Fireforming problems

[footpetaljones]

This morning I took 40 pieces of brass out to the range to try to fireform them for 3" .410 brass shells. Out of the 40, only 11 fired successfully, and of those only 1 was fireformed to an acceptable length. I had loaded them with 10 grains of Unique, followed by 1/2 a cotton ball, cream of wheat, and sealed with glue. To me, it looks like the primer strikes are too light. Would anyone be able to think of another source for my problems?

163967 163968

[Greg S]

Looks like alot of off center firing pin strikes. How do the firing pin stike look on the ones not fired? What are these being fire formed to? Is there alot of play in the case/chamber wall or os the lock up loose. What type of shell casing are you using?

I have heared of this practice although I have never used it. I thought bullseye was the powder of choice or some other fast powder.

[footpetaljones]

A few of the successfully fireformed cases appear to have primer strikes a bit deeper, but some don't appear much different from the ones pictured. I am using Hornady 9.3x74r cases to form into 3" .410 brass shells.

There is some play when the shells are inserted partially into the chamber. I am unable to determine the play when the cases are fully inserted due to the ejector protruding from the barrel (I am using a single shot Stevens 220A).

I would have preferred using Bullseye, but I did not have any on hand until I picked a pound up on my way back from the range.

[Bent Ramrod]

I've done fire forming on 9.3 x 74 shells by RWS to make something to shoot in a .40-3-1/4" and noticed the rims are somewhat thin compared to American rimmed shells. I would think that they would be quite a bit thinner than a .410 shotgun shell rim, and could easily slip too deep into a .410 chamber for the firing pin to fire reliably.

Did you try pointing the gun straight up when firing? Sometimes the weight of the shell and its inertia will allow for a good firing pin strike before the shell starts moving forward.

Your present load might be a little on the light side for a full cylindrical blow-out. I've used 9 gr. of Unique in a .30-30 shell, with the rest full of Cream of Wheat and a card wad to make .38-55s. I hesitate to recommend any fire forming load because they have no reliable pressure data published. What I did was gradually increase the powder, a case at a time, and observe the effect. Once I got a good cylinder I stopped there.

[bullet maker 57]

I think Bent Ramrod is correct. Rim to thin.

[footpetaljones]

Bent,

I measured 5 of the unsuccessful shells vs 5 of the successful shells. All of the unsuccessful shells read between .045 and .05 inches while all of the successful shells read between .048 and .05 inches. Perhaps with the variances in primer seating depth that could be the source of my problem, though the specifications for .410 rims are .0392" to .0532". Do you have any measurements for the rims on your brass?

I am starting to think that part of the problem might be the hardness of the primer cup compared to that of shotshell primers.

[brstevns]

Slide a little rubber O-Ring on them up to the rim and then close the action on the brass. Will make up for the thin rim.

[Cowboy_Dan]

I am starting to think that part of the problem might be the hardness of the primer cup compared to that of shotshell primers.

Are you maybe using rifle primers for this? Shotgun primers are more like pistol primers in heat and cup hardness.

[Chev. William]

You might measure the Rim rebate depth in the Shotgun or see what a Piece of "Plastigauge" will show as the Head space on one of your candidate Cases. I am talking of the plastic 'string' material sometimes used to measure Bearing clearances in Automotive Engine work.

Best Regards,
Chev. William

[footpetaljones]

Are you maybe using rifle primers for this? Shotgun primers are more like pistol primers in heat and cup hardness.

Yes, since 9.3x74r uses large rifle primers.

[Bent Ramrod]

The RWS cases are on the order of 0.0052" rim thickness. I also have some Norma cases that run more like 0.0050". Case rim thickness for .30-30 type cartridges are a nominal 0.063". I can't find a nominal rim thickness for shotshells in Cartridges of the World, but a 16-gauge shell I had lying around was on the order of 0.060".

The .30-30's I blew out were for my Hopkins & Allen .38-55 Shotgun. They did not fire reliably in the gun because the rim seat was too deep. It may have been set up for folded head cartridges, which might have had thicker rims. I cut a circular piece of shim stock, removed a bit for extractor clearance and soldered it into the rim seat. Every shell fires just fine now.

I would not think you have a problem with your main spring if your gun fires regular .410s OK. Usually there is plenty of snap in those single loaders for any primer.

[RPRNY]

A little JB Weld in the rim recess of your shotgun will sort this out. Or, buy some Magtech 410 brass.

I use 444 Marlin brass.

[Chev. William]

.410 shotshells seem to have .0532 nominal Rim Max. Thickness.
Chev. William

[GONRA]

Looks like a weak hammer / firing pin strike to GONRA.
In addition to all the above geat advice, checkout firing pin protrusion, etc.