Well, my 16 inch barrels probably help accuracy a little, but your shorter barrel should turn in comparable groups.  We took the red dot off my 10mm and put a decent variable on it. I had the advantage of having some young eyes along with me to do the dialing in. My old eyes require some concentration that my grandson doesn't have to bother with.
  One thing I have noticed is that when shooting a large, general target like a steel your groups will fall off. It's psychological I think.  Because you are shooting for a hit anywhere on the steel you tend to not focus down like you will with a decent Bulls-eye target.  Just natural l think, but if you try shooting at a bulls-eye target at the same range you'll be surprised at how things tighten up for you.
 

Pablo,
  Had a chance to go to the range Sunday afternoon. Had a little wind and a few sprinkles but a nice cool day for the range.
  My son in law and grandson came along and we took several pistols and rifles. Don't want to even think about how many rounds of various caliber see went through but I do know we put 150 rounds each through the 10mm AR and the 9x25 AR.  We had one hang up on the carbines when the 9x25 failed to feed one round by hand cycling. Dropping the bolt release and during firing it fed perfectly.
  My main reason for going to the range was I wanted to zero both builds at measured distances. We used 100 yards as a zero for both the 10mm and the 9x25 and adjusted for drop further out, as far as 200 yards. As I've said before, I am impressed with the accuracy of both builds. We found it fairly easy, even with a little wind, to shoot 2-2 1/2 inch groups at 100 yards with the 9x25 doing a little better than the 10 in the wind. The two stage triggers I'm using on my builds really helps and having a good table to rest on makes quite a difference. At three hundred yards my groups did grow quite a bit, out to 3 1/2 - 4 inches with several fliers I prefer not to talk about!  I have to attribute this to a shaky old man with old eyeballs. My grandson did better but I haven't admitted it to him yet!
  It seems both of our builds are pretty well dialed in now. I'm starting to have confidence that when I pull the trigger on mine they are going to go bang every time!  Now I just need to find a couple of hogs to volunteer for a little ballistics test I have in mind!

  I wanted to mention another problem I had when using the Korean, KCI .45 auto magazines in my 9x25 build.
  As most 10mm and 9x25 shooters know, these magazines can be converted from .45 auto to 10mm/9x25 by simply adjusting the feed lips down to the 10mm diameter. Usually this is enough to convert them although sometimes the spring has to be adjusted also.
  There is another problem that comes up when using these magazines to feed 9x25. Occasionally a mag That feeds 10mm perfectly will jam when feeding 9x25, with the rounds becoming stuck at the top of the mag. In some cases you can have as few as 3-5 rounds in the mag When this happens.
  The problem is with the shoulder of the 9x25 round. If you take apart the KCI mag You will see that there is a slight ridge stamped into both sides of the sheet metal of the mag Located at the top of the mag. These two ridges contact the front portion of the 10mm brass and guide the round into the feeding lips. However, the 9x25 brass is not straight like the 10mm is since it has a shoulder where the case drops down to 9mm. This 9mm part of the case happens to contact the ridges in the magazine rather than the 10mm section allowing  the rounds to angle off 1mm to each side causing a jam.
  The easiest solution is to take the magazine apart and extend the ridges on each side of the mag back toward the rear of the mag by using J.B. Weld.  It doesn't take much to extend the ridges back far enough that the 10mm portion of the case is contacting them. This forces the rounds in the upper portion of the magazine to set straight in the mag and move properly into the feed lips eliminating this kind of jam.
  Hopefully my discription here of the problem and the solution is clear but if you take your KCI mag apart and put a 9x25 round int the upper section you will see where the case is contacting the ridge. Compare that to where a 10mm case contacts the ridges and the situation becomes evident.

 

Quote from: Pablo on February 17 2016 06:49:53 PM MST
I keep thinking I'll have time to add detail and I just can't catch a break.

Pablo,
  Now that you have your 10mm running so well are you still looking at doing the 9x25?.
  I've got to say that the 9x25 is a great intermediate carbine round.  More versatile than the 10mm with almost as much close range stopping power and better gas pressure to run the AR. They are both a hoot to shoot!

Quote from: Pablo on February 17 2016 06:49:53 PM MST
I keep thinking I'll have time to add detail and I just can't catch a break.

