I picked up a P320 Custom FCU over the holidays and completed a build with the following additional components:
- Sig P320 RXP Carry slide
- Agency Arms Midline Compact threaded 9mm barrel (TiN)
- Griffin Micro Comp
- Sig Compact/Carry recoil assembly
- Wilson Combat Carry grip module
- Sig 17 rd & 21 rd mags

I got it to the range for the first time today with the intent of zeroing the Romeo1 Pro optic. I got 39 rds (30 rds S&B 124 gr FMJ & 9 rds Norma 115 gr FMJ) off before calling it quits due to the following results:
- 2-3 cleanly fired rounds with no issues
- 2-3 stove pipes
- 1 failure to go to battery
- the remainder were failures to feed

Unfortunately, I only brought the 17 rd mag, so I couldn't change that out- I do intend to try that. I don't have another barrel or recoil spring to drop in either as this is my first 9mm P320. Any ideas on what I should try or what the problem might be?

Not sure how Sig is going to handle warranty claims/repairs when they are encouraging folks to use other manufacturers components with the Custom FCU program, but it looks like I will find out!

Thanks for the help in advance.

Just a guess, but the FCU may not be the problem. I would look at the barrel first.

You may want to check that the extractor parts are correctly installed (spring, plunger, extractor), and that the correct parts are installed.

What makes you think the issue is the FCU?

My first thought was a magazine or barrel issue, but since this was a build from scratch I can only test the mag possibility.

Although more details about exactly what happened might assist in diagnosing the problem, the one common element that I see in what I understand the failures to be is the barrel. By “stove pipes” I assume you mean failures to eject. By “failure to feed” I assume you mean failures to chamber (unless the rounds are not being pushed up properly by the magazine, which is what “feeding” is).

Although ejection failures are not commonly due to the barrel, if it’s too tight in the slide and/or not properly lubricated, it might be the cause of low slide speed which is the most common reason for ejection failures. Anything that restricts the movement of the slide could also be the cause of the return to battery failures. What sort of lube are you using on the barrel?

Chambering failures can be due to the barrel as well if, for example, the transition at the top of the feed ramp into the chamber is too sharp.

I would be curious to learn what SIG says about the problems. They are clearly not due to the FCU, and because return to battery failures and slow slide speed problems could be due to a recoil spring that is too powerful or is too weak but can’t be both, I doubt they will take responsibility for what’s going on.

Your barrel should pull cleanly from the slide, during cycling. If it hangs on the hood, you'll need to shoot more to break in, or lightly lap the barrel hood. Check your locking lug also- the barrel should be modestly "loose" with the slide retracted about 30%.

Do you feel any drag, manually drawing the slide, or riding it forward? If so, check your rails, they may need some cleanup.

Lastly, do rounds drop freely into and out of your chamber? What about fired casings?

The short version is: you likely have a barrel issue. An overly tight chamber can give everything you describe...

Good comments, Rob1972.

.

Hi Mario ~ Wrek14

I like the direction Guppy, SigFreund, and Rob sent you in and if you are in the Southern California area, I would be happy to meet up at a local range to trade out your parts one by one with my P320's parts to isolate what is causing your problems.

I see this is just your 2nd post since joining SigForum in 2014. My email address is in my profile, just click on my user name to get it.

If you are located in SoCal area and would like to identify this using parts from my P320s, please feel free to contact me.

.

quote:

Originally posted by sigfreund:
By “stove pipes” I assume you mean failures to eject. By “failure to feed” I assume you mean failures to chamber (unless the rounds are not being pushed up properly by the magazine, which is what “feeding” is).

What sort of lube are you using on the barrel?

Chambering failures can be due to the barrel as well if, for example, the transition at the top of the feed ramp into the chamber is too sharp.

Thank you. Yes, the FTEs were literal stove pipes with the case trapped in the ejection port and you are right on the FTFs, as it appears to be better described by the term failure to chamber. The rounds made it out of the mag, but would would be jammed against the chamber at odd angles.

I've been using Frog Lube for many years and did clean and lubricate the parts when I completed the final assembly of the gun.

quote:

Originally posted by Rob1972:
Your barrel should pull cleanly from the slide, during cycling. If it hangs on the hood, you'll need to shoot more to break in, or lightly lap the barrel hood. Check your locking lug also- the barrel should be modestly "loose" with the slide retracted about 30%.

Do you feel any drag, manually drawing the slide, or riding it forward? If so, check your rails, they may need some cleanup.

