doublegunshop.com - home Forums General Discussion German & Austrian Sporting Guns @ doublegunshop.com Otto Bock BBF - firing pin bushing coming up

Hi all,

my favorite gun - the Otto Bock 1939 made Over/Under Combination gun with a .222Rem barrel insert in the 16bore shotgun barrel -
needs major firing pin rework.

Some time ago I noticed 'cratering'of the .222 primers which made it difficult to open the gun after firing.
On a closer look I noticed that the firing pin hole was worn out and there was quite a gap which produced the cratering.

a few months ago I made a bushing and a new firing pin
bushing: 5mm dia 5mm deep (on the deep side)
friction fit (freezer overnight)

the (top) firing pin on this over/under sits at an angle which makes things more complicated
approx 25-30 deg. up from horizontal
and approx 10-15 deg. from the side

machined at the correct angle, press fitted the bushing, filed the thing flush, new firing pin - went to the range: beautiful! no problems - firing pin in center and no cratering.

3 months and a 100 rounds later the bloody thing worked itself loose!
The hammering must have worked the metal and it nearly fell out.

The options - as I see it (and keep in mind that I am not a qualified gunsmith - just fairly handy with a lathe and milling machine) - are as follows:

a) use the existing bushing and secure it with a flat head screw on one side - or
b) make a proper, T-shaped bushing with a thread and two holes for a 'bushing tool'

solution 'b' is what appeals to me - one problem is that I need to watch the depth of this angled 'job'
as the workings of the 'Greener' crossbolt are very close behind a T-bushing (outside dia 8 or 9 mm) which at the deep end of the angle will be approx 6mm deep.

The other thing is that on a 6mm or 1/4" thread I will only have about 3mm or so of thread (provided I can find a proper bottoming tap -
the thread on the bushing I can do on my lathe
-needs to be a very fine thread
40 tpi on the 1/4"
or 0.5 on the 6mm I think ?

should I harden the bushing?
silver steel = harden/temper or
mild steel = case harden (with the powder)

I can do either

What say you?

I will post pictures as soon as my camera battery has recharged

best regards

G�nter (England)
NRA Life 1974

Gunter,
It's your gun and your decision, but Walter Grass replaced all three bushings in a Dural framed drilling for me, when we were rebuilding it in his shop( in Germany).They were typical bushings with a flange(you called it T shaped)threaded, but not with as fine a thread as you mentioned.They were made "square" and then cut and finished to the proper angle, after being screwed in. The centers of the primers were marked and the holes for the firing pins were drilled, using a fixture he made to align the drill on both ends(so it started at the correct location at the rear and come out at the center of the primer. The fixture looked like an "E", with a screw in the middle leg, through which the drill ran. The drill was held in alignment by a hole in the rear leg.A hole in the front leg was centered over the mark for the primer center.The whole thing was dimensioned to fit around the action, between the front and middle legs. When he built a new O/U he had to bend the tang up to reach the top firing pin and bend it back later. I would guess the EL is in the bottom barrel of your gun, so you shouldn't have this problem.Good luck.BTY you can make a bottoming tap by carefully grinding the end off a plug tap.
Mike

for the time being I'll set the existing bushing back in with some loctite 603 (green) bearing compound and file it flush again.

If it again comes out I can then make a flanged bushing and tap/thread it

The reason for thinking of a small pitch (40tpi or 0.5 on metric) was the fact that due to space restrictions I'll end up with a very short threaded bore - like 3mm or less

I can do 28 or 40tpi on my hobby lathe (or .5 .7 .8 1.0)to thread the bushing
with 28tpi or 1.0 I'll only get 2.5 - 3 turns of thread to grip - will that be sufficient?

the existing bushing is 5mm dia and sits in a 5mm milled seat (end mill)
you see the extreme angle in the photos

I can go 2mm deeper for a flanged bushing
But: the larger flange (at the deep end) would probably interfere with the crossbolt, which sits only 4mm back from the face

So, that's the main reason for first trying to set the existing bushing in with Loctite

I'm not very good at explaining technical stuff
I'm getting old and english is not my first language
so, forgive me if I use strange terms at times and muddle up
the sequence in which I should write.

regards from England

G�nter
NRA Life 1974

Gunter,
If you do that, it shouldn't be that much more trouble to go ahead and put a screw in to hold it. I think I would use some force to push it in for the loctight to set( C clamp?. If it was flush before and stands proud now, there must be some space behind it(you may want to "break the edge" at the rear end so it doesn't keep the bushinh from seating all the way.
Mike

just finished the job over the weekend and put it back together.

made a new firing pin while I was at it - the old one was slightly bent and snapped when I tried to straighten it.

set the bushing in with Loctite 603 bearing compound and hope that it will stay put.
If not, then I'll have to make a threaded bushing which means machining deeper and then tapping a 6mm thread into the 5mm hole.
at the angle of the firing pin a flange on the bushing would interfere with the crossbolt

I tried to machine/drill for a small retaining screw on the bushing, but could not get the action into a vise at the right angle - the top tang is too long and gets in the way and also the clamps to hold the bushing in when drilling - all prevented a vise-hold at the right angle.

So I can only hope that the Loctite might hold the thing
otherwise I'll have to find a bigger milling machine with a larger vise.

Best regards from England

G�nter
NRA Life 1974

Gunter,
It's pretty impressive that you are willing and able to to things like this, not too many are.
Mike

I have an LC Smith 20 ga that had a firing pin bushing replaced in 1956 and set in place with a brass screw. It's still there. I'd venture that RED loctite will hold it as long as you need it to hold. In my experience it will take a torch to get that stuff out.
Very nice work and nice project! I'm envious.

Mike: I've always liked to make things - taught myself by watching the professionals over the last 40 years or so - and then learning from my mistakes...
at my age now actually glad for any little project which passes the time - hehe

drduc: that's what I hope for (re:red Loctite) - time at the range will tell

will keep you posted

best regards

G�nter
NRA Life 1974