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

[MCMXI]

I took my new POF upper to the range today and what a disaster it was!! Yesterday I measured the chamber with a Stoney Point OAL gauge and loaded up some Winchester brass that had been full-sized and trimmed to length (1.750"). I used a Hornady 75gr BTHP bullet and couldn't seat it anywhere close to the "optimum" length of 0.020" - 0.040" off the lands due to the interior dimensions of the Bushmaster magazines. I ended up with a COL of about 2.270" which just fits in the magazine. Basically, I had to seat the bullet about 0.090" off the lands (long POF throat I guess). Anyway, now to the problem ... I only managed to shoot five rounds due to the fact that almost every round jammed during the chambering process. Take a look at the photo of the POF chamber below and compare it to the chamber of my DPMS upper (also below). The DPMS has two distinct feed ramps inline with each position that a round might occupy in the magazine. The POF doesn't have two distinct feed ramps. WHAT AM I MISSING HERE!! Is the POF upper supposed to use single stack magazines, a particular type of bullet, a specific COL? I'm really at a loss and am hoping for some ideas before I call POF. In case you're wondering, the lower that I was using is a Bushmaster, the magazines are Bushmaster 10 round versions with "new", gray no-tilt followers. The magazines work fine when used with a Bushmaster lower and DPMS upper. I'd REALLY appreciate some help here. On the bright side, the five shots that I managed to get off grouped well at 50 yards and the Troy sights are excellent.

POF chamber and feedramp:

DPMS chamber and feedramps:

 

[Duelist]

Use factory ammo.

 

[briansmithwins]

I agree to use factory ammo for starters.

However, it really looks like POF skipped the step where feed ramps are machined into the extension. Have you contacted POF yet? BSW

 

[taliv]

dude, that's messed up. i can't tell from the pic, but does it even have a feed ramp? try unhinging the lower and taking a pic from the bottom

 

[rbernie]

Looks like somebody forgot to machine the feedramps.

 

[gvnwst]

The feedramps are there, just not machined enough. I don't know why though...?

Try some factory ammo, mine has been flawless with any i have put through it.

 

[MCMXI]

First, thanks for your comments. I called POF this morning and they told me to ship it back to them with a note. When I asked their tech support guy if their upper can only handle factory ammunition he said that it should be fine with reloads but he basically implied that my reloads are probably "defective". Tell that to my DPMS that has devoured hundreds of them without any problems.

dude, that's messed up. i can't tell from the pic, but does it even have a feed ramp? try unhinging the lower and taking a pic from the bottom

Looks like somebody forgot to machine the feedramps.

However, it really looks like POF skipped the step where feed ramps are machined into the extension. Have you contacted POF yet? BSW

The feedramps are there, just not machined enough.

Four observations implying that the feedramps aren't machined enough ... BUT .... if you take a look at the DPMS image, imagine machining out the center "divider" between the two feedramps ... that's what POF has done. In other words, their feedramp is just one scalloped region that's as deep as the DPMS feedramps. The POF feedramp allows the round to over rotate AWAY from the centerline of the chamber. What was happening yesterday was the bolt would strip a round off the magazine, the bullet would hit the feedramp and continue rotating so that the case head would move AWAY from the bolt head rather than seat in the bolt head, and then the round would jam in the chamber because it's not going in straight.

I will try factory reloads in a couple of weeks. I sent an email to POF with the two photos in this thread so hopefully they'll have a better idea BEFORE I have to mail this POS (I mean POF) back to them.

Thanks for the comments/observations/thoughts.

 

[bonedust]

every company has a hiccup here and there. i have yet to come across any company in this industry that doesnt serve up a turd now and again. POF is great product imo, and will certainly make the rifle right.

i would also try factory ammo before returning the gun. juts my 2cents.

 

[Hoppy590]

those ramps are epic failures.

if those were a mistake, its a big one and some one should have caught it. if they are designed that way. i cant see them being effective.

