Potential hotload problem

unspellable · 06-10-2002, 02:20 PM

In the course of researching for my 7.65 Parabellum cartridge project it has become apparent that one may find almost anything in the way of a recoil spring in a Luger. This applies to both calibers. There are a lot of cutdown and non-original springs out there. The Lugers I've opened up have displayed a bewildering array of recoil springs.

I've seen a good deal of talk about hot loads for Lugers. The problem is the recoil spring must be matched to the load. If you are running hot loads in a pistol with a soft or shortened recoil spring you may be abusing the pistol.

Just a word to the wise.

unspellable

Thor · 06-10-2002, 02:56 PM

unspellable, you are ABSOLUTELY RIGHT ON TARGET! My findings as well! [img]eek.gif[/img]

Karl · 06-10-2002, 06:47 PM

Unspellable,

Of coarse I know relatively speaking what a hot load is but technically, exactly where does one draw the line between "standard" and "hot"? I would imagine that in addition to load, bullet weight would also be a factor in recoil. As a shooter, I would find a list of commonly available ammo rated according to load useful. I'm looking at a box of the Walmart Winchester ammo I use and it lists the weight of the bullet but not the load. By the way, I've been following posts on your research with interest. I'm curious, despite your observations about possible incomplete breech closing and substandard recoil springs is there a history of catastrophic failure in lugers? KFS

unspellable · 06-10-2002, 08:13 PM

There are two seperate considerations as to what makes a "hot" load. The first is pressure. You will have no problems here with any commercially available ammunition unless it is defective.

The second consideration is impulse and this is where we worry about the recoil spring. Impulse is a measure of the cartridge's ability to push the pistol backwards. It's not to be confused with recoil.

Impulse has two components. The first is easily calculated as the mass of the bullet times the muzzle velocity. (Don't forget to divide by 7000 to convert grains to pounds and divide again by 32.174 to convert pounds to slugs in order to have consistent units.

Next we have to add the impulse provided by expelling the powder gases and air from the barrel. This is trickier since we don't have an easy measurement of the velocity. There are several rules of thumb, one of which is to use 1.5 times the bullet's muzzle velocity.

So we have ((weight of bullet in grains + 1.5 * weight of powder in grains) * muzzle velocity) / ( 7000 * 32.174 )

If you've done the math right you should get an answer in the range of 0.5 to 0.8 lbf*ft/s for the 7.65 or 9 mm cartridge. (lbf means pounds force, the pound unit got changed from force to mass while you weren't looking.) This will allow you to compare one load to another.

As to what spring goes with what load, I'm still working on that problem.

In general the Luger is a strong pistol and not too prone to breaking. The most common problem is dropping the magazine on its head once too often. The Luger will take a lot of pressure and if you gradually increase the load to the point of destruction you are more likely to break it with excess impulse than with excess pressure. Of course a case full of Bullseye will blow just about anything apart without waitng around for the excess impulse to do the job.

(The difference between genius and stupidity is that genius has limits.)

unspellable

unspellable · 06-11-2002, 12:14 AM

A correction:

Sometimes my fingers type faster than my brains or something.

The unit of impulse is the lbf*s or pound force second, NOT lbf*ft/s as I stated in the previous post. The expected range of numbers from 0.5 to 0.8 is correct.

Also, for factory loads where I have not actually weighted the powder charge I assume 5 grains.

unspellable

unspellable · 06-11-2002, 01:35 PM

More on hot loads:

There will be a good deal of researching, calculation and experimentation before I come up with any final answers. I am in the process of developing a setup to measure spring strength and am planning some experiments to measure how far back the action goes with various loads. The ideal would be to have the action go back to .001 inch shy of hitting the stops. In the meantime here are some preliminary rough guides.

Usually you buy a replacement spring rated for so many pounds. This rating means the number of pounds force to compress the spring to its fully loaded length. It is an oversimplification as there are several parameters. First the diameter, if this isn't right the spring just won't fit. Second is the bound length when the spring is compressed to the point where the coils jam against each other. Again, if it isn't right it won't work. Since we are buying a spring alleged to fit a Luger we shouldn't have to worry about these two measurements. Springs are available in two types, linear and progressive or variable. For the Luger we want to stick to linear springs. That's the easy stuff.

