surgdog Posted December 26, 2016 Share Posted December 26, 2016 (edited) Got a Sig MPX and been waiting 200 days for the Form 1 so just took it out last weekend and had multiple FTE. Using my reloaded competition ammo 147 RN bullet over 3.3 gr Titegroup. Noticed cases landed within a foot of so from gun with ejection. Research implies that the gun is "under gassed" never heard that term before. Seems you have to do something with the gas return system but can't find details. Might just need a break in period with higher power ammo but you would think when paying well over $1000 for a gun it should work. I have a CZ Scorpion and it shoots everything. I was curious if anyone else on here was having similar problems and had a remedy? Searches didn't reveal anything. Thanks, MK Edited December 26, 2016 by surgdog Link to comment
Bigsampson Posted December 26, 2016 Share Posted December 26, 2016 Suggest you run about 500 rounds of factory loads and then go back to your reloads. Lots of people have a short break in period. Mine is sensitive to rounds with shorter oal. Some UMC factory is quite a bit shorter. It really doesn't like those. Link to comment
tyler2you Posted December 26, 2016 Share Posted December 26, 2016 I had to bump my 147gr loads up to 3.4 gr of Titegroup. After around 200 rounds, it runs like a top. Link to comment
Mulligan03 Posted December 27, 2016 Share Posted December 27, 2016 Agree with bigsampson.. mine wouldn't cycle 147 at first, but after couple hundred rounds it runs them with no problem Link to comment
surgdog Posted December 27, 2016 Author Share Posted December 27, 2016 Thanks for the replies. How far out does your gun eject the brass? My brass was hitting just to the right of my right foot. Makes me think not enough gas coming back to operate bolt. Will follow the recommendations above and shoot higher powered commercial ammo for several 100 rounds but don't see how this would improve my reloads ability to cycle gun. These are the same reloads I use for pistol competition and I'm basically lazy and don't want to do a separate 9 mm load for MPX. My CZ 75 and Scorpion work great with them. Have found this problem noted elsewhere but no definitive answer on how to beat it other than "breaking in". At this point with the cost of the gun and the now approved Form 1 have no choice but to continue on. May call Sig after 1st and see if they have any advice. Thanks everyone and Happy New Year. M Link to comment
Neomet Posted December 27, 2016 Share Posted December 27, 2016 (edited) As others have said run slightly hotter ammo for @ 250 to 500 rounds. I've found mine likes to be run pretty darn wet. More so than my .223 Even if low round count I would clean the piston assembly. if it is not moving freely it will mimick being undergassed. The MPX being piston driven often takes more powder than a blow back like the Scorpion. It will feel softer, just takes more powder to run the system. My 147 molys with 2.8 of E3 toss brass 6 feet or so. This is after 2K rounds Edited December 27, 2016 by Neomet Link to comment
IntenseImage Posted December 28, 2016 Share Posted December 28, 2016 It's what everyone is saying ... It's new and tight. That's a good thing. Run it for a few hundred rounds and try the lighter ammo again. Mine did the same thing and will eat my reloads just fine now Link to comment
surgdog Posted December 28, 2016 Author Share Posted December 28, 2016 OK, here's an update. Got a chance to go to range and shot 250 rounds of 115 gr S&B commercial ammo. Ejected great and no problems. Then tried my reloads again and there was improvement in that I had no FTE. Ejected brass going a little further. Only minor problem is that not getting last round bolt hold back with the reloads. Going to go clean it well including the tappet and oil it up good. Will cont to take it out and shoot commercial until confident in its reliability before shooting in competition. Appreciate everyone's spot on advice. MK Link to comment
Ray_Z Posted December 28, 2016 Share Posted December 28, 2016 The MPX is the same platform as the M-16 and they love to be wet. I always keep the carrier well supplied with silicone grease. Never have a problem with extraction. Using a chamber cleaning tool is the lase thing I do before putting the rifle away. Link to comment
Fastissmooth Posted January 1, 2017 Share Posted January 1, 2017 My MPX didn't run my 147 FMJ production loads when it was new. After several hundred rounds of different ammo it runs them without issue. 147 FMJ Precision Delta Viht N320 at 3.4 gr. Link to comment
GJM Posted January 1, 2017 Share Posted January 1, 2017 My MPX also required a break in period, of about 300 rounds of full power ammo. And, I needed to leave magazines loaded for a few weeks too. Link to comment
