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Posted: 12/16/2008 8:41:28 AM EDT
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Hi folks at ar15.com. I could really use some help now.
I´ve had Bushmaster Predator for a year now (I bought it in December 2007) and it´s been suffering from short stroking. The weirdness is that the short stroking begins after 100-150 rounds have been fired with the gun. Spraying Break Free on bolt carrier (through the gas holes of the carrier) helps the gun to keep on going for another 100-200 rounds but then the same thing happens again. The ammo I´ve been mainly using is Sellier Bellot 55gr FMJ and the gun has digested around 2000 rounds. During the time the gun was new I used American Eagle 55gr and Magtech 55 gr ammo. Sometimes the gun jammed because the tip of the bullet hit the upper receiver just under the feed ramps. This developed a small cavity under the feed ramps increasing the number of jams. The cavity has now been fixed the gunsmith and according to retailer it was caused by the lack of gas. The gun visited a gunsmith last week and he discovered that the gas port and the holes drilled under the barrel (to keep and allign the gas block in correct position) were not in correct position, so the gas block and gas port were not perfectly alligned. He chamfered the gas hole of the gas block a bit wider so the gas block would get the full gas from the gas port. Still the gun short strokes after 100-150 rounds. Last range visit went like this: - I tried loading magazines with 2 rounds each and firing quick double taps. No problems, the bolt locked back after last round. - I fired around 100-150 rounds and every now and then went to patch the targets. The gun worked well. - Again I tried loading magazines with 2 rounds each and firing quick double taps. First with some magazines the bolt didn´t lock back, then bolt didn´t lock back at all and after that came short stroking with every magazine I had. The gun jams because the locking lugs take a cartridges from the magazine when the cartridge is under the locking lugs, so the bolt clearly doesn´t travel far enough. So far what I´ve checked: - Not a magazine problem. I´m using C-Products aluminum and steel mags and 2008 built Magpul PMAGs - Bolt carrier moves ok in the upper receiver and gas tube as aligned with gas key. - Gas rings seem to be in good contidition and move freely. I also tested putting bolt/bolt carrier on the floor with the bolt head downwards. The bolt doesn´t go inside the carrier (idea from G&A Book of AR15 2008). - Gas key is tight. I haven´t found any leaks. - Gas port size seems to be within specification, I measured 2.35mm (0.0925") with digital caliber. - Gas block is in correct position. - Gas tube is not blocked. - Break Free is used to lubricate moving parts Even the retailer and the gunsmith are puzzled with this rifle and they are running out of options. They said that there was another Bushmaster Predator from the same batch which had the same problems as I´m having now but is now working correctly after some minor tweaking (gas port position problem). Somebody please help me with this gun. |
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sounds like the problem is cured when you lube the gun up well right? Wonder have you been cleaning the chamber really well between shootings? Could be a combination of a slightly tight chamber due to built up crap, when more crap is added it becomes too much.
Honestly don't know, just a guess. I would try cleaning the absolute hell out of it like you have never cleaned before and then lube excessively and see what happens. Over lube the thing, excess will be discarded by the rifle. |
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I´ve scrubbed the chamber with a nylon brush. I once even tried a poor mans micro grinding with a cleaning jag and regular tooth paste (worked with Ruger mk2 extraction problems :) ). I´ve experimented various amounts of lube with the gun but still the problem appears sooner or later.
Hammer tail didn´t show any marks. |
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