The next three measurements are free length, preloaded force and loaded force. The last is the rated strength of the spring. In the Luger the loaded length is 1.29 inches. ( 33 mm ) Wolff Gunsprings sells springs for the Luger rated at 36 lbf, 38 lbf and 40 lbf. These are on the heavy end of the scale. The lightest spring you can get away with is 30 lbf.

The mildest commercial load I am aware of in either caliber is the Fiocchi 7.65 load at slightly less than 0.5 lbf*s. This load seems to function with a 30 lbf spring, which is the lower limit for spring strength. I had a problem with the pistol not going all the way into battery when using this spring and some loads. It closed far enough to fire but was not locked so this is a very touchy situation. If your action is a little slicker than mine you might get reliable lockup but WATCH it! If you fire the pistol with out complete lockup you may have a true collector's item. Walk around the range and collect a piece here, collect a piece there.

For the 9 mm load with 124 grain bullet at 1050 fps we have around 0.61 lbf*s worth of impulse. For this cartridge a 36 lbf spring might be about right. If we get the same weight of bullet up to 1150 fps I'd use a 38 lbf spring. At 1200 fps use the 40 lbf spring. For the time being I'll not recommend any load hotter than that. With further research will refine the recommendations.

I have not yet run any actual experiments with impulse at the higher end of the range. All in due course. (You'll notice the 9 mm cartridge seems to be sneaking into my 7.65 mm project.)

Between now and the time you decide to mess with your spring start with the lightest available load and work up gradually until you get reliable functioning. Along the way make sure your magazine is up to snuff and not causing any malfunctions. Start by loading a single cartridge at a time and look for a load just hot enough to make the hold open work reliably. The typical malfunction with a load that is too weak is for the cartridge to stop half way from magazine to chamber but otherwise in a normal position. The breech block will stop with the lower edge against the side of the case a little in front of the extractor groove. This situation results from the breech block not going back far enough and the lower edge dragging the cartridge forward.

Incidentally, 0.5 lbf*s may sound like a small number. It represents a force of one half pound force applied for one second. But in the actual case the time involved is less that one millisecond. Divide the above number by half a millisecond and the actual force applied to pushing the slide back is approaching 1000 lbf. Remember it's all over with by the time the toggles hit the ramps.

unspellable

Karl · 06-11-2002, 07:18 PM

Unspellable,

Great info about loads and recoil springs. This should be condensed and posted as part of a permanent "shooter's guide" section.

Before I fired my shooter I replaced the springs with a new Wolff kit (#38) and it works fine, but there is evidence that this gun saw considerable abuse. There is a bulge in the frame into the back of the magazine well that could only have resulted from the recoil spring retainer slamming hard into the bottom of its pocket, as if it broke loose once. Also there are scars like half a pair of half moons on the inside rear wall of the frame from the firing pin guide/retainer slamming into it as the bolt traveled back. KFS

unspellable · 06-11-2002, 11:37 PM

It is my intention to put all this together in one place when finished. Got a long ways to go though.

Wolff Gunsprings arrived at 38 lbf as the standard spring based on measuring one example pulled from a WWII era Luger, one presumes it was a Mauser.

unspellable

Sieger · 03-01-2014, 12:04 PM

Quote:

Originally Posted by unspellable

It is my intention to put all this together in one place when finished. Got a long ways to go though.

Wolff Gunsprings arrived at 38 lbf as the standard spring based on measuring one example pulled from a WWII era Luger, one presumes it was a Mauser.

unspellable

Unspellable,

Did you ever complete this project, as GT and I have been considering a recoil spring project for some years now?

