Why will my replacement R50 bulbs not work? I have two sets of three R50 lights within my kitchen, recently...

I have two sets of three R50 lights within my kitchen, recently one bulb spoilt. I replaced with a exotic R50, this did not work. I then tried the second bulb contained by the pack this too did not work. Both bulbs seemed ideal. I then moved one of the working bulbs from its socket and replaced the blown bulb, this bulb worked so it be not the socket.
I have since bought three strange bulbs and none of these work as well. All come across perfect.
The bulb I am replacing is a R50 40 watt bulb screw thread. There is a ever so small difference contained by the shape at the end of the bulb, but ever so slight.

Has anyone any suggestions?
Help! i accedently glue my bottom to my...
Screw them in tightly and stop impersonate me.

How do i remove a tub faucert one...
Some ('safety') screw fittings do not engage the power until the bulb is screwed RIGHT down. If you look down the hub of the bulbholder there is a 'spoon' to the focus point.

Try putting the new bulbs surrounded by a bit deeper/more firmly?
Are smoke detector mountings uniform?
Answers:    Try respectively of the new lamp in a lampholder that you know works, if none of the lamp light they must enjoy all suffered wreckage (dropped) and the filaments are adjectives broken.