Headspace Mosin .410

[dragknee89]

I have a couple Mosins and was just given a T53 that is shot out. I'm on my winter layoff at work and for a fun project I want to try to convert it to a .410 shotgun. I went to school a few years ago for machining and have access to a mill and lathe, but this is my first major gunsmithing project. One of my dad's friends has a bit I can use to bore the barrel and I'm going to rent a chamber reamer. My issue though is headspacing.

I was told on chatroom last night that to correctly headspace the rifle I would have to pull the barrel and cut it down. I'm really not wanting to get into that. I know a lot of mosin headspace issues are resolved by changing the bolt head. It has a rim that is .064 above the bolt face. Since the .410 will sit slightly deeper into the chamber due to the tapered rim, could I compensate by turning this bolt head down the same amount?

A few of the mosin guys I have talked to say it will work, but I wanted another opinion. Either way the first shot will be done remotely. I don't think it will blow up, but a face full of hot gas/powder is possible.

Thanks guys, Brad

[leebuilder]

Any ideas on useing the chamber reamer though action?. Maybe a problem. Just sayin
pulling the barrel will let you bore and ream much more effeicently and solve any head space questions as or if they excist.
Been toying with the same idea but would recylce an old 410 barrel

[dragknee89]

With the 10'' extension I'll be able to ream through the action. I want to try to do it without pulling the barrel. I tried on another junker I have a nice barrel for and ended with a ***** situation. I dunno, I figure something out of scrap it for parts like the other one.

[leebuilder]

Been thinking. Is there anyway you can determine what the distance is between the chamber end of the barrel and the bolt face?. Maybe squish something in there and measure the distance between?. I am thinking 7.62×54r rim thickness might be to great. I am away from my shop so i cant compare to see for myself. Please feel free to ask and expand on this idea.
***** happens,,, trial and terror.

[LAGS]

I like your idea to convert a MN to a .410.
But there are several factors that you have not considered when you intend to Re- Bore the existing barrel and chamber.
First, you do not want to remove the barrel.
The chamber and cartridge on a 7.62x54 is .489 wide at the rear.
A .410 casing is only .477 wide.
That would mean you would have to set the barrel back a considerable distance to be in the area of the existing chamber where you can Cut the new .410 chamber.
Setting the barrel back would also solve the headspace issue.
But is there enough barrel shank to set the barrel back that far, and still have a shank to rethread to fit to the receiver.
My guess is you would have to shorten the rear of the barrel by 3/4' to 1' minimum
If you were to fire a ,410 in a chamber that is too wide, it would most likely expand the base of the shell and split right at the base of the rim.
Thus blowing gas and who knows what else to the rear into your face.
Also, the magazine and bottom of the receiver would have to be opened up to feed a.410 shell since the cartridge is straighter down the sides.
I like to see that you are trying to salvage what you have and try to use what you have.
but there are proper ways of doing gunsmithing , and you are going to spend Far More money to try and reserect an old damaged gun, rather to just buy an new barrel for what you have and replace it properly.
Back in my youth, I toyed with similar projects because I didn't have the proper tools or money to do things right.
But after further education, I am glad I didn't waste my time, and money on a project that I would never be satisfied with, and could be potentially Unsafe.
You really should do some more reading and learn all the factors in making a conversion before attempting such a project.
Good luck on your project , and keep us posted on your decisions or progress.

LAGS, - ( Larry A "Gun" Smith )

[leebuilder]

Home now just in the shop. LAGS is right, you can almost see the differance in dia, mics confirmed it, mosin barrel is no good.

[LAGS]

I am sure if someone really wanted too, they could bore and ream the barrel to .410 and ream the chamber straight and sweat solder a insert into the chamber, then cut the chamber for a.410 shotshell.
Then for the headspace issue, silver solder a shim to the bolt head face to take up the extra headspace gap.
But bottom line, the barrel would have to come off anyway, so why not save yourself the agravation , and order a barrel from GPC, or even a brand new one from McGowens Barrels.
Besides; A .410 on a MN action would make a pretty Poor Shotgun, as did the Lee Enfields that they converted to .410 for police riot control in India.

[Geezer in NH]

Gunsmith time IMHO Not a do it yourself project.

[LAGS]

I agree, This kind of " Experimental Project" should be left to someone with vast experience.
I take it, the reason for not wanting to pull the barrel is because you do not have a barrel Vise and action wrench to fit the Mosin Nagant.
A word of advise.
Do not attempt to remove the barrel in a regular Bench Vise and use a Pipe Wrench to remove the barrel.
You will surely warp and crack the receiver.
Also, "Do Not Use Heat" to try and break the receiver free from the barrel.
Heating the receiver is a sure way to ruin a receiver, either by warping it, Cracking it, or ruining the casehardening where it will be unsafe to shoot.
If you want to do your own gunsmithing, then Please learn the Proper way , and use the proper tools.
Your life and limb is worth way more then the money you will save by doing things the Billy Bob Bubba way.

[Ballistics in Scotland]

I'd endorse all the warnings above, and add only that the silver soldering of a chamber sleeve and shim to the bolt face, while feasible in this case, are not things anybody should do when the use of a powerful centrefire round is intended. Incomplete penetration of solder would permit a depression in the chamber and difficult or impossible extraction, and silver soldering on the front of the bolt would remove the heat treatment which is important there.

Drilling out a barrel isn't as easy as it sounds, either. I think an unpiloted drill, used in the lathe, would follow a 7.62mm. bore without wandering, but I am not totally sure. It would be better to have a piloted one, and preferable piloted on the shank by which it is pulled through the bore. You would have to drill first and then ream to get a good surface.

Had you been dealing with headspace alone, Brownells sell or used to sell a short ring to be soldered into a recess made at the rear of a 12ga. chamber. You then cut the chamber and rim recess in the normal way. This ring surrounds only the solid head of the case, and you could surely get the solder to penetrate the full joint. It therefore isn't so liable to swell. It wouldn't be difficult for the lathe user to make up something like this for the .410 chamber. In theory you could make this an integral part of a chamber reducing sleeve. But that is a lot of theory.

Anyone contemplating work of this sort should buy at least one good reference book on cartridge dimensions. I think the best is probably John J. Donnelly's "Handloader's Manual of Cartridge Conversions". Unlike most it gives full dimensions, such as length to the shoulder.


I agree, this conversion just isn't worth it. The result would be far too heavy for the purposes for which a .410 is customarily used. I can only see any point in jurisdictions where shotguns are subject to fewer controls. If you were going to all this trouble, it would surely be better to reline the bore as a rifle. www.trackofthewolf.com (http://www.trackofthewolf.com) is worth a look for their chrome-moly liners.