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Semi Bren Primer Flow
Guys,
Was shooting my L4 today and have some primers I am concerned about. Ammo used was factory Lake City 7.62x51 nato stuff. I am not getting flattened primers, but it does look like I am on the very verge of piercing the primers. Looks like there is a sheared bit of metal corresponding to the firing pin geometry that just hasn't liberated itself yet. Firing pin protrusion is 0.050" (1.27mm). It would seem to be a bit great in light of a rule of thumb I have read that one doesn't want to have firing pin protrusion much in excess of 1/2 the pin diameter which I'm using the narrow section of 0.078"..so it's ~0.015" greater than that.
Narrow section of pin to bolt channel clearance is ~0.003-0.004".
Something to bear in mind is that the semi firing pins are heavier on account of the length to get to the striker. Not sure how hard the striker is hitting it in comparison to the carriage post thingy in a full auto gun.
Anyhow, was going to start working the pin protrusion down until more normal primer conditions prevail.
Please let me know what you guys think, thank you in advance for any help...
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06-25-2017 11:18 PM
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I think you're worrying about nothing. If you aren't getting pierced primers then don't worry. The hole should appear in the dent of the primer anyway. The Bren FP has always nearly come out the mouth of the case. If you were shooting reloaded ammo then there might be an issue but this is factory. Don't worry about what hasn't happened...
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I'll try to put some pics up. Something looks clearly amiss to me...
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Possibly enlarged firing pin hole...so it appears.
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Holy shxx! That (photo 1) looks to me like........... Are you putting TNT in your reloads? The pressure in the case is forcing the primers back into the striker hole. Is the gun a standard UK
made L4 or a US re-weld/semi auto? While I don't know much about the US rewelds it LOOKS like the primer has blown right into the striker hole, driven the striker right back against its stop, THEN the primer has tried to extend further into the hole, wrapping itself around the striker to the point of almost exceeding the extent of its elasticity ALMOST ready to pop.
Never seen anything like it in my life and I've seen one or two Brens and L4's. You MUST compare and measure the striker hole in the breech block with a know good one. Is yours enlarged? It will be before long!
Just my view as a bit part onlooker.......
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Pin to hole fit looks good. I do not think its over pressure. Note primer isn't flat. Will double check headspace but don't anticipate problem there
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Originally Posted by
alterego
Pin to hole fit looks good. I do not think its over pressure. Note primer isn't flat. Will double check headspace but don't anticipate problem there
Can you post a photo of your semi auto firing pin and your breech block? Are you using an L4 BB and a South African barrel or a a South African BB with the South African Barel?
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303 bb, SA extractor and barrel. I've got a test I'll run tonight. I think I know what might be happening
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Cutting to the quick, if I might be so bold and with the utmost respect, but as an Armourer of one or two years standing and a graduate mechanical engineer, if that ain't over pressure what's caused that, for whatever reason, pray tell me what it is. I could be wrong of course as my wifey tells me most days. But whatever it is, can I please have one of those fired cases?
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