Wow Pablo, you seem to be a busy guy! That's why I updated the list. But, the board will be here next time you have some time.

Quote from: mrpipesmkr on February 12 2016 08:31:03 AM MST
Over the past five weeks or so Pablo and I have been in close communication discussing our 10mm and 9x25 carbine builds from RMW extreme.  By explaining to each other improvements we had done to our builds and future plans to improve them we set up a situation where we brainstormed our way into making our carbines run very reliably.  They can be made to be very reliable, and when you reach that point they are a lot of fun to own and shoot.
  This excersize has proven to be a lot of fun for both of us and a learning experiance that is hard to match in terms of pistol caliber DI AR's.   But, we don't believe that every owner of an RMW extreme build would want to go through the many ideas and changes we have had for our builds.
  Our hope has always been to distill what we have done to our builds down to an easy to follow list of important improvements that others could use to improve thier builds.
  So, the following is a distilled list of things we have done. The list is in no particular order but is fairly comprehensive. We will add any other improvements we might have done should we recall them at a future date.

1)    installed Tubbs flat wound spring, Pistol and 300Blackout model.
2)    installed H2 buffer, weight 4.4 ounces
3)    made sure the buffer and spring were lubed
4)    used both the JP and standard rings, depending on build, well broken in
5)    Polished the bolt face until it shined, making sure any ridges were well rounded
6)     polished the cam pin, rails the carrier runs on, hammer face and the ramp the               
        Hammer runs against.
7)     used 600 and 800!grit paper to smooth the chamber walls
      polished the chamber walls including the cone at the start of the chamber
9)      polished the firing pin
10)    Trimmed, rounded and polished the bottom two feeding lugs on the bolt insuring that enough material
         was removed to insure the lugs cleared the magazine. Smooth polish eliminates drag on the
         next round feeding in the magazine


    Both Pablo and I will try to answer any questions you might have. The important thing to remember is that with a little tune up work you can have a very reliable carbine that is tremendous fun to shoot.
   It is important to remember that Pablo's build and my two builds are a little different.  Pablo's build is based on a lower that uses GG magazines. My builds both use the QC10 lower and run Glock magazines.  Still, the work we did on our pieces was very similar with a few small variations.

  I wanted to clarify number 10 on my list. Pablo and I had been discussing the trimming we did on the two bottom feeding lugs of our AR's, even exchanging pictures. He pointed out to me that he had removed material from the rear of both lugs before polishing them, something I had not done.
  The idea here is that by removing the material you lower the height of the lugs and they taper up to full height at the front. This leaves plenty of material at the front to strip rounds from the magazine but allows the rear of the lugs to pass over the round in the magazine with minamal contact until the lug is beyond the crimp. Polishing means that as the two lugs scrape across the top of the magazine round they have very little friction or drag. Because of this, they also tend to move the magazine very little. All this contributes to a much smoother feed, ejection, ect.
  So, to trim your lugs you need to take material off the outside of both lugs, thinning them enough that they clear both sides of the magazine and lower the rear of the lugs so that they taper up to the front, which is left full height. Polishing all contacting surfaces insures minamal drag.
  I left a little height on the rear of my lugs so that they will somewhat lock into the barrel extension lugs, but I don't believe this is a huge consideration because the lock, designed for a .556 round, is more than strong enough to handle the 10mm.

Quote from: sqlbullet on February 14 2016 06:00:13 PM MST
Thanks!

I will add it to the list in place of the sprinco orange.  Or maybe in addition.  $30 on this build won't break the bank.

I also came across this the other day:

http://www.vertexops.com/V_Seven_308_AR10_DPMS_SR25_Titanium_BCG_p/v7-bcg-ti-ar10.htm

Same price within a few bucks as the JP low mass, so I am gonna grab one when they are back in stock.

Once I get to the actual build part I will post up a thread on how it goes. Appreciate the input guys!

I've got to echo Pablo.  WOW!!  Looks like quality stuff though.   How hard does the .358 feed?  Is it possible to have too light a weight in the BCG?  I suppose a heavier spring or buffer could be used if the BCG is a little light, and still represent a weight savings.
  Don't make book on it, but I believe the thermal properties of titanium are similar to aluminum.

