Feed ramp issues on new POF upper ... need HELP!!

[gvnwst]

Okay, something is messed up with the bolt and or cam pin. Here is a pic (welll, 2) of my POF bolt, with the pin in. Sorry, one is not the greatest, but the camera was free, and better than having to use film...:

 

[MCMXI]

gvnwst, thanks for posting the photos. After spending a while honing the cam pin hole, so that the pin rotates freely and now falls all the way through the hole, I reassembled the bolt and carrier with high hopes that this would be it. NAHHHHH!! :banghead: The action jammed again on the even numbered rounds (in the magazine). So I finally gave up, removed the gas rings from the DPMS bolt and assembled the POF bolt/carrier and upper with the DPMS bolt. Everything's fine in that configuration with dummy rounds flying around the room at will. I installed the POF bolt in the DPMS upper where it's about 80% reliable so the POF bolt is basically EVIL I'm going to call POF tomorrow to ask them to send me a new bolt but they probably won't agree to that. I looked online to see if I could buy a bolt but DPMS, Stag Arms, Midway, PRI are all sold out!!

What function do the bolt gas rings serve on "regular" uppers? They're kind of like piston rings but what exactly is there purpose?

Anyway, short of an epiphany, act of God, or other divine intervention, this is it for me. I don't have the time or the energy to figure out what the heck is wrong with the POF bolt.

 

[gvnwst]

You know how DI works, right? Basically it shoves the gas into the BCG, and pushes on that part of the bolt. Hence the gas rings. They are to seal it, the POF, not having that gas, doesn't need them.

 

[rino451]

Doesn't need them but I bet that the lack of them allows the bolt to rock w/i the carrier causing the bolt case interface to be off kilter.

 

[taliv]

uhh, dude, i hate to tell you this, but the cam pin is NOT supposed to fall all the way through that hole. it's closed on purpose to prevent our boys in uniform from installing the bolt rotated 180* which would eject the spent case left into the side of the receiver instead of right out the aptly named ejection port

if you've filed that away, that's not good

 

[MCMXI]

if you've filed that away, that's not good

Why's that taliv ... it's my AR and I KNOW which way the bolt goes in the carrier so do you really think that I need to have an indexed cam pin hole in the bolt? I know why the cam pin hole is indexed but thanks for your concern.

Doesn't need them but I bet that the lack of them allows the bolt to rock w/i the carrier causing the bolt case interface to be off kilter.

Good thought process but the DPMS bolt WITHOUT the gas rings is working just fine in the POF carrier.

You know how DI works, right? Basically it shoves the gas into the BCG, and pushes on that part of the bolt. Hence the gas rings. They are to seal it, the POF, not having that gas, doesn't need them.

Yes, I know how dgi works but the point of my question is whether or not the POF bolt without the gas rings will function properly (at least for a while) in the DPMS upper. The gas doesn't act on the bolt directly, it acts on the bolt carrier KEY which is in top of the carrier so I'm wondering if the gas rings are there to prevent blow-by so as to reduce the amount of fouling that gets into the bolt. In other words, the bolt may need to be cleaned more often but it'll still work ok in a pinch. The pinch here is that I need to order new gas rings which aren't available at the moment.

 

[charlesb_la]

Originally Posted by 1858
The gas doesn't act on the bolt directly, it acts on the bolt carrier KEY which is in top of the carrier so I'm wondering if the gas rings are there to prevent blow-by so as to reduce the amount of fouling that gets into the bolt.

You are incorrect, the gas carrier key is only there to conduct the expanding gasses into the bolt carrier. Inside the bolt carrier the gas forces the bolt carrier back AND the bolt forward. This pushing back on the bolt carrier cams the bolt open via the cam pin. The gas rings are required for operation. Without the gas rings the gas will leak by and not exert enough force on the carrier.

 

[taliv]

I know why the cam pin hole is indexed but thanks for your concern.

then why did you file it off?

 

[MCMXI]

You are incorrect, the gas carrier key is only there to conduct the expanding gasses into the bolt carrier. Inside the bolt carrier the gas forces the bolt carrier back AND the bolt forward. This pushing back on the bolt carrier cams the bolt open via the cam pin. The gas rings are required for operation. Without the gas rings the gas will leak by and not exert enough force on the carrier.

