How can I tell if I need a new mainspring?

maxmanta · 03-13-2005, 01:59 AM

I have read about changing out a Luger mainspring and I dread to even attempt it. Therefore, I am NOT going to attempt it unless absolutely neccessary.

How can I tell when it is neccessary to change the mainspring in a Luger? Is there a difference between the .30 and the 9mm mainspring?

Thanks!

unspellable · 03-17-2005, 03:28 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.

DougT · 03-17-2005, 06:10 PM

Unspellable, thank you for the truly excellent information about the hows and whys of the Luger recoil springs--I made a hardcopy of your post and will keep it in my Luger file. I have installed new Wolfe recoil springs in my 1917 Erfurt and 1923 Commercial, and I would say that although it can be accomplished, it is not a job for the faint of heart. I noticed some slight peening on the ramps of my Erfurt, and Thor pointed out to me that this was a possible indication of a weak spring. I installed the regular power Wolfe recoil spring, and that old Erfurt fought me every step of the way! I put the reduced power spring in my '23 (it's a .30), and that made the job somewhat easier. Thanks again for the great explanation.
DougT

unspellable · 03-18-2005, 09:17 AM

It is normal to get slight peening on the ramps. If the peening is excessive it's more an indication of an overly hot load. The strength of the recoil spring will have little to do with it.

The amount of peening will be determined by the slide velocity. The slide velocity will be determined by the impulse of the load. The recoil spring strength has very little effect on the slide velocity. It's job is to bring the togglees to a near stop by the time they reach the end of travel.

The explanation here is that when the pistol is fired, the cartridge impulse will exert a rearward force in excess of 500 lbf. Whether it's a 26, 28, 30, or 32 lbf spring will make little difference to the velocity imparted by a force in excess of 500 lbf.

03-13-2005, 01:59 AM	#1
maxmanta User Join Date: Mar 2005 Location: I'm in HELL! That's where I'm at! Posts: 14 Thanks: 0 Thanked 0 Times in 0 Posts	How can I tell if I need a new mainspring? I have read about changing out a Luger mainspring and I dread to even attempt it. Therefore, I am NOT going to attempt it unless absolutely neccessary. How can I tell when it is neccessary to change the mainspring in a Luger? Is there a difference between the .30 and the 9mm mainspring? Thanks!

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03-17-2005, 03:28 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.

03-17-2005, 06:10 PM	#3
DougT User Join Date: Oct 2003 Location: So. Cal. Posts: 171 Thanks: 0 Thanked 0 Times in 0 Posts	Unspellable, thank you for the truly excellent information about the hows and whys of the Luger recoil springs--I made a hardcopy of your post and will keep it in my Luger file. I have installed new Wolfe recoil springs in my 1917 Erfurt and 1923 Commercial, and I would say that although it can be accomplished, it is not a job for the faint of heart. I noticed some slight peening on the ramps of my Erfurt, and Thor pointed out to me that this was a possible indication of a weak spring. I installed the regular power Wolfe recoil spring, and that old Erfurt fought me every step of the way! I put the reduced power spring in my '23 (it's a .30), and that made the job somewhat easier. Thanks again for the great explanation. DougT

03-18-2005, 09:17 AM	#4
unspellable User Join Date: Jun 2002 Location: Iowa Posts: 768 Thanks: 0 Thanked 19 Times in 11 Posts	It is normal to get slight peening on the ramps. If the peening is excessive it's more an indication of an overly hot load. The strength of the recoil spring will have little to do with it. The amount of peening will be determined by the slide velocity. The slide velocity will be determined by the impulse of the load. The recoil spring strength has very little effect on the slide velocity. It's job is to bring the togglees to a near stop by the time they reach the end of travel. The explanation here is that when the pistol is fired, the cartridge impulse will exert a rearward force in excess of 500 lbf. Whether it's a 26, 28, 30, or 32 lbf spring will make little difference to the velocity imparted by a force in excess of 500 lbf.