 

[MCMXI]

So I tried feeding some factory ammunition today loaded in GI issue magazines with Bushmaster no-tilt followers. The ammunition is Remington something or other that I had lying around in magazines (box long gone). I always feel "nervous" letting the slide strip off a live round at home in case of a slam fire ... the local police would love that! Anyway, it didn't work either and the round got jammed half way in the chamber. Here are some more photos. In the first photo, you can see that the round isn't aligned with the bolt and the head of the case isn't seated against the bolt face properly.

I'm going to call my local gun shop where I bought the upper and see if they has any ideas before I send it back to POF. They had four come in so maybe he'll do a swap but I doubt it. At this point I'm starting to think it's defective rather than being my ammunition, magazines etc. One last thing to check is the ejector/extractor or whatever it's called.

 

[flynlr]

while I am sure you have a problem with that upper and you confirmed it with factory ammo. the MAX OAL seen in all the reloading manuals I have is 2.260

I ended up with a COL of about 2.270" which just fits in the magazine

 

[MCMXI]

while I am sure you have a problem with that upper and you confirmed it with factory ammo. the MAX OAL seen in all the reloading manuals I have is 2.260

I've fired many, many rounds (77gr SMK HPBT) through my DPMS upper with a COL of 2.270" (0.025" off the lands) without a single feeding problem. Basically, if the round will fit in the magazine and you've measured the chamber to determine the max COL then 2.270 isn't a problem.

 

[Target in sight]

I recently had some issues with my POF in which I believe the issue to be in the extractor. While searching to increase my knowledge I came across this post. I also found another post that seems to describe your issue.

http://wintersoldier2008.typepad.co...nctioning-issues-with-the-ar-style-rifle.html

You will find it about two thirds of the way down in the article. I hope this helps since my upper is now on its way back for the second time from POF. I do have to say they have been very responsive to my problem, but I do hope the issue is finally resolved.

I notice on a lot of sites people never post back after I assume they resolve their issues. Please post back with your success/failure.

 

[MCMXI]

Target in sight, thanks for the link ... very interesting and it may well help me to resolve this issue.

I called the gun shop on Monday that I ordered the POF upper from and he told me that another upper from the same lot has/had the same problem. I don't know if the other two from the same order have been picked up or fired yet. He must have sold it to a friend since he said he was at the range trying to help him with it this past weekend. He claimed that after 20 or so problematic feeds followed by firing, the upper became 100% reliable. When I called him a second time he was starting to get annoyed and basically told me that it's between me and POF. Not the kind of response that I was expecting since he was the one that recommended POF in the first place. Anyway, I called POF twice and they offered no explanation for the different feedramps other than "that's how we do it". I will add that I no longer think that the feedramps are the problem based on the 50 or so attempts to chamber a round using dummy rounds. I seated a couple of 55gr bullets in cases that had been trimmed to the correct length. I didn't use any powder or a primer and must have cycled the action more than 50 times. I found that with one round in the magazine I had a higher success rate than with two which failed to chamber 99% of the time. I'm now convinced that it's something else and if I can swap the bolt from my other AR I'll try that tonight. I don't know if the bolts are interchangeable but if they are that will certainly help the troubleshooting process. I did try a different charging handle just in case but that didn't help.

I'm still confused about the twist rate of the barrel. Chris at POF said that it's 1:8 but I'm sure that it's 1:9 based on the rotation of a cleaning rod and patch. My DPMS upper which has 1:8 stamped on the barrel checks out at that twist rate with a cleaning rod and patch.

Well, this hasn't turned out to be a great experience thus far. It's a pity since the POF looks to be very well made and just reeks of quality. I'll report back once I resolve this issue. I'm trying to avoid sending the upper back, but if I can't make any progress I'll have to ship it to POF.

 

[gvnwst]

If you are using just the bolt, it should work, POF says they are the same....they are. Firing pin and everything is also the same.

 

[MCMXI]

gvnwst, thanks ... I don't have the upper in front of me but I suspected that the bolts would be interchangeable ... the carriers are a different story of course. Changing bolts could help me to figure out if it's the extractor/ejector or bolt head that's causing the problem. The chambering process beat the crap out of the two dummy rounds that I loaded so I'll make up a couple more.

