POF P308 PRS Conversion Issues

[FaintlyLucky]

Greetings,

I'm having cycling issues after the conversion (FTFeed,FTX) and I'd really appreciate another few sets of eyes on this and some advice.

Please let me begin by saying that I realize that others have posted about cycling issues after converting P308s from a collapsible stock to a PRS stock. I read those threads before I did the conversion because I ran into the same issue that others ran into finding information on what parts were needed. Using the information from those threads and the POF website, I ordered these parts:

DPMS LR-308 buffer - part number 308-BS-11 - measured for correct length but not weighed (no scale, working on finding a person who has one)
DPMS .308 standard length buffer spring - part number 308-BS-10B - measured for correct length and coil count.
Buttstock extension tube - part number BS-09

I did the conversion, then took the rifle out to the range for testing. Fail. FTX, FTF, stovepipe, even a lockup. The BCG was obviously not retracting far enough. Mags are known-good PMAG G3s. I verified that the gas system was set to normal and hadn't somehow ended up in the suppressed or off position. Frustrated since I had done my research and ordered the correct parts with both the forums here and the POF website as a guide and not having brought the old spring and buffer, I went home.

After consulting the POF website again, I performed the recommended cleaning process after watching the video to rule out fouling issues, though I had never had a problem with FTF or FTX prior to the conversion, with ANY ammo. I also re-verified that I had the correct parts with the correct measurements.

I returned to the range yesterday, making sure to bring the old spring and buffer (post 2012). Here are the results of that testing:

New buffer and new spring - FTF every time, no FTX, one double feed over 10 rounds
New buffer and old spring - FTF every time, no FTX, over 10 rounds
Old buffer and new spring - no FTF or FTX, kicked like mule (big surprise)
Old buffer and old spring - no FTF or FTX, kicked like mule (big surprise)

But, wait a minute! I did my research and ordered the right parts according to this forum and the POF website, so why am I having cycling issues with the new parts? I'm certainly not a gunsmith, but common sense gives me a few ideas:

1. The buffer is the right length, but heavier than it should be.
2. The new spring is the right length, but heavier than it should be for some reason - not too sure about this one, but I know that there is a direct correlation between buffer length/weight and spring length/weight.
3. The gas piston system is operating below spec for some reason - It's obviously not transferring enough energy to the BCG to allow it to push the new buffer back/compress the buffer spring enough for proper cycling, but these are the parts that POF says will work on a fixed stock conversion and that others have confirmed will work, so if the part numbers and specs are all correct.....
4. I can't rule out user error during the conversion process because this is the first time that I've done it, but I did the research and followed the process exactly to the best of my knowledge.

As I said before, any advice would be greatly appreciated.

Thanks in advance,

Lucky

 

[samnev]

Since you ordered all the correct parts the only other problem that I have heard was not using the correct screw, the one that comes with the PRS rather than a longer one some have mistakingly used from an AR 15's riles butt stock. This was not allowing the bolt to retract far enough causing the problems you encountered. But since you are so careful about the parts you ordered I doubt that is the case. But it's the only other thing I've heard go wrong. I also ordered the same parts on my POF P-308 and had no problems.
Do you have another AR 15 20" rifle that you could switch out the buffer and spring with? Perhaps the trouble lies there.

 

[FaintlyLucky]

First, thank you for the reply. As you can probably tell, I need all the help I can get on this one.

I made sure to use the screw included with the (AR-10) PRS stock since I had already read about it causing issues. Even so, I also checked to make sure that it wasn't protruding into the end of the tube both before and during testing.

As for having a spare AR-10, unfortunately I do not. I'm almost tempted to fork over the money for a second P308 and do a conversion on it with the same parts to see if there's a difference, which I think would point toward a gas system problem if it worked on one, but not the other. However, that would be a very expensive test, so I'm hoping that I can figure out what's going on without doing that.

I ordered a Tubb AR-10 buffer spring this morning for giggles to see if it will make any sort of difference, but beyond that, I really don't want to spend any more money until I've got a better idea of what I'm dealing with.

 

[samnev]

Rather than getting another POF, I wouldn't either, I'd talk to the Tech's at Brownells to see what the have to say and perhaps they can recommend a buffer and buffer spring to order that would solve your problem. They have a 100% satisfaction guarantee so if the 2 new parts do not solve your problem you can always send them back for a refund. The tech's at Brownells have always been a great hep to me when I had a problem. The cost of a new buffer and spring is minimal so i'd call them explain what is going on and ask for their input.

 

[FaintlyLucky]

I actually have some semi-good news to report.

I spoke with Don over at POF this morning and told him about the issues that I had. After verifying that I did indeed get the correct parts for the conversion, he said that he thought it was a gas system issue, specifically the diameter of the gas piston. I emailed him my address and he said that he will be sending me two pistons with different diameters to try out to see if that takes care of the cycling issue. If it does, then great, but if not, then he asked me to send it in so that they could work on it.

I'm cautiously optimistic and will post back once I receive the pistons and can determine whether one of them fixes the issue.

 

[hunterb]

Please let us know! I have a PoF P308 20 inch and I was looking to do this EXACT thing to my rifle. Thank you for posting this OP, eagerly awaiting your update!

 

[desertfox01]

the 308s are finicky in this style of piston system. changing the weight of buffer, strength of spring can cause problems, as you have experienced. Soon as I started reading the OPs first post I was saying to myself "Piston". There is a reason POF has various sizes of pistons on hand. To tune each rifle to run with various stock setups or ammo.

 

[FaintlyLucky]

Well, I didn't receive the pistons last week and I also didn't receive any sort of feedback indicating that they were on the way, so I emailed again on Thursday night. I realized that I had forgotten to register for the warranty when I bought the rifle in 11/13, so I corrected that oversight, then sent the email and made sure to include my S/N. I realize that might be the reason that I haven't received them yet.

I still haven't received any sort of reply, so I have no idea whether the pistons are on their way or not. If I don't hear anything or receive them by tomorrow, I will call POF and try to get a status.

 

[FaintlyLucky]

So, after much confusion, I received the pistons today.

I will test each piston and post back with the results.

 

[-Nick-]

If also fails you might consider the Battline Industries S.A.P.R.

 

[samnev]

So how did the new pistons work out?

 

[dirtyharry44mag]

i just grabbed my pof308 bout a yr ago, and right of the box all ammo works but fiocchi. it stovepipes every case extrction with that brass. drives me nuts!!! i haven't changed anything on the rifle, and i love shooting it. but that ammo will not cycle at all.

 

[samnev]

The POF P-308 can be finicky. Fortunately mine shoots any brass I feed it wether it's mixed hand loaded brass or factory. However I never tried Fiocchi. Perhaps it something in the load they use.

 

[FaintlyLucky]

Well, the first new piston that I tried worked! Cycles like a dream again for now.

I'll do some long term reliability testing as soon as I get some scope issues worked out. It looks like my next purchase will be a new scope and mount because I think my scope got damaged somehow in the whole process.