Quote from: sqlbullet on February 12 2016 04:33:39 PM MST
Thanks for the feedback.

At some point I wanna build a DI 10mm upper, but it is down the road.

Short term this is relevant to me on my 358 Win build.  I want to see how light I can do it.  Based on mfg. information, I think I can end up under 7lbs on an AR-10 with iron sights.  But, there are two big parts of getting there and one is a JP Rifles low mass BCG for DPMS pattern AR-10.  That bolt is used in conjuction with an adjustable FSB, and probably a Springco Orange spring.  The idea is to use the light bolt, buffer, dial back the gas to get full bolt travel without battering and then let the extra power spring provide the umph to get the next round fed.

I have a good head start in weight using the new TN Arms polymer AR-10 lower, which only weighs 6.8 oz.  And I tracked down a 16" medium contour 358 barrel from KAK.  I may pay to have it re-contoured to more of pencil profile if I just can't get the JP low mass to run.  The idea would be to shave 3-4 oz from the barrel contour to add back into the buffer and BCG.

Cutting to the chase, I am keenly interested in properly understanding the results of changing reciprocating mass components.  I would love to end up with a guide sized gun with 25 rounds of 358 Win on tap as fast as you can squeeze the trigger.  LPK gets here next Thursday.  Handguard is on backorder and that wicked expensive JP BCG has to wait for my 2015 bonus to be paid, probably in March.

Sqlbullet,
  I've got to say, you are a very ambitious guy to come up with the idea for a rifle like the one you describe!  I carried an M16 around in the military along with some heavier stuff and can appreciate your desire to knock every ounce possible off your build.  It can be done I think, but you are going to have to do a very precise balancing act with your components to make it run. You'll end up with a pile of spare AR parts that were tried but did not work. That's not really s bad thing as you seem to have several other AR's to keep running also.
   I was thinking about your build and my response to your question regarding the H2 buffer and spring.  Weight wise, the H2 is out for your build unless you just have to have the added mass to get your weapon to cycle. 
   However, I wanted to suggest to you that it might be worthwhile to look into the Tubbs flat springs for your build, either the carbine or rifle spring, depending on your build.
   The way the Tubbs springs exert more power with the bolt closed and the way they smoothly stack in recoil would, I believe help your build to be more reliable without adding much, if any, weight.
   Just a thought on my part but check them out.  I really like the way they run in my builds.

Quote from: Pablo on February 12 2016 01:12:22 PM MST
Before we do a better consolidation, feeding an AR with a case mouth spacing untapered round can be problematic as well. If the ammo has zero crimp, the gun will choke. Generally a mild crimp will be fine if every area from the magazine to the chamber is deburred and polished.

Pablo is dead right on this.  I hadn't really noticed the lack of crimp on the factory rounds I have bought. After talking with Pablo I checked out the crimp on some Armscore rounds I had purchased on sale. No real crimp on them at all! Just the bell removed and that's it.
  If you look at a10mm round you can see why this creates a problem. The case mouth on the 10mm is always very far up the bullet, just at the point the ogive is ending. This is the perfect position for the rim to hang up on anything and everything, which it does. Check your rounds out and crimp them if they need it!  It doesn't need to be an exceptionally tight crimp, but it must roll the rim into the bullet at least slightly. It will still headspace properly with a good roll crimp.

Quote from: sqlbullet on February 12 2016 09:15:55 AM MST
Sorry to be that guy, but I don't wanna dig back through the 10 pages.

You went to an H2 buffer.  What weight buffer did you start with?

I am a relative AR-noob, with only 2 completed builds (5.56 SPR and 300 BLK Carbine), and four in progress (CMP Service Rifle, 5.56 Carbine, 308 Win and 358 Win), and two yet to be started (260 Remington and an undecided 6.5mm in an AR-15).

It seems to me that an undergassed gun would want as little reciprocating mass as possible, aka a carbine buffer.  And possibly a JP Rifles low mass bolt carrier.  I have been reading the thread as you went and I don't recall these being discussed, but I may have missed it.

You I am curious of the H2 was chosen for additional momentum for feeding, and the gun was well enough gassed to drive it with a light-ish spring, or if I just am missing something.

