I bought a 20" barrel from a well known vendor on this site. It won't cycle, even with 2" cut off the recoil spring. The gas port appears to be .070.
I have found a couple references on the net that it should be .093, or even .096 or .098.
A .075 bit won't fit and with calipers it looks like .070 but its hard to measure a hole that small with calipers.

.093

Did you call the vendor and ask what it's supposed to be when it leaves the factory ??

Did you contact the vendor with your concerns after it didn't cycle  ??

And you do realize that you shouldn't cut a spring....
Because when a gun won't cycle, 99.9% of the time it isn't the spring length.
And now you gotta buy another spring.



_

Colt spec is .092"-.093".

This is the correct answer. Contact the manufacturer and get it replaced.

That said, I'd love to have a 20" barrel with that tiny a gas port. It would be a fun way to experiment with port diameters. I'd keep working my way up until I got the gun to run the way I wanted it. A 20" rifle gas is already super smooth and soft. One with a port under the spec with lightweight components would be fun to toy around with.

To answer your questions, I did contact the company, but I waited until I had troubleshot everything and took the fsb off to see what was going on.
The vendor was PSA. They said if I removed the fsb I voided the warranty. I IMed the PSA person on here last night to confirm that, I'm not sure it's not the same person. I paid a lot more money for a nitrided barrel, I'm not sure if I can even drill the port on a nitrided barrel. I guess I bought a $200 boat anchor.
Re the spring, I've shortened springs before to help get a gun to run and it had worked before. I had a spare spring anyways.

If PSA won't help you because you removed the FSB to measure the port, that's bullshit. If their barrel has a port that's. 023" too small, then you taking the FSB off has no effect. What you did didn't have any effect on the gun not running and they shouldn't give you shit or leave you hanging because of their screw up.

On the bright side, if they do refuse to replace the barrel for you, I'll buy it.

If you wanna keep it and fix it yourself, it won't be hard to open the port up. I've done lots of barrel work to melonited/nitrided barrels and they're not that hard to work with. You'll be able to open the port up just fine. A #42 or a 3/32" drill bit will open the port to .093". The #42 bit is just a hair smaller, but they're both essentially .093".

So putting it together basically requires fsb removal and install. What a load of bs! I had a minor problem with a psa upper once, they made it right with no problem.

Has anybody enlarged a gas port on a nitrided barrel with a TiN coated bit? I've read you should use carbide, but it's a 70 Mile drive to go get one.
Pallmetto state armory hasn't answered my IM today, so I guess they aren't going to cover this.
ETA, for those concerned I will post the e mail exchange between PSA customer service and my self. I actually think there was more wrong with this barrel than just the port size as you can see in my e mail, but I beleave it would function if the gas port were the correct size.
My e mail to them:
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I bought this barrel, SKU 516444649, back on 4/28/2017, I realize it's been a while, but I just got around to assembling and test firing it and something is wrong with it big time. When I assembled it I noticed that I couldn't get my usgi a2 handguards to go on without wittling on them with a knife, they were used on other rifles before without issue. When I test fired it would not cycle. The most it would do is pull the spent case out enough to come to rest with the case mouth jambed into the face of the barrel inside the barrel extension. I cut off about 2 inches off a PSA rifle recoil spring and it didn't get much better. I tested it on a carbine lower I'd used with other uppers, same result. Tested it with a well used bolt carrier group, same result. I removed the fsb and could see that it appears the fsb was mounted to far back, I could see the circle left by the opening in the fsb and it overlapped the gas port. I tried opening up the hole in the fsb so it would align better, but it is still grossly under gassed. I just test fired it and with the shortened recoil spring it still wouldn't even lock back on an empty mag. I've checked the gas tube and made sure the gas tube hole lined up inside the fsb. Something else that was wierd was that I had to just about bottom out the front sight post to zero it at fifty yards with an A2 upper. I can live with that. Please let me know what you can do.
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Their reply:
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Hello,

When you opened your gas port, did you remove the front sight gas block entirely? If you did, this has voided your PSA warranty.

As long as you did not completely remove the gas block, I can issue you a return label. To ensure accuracy of my information please provide me with

1.      First and last name
2.      Order number if applicable
3.      SKU number if you know it
4.      What you will be returning
5.      Serial number if applicable
6.      Preferred email address
7.      Return address
8.      Preferred phone number

Best regards,

Dylan D.
Customer Service
Palmetto State Armory
(803) 724-6950
[email protected]
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ETA: note where he says I enlarged the gas port. Look at my message, I didn't say that. I said I enlarged the hole in the fsb. I sort of put a funnel shape to it to make sure it wasn't partially blocking the gas port. I realize I probably shouldn't have messed with it, but what difference does it make? They can't really resell these parts as they are all used and or defective. If I hadn't pulled the fsb they probably wouldn't have identified the problem either.

If I was OP, and you were my vendor in this particular case we'd have a problem. OP didn't make the hole smaller by dicking with it. The vendor did. Now if the vendor wants to say "I'll exchange your naked barrel for one that is to spec and then you are on your own." then fine. But OP taking the fsb off has no bearing on the fact he was sold an improperly machined part. He should get a new barrel (because he paid for a nitrided port, not a re-drilled untreated one).

