STI DVC Open 9 Major question...

jakfrost

jakfrost

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Hi all, and Happy New Year to all fellow CGN'rs...! Made it out to the range over the holidays to do some chrono testing and had, for the first time ever with this gun, 2-3 'light taps' resulting in FTFire's.

The load is once fired WW brass, using a Fed small rifle primer lighting up 8.4gr of 3N38 and pushing a 125 HP Zero bullet down the barrel at a fairly rapid rate of knots...at least when the firing pin does its job.

I had a suggestion from a fellow shooter to take a couple of coils off the firing pin spring...I don't have a spare just now, so before I do that, any suggestions or comments on this line of thought? The spring appears to be stock, with a titanium firing pin.

Cheers,
Jim
 
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If you have a spare steel firing pin, that might be worth a try before modifying any parts.
I tested both a titanium and steel firing pin in my 1911 using a highly scientific and precise method: cocked the hammer, slid an ordinary lead pencil (eraser end first) into the barrel, and squeezed the trigger, pointing straight up. The steel firing pin ejected the pencil some 30-50% higher than the titanium pin.

Small rifle primers are likely harder and/or thicker than small pistol, so I can see why your using them for Major 9.
I can't remember which type of primers have a difference in the depth of the cup between the pistol and rifle versions, even though the diameter is the same for both.
 
if you have access to Federal small pistol primers try them as they are the softest, if they don't go off then it is some other problem other than type of primers......next to check would be the primer seating depth, you definitely need all your primers set so they are recessed and not too high.........if those both pass the test then I suggest to put in a lighter firing pin spring (with an extended firing pin)
 
Thanks all for the input...I would love to try the 'pencil test' but unfortunately I only have 2 firing pins right now, both titanium...I do check primer depth, part of my overall check of each and every cartridge using my 100rd 'Shock Bottle' case gauge. You would be surprised what gets flagged using this tool!

I will check to see if my spare pin is slightly longer than the one in the gun now, might be worth a try if it is longer...?
 
If there is oil, combined with cold Temps, could have a hydraulic effect and hinder the forward movement of the firing pin.
 
If he's trying to make major power factor with a 9mm then that's a pretty potent load, I can understand why he's using small rifle primers.
 
Many people shoot 9mm major in open division and this is the first time I heard of anyone using rifle primers. Most everyone shooting anything with a lightened trigger is using federal pistol primers due to them be the softest available and less likely to cause light hammer strikes which can happen with harder pistol primers like CCI and it is my understanding that rifle primers regardless of brand are even harder.
 
I have used 10,000+ of the Dominion small rifle primers with a similar load - during the primer and powder shortage a while back. Depending on the gun, I found that they worked fine until they didn't. In one of my STIs they worked all the time until I was on the clock. In the other one, they had a greater FTF rate. I never did change out to a different pin, I just went back to CCI or Dominion small pistol primers, 100% success rate. Some guns are more prone to firing pin length issues than others.
 
rifle primers are common in Open, with the powder charge you need that extra burn from the primers to get a good ignition.
with a SA gun I'm not sure why you would clip spring coils on the mainspring?
 
mrclean said:
Was th brass that gave you the problems all the same headstamp?
Click to expand...

Hmmm, hard to say now because I ran them thru again and both of them lit off normally...but they were supposed to be once fired WW brass. I suppose its possible certain brands of brass might be more susceptible to the problem than others, is that what you are suggesting?
 
You could try giving Freedom Ventures a call, I recall seeing extra long firing pins on their web site, and they are the go-to guys for my STI needs.
 
Just get an extended firing pin from Freedom ventures. I have one in my edge .40 and its lights 99.9% of my SB small rifle primers. ( got a great deal on them, so I use them in practice ammo) I got a 2 in 10 fail with the regular pin...
 
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