Same Ammo, two different rifles, one blows holes in the primer????

Jerengineer

Jerengineer

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So I was at the range today. I'm shooting my Kel-Tech RFB and my friend is shooting his SG 542 Famae. Both in 7.62. We are using norinco bulk ammo. In the picture below, the cases on the left are from the RFB, cases on the right from the SG. Why is the RFB blowing the ####e out of the primer?

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General answer is that firing pin protrusion and shape could be different between the two rifles.
That can result in piercing (or not).

Suspect others will talk about know issue and fix for this specific model rifle...
 
Wow - lots of a Norinco through my RFB and never an issue.

Edit.

Ok - just did some research.

The suggestion is that the system is over pressured.

Adjust the gas setting as per instructions.

Worth a try for sure.
 
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I already setup the gas system for this ammo... this is the first time I've shot this rifle in above 0 degree weather though. Maybe it needs an adjustment.
Since I live 5 minutes from the range, I'll going to run out there, try it and get back to you.
 
Perhaps there is an issue with the bolt face. I just had a rifle start blowing primers on an everyday load that shot without difficulties for weeks prior. After close inspection, the bolt head around the firing pin hole is starting to erode into a cup, allowing the primer to be unsupported around the point of firing pin impact.

Just an idea...
 
I am no expert but ....

- is it a Gen1 or Gen2 RFB?
- the Gen2 has several mods and a different Gas Plug
- have the head space checked
 
push it out and check protrusion, also check COAL after firing, sometimes a little extra headspace allows primer to back out a bit. It may need to be bushed, but on a newer rifle I would advise the manufacturer. They may fix it or may not, but a negative story would cut into sales… good luck
 
I'm beginning to think that the primer is too pointed. Read http://www.shootingillustrated.com/index.php/21625/problems-with-primers/

Here is a shot with the firing pin removed from the bolt.
1407211996314_zps3823c769.jpg
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Firing pin protrudes 1.6mm. The diameter of the bolt hole is 2.6mm. Diameter of firing pin head is 1.83mm.

I used a digital caliper so these measurements are very accurate.
 
As a general rule, centerfire rifles and handguns usually measure between .050” and .060” for firing pin protrusion.

0.050" is 1.27mm
0.060" is 1.524mm

1.6mm is 0.063", which seems a bit on the excessive side.

Measuring firing pin protrusion is tricky, I bought the gage from Brownells for that.
There are also armourer go/nogo firing pin protrusion gages too.

ht tp://www.brownells.com/.aspx/lid=10379/guntechdetail/How_Does_It_Work__Brownells_Firing_Pin_Protrusion_Gauge
 
That gauge would be handy, I measured again using a different method just now. Measured the entire length of the bolt, then the length of the firing pin. Subtracted the two and now have 0.056".

 
0.056" protrusion should be fine, assuming the firing pin tip looks like it has a smooth radius.

Excessive pressure (which can have many causes in both ammunition and/or specific firearm) can also result in pierced primers too :-(

Scuffing/extrusion of the headstamp surface in the cartridge is another sign of excessive pressure.

I'm not seeing much difference between the two sets of cases in that area in the supplied photos.
 
If you use the same ammo in different rifles with the same barrel length, wouldn't the pressures be the same? If both barrels are sized for 7.62 are they not basically identical excluding length? What I'm getting at is, if this ammo doesn't have excess pressure in other rifles then why would it have excess pressure in mine?
 
Manufacturing tolerance or even manufacturing defects can result in different pressure for same ammunition in two different rifles.
 
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