 

[MCMXI]

OK ... I'm making some progress so thanks again to Target in sight for the link which persuaded me to continue trying to figure it out. After switching the extractor, checking the ejector, changing the cam guide (or whatever it's called), and finally changing the whole bolt, I can say without a doubt that it's the POF BOLT that's causing the feeding problems. The DPMS bolt has gas rings on it but it fit in the POF carrier. I tried three magazines loaded with four dummy rounds and despite being badly beaten up, all of the rounds chambered effortlessly multiple times and were ejected without any problems. As soon as I installed the original POF bolt, the action would jam immediately when trying to chamber a round. I don't know what it is about the bolt that's causing the problem but it's 100% the bolt and NOT the feedramps. The ejector looks ok and doesn't appear to be stuck. The extractor is a bit stiff compared to the DPMS extractor but swapping them out didn't help so it probably isn't an extractor problem. The link posted by TiS mentions honing the bolt face to make sure that there aren't any burrs or other irregularities. This seems to be the next logical step before calling up POF and requesting a new bolt. Other than that, I'm not sure what the problem could be with the bolt.

Anyway, my apologies to POF for implying that their feedramps are rubbish ... I should have said that their bolts are rubbish as is their quality control and testing before sending their products out the door.

 

[taliv]

you forgot their customer support

 

[rbernie]

Anyway, my apologies to POF for implying that their feedramps are rubbish

I would still maintain that their feedramps are rubbish, regardless of the fact that they INTEND for them to look that way.

But that's just me.

 

[Walkalong]

I am no expert by a long shot, but those feed ramps, or lack therof, on the POF don't look like anything I have seen on an AR or in any pics of AR feed ramps.

I looks quite different from this pic for sure.

 

[jerkface11]

But I thought gas piston AR's were uber reliable.

 

[MCMXI]

But I thought gas piston AR's were uber reliable.

First off, I'm telling it EXACTLY like it is for good or bad ... that's always been my approach in life and on this board. With truth comes understanding and honest assessments of a system enable others to make informed choices. I will say that I categorically DID NOT make an informed choice. However, knowing what I know now I would STILL buy a POF upper for a number of reasons. First, because I don't think that the POF feed ramps are inherently unreliable. In fact, I've spent so much time focusing on the feed ramps and their interaction with the round as it's chambering that I'm now convinced that the design is solid. Second, the bolt problem isn't unique to the gas piston system ... in fact it has nothing to do with it and ANY AR platform could have the same issue. Third, I still like the idea of an action that runs cooler and cleaner and for that, a gas piston system is needed. Finally, the upper is EXTREMELY well made in terms of the machining, fit, finish, quality of materials etc.

I did have a thought last night about the bolt, I'm going to install the POF bolt in the DPMS upper and see if it cycles without any issues. That might shed more light on what's going on.

Walkalong, thanks for the photos of the M4 and "regular" feed ramps. This thread may well help others who are thinking about buying an upper.

I don't know how others here feel but I become more "connected" to a tool or piece of equipment when I work on it. Must be like a doctor/patient type of thing. I've cycled the action so many times on this upper, removed the bolt about 30 times, switched stuff around, cleaned, inspected, cleaned again ... we've formed quite a bond and it's done wonders for my AR handling skills.

 

[jerkface11]

Yup the problem obviously has nothing to do with nonstandard parts. Oh wait it isn't a standard bolt is it?

 

[MCMXI]

Yup the problem obviously has nothing to do with nonstandard parts. Oh wait it isn't a standard bolt is it?

Yes, it's a standard bolt but without the gas rings which could be added/removed if necessary since the annular gas ring groove is there. As I mentioned above, a DPMS bolt in the POF bolt carrier worked perfectly.

 

[MCMXI]

Notice anything different comparing the POF bolt (silver) to the DPMS bolt (black)? The arrows may help.

I installed the POF bolt in the DPMS carrier (using the DPMS upper) and the first round fed ok, the second one jammed, but after that, 25 rounds fed without a hitch. I don't know for sure that the problem is the cam (or whatever it's called) but I'm in the process of honing the POF bolt where the cam resides.