cases have been used since the dawn of time, and there is no law against them.

The only thing I am changing is I am using a 44 caliber bullet, rather than 41. I am fire forming 9.3x74r brass to a .410 shotgun. We are discussing minor differences here, but that is only because of a lack of good, reasonably priced .410 brass. I will be shooting .410 brass shells in a .410 shotgun with a rifled barrel. The only thing wild cat about it is the amount of powder I'm going to use. Spirit of the law, that's a good one! If the intention was to limit range for sporting or safety purposes, why can't we use buckshot? I'd much rather use my favorite shotgun and 000 buckshot. This project is mostly for fun.

Magtec brass is no good for a number of reasons discussed in my other thread in the special projects section.

Anyway, thanks for the tape idea for centering the brass. As for headspacing, on actual cartridges I don't see much difference for rim thickness. A plastic shotgun shell is anything but precision. I would much rather headspace for the 9.3x74r cartridge, and have it a tight fit for .410 plastic shells. Being a bolt action, I don't think it will be a problem. Savage actions have been chambered in rimmed cartridges before, so I don't think it will be a problem. A sharp edge on the barrel shank should do the trick. I already don't expect it to feed from the magazine, and will use this as a single shot.

[AntiqueSledMan]

Hello megasupermagnum,

I had a conversation at the local gun shop today on this topic,
he claimed that the state is considering making straight wall
cases legal in shot gun zones. That would make it a lot easier.

AntiqueSledMan.

[megasupermagnum]

Yes it would. It was up for vote this year, did not get passed. As far as I know, us and NY are the only two states who have not allowed straight wall cartridges yet. Personally I think the whole thing is ridiculous. Just allow firearms during the firearms season, don't even dink with only allowing some straight wall cartridges. The best season is muzzleloader anyway. I've always said the regular firearms deer is the 2 weeks out of the year even non-hunters come out, get drunk, and shoot deer. I'm glad they do. 2 weeks to get it out of their system, and the rest of the year is perfect for hunting. I'm just fortunate to have private land to hide on for regular firearms deer.

Anyway, that's why I'm building this rifle. It's currently legal as a shotgun. When straight wall cartridges are allowed, it will still be a top choice. For kids, it can't be beat. I believe my nephew will be using it in a couple years, and loaded to handgun levels will have no recoil. For the rest of the year, I think it would be great to shoot blackpowder for fun. This rifle checks all those boxes.

I called a gunsmith today, he says he sees no problem with it. Find a contoured barrel, bring him the reamer, and $250, done deal.

[GhostHawk]

Well I agree with you, and I don't.

There is a difference between a rifled shotgun barrel, shooting shotgun slugs.

And a .44mag barrel designed to shoot essentially a center fire rifle. With resulting higher pressures and speeds. Which happens to be chambered to also fit a .410 shotgun in order to get around a law.

Pressures, speeds, are vastly different. Where the law is concerned I suspect your in a gray area.


But, as I said, its your project, your money, your reputation that you are putting at risk.
Only you can decide if it is worth it.

But IMO there is a big difference between a rifled shotgun barrel shooting factory or hand loaded slugs at 12-1500 fps.
And a center fire rifle that can easily enough kick that up into or above the 2400fps. To me you are violating the intent of the law. That being to limit the range that a stray bullet can travel before it hits ground, tree, or someones house.

I do agree they need to define what is a shotgun and what is and what is not allowed.

Having grown up hunting deer with shotgun and slugs in northern Minn I think I disagree with the way you are going about it. Play the game straight up, no blurring of lines, no fudging of rules. Just get sneaky, get close, and put them in the freezer and hang them on the wall.

But I could be wrong, have been before, will be again. No ill will or hard feelings intended. It is an interesting discussion and project.

[GregLaROCHE]

Buy a .45-70 and be done with it. Unless you’re hunting in a shotgun only area and trying to slip past the regs. If so when building this gun, make sure you choose the correct rifle twist for the boolit and charge.

Good luck and let us know how it works ou.

[megasupermagnum]

I mean no insult, but I am genuinely curious. In what way is a hot loaded .410 plastic shell ok, and a hot loaded brass shell not? Nowhere does it say you have to use plastic, or paper, or one of the other things shotgun shells have been made out of. Would it be better if I used a .410" groove barrel?

The law is gray. Unless they specify smooth bore barrels with slugs or buckshot, there is no such thing as playing it straight up.

If the intent of the law was to limit over travel of a bullet, buckshot would be legal. It is not.

Let me put it to you another way. A number of factory loaded 12 gauge sabot slugs are a 300 grain bullet at 2000 fps. The 3" Remington AccuTip is a 385 grain bullet at 1900 fps. Realistically, my .410 shotgun will be able to launch a 300 grain bullet at 2200 fps, a 350 grain at 2000 fps or so.

[megasupermagnum]

Buy a .45-70 and be done with it. Unless you’re hunting in a shotgun only area and trying to slip past the regs. If so when building this gun, make sure you choose the correct rifle twist for the boolit and charge.

Good luck and let us know how it works ou.

Yep, shotgun only zone.

I'm looking at a Pac-Nor 44 caliber 1:18" twist. That should do the job.

[17nut]

Why not put the buggy in front of the horse?

Why not cut the chamber to fit the 9,3 cases perfect and then have a small handfull of .410 shells that you size while loaded so they fit your chamber?