Rimfire Accuracy Improvement

[Picher]

I posted about this a while back on another thread, but it didn't get much traction. People may not have grasped the importance of a strong firing pin strike in the right location that produces better, more consistent powder burning.

Most rifles firing pins are not shaped properly to hit just below the fold of the rim, where the priming mixture is and where the metal is easier to dent. The ideal firing pin nose is best shaped to avoid hitting the fold and shaped to provide a sufficiently narrow, yet rounded have edges, with the most forward portion at the bottom, where it can create a fanned flame that provides the best priming mixture and powder ignition.

A great rimfire rifle gunsmith, Calfee discovered this firing pin improvement method and it really works great. IMHO, it's especially important for .17 HMR and .22 Mag shooters interested in long distance accuracy from their pet rifles.



Before (left) and After firing pin shape mods.

Having such a firing pin shape and impact location also tends to minimize semi-auto vertical bolt movement effects on the shot, whether by sloppy bolt travel or varied upward pressure by vertical-stacked cartridges in a box magazine. Note that some shooters don't fully load their magazines because they've noted first-shot variation in groups. (Also note that rotary magazines may provide more consistent upward force on bolts.)

 

[Rembrandt]

Interesting about where the firing pin hits the rim, thank you for the information.

 

[entropy]

I see where that would make a difference.

 

[ColtPythonElite]

Could be.

I have also heard speculation on where the firing pin is in the bolt having an affect on accuracy. Theory is on the bottom of the bolt so the pin hits the rim in the 6 o'clock position is preferred because the powder is laying on the low side of the case....My benchrest 40x has the firing pin on the bottom.

 

[Riomouse911]

Two things;

1) The CCI at the top-right looks like it was pierced, was it? Recently having a .22 Mag cartridge head fail where the pin stuck the cartridge head in my Henry sent bits of burning and unburnt power back towards my son's face as he fired. (Luckily he was wearing glasses when his face got peppered!)

2) I have always wondered why rimfire rifles don't have either wider firing pins to strike a wider area, or a split pin to strike the cartridge head in two spots. Both are in order to increase the likelihood of cartridge ignition when fired...

Just a wonderin'

Stay safe!

 

[jmorris]

there have been a number of folks that have played with 6 o’clock, 12 o’oclock and even dual pins on rimfires. Starting back in the 1800’s.

 

[caribou]

My favorite .22lr is a Romanian M-69 Trainer.
My personal favorite is long gone, but Im looking for another....I bought quite a few on them in early 2000's, and all needed the firing pins reshaped/sharpened, and 1/2 a burr starting at the chamber from dry firing. Heavy but honest use, I think they were kept at a shool and maintained properly, though dry firing seems to have been a norm.

We had to tweek them and the firing pins really needed attention.
Wide, light strikes across the rims set off most of them, but a file and then stone brought them into line.

Not much work, but careful. As well, I shimmed the driest stocks to the actions so they would feed properly.
Just a little tuning and they perform 100%

Ive met many a .22lr that had this problem.