I initially posted this on the ammo side since I thought it could be an issue with the ammo:

Problems with Prvi

Here's the run down:

I have a DPMS stripped lower with a Del-Ton A2 mid length upper kit.  This is also a chromed lined barrel.  I have used Federal Brown Box and PRVI 5.56.  I have also used Wolf FMJ Black Box after the problems occurred to test various ammo.

I have used 3 USGI, 2 C Product and 3 PMag 20's and 3 PMag and 1 Bushmaster 30's for magazines.

This rifle has been fired 3 times and here are the problems:

Session 1:
-120 rounds of Federal Brown Box
-Cycled fine and excellent groupings
-Would not lock the bolt back when empty with any mags

Session 2:
-80 rounds of Federal Brown Box
-Cycled fine
-Would not lock the bolt back

Session 3:
60 rounds Federal Brown Box, 140 rounds PRVI 5.56 (what AIM is selling)
-Federal performed the same as previous 2 sessions
-PRVI performed the same as the Federal for the first 100 rounds

After those 100 rounds, I was getting FTE's, stovepipes and weak ejection (a few inches) with the PRVI.  The upper was broken down and inspected.  Nothing was noted yet this continued.  It should also be noted that the gas rings are offset.

My friend was shooting Wolf FMJ Black Box and suggested I try them.  They functioned flawlessly.  I put 100 rounds down range, both slow aimed shots and rapid fire.  No FTE's, no stovepipes and the bolt locked back when empty.  The gun was not cleaned between the PRVI and Wolf.

This rifle has been thoroughly cleaned between each session.  The chamber has been inspected with no apparent flaws.  I also have the correct buffer installed.

This is a 5.56 chamber.

My question is this:  Why would I have so many problems with 5.56 brass cased ammo yet function flawlessly with Wolf?  

Logic would say the weaker pressure ammo would cause the problems.  Could it be that the bolt is cycling too fast with the 5.56?

Another thing I noted is that the bolt, while able to move freely in the carrier, still seems to "stick" more that what I remember when qualifying in the military.  I seem to remember the bolt on my M16A2 sliding very loosely in the carrier.

This is a new upper and parts?

New bolt & BC will be stiff until the parts get broken in.  200-500 rounds depending.

Check the gas key on the BC.  Make sure it's solid and no signs of gas leakage, screws should be staked or else you need to check the torque on them.

Make sure you have cleaned any preservative oil or grease from the parts and then lubricated well, especially the extractor, ejector, cam pin, bolt body and gas rings.  I prefer a light oil during the break in period with frequent cleaning and relubing.  I also recommend lubing the bolt with light oil and just cycling it in and out of the BC by hand a few hundred times to break in and seat the gas rings.

Any signs of gas leakage around the FSB?

What weight buffer are you running?

Quoted: Logic would say the weaker pressure ammo would cause the problems.  Could it be that the bolt is cycling too fast with the 5.56?

It's possible, it's also possible that the different characteristics of the steel case ammo might be giving you different results.

This is a new upper and parts? New bolt & BC will be stiff until the parts get broken in. 200-500 rounds depending. Check the gas key on the BC. Make sure it's solid and no signs of gas leakage, screws should be staked or else you need to check the torque on them. Make sure you have cleaned any preservative oil or grease from the parts and then lubricated well, especially the extractor, ejector, cam pin, bolt body and gas rings. I prefer a light oil during the break in period with frequent cleaning and relubing. Any signs of gas leakage around the FSB? What weight buffer are you running?

This is a new upper.  The "stiffness" in the bolt appears to be a good thing and shows serviceability of the rings.  The gas key is staked and solid, with no apparent leaks.

I have not seen any powder residue around the FSB and the buffer is the A2 that comes with the kit.  Not sure of the weight but it is the correct one for the supplied kit.

So this is a fixed stock?

A fixed stock spring in a telestock tube might be causing problems.

Does it lock back properly when cycled by hand with an empty mag?

Does it lock back properly when cycled by hand with an empty mag?