Sqlbullet,
  No problem, I wouldn't want to read through 10 pages of old posts either! That's why Pablo and I decide to post our list on the board.  We will help all we can and try to clarify anything that seems confusing.
   I originally used a standard carbine buffer (app. 3 ounces) in my builds.
   Installed the H2 buffer in both my builds. You are right about the reciprocating mass and weight. I found that increasing the buffer weight (4.4 ounces) helped my builds to feed easier. I was having trouble getting proper feed out of my Glock mags when they were full.  Adding the mass seemed to help and both builds have enough gas to run the buffers. Pablo is right that I run somewhat hot loads. My standard is a 180 grain Hornady HAP pushed by 9.6 grains of Longshot with a standard primer. I have run other loads such as 155 gr with equal success.  Lighter bullets use more powder which in turn creates more gas volume and pressure.
  The Tubbs flat wound pistol and 300 blackout spring was a big help with this. It ran somewhat with the standard carbine spring and not at all with the Wolf extra power spring.
  The Tubbs spring is designed to exert equal force throughout its travel where the standard spring creates increasing force as it stacks up. This means the pressure created by theTubbs when the bolt is closed on a round is greater, requiring more pressure to move it, increasing lock up time and the available pressure to move the bolt and carrier.  As the bolt and carrier move back they encounter less resistance from the Tubbs spring than they would with the standard spring when it begins to stack. Therefore you don't lose much if any velocity on the bolt and carrier.
  It's important to point out here that my 9x25 build has an adjustable gas block on it which I can use to help tune it to the H2. I put the H2 in the 10mm, got it to run, liked it, and then put it in the 9x25 with a slight adjustment to the gas block.  The adjustable gas block cannot be installed on the 10mm because there is not enough room in the gas system for it and besides it needs ALL available gas.
  I hope this info helps clarify!

Over the past five weeks or so Pablo and I have been in close communication discussing our 10mm and 9x25 carbine builds from RMW extreme.  By explaining to each other improvements we had done to our builds and future plans to improve them we set up a situation where we brainstormed our way into making our carbines run very reliably.  They can be made to be very reliable, and when you reach that point they are a lot of fun to own and shoot.
  This excersize has proven to be a lot of fun for both of us and a learning experiance that is hard to match in terms of pistol caliber DI AR's.   But, we don't believe that every owner of an RMW extreme build would want to go through the many ideas and changes we have had for our builds.
  Our hope has always been to distill what we have done to our builds down to an easy to follow list of important improvements that others could use to improve thier builds.
  So, the following is a distilled list of things we have done. The list is in no particular order but is fairly comprehensive. We will add any other improvements we might have done should we recall them at a future date.

1)    installed Tubbs flat wound spring, Pistol and 300Blackout model.
2)    installed H2 buffer, weight 4.4 ounces
3)    made sure the buffer and spring were lubed
4)    used both the JP and standard rings, depending on build, well broken in
5)    Polished the bolt face until it shined, making sure any ridges were well rounded
6)     polished the cam pin, rails the carrier runs on, hammer face and the ramp the               
        Hammer runs against.
7)     used 600 and 800!grit paper to smooth the chamber walls
8)      polished the chamber walls including the cone at the start of the chamber
9)      polished the firing pin
10)    Trimmed, rounded and polished the bottom two feeding lugs on the bolt insuring that enough material
         was removed to insure the lugs cleared the magazine. Smooth polish eliminates drag on the
         next round feeding in the magazine


    Both Pablo and I will try to answer any questions you might have. The important thing to remember is that with a little tune up work you can have a very reliable carbine that is tremendous fun to shoot.
   It is important to remember that Pablo's build and my two builds are a little different.  Pablo's build is based on a lower that uses GG magazines. My builds both use the QC10 lower and run Glock magazines.  Still, the work we did on our pieces was very similar with a few small variations.

