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Well I took my new (to me) Grade B to the range today. Shot great for the first 80 rounds or so. Great accuracy, nice recoil, nice trigger, everything I had hoped it would be. Then, on the last round of a magazine the slide stuck open about 1/2 inch. I cannot for the life of me pull the slide back. I can push it fully closed (with some force). The squeeze cocker appears to work just fine. Any ideas on what went wrong or how to fix it? I think this is a great firearm and want to use it as my CCW, but I must say I am now a bit worried. Hopefully this is an isolated problem. Thanks in Advance.
 

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Well I took my new (to me) Grade B to the range today. Shot great for the first 80 rounds or so. Great accuracy, nice recoil, nice trigger, everything I had hoped it would be. Then, on the last round of a magazine the slide stuck open about 1/2 inch. I cannot for the life of me pull the slide back. I can push it fully closed (with some force). The squeeze cocker appears to work just fine. Any ideas on what went wrong or how to fix it? I think this is a great firearm and want to use it as my CCW, but I must say I am now a bit worried. Hopefully this is an isolated problem. Thanks in Advance.

CI:

Here is some background and info below that may help.

Likely you have a serious build up of molten lead in the back of the gas cylinder that the end of the gas piston has stuck into. Happens when folks shoot lead bullets in a pistol with a gas cylinder which is why the manual tells the owners to shoot only jacketed ammo in the P7. Small amounts shave off and melt and form into the back of the gas cylinder. Try removing the firing pin assembly/bushing and lightly tap the rear of the slide with a leather or rubber hammer to free the piston from the cylinder. Once free use the metal scraping tool to remove the build up. Didn't get one with the pistol? Contact HK for one before shooting it again. Can't get it loose? Send it in to HK for repair. They have a special cutter to remove heavy build ups and guages to check your piston.

Some related useful P7 info
------------
This is not an uncommon stoppage with 147 grain ammo in the P7M8 or P7 PSP. These stoppages are called "nosing up" and are in fact failures to feed. They are caused by "over function", too much recoil impulse to the slide. Let me guess. These stoppages occur on the last or 2nd last round? If so what is happening is that the heavy 147 grain bullet is imparting excessive recoil energy to the slide (the P7 was designed for 124 grain NATO ammo). When it does so it increases the slide velocity rearward. This causes the slide to strike the frame at its most rearward position harder than normal. When it does the top round slides slightly forward in the magazine (due to less upward pressure on the round under the feed lips towards the end of the magazine). When the slides comes forward again at higher than normal speeds and strikes that partially fed round the round “jumps” out of the magazine rather than being pushed forward by the slide under controlled feed as designed. It then often ends up sticking up and out of the ejection port or impacts on the top of the chamber when the slide comes to rest out of battery. This problem is increased when the piston is worn and there is thus less braking effect in the gas retardation system. It is also made worse by weak magazine springs. Likely the reason others here do not report the problems with 147 grain ammo is related to the state of their mag springs and piston, the specific ammo characteristics (not all 147’s are the same) or they shoot P7M13’s where this problem is less likely to occur.

So how do you fix this? Don't shoot 147 grain ammo. 115-124 is best and +P or +P+ is okay (US +P+ is @ NATO spec). It is the excessive bullet weight that causes the issue. This is why the .40 S&W P7M10 has such a massive slide, to slow down the slide velocity. Or try replacing your magazine springs and/or piston. HK makes a little go/no go gauge for the piston. Send it in and have HK check it out. This does not happen in the P7M13 because the magazine springs are stronger and the feed lips are longer. Newer (after @ 1990) have longer feed lips like those of the P7M13 to help reduce this. They are marked with a date code but I do not recall what that was. If you keep you P7M8 magazines fully loaded I would replace them every 5 years or less and leave the magazine down loaded by one round (7 versus 8) regardless of the ammunition used. That will extend the life of the springs considerably and thus insure the best reliability. Cheap life insurance.

Always remember to clean the gas cylinder with the brass bristle brush AND the metal tool provided after each firing. If you don’t have the tool, contact HK to get one. NEVER clean the piston with metal brushes (nylon brush and solvent only). Also never shoot lead bullets in a P7. Small particles of lead get shaved off and melted and build up in the back of the gas cylinder. In time that accumulation may cause the piston to stick to the lead build up in the cylinder and impair the free movement of the slide.