Sieger

06-10-2002, 02:20 PM	#1
unspellable User Join Date: Jun 2002 Location: Iowa Posts: 768 Thanks: 0 Thanked 19 Times in 11 Posts	Potential hotload problem In the course of researching for my 7.65 Parabellum cartridge project it has become apparent that one may find almost anything in the way of a recoil spring in a Luger. This applies to both calibers. There are a lot of cutdown and non-original springs out there. The Lugers I've opened up have displayed a bewildering array of recoil springs. I've seen a good deal of talk about hot loads for Lugers. The problem is the recoil spring must be matched to the load. If you are running hot loads in a pistol with a soft or shortened recoil spring you may be abusing the pistol. Just a word to the wise. unspellable

06-10-2002, 02:56 PM	#2
Thor User Join Date: Jun 2002 Location: Rio Rancho, New Mexico Posts: 4,583 Thanks: 958 Thanked 970 Times in 276 Posts	unspellable, you are ABSOLUTELY RIGHT ON TARGET! My findings as well! [img]eek.gif[/img] __________________ Thor's Luger Clinic http://members.rennlist.com/lugerman/ Ted Green (Thor Yaller Boots) 725 Western Hills Dr SE, Rio Rancho, NM 87124 915-526-8925 Email [email protected] ----------------------------------- John3:3 Jesus answered and said to him, "Most assuredly, I say to you, unless one is born again, he cannot see the kingdom of God."

06-10-2002, 06:47 PM	#3
Karl Lifer - Twice Over Lifetime Forum Patron Join Date: Jun 2002 Location: Savannah Posts: 522 Thanks: 0 Thanked 271 Times in 118 Posts	Unspellable, Of coarse I know relatively speaking what a hot load is but technically, exactly where does one draw the line between "standard" and "hot"? I would imagine that in addition to load, bullet weight would also be a factor in recoil. As a shooter, I would find a list of commonly available ammo rated according to load useful. I'm looking at a box of the Walmart Winchester ammo I use and it lists the weight of the bullet but not the load. By the way, I've been following posts on your research with interest. I'm curious, despite your observations about possible incomplete breech closing and substandard recoil springs is there a history of catastrophic failure in lugers? KFS

06-10-2002, 08:13 PM	#4
unspellable User Join Date: Jun 2002 Location: Iowa Posts: 768 Thanks: 0 Thanked 19 Times in 11 Posts	There are two seperate considerations as to what makes a "hot" load. The first is pressure. You will have no problems here with any commercially available ammunition unless it is defective. The second consideration is impulse and this is where we worry about the recoil spring. Impulse is a measure of the cartridge's ability to push the pistol backwards. It's not to be confused with recoil. Impulse has two components. The first is easily calculated as the mass of the bullet times the muzzle velocity. (Don't forget to divide by 7000 to convert grains to pounds and divide again by 32.174 to convert pounds to slugs in order to have consistent units. Next we have to add the impulse provided by expelling the powder gases and air from the barrel. This is trickier since we don't have an easy measurement of the velocity. There are several rules of thumb, one of which is to use 1.5 times the bullet's muzzle velocity. So we have ((weight of bullet in grains + 1.5 * weight of powder in grains) * muzzle velocity) / ( 7000 * 32.174 ) If you've done the math right you should get an answer in the range of 0.5 to 0.8 lbf*ft/s for the 7.65 or 9 mm cartridge. (lbf means pounds force, the pound unit got changed from force to mass while you weren't looking.) This will allow you to compare one load to another. As to what spring goes with what load, I'm still working on that problem. In general the Luger is a strong pistol and not too prone to breaking. The most common problem is dropping the magazine on its head once too often. The Luger will take a lot of pressure and if you gradually increase the load to the point of destruction you are more likely to break it with excess impulse than with excess pressure. Of course a case full of Bullseye will blow just about anything apart without waitng around for the excess impulse to do the job. (The difference between genius and stupidity is that genius has limits.) unspellable

06-11-2002, 12:14 AM	#5
unspellable User Join Date: Jun 2002 Location: Iowa Posts: 768 Thanks: 0 Thanked 19 Times in 11 Posts	A correction: Sometimes my fingers type faster than my brains or something. The unit of impulse is the lbfs or pound force second, NOT lbfft/s as I stated in the previous post. The expected range of numbers from 0.5 to 0.8 is correct. Also, for factory loads where I have not actually weighted the powder charge I assume 5 grains. unspellable