Thanks, I appreciate the education/clarification ...that's what this board is all about for me. I've learned an incredible amount here. After reading your post, I took the DPMS bolt/carrier apart and using a flashlight I can see the port in the carrier beneath the carrier key that I didn't know was there. I straightened out the gas rings from the DPMS bolt and installed them on the POF bolt. Now I have two functioning uppers but it's been a PITA to get to this point. On the bright side I feel that I know more about the AR system than I did last week.

taliv , I wanted rule out as many variables as possible in my failed attempts to figure out why the POF bolt won't work in the POF upper, but will work in the DPMS upper. Allowing the cam pin to move up/down without any resistance was part of that process. Since I'm not worried about the chance of installing the cam pin 180 degrees off, I didn't (and don't) have a problem with what I did. Now, if you know of another reason why that was a bad idea (that can easily be corrected with a new bolt), then PLEASE let me know. I've already proven my spectacular lack of knowledge regarding the AR system so another erroneous assumption on my part is neither here nor there.

Many, many thanks to everyone for your input and help. I will be calling POF today to ask for a new bolt and to find out if they've had a bunch of bolt-related issues recently. I don't know if they manufacturer their own bolts in-house or if they order them from another vendor but I'll ask about that too.

 

[MCMXI]

I spoke to the guys at POF this morning and they have had some bolt-related issues. Their bolts are made by Stag Arms but in order to have POF replace the bolt, they need the upper back. I mentioned that I could buy a new bolt for the cost of the shipping and they offered to cover the cost of shipping back to them. However, since the POF bolt is just a regular bolt (with some chrome on it), I don't see a problem keeping the DPMS bolt in the POF carrier and the POF bolt in the DPMS carrier so that's what I'm going to do.

Thanks again for all of your help ... that should be it ... and I hope I won't have to bore you any more with my trials and tribulations.

 

[charlesb_la]

Glad to hear that POF is standing behind their product. I've had one for a couple of years and it had never had a stoppage of any kind. Every manufacturer has problems so don't let it get you down on your rifle, when you get it straightened out it will run and run.

As far as the education I think most shooters think that dgi works like a hose spraying into a cup, until they delve deeper into the system. I know I did.

Enjoy the rifle, it's a nice one.

 

[MCMXI]

What a difference a week (and a DPMS bolt) makes!!! I put 25 reloads through the POF upper on Saturday without a single issue. The bolt went into battery every time and all the cases ejected without drama ... I KNOW I'm going to love this upper. I got the Troy sights dialed in at 50 yards (1" grouping) and then got them very close at 100 yards with perfect windage but maybe an inch or two high before the end of the day. The ejected cases end up three to four feet forward and to the right which makes brass retrieval a lot easier.

Every manufacturer has problems so don't let it get you down on your rifle, when you get it straightened out it will run and run.

Very true ... it's how a company DEALS with those problems that makes ALL the difference.

As far as the education I think most shooters think that dgi works like a hose spraying into a cup, until they delve deeper into the system. I know I did.

Yep, that's what I thought but now I know better ... thanks.

I bought a one-piece gas ring yesterday so I'll put that on the POF bolt and run it next weekend in the DPMS upper to see if everything works fine. If it does, then that's where it'll stay.

 

[MCMXI]

Headspacing question.

I need a quick reality check here ... headspacing isn't an issue with the AR platform right? In other words, any bolt should be fine in any carrier with any barrel ... is that correct? The reason I'm asking is that the DPMS bolt is working perfectly in the POF carrier. IF the POF (Stag Arms) bolt works perfectly in the DPMS carrier I'd like to leave them where they are ... that's if headspacing is not an issue.

My current "theory" as to why the POF (Stag Arms) bolt doesn't work in the POF carrier is based on the Gaussian distribution of error found in ALL machined parts. It's my contention that the POF (Stag Arms) bolt is at one end of the curve (mean minus 3 standard deviations) and the POF carrier is at the other end of the curve (mean plus 3 standard deviations). The DPMS bolt and carrier are both in the middle of the error curve so the POF bolt works with the DPMS carrier (3 SD apart) and the DPMS bolt works with the POF carrier (3 SD apart), but the POF bolt doesn't work with the POF carrier (6 SD apart). Got it?

Thanks.