Lastly, do rounds drop freely into and out of your chamber? What about fired casings?

The short version is: you likely have a barrel issue. An overly tight chamber can give everything you describe...

Thanks Rob. The barrel doesn't appear to be hanging on the hood, but it is tight when checking it with the slide 30% retracted. I'm not feeling any drag when drawing or riding the slide forward. And, rounds do drop freely into and out of the chamber, but spent casings drop in about 85-90% before stopping and then need to be plucked out.

quote:

Originally posted by sleepla8er:
.

Hi Mario ~ Wrek14

I like the direction Guppy, SigFreund, and Rob sent you in and if you are in the Southern California area, I would be happy to meet up at a local range to trade out your parts one by one with my P320's parts to isolate what is causing your problems.

I see this is just your 2nd post since joining SigForum in 2014. My email address is in my profile, just click on my user name to get it.

If you are located in SoCal area and would like to identify this using parts from my P320s, please feel free to contact me.

.

Thank you very much, I really appreciate the offer. I actually had 7.5 years total living in San Diego up until 2009 when I was active duty, but we are currently in the Atlanta area now. I've been fortunate to do a business trip back there now and again. Sorry you have to put up with the Cali gun BS, one of the reasons I refuse to go back.

You did get me thinking though, maybe my range will loan me some parts from a rental gun to trouble shoot. I suppose it couldn't hurt to ask!

Based on your comments and what little reference I could find in reviews of Agency Arms barrels, I would be most suspicious that a tight barrel is causing the cycling problems. In my experience breaking in the barrel by shooting it more might correct that issue. And although I don’t know for certain, it might fix the chambering problems if they are caused by hesitation in the slide movement due to a tight barrel.

Please keep us posted on how things turn out for you.

Thank you all for the troubleshooting and advice. I'll be sure to let you know how it works out.

quote:

Originally posted by sigfreund:
Based on your comments and what little reference I could find in reviews of Agency Arms barrels, I would be most suspicious that a tight barrel is causing the cycling problems. In my experience breaking in the barrel by shooting it more might correct that issue. And although I don’t know for certain, it might fix the chambering problems if they are caused by hesitation in the slide movement due to a tight barrel.

Please keep us posted on how things turn out for you.

^^This. I had an STI BLS, years ago, that I ran 200 hand-cycled rounds through, getting the chamber right.

I would use a Dremel felt bob and polishing compound, and polish your chamber and feed ramp. I would even go so far as to say spend 5 minutes or so polishing with the red rouge, clean it well, then another 5+ minutes with Mother's Metal Polish, Flitz or similar.

If that fails, definitely have someone knowledgeable shoot the gun with you and do an assessment. If polishing doesn't work, I think you might need a finishing reamer chased in there.

quote:

Originally posted by Rob1972:
I would use a Dremel felt bob and polishing compound, and polish your chamber and feed ramp. I would even go so far as to say spend 5 minutes or so polishing with the red rouge, clean it well, then another 5+ minutes with Mother's Metal Polish, Flitz or similar.

If that fails, definitely have someone knowledgeable shoot the gun with you and do an assessment. If polishing doesn't work, I think you might need a finishing reamer chased in there.

Thanks Rob! I'll give it a shot.

After considering polishing, I thought I might compromise the TiN coating, so I decided just to return the barrel and try another. Rainier Arms took it back and I replaced it with an L2D Combat Precision Match barrel. Put a couple hundred rounds through the gun today and it functioned flawlessly. Thanks for all the help and advice!

Thanks for the update, and glad to learn that you've evidently been able to correct the problem.

This is the problem with "builds". For many years barrels had to be fitted to slides - remember the unfinished top of the barrel hood on old Sigs? That was due to final fitting.

Now with better machining tolerances, Sig can make slides and barrels that are true drop ins. But other brands can and will vary. Personally, I would use a barrel and slide from the same company - like Sig/Sig, Zev/Zev or Agency/Agency, or whatever you like.

UPDATE:

I now have two ZEV Slide/Barrel combos for my FCU - Full Size and X5. Waiting for recoil springs and an AXG grip from Sig. The barrels drop in with no binding. In reality the ZEV barrels and slides are made in collaboration with Sig so they should be dimensionally the same as Sig, just with the extra appearance upgrades.

Next up I might try a Killer Innovations Slide and Threaded barrel with their comp. They said they are 6-8 weeks out on availability...

This message has been edited. Last edited by: Lefty Sig,