Firing pin and block are VERY stuck

I just bought a semi auto bren MKI conversion by Stemple, and everything seems to be in order except for the firing pin and bolt block. The pin is completely immobile, and no amount of oil or hopps solvent seems to loosen it. Based on how sticky the retaining pin in the block was, I assume grease and grime has completely stuck the pin and spring in it's captive spot. I am taking it to a gunsmith on Monday to see if it can be removed and still used, but if it can't, where can I buy replacement semi auto parts? I've looked at firingpins.com, wiselite, sarco, and pretty much everywhere else I know of that used to have such items, but nothing is available.

Hi Raptor, if you're not already, register on Weapons Guild. There is a ton of information over there for building semi conversions and parts. Good luck with your Bren. I am not implying that this is not a great forum also and if this offends anyone, please have a moderator delete the post.

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Originally Posted by SNAFU22

I am not implying that this is not a great forum

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But still you send him away right away...

Its hard to say just from those pics why it's stuck solid, but hang on a minute...

Hi Raptor, there were two common styles of firing pins. One milled a slot through the post and the other uses a box (rectangle) around it. It looks like you have the slotted post. More pics would help. Unfortunately the people that designed those are on other forums. The pic I attached is one style of one design. It may match yours or not. If you could contact people that are familiar with your Bren builder I am sure they could help. You or your smith should be able to make a new pin if one is not available. I use O1 drill rod for firing pins. There is an older post here "Bren semi build USA" I don't know how to link it so you will just have to search for it. It looks like the same setup as yours. Also the face of the bolt should be smooth. Good luck

https://i.postimg.cc/9MvnVqHP/BREN-FIRING-PIN-002.jpg

So I have no opportunity or desire to learn how to modify these parts myself, but I do know a few gunsmith's who might. I don't think that's the style of my firing pin. I can't see more than half of it of course, but it looks a little more rounded on the back half. I'm pretty sure it has the slot, though that's just a guess unless I can get it out. Are there any specifications for modifying the block? I know you have to shave away two ridges at the firing end, and I think all the ones I've seen for sale are unmodified.

I am including a couple more pictures. Let me know if you want a specific angle.

Here's a drawing in post one of this thread showing measurements and they may shed some light. https://www.milsurps.com/showthread.php?t=62508

The described thread had no info about this problem.

From your top pic showing the firing pin from the back there looks to be something in the channel on both sides of the firing pin.

I'm not sure what you mean by something in the channel blocking both sides of the firing pin? There's the captive holding pin in the side, but that's the only thing I'm aware of.

The hole in the bolt that the firing pin goes through, look at the picture you posted. At the back you can see something inside the firing pin channel. Nothing to do with the transverse pin sticking out.

At the ten and two position of the firing pin channel... Like there's something else in there.

Oh, yeah, I noticed that too. I couldn't tell if it was globs of the oil that I tried to inject reflecting light, or metal. Surely it's not been welded in there? I don't know why that would be done, but it's a serious case of false advertising if it is. In either case there is no external indication of what that is, or how to remove it if it's another captive pin.

All the deformations or peen marks won't help, in fact in my experience such things do a very good job of jamming close-fitting parts together.

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Originally Posted by Raptorjamboree

Surely it's not been welded in there?

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Just looks deformed and perhaps those are misshaped enough to jam it.

Ok, I think those metallic looking slivers mentioned at the 10 and 2 positions of the firing pin shaft are oil. It's not the captive pin; that's out in the latest picture I've provided.

So before I take this to a gunsmith tomorrow, I figured I would take some general pictures of the rest of the bren. Please let me know if there are any obvious problem areas. I would really like to try and get this functional, but I'm getting more and more worried that I may have to ask for a refund and return.

I'll bet the transverse pin has been peening the firing pin where they meet and swelled the firing pin so it's jammed. Once that's good I'll bet it's fine.

Looking at your photos again, I'm sorry to say, but what I can see suggests a lot of very worn parts; worn out in some cases. Massive erosion on the bolt face from primer leakage. Burrs extending out from the ends of the guide slots (my term) from extreme wear, pitting all over the extractor....

The hole in this part is so badly worn that whatever fits into the larger countersink has gradually pounded the hole ovoid while the lower side looks to have worn away against something else. :eek:

From about the 6:30 to 8:00 o'clock portion of the circumference it looks like a large chunk is starting to crack off.

As for the stuck pin, that looks like silver solder to me. Which might explain the visibly glass-beaded surface: remove the discoloration from the heat of the torch.

And what's with the pits and the deformed hole in the last photo? That's what happens when people grind welds with blending pads. Looks like there's still some lumps of weld proud of the surface though. I'd hazard a guess those are "grounding scars" where the current arced from the welding table to the part because they didn't ground directly to the part. Not to mention the unfilled pits....

Who does these "conversions" again? I don't know much about Brens but you don't need to for this.

This one was done by John Stemple, but from my reading elsewhere on this forum it was a one-off thing, not a production line. Of course, the same user also said it was supposed to run well and have a good reputation. I can't find information about this specific conversion anywhere else.

Who is the John Stemple that is reported to have manufactured this weapon? Is the gun marked with his manufacturing information? If this link is to the supposed maker... Memorial He passed away in Feb of 2007. Can the previous owner provide any documentation as to the manufacture of this gun?

The images show a weapon that is employing the striker method of ignition - however, the machining pictured of the striker appears to be rather crude - it might work fine, but it looks sloppily constructed.

The firing pin issue photographed looks like the firing pin has been bound up by something within the bolt body... there is supposed to be a spring inside so that is one possible source. Per the illustration of a firing pin... the FP could have been rotated in the bolt body and the retaining pin capture slot is now bound up on the FP retaining pin end or parts of a broken firing pin spring... hard to diagnose remotely from these pictures. In normal condition you should be able to push forward on the rear of the FP and see the tip move out of the front of the bolt face.