06-11-2002, 01:35 PM	#6
unspellable User Join Date: Jun 2002 Location: Iowa Posts: 768 Thanks: 0 Thanked 19 Times in 11 Posts	More on hot loads: There will be a good deal of researching, calculation and experimentation before I come up with any final answers. I am in the process of developing a setup to measure spring strength and am planning some experiments to measure how far back the action goes with various loads. The ideal would be to have the action go back to .001 inch shy of hitting the stops. In the meantime here are some preliminary rough guides. Usually you buy a replacement spring rated for so many pounds. This rating means the number of pounds force to compress the spring to its fully loaded length. It is an oversimplification as there are several parameters. First the diameter, if this isn't right the spring just won't fit. Second is the bound length when the spring is compressed to the point where the coils jam against each other. Again, if it isn't right it won't work. Since we are buying a spring alleged to fit a Luger we shouldn't have to worry about these two measurements. Springs are available in two types, linear and progressive or variable. For the Luger we want to stick to linear springs. That's the easy stuff. The next three measurements are free length, preloaded force and loaded force. The last is the rated strength of the spring. In the Luger the loaded length is 1.29 inches. ( 33 mm ) Wolff Gunsprings sells springs for the Luger rated at 36 lbf, 38 lbf and 40 lbf. These are on the heavy end of the scale. The lightest spring you can get away with is 30 lbf. The mildest commercial load I am aware of in either caliber is the Fiocchi 7.65 load at slightly less than 0.5 lbfs. This load seems to function with a 30 lbf spring, which is the lower limit for spring strength. I had a problem with the pistol not going all the way into battery when using this spring and some loads. It closed far enough to fire but was not locked so this is a very touchy situation. If your action is a little slicker than mine you might get reliable lockup but WATCH it! If you fire the pistol with out complete lockup you may have a true collector's item. Walk around the range and collect a piece here, collect a piece there. For the 9 mm load with 124 grain bullet at 1050 fps we have around 0.61 lbfs worth of impulse. For this cartridge a 36 lbf spring might be about right. If we get the same weight of bullet up to 1150 fps I'd use a 38 lbf spring. At 1200 fps use the 40 lbf spring. For the time being I'll not recommend any load hotter than that. With further research will refine the recommendations. I have not yet run any actual experiments with impulse at the higher end of the range. All in due course. (You'll notice the 9 mm cartridge seems to be sneaking into my 7.65 mm project.) Between now and the time you decide to mess with your spring start with the lightest available load and work up gradually until you get reliable functioning. Along the way make sure your magazine is up to snuff and not causing any malfunctions. Start by loading a single cartridge at a time and look for a load just hot enough to make the hold open work reliably. The typical malfunction with a load that is too weak is for the cartridge to stop half way from magazine to chamber but otherwise in a normal position. The breech block will stop with the lower edge against the side of the case a little in front of the extractor groove. This situation results from the breech block not going back far enough and the lower edge dragging the cartridge forward. Incidentally, 0.5 lbf*s may sound like a small number. It represents a force of one half pound force applied for one second. But in the actual case the time involved is less that one millisecond. Divide the above number by half a millisecond and the actual force applied to pushing the slide back is approaching 1000 lbf. Remember it's all over with by the time the toggles hit the ramps. unspellable

06-11-2002, 07:18 PM	#7
Karl Lifer - Twice Over Lifetime Forum Patron Join Date: Jun 2002 Location: Savannah Posts: 522 Thanks: 0 Thanked 271 Times in 118 Posts	Unspellable, Great info about loads and recoil springs. This should be condensed and posted as part of a permanent "shooter's guide" section. Before I fired my shooter I replaced the springs with a new Wolff kit (#38) and it works fine, but there is evidence that this gun saw considerable abuse. There is a bulge in the frame into the back of the magazine well that could only have resulted from the recoil spring retainer slamming hard into the bottom of its pocket, as if it broke loose once. Also there are scars like half a pair of half moons on the inside rear wall of the frame from the firing pin guide/retainer slamming into it as the bolt traveled back. KFS

06-11-2002, 11:37 PM	#8
unspellable User Join Date: Jun 2002 Location: Iowa Posts: 768 Thanks: 0 Thanked 19 Times in 11 Posts	It is my intention to put all this together in one place when finished. Got a long ways to go though. Wolff Gunsprings arrived at 38 lbf as the standard spring based on measuring one example pulled from a WWII era Luger, one presumes it was a Mauser. unspellable