New RDB - 6.5 MOA?!?!

Discussion in 'RDB Bullpup Rifle' started by NeilFromSeattle, Jul 7, 2017.

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  1. NeilFromSeattle

    NeilFromSeattle Member

    25
    Oct 7, 2010
    I’ve been looking for an RDB for years when two weeks ago my local gun store happened to have two in stock! I grabbed the tan one - serial number Z0U2x. In anticipation of finally taking it to the range I stripped it down, oiled it up, and stole my Primary Arms 5x ACSS scope from a different gun and boresighted it.

    This morning I dragged everything to the range, zeroed the scope, and was getting 1 5/8” groups at 25 yards! This was with a Caldwell shooting rest. Taking it out to 100 yards the group opened up to 6.5 inches! Based on shooting my other rifles with this same rest, my contribution to that group should have been no more than 1/4 inch. Even my self-built junker AR can get 2.5 MOA.

    The gas setting was +1 above how it came from the factory. The bolt wasn’t coming all the way back with the factory setting. It would eject and lock back, but not the last quarter inch or so which means I couldn’t use the bolt release. I had to use the charging handle to pull it back the last bit (which was very stiff.)

    Has anyone else had such a bad grouping? Before anyone asks, all rail screws were tight (the screw between T8 and T6 managed to turn about 1/8th turn, but it didn’t help the groups.) The scope bolts were tight. All takedown pins were in and nothing else on the rifle seemed loose. Anything else I should check for?

    Thanks in advance for any help!
    Neil

    Edit - this was with Armscor 62 grain FMJ ammo.
     

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  2. mikego_34

    mikego_34 Member

    77
    Aug 13, 2013
    Where you putting any upward pressure on the handguard when shooting? i.e. bipod, laying the front handguard on a sandbag, etc.
     

  3. Liberty4Ever

    Liberty4Ever Moderator Supporter

    May 19, 2006
    Lexington KY
    Despite your assurances, I still think there's likely to be something moving somewhere in the optic mount to be getting 6.5 MOA groups, perhaps below where you're looking. There have been a few threads on RDB rail mounts that might be worth reviewing. Or wait a day or so and someone with direct experience will probably chime in.
     
  4. NeilFromSeattle

    NeilFromSeattle Member

    25
    Oct 7, 2010
    There's a possibility it could be the sight - I bought it back in Jan to replace a 2.5x model that wasn't quite enough magnification for my M700. I think it's only had about 20 rounds through it (zeroing it) and it has sat in my safe since then. I'll be bringing a second rifle and sight to the range next week to test it out. It was dead accurate through the limited firing on the M700 though.
     
    Last edited: Jul 7, 2017
  5. NeilFromSeattle

    NeilFromSeattle Member

    25
    Oct 7, 2010
    Yes, the front handguard was resting on my Caldwell rest like you see in the attached picture. I've had guns that would vertically string when using the rest, but these groups were more random - lots of side to side shifting as well.
     
  6. NeilFromSeattle

    NeilFromSeattle Member

    25
    Oct 7, 2010
    This weekend I stripped the gun down, carefully cleaned and lubed everything, cleaned and put locktite on all the rail screws, staked the front rail screws, and otherwise inspected everything.

    Today I went to the range with a known-good 2.5x Primary Arms scope (I received a riflemen badge from an Appleseed shoot just a few weeks prior with it.) I also brought some American Eagle 62 grain FMJ to help rule out ammunition. I had the same poor accuracy (6+ MOA from benchrest.) This time I had the rifle laying on the back of the handguard (closest to the trigger) to minimize potential muzzle rise.

    I also had the same issue as the first trip where occasionally the bolt wouldn't cycle all the way back - it would eject the round, but get stuck most of the way back. It was VERY hard to manually cycle it the last inch. Once it was out of the "stuck" area it would smoothly cycle by hand. I increased the gas by one more click (+2 from the factory) and realize it was maxed out. For fun I closed the gas all the way and shot a single shot until it would cycle the action all the way. It first cycled on click #16. Factory was #19 and fully open is 21. The first two attached pictures are where the bolt gets stuck.

    With a little experimentation I figured out the bolt "sticking" only happening on the last round of the mag and only about 1/3rd of the time. I tried three different mags (the pmag it came with, a 20-round c-product, and a 30-round lancer) - and had the same problem with all three. I was also able to replicate it with no magazine inserted which rules out excessive rubbing of the bolt hold-open. It seems like having the additional upward pressure on the bolt from extra cartridges in the mag helped prevented it from sticking.

