Is my Mosin Barrel FUBAR?

[Bolivar]

Hello all. I am running into a new to me problem with a Finnish M39

Here are the pertinent details:

Mosin Nagant Model 39
Bore Slugs to 0.313
Bullets: Hornady 174 GN RN Diameter 0.312
Brass: Graf and Sons
Powder, Reloader 15 46.6 Gn (Box max per Hornaday)
Book Velocity 2600 fps
Measured Velocity 2200-2300 fps average

All cartridges come out of chamber with powder residue and there is powder residue on bolt.

Also there is a bad smell after firing (like sulphur)

It seems to be that pressures must be low and eratic (hence low and variable velocity). Since the brass is coming out dirty and I have that smell issue, it seems like the cases are not expanding to the case walls in firing to properly seal the breech.

I think the throat (at least) is toast.

Any different ideas or confirmation of my theory?

Thanks

 

[Calum]

Perhaps try other ammo.
But if in doubt take it to a gunsmith.

Also what do the firing pins look like?

 

[louthepou]

I would double check the reloading data - I didn't find something similar on the Hdgdon's site, but I wonder if too-low pressure could cause this? Have you tried factory ammo?

Lou

 

[Hitzy]

Try magnum primers.

 

[ollie]

Are you piercing primers? You can unintentionally alter firing pin depth when cleaning, and it can pierce the primers, causing some of the symptoms you mention.

 

[tiriaq]

The bore slugs .313"? What is the groove dimension?

 

[Bolivar]

Fireing pin looks fine and no piercing of the primer

Load data is max as per Hornady Manual

I hadn't thought of magun primers being needed. Might be worth a try

Land diameter 0.305
Groove diameter 0.313

 

[Gary D]

I haven't been reloading long, and I don't own a Mosin so I'm not the expert on such matters by any stretch, but still 46.6gr under a 174gn bullet should create plenty enough pressure one would think. From another angle, are you wiping the case lube off the completed rounds, if not the case is not going to seal well to the chamber when fired.

An oversize worn chamber should show distortion of the brass should it not? Not complete blow-by. As the brass with less pressure than that load should still expand enough for a seal even in a well worn chamber. Could the rifle have been re-chambered for a larger case by a previous owner?, because that would have to be a seriously oversized chamber I would think.

My first suspicion would be the powder is no good and not igniting properly. If the chamber seems to fit well enough I'd go buy a different powder from a different store to make sure the powder is of a different batch (or brand) and being stored under different storage conditions.