doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Question on action pins vs screws

Looking for information on the possible action differences on the two guns below �
Note placement and number of screws vs pins on the similar receivers:
Gun #1



Gun #2


Thanks,
Best Regards
JBP

Hammer and sear pins. Same same. One has locking pins, one has push pins. They do the same job.

Looks like some quality differences in the two guns.

In English gunmaking screws are meant for wood, pins are screws that screw into metal and axles are threadless pins.

From the engineering point of view, axles are prefrable to pins (screws in the US) since the threads can act as stress points. They are also easier to get them right and easier to replace if necesary.

However, screws are regarded as a quality feature and some gunmakers insist on using them on higher grade guns. I had a long talk with my Italian maker re axles on my boxlock. He nodded like he understood, the gun was eventually delivered with pins (screws) and locking screws. He told me that there was no way one of his best guns would be made with axles. It is a pain to disassemble since the pins (screws) have the typical small Italian style slots and are engraved.

I guess the maker's approach in the two OUs was similar to my Italian maker's.

Not arguing the axels vs pins vs screws point, but an observation of these pictures...

Gun #1 shows LH view. Gun #2 shows RH view. The RH view of gun #1 should look the same as gun #2 as only the end of the pins will show.

My $.02

John

Shotgunlover-

Interesting insights. Would you please explain this more:

"From the engineering point of view, axles are preferable to pins (screws in the US) since the threads can act as stress points."

I'm not questioning it, I'm genuinely curious.

I would have thought that the threading would strengthen a pin's/screw's connection to the surrounding metal by increasing the overall surface area involved.

Thank you,

OWD

Personally, I prefer screws (pins) to pins (axles). That, of course, is just one man's opinion. I do prefer them to have a decent slot for a sensible screwdriver (turnscrew).

OWD, the "trick" here is in how carefully the thread roots at the terminis of the threaded section is handled. Any truly sharp corner can act as a stress riser when force is applied to the pin/ screw. The force will be shear as the set-up doesn't allow for the screw/pin to have axial tension beyond tightening torque and no compressive forces at all. "Vee" screw form threads are usually visualized as having a very sharp corner at the thread root/bottom and top. Standardized threads have a flats at the top and bottom of both male and female threads to mitigate stress risers.

DDA

The height (H) of a sharp V 60� thread is 0.866 times the pitch. The points forming the roots should be cut off @ 1/8H. Some British threads are cut with a radius in the roots, as well as on the crests to fit. Probably not that much stronger than the flats, but sure enough a pill to cut.

The Tap drill size for most threads gives approximately a 75% thread. A very good approximation of this, if it is not a super critical thread, is to subtract one pitch length from the threads nominal OD. Realize that English threads are given in threads per inch so one pitch length is equal to1/tpi so tap drill for a �-20 = � - 1/20 or .200". On your Handy-Dandy little pocket calculator just enter the 20 & hit 1/X.

Obsesed with Doubles, Rocketman above describes the engineering aspects of threads as stress risers clearly.

As for the original post and pics. there is no difference in the internal parts attributable to the number of screws. There seems to be lots of screws because each screw (pin) has a locking screw beside it, presumably to stop it coming loose from the swivelling motion of internal parts that are anchored on the screws. The plain axles in the bottom pic correspond to the main large screws in the top pic, which is to say two, one for the tumbler and one for the sear.

What is more interesting is that the guns in the pics are OUs built on Anson-Deeley type actions. The maker managed to make room inside an OU action to house the AD bits. It would be interesting to see a top down pic to get an idea of the width of these actions. Something tells me that they are wider than most OUs.