Yes, the bolt locks back when hand cycled and when using Wolf

Yes, you do have that correct, but are confusing which ammo is weaker. Wolf is loaded to 223 SAAMI standards, while the other ammo may not be loaded even this level. If you're looking for hot ammo in USGI Nato standards, the M-193 in the 55/62Gr range using standard burn rate gun powder is the ticket. As for the 62+ gr ammo's, they are loaded with slower burning powder, hence has a different port pressure at unlock due to the longer burn duration (more pressure at the port).

Both the Federal and PRVI are 55 gr. M-193 spec.  This same ammo causes the FTE's and fail to lock the bolt back.

clean the chamber.

Went to the range today and the same damn thing happened.  I brought Federal 5.56, PRVI 5.56 and UMC .223.  In all cases, I could not fire 5 rounds without jams and FTE's.

I thoroughly cleaned this upper before going today too.

Describe the jam in great detail.

The round fires and is extracted from the chamber.  The spent casing is then jammed up into the charging handle while the next round tries to go into the chamber.  The bolt obviously is coming back far enough to strip the next round but the previous round isn't kicking.

The ejector pin has a good, strong spring and the extractor works fine.

Del-Ton thinks its a gas issue.  I'm getting a return order # from them so they can try and figure it out.  The only possibility that makes sense to me it that it is a really tight chamber.  The brass 5.56 and .223 would extract fine until the chamber heated to a point where they would "stick" to the walls.  That in turn could slow down the action to the point of a jam.  That could also explain the Wolf.  Since the steel case wouldn't expand as much, it would in turn extract easier.

That said, it still wouldn't explain why it has gotten worse every time since I scrub my chamber and lugs thoroughly.  I even CLP powder blast the lug area and Q-tip the area to remove all debris.

Now this is starting to make sence. Despite claiming to be loaded to SAAMI specs, every chrono report I've ever seen on steel cased Wold .223 has it running right around 3,000 FPS. The Privi and Federal usually clocks in at around 3,200 FPS, but Privi is known for baing a little hot due to QA\QC issues. It is entirly possible that the Privi being the hotest load was giving you the most drag on the chamber. The Federal was still draging, but just not as much so it was ejecting and not giving the BCG enough dwell time to allow the bolt catch to spring up.

Quoted: Del-Ton thinks its a gas issue.  I'm getting a return order # from them so they can try and figure it out.  The only possibility that makes sense to me it that it is a really tight chamber.  The brass 5.56 and .223 would extract fine until the chamber heated to a point where they would "stick" to the walls.  That in turn could slow down the action to the point of a jam.  That could also explain the Wolf.  Since the steel case wouldn't expand as much, it would in turn extract easier. That said, it still wouldn't explain why it has gotten worse every time since I scrub my chamber and lugs thoroughly.  I even CLP powder blast the lug area and Q-tip the area to remove all debris.

Well, I sent it back to Del-Ton today.  We'll see what they say.

Please report back. This was an interesting one for sure.

I finally got a reply from Del-Ton

They cleaned it, fired it, and it locked up on them.  So, they drilled the gas port hole a smidgen and it still stovepiped, but not as bad.  They changed out the bolt and it worked just fine.

I guess it was a gas issue.  In this case, a leaky gas key.  I still think the chamber might be tight since Wolf worked before, but if it's getting more gas now to properly extract the casing, I'm fine with that.

I'll take it to the range this weekend and give it a good workout.

Interesting. Opening up the gas port actually reduces the pressure. I don't know what was out of spec with the bolt , but if it runs who cares.

Quoted: I finally got a reply from Del-Ton They cleaned it, fired it, and it locked up on them.  So, they drilled the gas port hole a smidgen and it still stovepiped, but not as bad.  They changed out the bolt and it worked just fine. I guess it was a gas issue.  In this case, a leaky gas key.  I still think the chamber might be tight since Wolf worked before, but if it's getting more gas now to properly extract the casing, I'm fine with that. I'll take it to the range this weekend and give it a good workout.