surgdog Posted January 1, 2017 Author Share Posted January 1, 2017 When I got back from shooting commercial ammo and cleaned it that gas valve and tappet where filthy and very stiff. After taking apart, cleaning and oiling they feel much looser so I'm hoping this will help. My production load--147 gr xtreme RN bullet over 3.3 Titegroup at 1.160 OAL was shooting better after commercial ammo so hopefully now after a good cleaning it will get even better. Happy New Year to all. mk Link to comment
linde1411 Posted January 11, 2017 Share Posted January 11, 2017 what bullet weight and fps runs the best in the mpx ?Sent from my iPhone using Tapatalk Link to comment
Mulligan03 Posted January 14, 2017 Share Posted January 14, 2017 Having to send my mpx back to sig. have put about 1000 rds through it and haven't had a issue until lately.. it won't cycle any ammo.. shot high power loads and low power loads and nothing.. stripped gun and cleaned it didn't see any issues.. guess we will see when sig takes a look at it.. Link to comment
tyler2you Posted January 14, 2017 Share Posted January 14, 2017 11 minutes ago, Mulligan03 said: Having to send my mpx back to sig. have put about 1000 rds through it and haven't had a issue until lately.. it won't cycle any ammo.. shot high power loads and low power loads and nothing.. stripped gun and cleaned it didn't see any issues.. guess we will see when sig takes a look at it.. Can you describe what kind of malfunctions you're having? Have you pulled the gas system apart and cleaned it? Link to comment
Mulligan03 Posted January 14, 2017 Share Posted January 14, 2017 Yea.. took it all apart.. with 147gr gun fires and casing doesn't Eject, bolt doesn't move at all.. with 115gr the bolt moves enough to pick up another round but spent case remains in chamber and gets caught up every time.. seems to be a gas problem to me but I can't figure out what he problem is Link to comment
tyler2you Posted January 14, 2017 Share Posted January 14, 2017 2 minutes ago, Mulligan03 said: Yea.. took it all apart.. with 147gr gun fires and casing doesn't Eject, bolt doesn't move at all.. with 115gr the bolt moves enough to pick up another round but spent case remains in chamber and gets caught up every time.. seems to be a gas problem to me but I can't figure out what he problem is Strange that it ran without issue for some period of time and now won't. Sure sounds like it's not getting enough gas. Do the gas rings still fit tight when you put the piston and valve back in the cylinder? Link to comment
Mulligan03 Posted January 14, 2017 Share Posted January 14, 2017 Felt tight enough to me Link to comment
linde1411 Posted January 14, 2017 Share Posted January 14, 2017 shot my mpx for the first time today. Very happy with it. Love the gun Ran about 100 rounds of factory 115 and 124 with no problems But Used some reloaded 147 pistol loads that it wouldn't cycle Sent from my iPhone using Tapatalk Link to comment
alma Posted January 15, 2017 Share Posted January 15, 2017 Reports are that it takes takes bit to break it in to run light loads. If you still want lighter then send it to Taylor Pickerell to get the gas port opened up. Link to comment
speed Posted October 8, 2018 Share Posted October 8, 2018 zero 147 gr JHP oal 1.130 all day long without an issue mine runs like a champ! Link to comment
hgr2 Posted October 9, 2018 Share Posted October 9, 2018 147 Zero, 3.3 TG. Runs without issue. Link to comment
Rolex Posted October 18, 2018 Share Posted October 18, 2018 Just needs more gas. That's all. Link to comment
Nathanb Posted October 18, 2018 Share Posted October 18, 2018 On 1/13/2017 at 9:10 PM, Mulligan03 said: Yea.. took it all apart.. with 147gr gun fires and casing doesn't Eject, bolt doesn't move at all.. with 115gr the bolt moves enough to pick up another round but spent case remains in chamber and gets caught up every time.. seems to be a gas problem to me but I can't figure out what he problem is Funny enough mine did the same thing. I had a cracked bolt carrier. Sent it back they replaced it and now it doesn’t run. I have yet to tackle it to see why. Thing are everything before. Link to comment
mofo1111 Posted October 18, 2018 Share Posted October 18, 2018 I had an issue with reloads as well. Factory ammo ran fine. I had some flat point bullets that the MPX didn't like. I came home and measured the factory ammo. Winchester White Box and Federal Champion are the factory loads that worked, both in 115 grain weights. I ended up using a COAL of 1.156-1.158". It seemed as the new gun light a longer COAL. I haven't tried a shorter COAL since to see if the problem still exists. Link to comment
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