Good luck.

G3Kurz
 

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Well I took my new (to me) Grade B to the range today. Shot great for the first 80 rounds or so. Great accuracy, nice recoil, nice trigger, everything I had hoped it would be. Then, on the last round of a magazine the slide stuck open about 1/2 inch. I cannot for the life of me pull the slide back. I can push it fully closed (with some force). The squeeze cocker appears to work just fine. Any ideas on what went wrong or how to fix it? I think this is a great firearm and want to use it as my CCW, but I must say I am now a bit worried. Hopefully this is an isolated problem. Thanks in Advance.
It would help if you gave more information on what ammo you were shooting
 

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CI:

Here is some background and info below that may help.

Likely you have a serious build up of molten lead in the back of the gas cylinder that the end of the gas piston has stuck into. Happens when folks shoot lead bullets in a pistol with a gas cylinder which is why the manual tells the owners to shoot only jacketed ammo in the P7. Small amounts shave off and melt and form into the back of the gas cylinder. Try removing the firing pin assembly/bushing and lightly tap the rear of the slide with a leather or rubber hammer to free the piston from the cylinder. Once free use the metal scraping tool to remove the build up. Didn't get one with the pistol? Contact HK for one before shooting it again. Can't get it loose? Send it in to HK for repair. They have a special cutter to remove heavy build ups and guages to check your piston.

Some related useful P7 info
------------
This is not an uncommon stoppage with 147 grain ammo in the P7M8 or P7 PSP. These stoppages are called "nosing up" and are in fact failures to feed. They are caused by "over function", too much recoil impulse to the slide. Let me guess. These stoppages occur on the last or 2nd last round? If so what is happening is that the heavy 147 grain bullet is imparting excessive recoil energy to the slide (the P7 was designed for 124 grain NATO ammo). When it does so it increases the slide velocity rearward. This causes the slide to strike the frame at its most rearward position harder than normal. When it does the top round slides slightly forward in the magazine (due to less upward pressure on the round under the feed lips towards the end of the magazine). When the slides comes forward again at higher than normal speeds and strikes that partially fed round the round “jumps” out of the magazine rather than being pushed forward by the slide under controlled feed as designed. It then often ends up sticking up and out of the ejection port or impacts on the top of the chamber when the slide comes to rest out of battery. This problem is increased when the piston is worn and there is thus less braking effect in the gas retardation system. It is also made worse by weak magazine springs. Likely the reason others here do not report the problems with 147 grain ammo is related to the state of their mag springs and piston, the specific ammo characteristics (not all 147’s are the same) or they shoot P7M13’s where this problem is less likely to occur.

So how do you fix this? Don't shoot 147 grain ammo. 115-124 is best and +P or +P+ is okay (US +P+ is @ NATO spec). It is the excessive bullet weight that causes the issue. This is why the .40 S&W P7M10 has such a massive slide, to slow down the slide velocity. Or try replacing your magazine springs and/or piston. HK makes a little go/no go gauge for the piston. Send it in and have HK check it out. This does not happen in the P7M13 because the magazine springs are stronger and the feed lips are longer. Newer (after @ 1990) have longer feed lips like those of the P7M13 to help reduce this. They are marked with a date code but I do not recall what that was. If you keep you P7M8 magazines fully loaded I would replace them every 5 years or less and leave the magazine down loaded by one round (7 versus 8) regardless of the ammunition used. That will extend the life of the springs considerably and thus insure the best reliability. Cheap life insurance.

Always remember to clean the gas cylinder with the brass bristle brush AND the metal tool provided after each firing. If you don’t have the tool, contact HK to get one. NEVER clean the piston with metal brushes (nylon brush and solvent only). Also never shoot lead bullets in a P7. Small particles of lead get shaved off and melted and build up in the back of the gas cylinder. In time that accumulation may cause the piston to stick to the lead build up in the cylinder and impair the free movement of the slide.

Good luck.

G3Kurz
thank you G3, you should write the book for HK, I just picked one up and your info is always helpful.
printed this to put in my HK manual.
 
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