A customer touching something he bought is not an excuse for a vendor to wash their hands of defective merchandise when it is clear who is at fault.

What if I had had a home built rifle that wouldn't cycle and I immediately blame the barrel and send it back and they claim everything is fine? As others have said, it's pretty obvious the barrel was machined wrong regardless of what I did.
You'd think they would have wanted to know what batch it was out of in case a bunch of barrels got machined this way, but instead they look for ways to not cover it.
If I'd known I was going to have a problem and have to be doing machining on it I certainly wouldn't have bought a $200 barrel from PSA, I would have just bought a $65 or $99 barrel from BCA or classic firearms, which is what I will be doing from now on. I've bought several BCA barrels and never had an issue.

Ignoring if the OP reamed the hole in the FSB:

You have to take off a FSB to install a hand guard or to even mount the bare barrel to an upper. How can FSB removal void a warranty on a barrel? I can understand a complete rifle or upper receiver group.

I'm going to be getting drill bits today to fix it my self. I'm hoping I don't break a bit off in there. Honestly I was surprised when I looked at PSAs warranty and it said lifetime, I was surprised it was more than 30 days. I know I f'ed up by waiting several months, but it did surprise me that the one thing that voided it was removing the fsb to identify the gleeming issue. I'd also think they'd want to know if some guy in there shop is drilling the wrong size port.

It says it's non-returnable, not out of warranty. How would you know it didn't work unless you fired it? How would you know the gas port was undersized unless you removed the FSB?

Yes! Without assembly and test fire, the only way to know that the port is the right size would be to remove the fsb.
ETA: not trying to get it covered at this point. I started this thread asking what size the port should be. It looks like I was right, it should be bigger. I'll know for sure after I drill it out, then for sure I will have voided the warranty.

0.070" is the correct size for a carbine barrel, not a rifle barrel. PSA screwed up and if they won't fix it, thats pretty shitty.

.058-.063 for a 14.5 or 16 carbine. .070 for 10.5.

I drilled it out with a 3/32" Cobalt bit, couldn't get carbide in my AO. It drilled super easy. I bought 3 bits because I'd heard how difficult it is to drill nitrided barrels, but it was easy. It now cycles.

I've been trying for weeks to get an answer from PSA for the following:

"What is the gas port diameter on you barrel #7782785 - 5.56mm 16" Nato with FS Marked F (mid-length gas tube)?
Thanks in advance. "

I bought a couple of these barrels and fail to understand their lack of response.

I have a 20" BCM rifle length barrel with a .750 gas port. Of course it has a piston kit on it now but I've never had any issues with gas.

I've also read- "don't try to drill something that is nitrided- it's a nightmare". I drilled and pinned a nitrided barrel for an A2 FSB a few weeks ago and I had no issues at all with a 'regular' drill bit (TiN coated High Speed Steel)
What's all the hype?
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PSA probably doesn't know. They are most likely ordered from a contractor who also installs the FSB.

PSA Customer Service responded - 0.075"
Thank you PSA.

Wow. Not much barrel left, huh?

I figure they just don't give a shit any more. When I started this thread I withheld the name of the vendor pending a response from them. They never replied to IMs on here or chimed in in this thread. I'd like to say I'll never buy from them again, but they do have good deals... If the product works.... Or if they ship the thing you ordered.

I like PSA deals but I do admit my experience with their CS has been absolute shit the twice I needed it.

Nitriding is a case hardening type treatment that will produce around 55 Rc hardness on 4140/4150 alloys.  Typical HSS twist drills are north of 60 Rc.  In short, they are harder than a nitrided chromoly steel, but not by a lot, so they will wear quickly trying to cut it.  Keep speeds low, pressure high and use cutting oil, though, and you'll have good results with sharp cutters.

The biggest issue is deflection; a drill has more difficulty starting on a hard surface, so it will tend to walk a lot more-especially on a radius.  Use punches and starter drills, and if the hole isn't gonna be deep, stubby drills are more rigid than standard jobber length, ergo preferable.  

I generally use 1/8" carbide end mills to spot drill for pin & weld, as they won't try to go into the valleys of threads like a drill, and it leaves a flat bottom hole.  But end mills tend to oscillate a bit when drilling, even in a rigid machine; using a .125" end mill, the holes in steel will typically end up ~.130" on my Lagun.  They won't get along well with a drill press at all, high probability of breakage, so you're better off using split point twist drills if a press is what you have.

I just bought another barrel from bear creek arsenal!
link to barrel.
$66.50 shipped! I paid $200 plus shipping for the chf barrel from PSA. (It did have a fsb installed though)
Bear Creek even lists the gas port size in the specs, the propper .093, PSA wouldn't even answer the question.
I'm going to keep using the PSA barrel, but now I have a spare, or the start of a new build.

Do I understand this correctly?

If I buy a PSA barrel with gas block or FSB and I need to remove said item from barrel to install a free float handguard I voided their warrany?