    When I went to clean up, I also noticed some torn necks on the brass (the last attached picture.) I can't tell if these happened during chambering or ejecting. I assume if it were to happen while chambering the bolt wouldn't be able to seat fully. I'm not sure how they would be torn like that during ejecting though. It worried me enough that I didn't want to shoot any more rounds until the problem is resolved. <EDIT - I found this thread that seems to explain what is happening: https://www.thektog.org/threads/rdb-223-dial-a-gas.267751/ . It sounds like that brass came from me cycling through the gas settings.>

    The bolt and carrier is also very sooty for a ~160 round range trip. Is that normal? It's on par with an DI AR bolt. I also get the smell of gas at my nose during firing. Is it possible the piston may not be sealing properly? That could explain the high gas settings required for operation.

    Anyone have any thoughts? If not I'll go ahead and ship it to Kel-Tec. At the very least the sticking problems can be fixed. I'm hoping that fixes the accuracy too. Does anyone know if Kel-Tec would consider 6+ MOA a fixable issue? It's a shame because I've got 16 boxes of different ammo that I was going to post an accuracy write-up about and use the data to tune a handload for the rifle.
     

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    Last edited: Jul 11, 2017
  7. mikego_34

    mikego_34 Member

    77
    Aug 13, 2013
    You sound like a diy kind of person, but at this point id get Keltec involved and have them make it right. Ive read some minor overall issues here about people's rdbs but yours seems a little more tricky. Have you discussed with Keltec on what their resolution is? Sounds like they would almost certainly say to send it back. I had an issue with my KSG not cycling properly and sent it back to them they remedied the issue and had it back to me in less than a month. Not sure if its hot in your part of the world but its too hot to shoot for me down in south texas, if I was having these sort of issues with mine, right now would be the best time for me to send it back.
     
  8. NeilFromSeattle

    NeilFromSeattle Member

    25
    Oct 7, 2010
    Yeah, I'm definitely a DIY kind of person, but it does sound like it needs to go back. I'm up in Seattle and the weather is perfect for shooting right now. I just finished up my previous job and am taking six weeks off before looking for a new one. The RDB was a present to myself out of my company's severance payout. Working on the cabin and shooting/load development for the RDB was going to fill up that time :(. It looks like I'll be spending time on my AR-47 build instead (have to enlarge the gas port in that one.)
     
    762Cattus likes this.
  9. iamscottasus

    iamscottasus Well-Known Member

    387
    Feb 21, 2014
    I posted Dial-a-Gas. My brass was getting ripped like that too. Some just bent.
    Im sure it happens in a return to battery cycle after FTE. Perhaps getting caught on the bolt hold open. Then crammed into the chamber. Wierd huh?
    I attributed it to under gassing as i was testing the whole dial range to see what the least gas point was. For me that was 5-6 from CCW (shooter POV) with fed .223 55gr. I didn't run much more after i found my working setting and it didn't get dirty. Every jam got a full field strip and cleaning.
     
    Last edited: Jul 11, 2017
  10. NeilFromSeattle

    NeilFromSeattle Member

    25
    Oct 7, 2010
    Yeah, your theory does make sense, and would account for why I didn't see any brass like that on my first trip. The peeling back of the neck looks like it could only happen when inserting a round. Ejecting should dent it or smash it inwards. If it did that while chambering a live cartridge I doubt it would be able to close the bolt all the way with the extra material at the shoulder.

    When I get the RDB back I'll run the gas ladder test again and watch/mark the brass.
     
    iamscottasus likes this.
  11. iamscottasus

    iamscottasus Well-Known Member

    387
    Feb 21, 2014
    Yea. All my rounds fired. All the ripped ones were all FTEs for me. My ejects didn't even have dented rims. This gun definitely is not over gassed.
     
  12. HBeretta

    HBeretta Active Member

    154
    Oct 26, 2016
    did you mess with your gas settings at all prior to shooting? just so that we're on the same page...factory default is setting 3. it appears you adjusted both ways, but clockwise facing the front of the gun for more gas...counter clockwise...less gas. mine wouldn't cycle around 7 or 8 gas setting if i recall correctly and my spent casings looked identical. believe i'm on four currently and have only a slight indentation on spent casings.

    anyway, the accuracy issue alone was enough for you to send it in. that's the drawback with kel-tec, the quality control. thankfully, you have a lifetime warranty. good luck with getting this resolved.

    the gun is definitely capable of being accurate...i'm happy with the accuracy with mine. thus far, i've averaged about 2 moa with bad days hovering around 3 moa or slightly over. i've also had a couple sub moa or right at moa 4-5 shot groups.

    i'm liking the tan as well.
     
  13. BlakeHanson

    BlakeHanson Well-Known Member

    May 31, 2015
    I believe Neil's gun has an out-of-spec chamber in the neck/throat area.
    Notice the amount of soot on the side of the casings and the neck area:
    [​IMG]
    Even in a really dirty gun, they won't come out like that.
    Compare them to Scotticus' shot-cases.
    If it's loose enough to blow by the cases, that would explain:
    Poor accuracy.
    Very dirty breech area (and smell of gas when firing).
    Impossible to set a consistent gas setting.
    I would send it back pronto with shot-cases and the target.
    Anything else would just be a wasting more time IMHO.