The normal profile (and we do not know if this semi FP meets normal specs for its forward end profile) of the firing pin is rectangular to match the shape of the opening in the bolt face... in the pictures it looks either round or like it is rectangular but has been twisted so that its long dimension is no longer vertical.. but horizontal - back to my twisted and jamed conjecture.

Word of caution, If this is really a "one of build"... you need to determine if enough of the BATF semi auto only modifications have been performed in this design's execution. If not... it could still be classified upon inspection as a contraband manufacture machine gun. Only the maker can tell you whose approved design he followed...and how rigorously he followed the approved design... and there are only a few BATF approved designs out there.

Best of luck - I'd recommend seeing your gunsmith and hope he has some understanding of how a striker fired semi auto Bren is supposed to function.

Hi Raptor, what did you find out? Your striker looks like an older design. The new and improved ones are lighter and use a different spring setup. A new bolt will need to be headspaced. The extension (bolt carrier and gas piston) with the post inside it has been filled with weld where the full auto sear catch was. This area is milled away on the more modern designs. I think the Bren is a great gun and a semi is the least expensive way to own one. Also the manuals by Skennerton are invaluable. Good luck
https://i.postimg.cc/J00XwnHJ/P2220491.jpghttps://i.postimg.cc/056kMDvm/P7130624.jpg

Hi everyone, thanks for your help. I called the seller today, who put me in touch with the consignor of the gun as well as Mark Stemple (the builder's son, I believe). They both said they have tons of spare parts and would be happy to fix the rifle if I send it back. So I'll let you know how the repair process goes. Hopefully it won't take too long.

Good luck. You might want to ask for photos of the parts before they're fitted.

Ok, so I got the firing pin and FP spring replaced, and they fit and seem to work!

Unfortunately, I can only get one shot off before it fails to fire. It feeds and loads well, but I'm pretty sure the striker is not coming forward properly after the first shot. As you all can see from my pictures, the striker looks to be in pretty bad shape. Is there anywhere I can get a new striker and spring? No where online seems to have any in stock, but I haven't emailed Historic Arms yet.

If I get a new striker, will it just fit in, or would I then have to get a new fitted bolt?

Thanks for all your help so far.

Any advice? Basically, I'm asking if you guys think it will take a lot more time and money to fix, if I will have to get all new internal parts instead of just a new striker.

P.M. sent

Get rid of that huge spring and use an inner return spring from an FAL.
It should work with your striker. You will need to cut the spring to length. If you decide you want to try this I will pull my spring out and measure it.

Where are you located ? If you’re local I’d be happy to help. I’ve repaired and troubleshooted a few in my time

Raptor,

Yes, I recognize that gun as it was on Gun Broker and I had inquired about it. Of course John Stemple was well known for this S&W Model 76 copies. But the person who had the gun listed, replied that John had only built ONE Bren semi auto!? Something I guess he wanted to try late in life. R.I.P. Obviously, John knew firearms, but he may have not been completely up to date with all that makes these semi autos run properly. They can be frustrating. He passed in 2007, so it has been over 13 years of continued (somewhat) development.

Yes, your bolt is worn. The last time I saw a bolt with this much primer erosion was on an AR-180 I owned that ran a bunch of reloads that had loose primers, hence the gas cutting in that circular pattern around the firing pin. And in case you do not know, Bren firing pin faces are rectangular (sort of) like a Glock firing pin (NOT interchangeable). But if the bolt still head spaces, I would work with it. Don't grind or polish the rear, or the face of the bolt, as those areas help establish head space. The gas cut ring should not hurt too much, unless your primers are backing out and hanging up on the circular groove. My AR-180 ran find with a bolt like that.

Certain parts for these semi auto are very hard to come by. At the present time, I only know of Historic Arms and Kiwi who are still making the guns in any form of series. They may be a source to get a replacement striker? Your design is very similar to the Historic Arms internals. Len (of Historic Arms) removes the buffer plate at the back of the trigger frame and uses the large diameter striker spring as Stemple did in this gun. The firing pin has an extension welded to the rear so the striker can impart force upon it, but the forward part of the firing pin is normal Bren, and those are still available. Look up a normal Bren firing pin and you will see the difference in the two. The semi has the long tail welded on.

It may be possible to "rebuild" your striker, by having some areas built up with weld, filing to shape and size and having it heat treated. The striker "head" or portion that contacts the rear of the firing pin appears to be battered. That should possibly be built up and squared off? There is a wonderful striker set up by "Mighty Lime", but not sure he makes them any more? Mighty used to be on here and at WeaponsGuild. My only problem with the Mighty Lime set up was within a Project Guns Bren. It would touch off the commercial ammo fine, but seem to be a tad light to touch off the harder primers on surplus military ammo. I ended up going back to the original striker (closer in design to yours) and worked with the spring tensions in both the striker spring and the return spring areas. It is a bit of a trial and error to get them balance right and then that is dependent on the gas setting you have the barrel set to.

Welcome to the world of Brens. If you ship it back to the guys (Stemples son) hopefully they have enough extra parts to get it cleaned up and running properly. I hope they themselves are aware of the intricasies of the semi auto Bren. They can be frustrating at times. All the best.

By the way, I suspect if you pull on the firing pin from the rear, with a pair of channel locks to get a good grip, and having the firing pin retaining pin backed out, ready to let the firing pin pass by, it would probably come out. Give it a twisting motion as you work it back. You either have a bound up, kinked firing pin spring or a bit of debris that has gotten into the firing pin channel and is binding things together.