Pablo,
  I believe the titanium pin should be stronger than standard, no more bent pins!
  It s hard for me to say what your problem with feeding is without watching the action work. I believe the lugs contacting the mag lips is not a good thing if occasionally it causes a jolt to the mag which throws off feeding, but it sounds like there is no major contact between the lugs and the lips.
  If the round is going nose up as it exits the magazine causing a missfeed you might check and see if the front of the round or the case lip is contacting the front of the mag, throwing the nose up. If it appears this is happening, taking a little metal off the front of the mag would give better clearence.
  When the lugs contact the round are they hitting it low, below the rim, somewhere near the center of the case head? This would tend to make the round go straighter into the chamber.
  Anyway, it sounds as if most of the bugs are being worked out of your build! Let us know how your next range trip goes!

Quote from: Pablo on January 06 2016 01:28:17 PM MST
Does make me wonder if the shouldered 9x25 would feed easier and my problem would be cured. I did receive my titanium firing pins last night. Wow they feel light.

Pablo,
  My experience is that the 9x25 does feed easier than the 10. Smaller bullet going in to a large chamber.  Less rubbing, less drag.
  The Titanium pins sound interesting, let us know how they work.

Quote from: sgmtino on January 06 2016 01:35:36 PM MST
I have a di qc10  10mm ar that im trying to get the bugs out of as well my issue is the bolt doesn't close all the  way on the first 7-9 rounds and I have to eject the mag and slam the bolt shut till I get to about 5-6 rounds left then the weapon cycles fine I already have the updated lower receiver that helped a bunch any tips from you guys

Sgmtino,
  First of all, welcome aboard!  Always good to have another 10mm DI AR owner to contribute their experience to the board.  I think the idea here is that by pooling our knowledge and fixes we all can end up with reliable 10mm and 9x25 builds. A couple of us have builds that are running pretty good.  The 10mm in a carbine or SBR is just a whole lot of fun.
   Can you give us more info on your build?  Who did the upper, barrel length, Glock mag or other (QC does build other lowers) ect. This will help to compare yours to others.
   The first thing I would say to you is take the time to read all the posts on this board and see if any of the info and fixes can be applied to your build. There is a lot of info posted by the various members dialing in there builds and some of it will be useful.
I think I have experienced the type of problem you are dealing with and have, for the most part, cleared it up. I still have an occasional partial feeds with new mags but they are fewer than before. In my case the round was feeding straight into the chamber but stopped before the bolt fully locked. I usually just have to tap the forward assist to close the bolt.
  I think what was going on with mine was simply that the bolt carrier was not returning with enough force to close the bolt. I think this is because these builds tend to be quite tight when new, before break in. The 10mm does not have the gas pressure of say, a .556 so the carrier may not be moving all the way to the rear of the buffer tube and therefore does not close with enough force.
  As Pablo suggested I went in and used polishing compound to "loosen up" my bolt and smooth out the rings and bore that they run in. This takes some repetition but does take the stiffness out of the bolt. Pablo has also gone to the one piece ring and feels this was an improvement, I have not, yet.
Because these builds tend to be stiff due to the coating used on all parts I also decided to help break in my build by polishing some of the wear points in the upper and lower.
  I used a Dremel with felt pad and polishing compound to smooth out and remove the coating to cut down on friction and drag. You don't have to polish to a high shine on these wear areas but you do want to polish until they are smooth. Polish all four of the rails the bolt carrier runs on, the bolt and rings (as stated) the retainer pin, the tail of the bolt, the face of the hammer and the portion of the carrier the hammer runs against.
  This should help minimize the drag and improve the speed of the carrier as it moves forward.
  Also check to see if the bolt lugs or carrier is rubbing against any part of the mag causing a slow down.
  I have also ordered some of the Militec lube. I think if it is applied properly, according to instructions, it will help reduce drag.
  Let us know how it goes and we will all work together to perfect our builds. All in all, they are a ton of fun!

Pablo,
  I know what you mean about chambering live rounds! I get queasy every time I have to do it!
  No problem if you are busy at work! We gotta make money somewhere to pay for our expensive toys! I just wasn't sure if I was making sense or not, trying to describe the work we did to the lugs on my builds and I wanted to be sure my meaning got through. I hope the pics made more sense than my verbal description. I know it was something that helped my builds and hopefully could help yours.
  Again, you have to be the judge as I have next to zero experience with the GG mags but if they feed from the center then it needs to be looked at!
  Did you decide on the 9x25?