RMW Extreme Build. It has begun.

[Pablo]

Pablo,
   How's your 10mm running? Did the lube help?

I won't make it to the range until Friday at the soonest.

[sstewart]

Here is the completely finished upper (well I still need to Loctite things):

What length of barrel is that? 10.5 or?

[Pablo]

11". It's in the OP.

[Pablo]

Pablo,
   How's your 10mm running? Did the lube help?

Lubing every moving part helped a bit but problems not completely solved. It was pretty juicy. Cleaning sure was easy though.

Mainly the short stroking remains. Even the hottest high pressure 10mm loads it happens. It's frustrating because it's not frequent, seems to happen more when I fire rapidly though.  I think the fact the brass is pitched 1-2pm (1pm mostly) is another clue.

What next? Buffer and spring. The more I read it comes down to being under gassed.

My buffer is a 3.0 oz carbine buffer. It looks normal. I knocked the pin out, insides normal. I took two of the steel slugs out and replaced them with 1/2" OD oak dowel cut to ~0.6" long. Finished weight is ~1.8 oz for the buffer now.

Will try soon.

Next I have ordered this lightweight spring: http://www.davidtubb.com/ar15-tubb-parts/ar15-buffer-spring-stainless

[sstewart]

I was talking about this lube: ( not lube in general)
http://www.militec1.com/miva/merchant.mvc?Screen=PROD&Store_Code=militec1&Product_Code=BONUSPAK&Category_Code=1

frustrating for sure. The lube is above is great. You can shoot gun to generate the heat to penetrate the metal parts or bake metal parts in oven. (my wife would freak out about that part)

[Pablo]

The Tubb buffer spring arrived. VERY nice flat wire spring. I think I may get the standard versions for my 5.56 and 6.8SPC.

Going to the range tomorrow with various springs and buffers. Looks like perfect weather.

[Pablo]

The spring worked great. Buffer weight didn't seem to matter.........or did it.......more later........

[sstewart]

Such a teaser .....

[Pablo]

I don't have a ton of time to type, so some amount of trust will be necessary from the reader, that I indeed was somewhat scientific about trying the springs and buffers.

Gun oiled up pretty good with CorrosionX only.

Target at 30 yards. Not precise shooting, standing.

Basically I loaded up 2 magazines (with slightly different feed lips) with 5 rounds each of 180gr medium hot rounds. More or less my standard. Started with my light 1.8oz buffer and Tubb flat spring. All 10 rounds fired flawlessly. Next 10 rounds in each. 20 rounds flawless. 15 in each, 30 flawless. WOW 60 rounds, no issue. Call a cease fire, pick up the brass all in a 2 foot circle, 5-6 feet ahead at 1 o'clock. So then I yacked with the one other guy at the range at 8:30AM, gun cooled down, maxed out the magazines (32 rounds) - first round, fails to go into battery. Hmm....

So I stop, clear, offload the magazines to 5 rounds and try again.....maybe 1 every 4-5 rounds, fails to fully seat in battery. My thoughts are racing a bit, thinking dirty tight chamber, etc....

I swap to H buffer 3.8 oz, gun behaves exactly the same. Try other ammo, try one minor tweak of the feedlips on one mag. Same behavior.

I come home, pull the carrier and the bolt just barely moves in the cylinder and it's dry as a bone. Never felt a bolt so grindy tight

if you lube the rings on a pistol cal the hot gasses stick to the rings & will slow it down. Just run them dry on the 10mm.

RMW Xtreme

I'll just leave that here.........

[Pablo]

[Pablo]

To summarize:

No stovepipes, no failures to extract. Locked back as expected when bolt lock button held.
I will stay with the light flat buffer spring designed for pistol caliber carbines and I will use the standard 3oz buffer.

Multiple rounds fired with no issue, gun cooled down, bolt become almost impossible to move as a piston. Most likely a lubricant issue.

I detail cleaned the bolt and carrier spotlessly. Reassembled with no lubricant. It seems relatively tight compared to my other AR bolts, but will not attempt any mechanical fix. Took carrier apart again and soaked ring area, and carrier in 2 stroke engine oil. Reassembled very wet and the bolt seems to move freely enough. Next trial will not change other variable and will see if some type of seizure occurs when gun cools and reheats. May remove bolt carrier during trial.