 

[charlesb_la]

Well maybe. The headspace is set when the barrel is installed into the barrel extension. If both barrels were installed correctly and both bolts are in spec it shouldn't matter. It would also depend on how much wear on the bolts. If they were both relatively new the it shouldn't be a problem.

The safest way would be to drop by a local gunshop and test them both with GO/NO GO gauges.

When I went through basic and we were cleaning the bolts we threw the whole platoons' bolts in one bucket of cleaning solution and then everyone just pulled one out and used it. No Kabooms but with your POF being new you might want to run the gauges to be sure.

Oh and I'm not to sure about Gaussian distribution of error, I just call it tolerance stacking.

 

[charlesb_la]

Another thing I just thought of. It could be a tolerance stacking issue with the coating that POF applies to the upper and the bolt. If it was just a little too thick on each it could add up to enough to cause problems even though each was in spec before coating. This could explain why the POF bolt works in the non coated DPMS upper and the DPMS bolt works in the POF upper. If this is the case it may wear in over time if it's just a hair to thick.

 

[MCMXI]

The DPMS upper is fairly new too with about 100 rounds through it so I should be ok if I understand you correctly? That's an excellent point about the coating on the POF bolt and carrier and I had thought about that as being an explanation as to why it took 20 to 30 rounds for the other POF upper to feed reliably. You would think that POF would be aware of that "wearing in" issue if it takes that many rounds for the "high spots" on the coating to wear away ... anyway, just a guess on both our parts but certainly plausible. I don't know if Stag or POF coats the Stag bolts ... ultimately it doesn't matter.

I'm going to order a POF upper in .308 in the next couple of months so I hope that I don't have the same problem since I don't have a spare .308 upper to swap parts with.

Thanks.

 

[charlesb_la]

Just be careful. The only thing that bothers me is that the POF is new and you haven't really established a track record with it so you can't be sure it was headspaced correctly in the first place. It's rare but does happen.

If you don't check the headspace be sure to check your fired brass for any signs of too much/ or too little headspace.

You could also post on the POF industry forum on ar15.com for responses from more knowledgable people than me.

http://www.ar15.com/forums/forum.html?b=2&f=206

 

[Target in sight]

Well, since earlier I had made the comment that a lot of people don't post their final outcome to problems I decided I had better report mine. My POF upper came back from the factory again after I was having issues with jamming and tiny dents on the spent rounds. I then conducted a test with six different brands of ammo. It turns out the PMC Bronze was the culprit. Maybe just a particular batch, but the gun would fill with unburned powder after each shot until it accumulated enough to jam the loading round. The dents.. unburned powder that sandwiched between the shell case and the chamber wall during obturation when fired. In my test I used PMC Bronze, American Eagle, Norinco, Wolf, Centurion, and some old 1980 PMC. Only the Bronze Box PMC gave me trouble. A little research showed that PMC changed to a new powder that they designate PMC2222. I am shooting an sbr so I am sure it has to with the powder/primer combination of the load and barrel length. I don't know about others, but Greg at POF was great about trying to resolve my problem I relayed my test results to him which he said would be passed on. I was left with a good feeling from POF. Good thing, you don't want to have a bad taste in your mouth every time you pick up the high $$$ toy. That kind of takes the fun away.
One more note. The PMC bronze fired fine in 16"plus barrels.

 

[MCMXI]

Target in sight, good to hear that you resolved your issue. POF has been very good in terms of customer service/support. I managed to get through to Chris (and Greg) immediately on three occasions, and the one time I didn't, they called back within 10 minutes. They've followed up with emails and offered to pay the cost of shipping the upper back to them if necessary. All in all I'm very pleased with the support that they've given. I don't think it's their fault that the Stag Arms bolt is problematic. I will certainly be ordering another upper (in .308) from them in the near future.

As for my POF upper ... I installed the POF (Stag Arms) bolt in my DPMS carrier/upper and shot 35 reloads this weekend. I had four FTF events with the bolt not going into battery on two rounds but the last eight all chambered/fired without issue. In the end, I hope that I've worn the Stag Arms bolt sufficiently that it'll work in the POF carrier. I installed a new one-piece gas ring on the DPMS bolt and put it back in the DPMS carrier where it's going to stay. I removed the three gas rings from the Stag Arms bolt and that's back in the POF carrier.