LugerForum Discussion Forums - View Single Post - How can I tell if I need a new mainspring?

unspellable · 03-17-2005, 02:28 PM

First, I think you are talking about the recoil spring. The main spring is the one inside the breech block that drives the striker. Very easy to change.

The Old Model (with a flat recoil spring) had the same recoil spring in either caliber. The New Model (1906, most Lugers, with a coiled recoil spring.) had a different spring in each caliber.

Many many many shooter grade Lugers have had their mainsprings messed with, messing about by the unknowing is the main reason for a bad recoil spring. They really don't weaken until shortly before total failure. We have spring drawings available so you can identify the spring as original or not.

First and most important check: regardless of load, the recoil spring must be strong enough to return the breech block fully to battery each time and every time. This is a SAFETY issue! If the breech block stops just shy of battery the pistol WILL fire in an unlocked condition. The consequences will not be pretty!

Second test, known as Thor's test: Does the hold open work every time? If the spring is too strong or the load too weak the hold open will occasionally fail to latch. (Assuming the pistol is clean and properly lubed.)

Third test: Put three layers of masking tape across the rear of the frame where the toggle tail contacts it and test fire. If the toggle tail fails to mark the tape the spring is too strong for the load. If it dents the tape wihtout cutting it, you have a perfect match. If it cuts clear through the tape the load is on the strong side or the spring is on the weak side. How ever this is NOT time to panic. It's normal to have the tail hit the frame fairly briskly, this just indicates you are past optimum, not that it's time to change springs.

If you have a very heavy load combined with a very strong spring, you may be in balance, but the breech block will return to battery too fast to pick up a cartridge from the magazine and leave the chamber empty. The same symptoms arise from a weak magazine spring, so it could be from either cause. A full magazine will aggrevate either condition so make the test with a full magazine. The magazine can be eliminated by using a couple of known good magazines. Note that this malfunction is not a jam. The breech block will go all the way to battery on an empty chamber and leave the top cartridge in the magazine.

03-17-2005, 02:28 PM	#2
unspellable User Join Date: Jun 2002 Location: Iowa Posts: 768 Thanks: 0 Thanked 19 Times in 11 Posts	First, I think you are talking about the recoil spring. The main spring is the one inside the breech block that drives the striker. Very easy to change. The Old Model (with a flat recoil spring) had the same recoil spring in either caliber. The New Model (1906, most Lugers, with a coiled recoil spring.) had a different spring in each caliber. Many many many shooter grade Lugers have had their mainsprings messed with, messing about by the unknowing is the main reason for a bad recoil spring. They really don't weaken until shortly before total failure. We have spring drawings available so you can identify the spring as original or not. First and most important check: regardless of load, the recoil spring must be strong enough to return the breech block fully to battery each time and every time. This is a SAFETY issue! If the breech block stops just shy of battery the pistol WILL fire in an unlocked condition. The consequences will not be pretty! Second test, known as Thor's test: Does the hold open work every time? If the spring is too strong or the load too weak the hold open will occasionally fail to latch. (Assuming the pistol is clean and properly lubed.) Third test: Put three layers of masking tape across the rear of the frame where the toggle tail contacts it and test fire. If the toggle tail fails to mark the tape the spring is too strong for the load. If it dents the tape wihtout cutting it, you have a perfect match. If it cuts clear through the tape the load is on the strong side or the spring is on the weak side. How ever this is NOT time to panic. It's normal to have the tail hit the frame fairly briskly, this just indicates you are past optimum, not that it's time to change springs. If you have a very heavy load combined with a very strong spring, you may be in balance, but the breech block will return to battery too fast to pick up a cartridge from the magazine and leave the chamber empty. The same symptoms arise from a weak magazine spring, so it could be from either cause. A full magazine will aggrevate either condition so make the test with a full magazine. The magazine can be eliminated by using a couple of known good magazines. Note that this malfunction is not a jam. The breech block will go all the way to battery on an empty chamber and leave the top cartridge in the magazine.