The thoughts for the 2 stroke oil: It should prevent rings from sticking in cylinder with heat and force. We shall see!

Frankly, for lack of better words, the gun now feels badass. Light (around 5 pounds), easy to shoot, and accurate as I want it to be. Fun project!

[mrpipesmkr]

Pablo,
  Just a quick thought. It sounds like your bolt and rings are too tight in the carrier. The rings, when inserted into the carrier completely close the gap that each ring has prior to insertion. Forcing the bolt into the carrier gets the rings in but leaves less than zero tolerance. With the lube burned off by firing the weapon the bolt and rings seize up.
  If this is the case firing the weapon enough will eventually break it in, but this might prove to be very frustrating and time (and ammo) consuming.
  You might try lapping the rings to mate them to the carrier with a tolerance loose enough to move freely but tight enough to allow the gases to function the bolt.
  Ther are several polishing compounds used by gunsmiths to lap parts together to insure a perfect fit but I have found that Turtle Wax polishing compound is available in most automotive parts stores and works well.  Just remember that you want to use the white polishing compound that comes in a green container, not the rubbing compound that is red and comes in a red container.
  Put some of the compound on the rings, insert the bolt into the carrier and work the bolt back and forth until it loosens up. Make sure the gaps in the rings are not lined up and change their positions each time you refresh the polishing compound on the rings. Do this until the bolt does not seize in the carrier but still requires some effort to move. Test fire the weapon and repeat if needed.

[Pablo]

Pablo,
  Just a quick thought. It sounds like your bolt and rings are too tight in the carrier. The rings, when inserted into the carrier completely close the gap that each ring has prior to insertion. Forcing the bolt into the carrier gets the rings in but leaves less than zero tolerance. With the lube burned off by firing the weapon the bolt and rings seize up.
  If this is the case firing the weapon enough will eventually break it in, but this might prove to be very frustrating and time (and ammo) consuming.
  You might try lapping the rings to mate them to the carrier with a tolerance loose enough to move freely but tight enough to allow the gases to function the bolt.
  Ther are several polishing compounds used by gunsmiths to lap parts together to insure a perfect fit but I have found that Turtle Wax polishing compound is available in most automotive parts stores and works well.  Just remember that you want to use the white polishing compound that comes in a green container, not the rubbing compound that is red and comes in a red container.
  Put some of the compound on the rings, insert the bolt into the carrier and work the bolt back and forth until it loosens up. Make sure the gaps in the rings are not lined up and change their positions each time you refresh the polishing compound on the rings. Do this until the bolt does not seize in the carrier but still requires some effort to move. Test fire the weapon and repeat if needed.

THIS. This exactly had crossed my mind. I am actually super grateful you posted, because there is pretty much no doubt I would have started with something too aggressive if all it takes is car paint/clear coat polishing compound.

[mrpipesmkr]

No problem Pablo, I hope it solves your problem.  I have used this same product on rough bores and with patience it works well. Even chromed bores can be improved this way although it is important to avoid polishing in the area of the crown too much on any bore.
  Your carrier is probably chrome lined also and will resist wear.  The rings will probably wear a little quicker which is what you want. Have fun and let us know how it goes.

[Pablo]

So I compared the feel of the bolt in the carrier bore with my 5.56 and my 6.8. The 10mm is much rougher (not even close) and does have a sticky point. So I tried the polish. First of all it started pretty rough with the polish as the only "lube". But it got easier, and the rough beginning sort of broke through. The absolute most amazing thing? The amount of metal flakes and crud that flushed out!  REALLY SHOCKING!! After that I triple cleaned it, blew it out then flushed with spray lube. Super clean now and re-assembled with 2 stroke oil on the rings. WOW, it's piston gas tight feeling but nice and smooth.

I actually think the lube and rings were allowing the rings to move over this junk - but the polish didn't allow this and just took the stuff out.

Not sure when I can take the gun out.