    Anybody want to bet it comes back with a different barrel lol.gif ?
     
    Liberty4Ever likes this.
  14. NeilFromSeattle

    NeilFromSeattle Member

    25
    Oct 7, 2010
    Ah, does setting 1 = gas fully open? I was assuming it was opposite. In that case, yes, the factory setting was 3 (two more clicks until fully open.) The first time the bolt "stuck" most of the way back I increased the gas setting one more (so setting 2.) On the second range trip yesterday it got "stuck" again and I added another click of gas and realized it was now maxed out. When that happened, I did the gas ladder test and the bolt would first started locking back at 6.

    Glad to hear the accuracy isn't normal. I would be happy with anything under 3 MOA since from experience I can usually squeeze another 1 MOA once I find and load the best ammo for it. I opened a ticket online yesterday - I'll let you know what they say.

    When it does come back I've got quite a range of ammo to test it with:

    Hornady .223 Remington Ammunition, V-Max, 55 Grains
    Hornady BLACK 5.56 NATO Ammunition 62 Grain FMJ 3060 fps
    Hornady Match .223 Remington Ammunition73 Grain ELD Polymer Tip BT
    Hornady .223 Remington Ammunition, Match BTHP, 75 Grain
    Hornady .223 Remington Ammunition, Match BTHP, 68 Grain
    Federal Gold Medal Match .223 Rem 77gr SMK BTHP 20rds
    Federal Gold Medal Match .223 Remington Ammunition 69 Grain Sierra Match King BTHP
    Federal Lake City 5.56 NATO Ammunition 20 Rounds OTM 77 Grain
    Barnes 5.56 NATO Ammunition 20 Rounds, TSX BT, 70 Grain
    Barnes 5.56 NATO Ammunition 20 Rounds, VOR-TX TSX BT, 62 Grain
    Nosler Defense .223 Rem 64 Grain Bonded PP
    Barnes Precision Match 5.56 NATO Ammunition, OTM BT, 69 Grain
    Armscor USA .223 Rem Ammunition, FMJ, 62 Grain
    Wolf Gold .223 Rem 55 Grain FMJ Bullet
    American Eagle .223 Rem 55 Grain BT FMJ
    American Eagle .223 Rem 62 Grain BT FMJ
    Handload 55gr Hornady FMJ, 1.6cc (~22 grains) Varget
    Handload 55gr Winchester PSP, 1.6cc (~22 grains) Varget
    Handload 55gr Hornady V-Max, 26.7 grains Varget
    Handload 64gr Nosler BSB PPT, 25.2 grains Varget
     
  15. NeilFromSeattle

    NeilFromSeattle Member

    25
    Oct 7, 2010
    Lol, is now the time to mention I rinsed the brass first because it was turning my hands black. The paper towel in the background is what they were sitting on to dry. So those are (slightly) cleaned cases. :p
     
  16. BlakeHanson

    BlakeHanson Well-Known Member

    May 31, 2015
    go crazy.gif
    That's a very important symptom! brickwall100.gif
    Edit: Just for S&G, post a pic of some you didn't clean.
     
    Last edited: Jul 12, 2017
  17. Liberty4Ever

    Liberty4Ever Moderator Supporter

    May 19, 2006
    Lexington KY
    I'm kind of with Blake on this one. Once I saw the cases that look like they were fired in a blow back operated rifle, I knew something wasn't right. Out of curiosity, when the gas setting wasn't mangling the cases, were they powder charred as well?

    I'd also concur with the suggestion of sending the targets demonstrating ridiculously bad accuracy, mark them as bench rest targets, and maybe enclose a copy of a target from your Appleseed shoot to demonstrate it's not you. I'd send examples of the mangled dirty cases with a note briefly explaining that this isn't just a loose rail, so no doing the Loctite fix and sending it back.

    Kel-Tec generally function tests a repaired firearm (does it go bang a few times?) but they typically do not test for accuracy. In this case, I think they should, and they should be paying close attention to the cases that are ejected to ensure that they did the proper repair.

    There are amateur gun smithing things you could do to determine if the rifle is properly chambered, and that might be interesting, but you may just want to leave that up to Kel-Tec.
     
    850sub likes this.
  18. HBeretta

    HBeretta Active Member

    154
    Oct 26, 2016
    makes sense you'd ladder the gas settings...what i would've done. again, first thing i thought was not enough gas with the bolt not reaching the breech and mangled casings.

    the best i've shot with is 77gr match...hovered under 2" easily...just above 1" groups. i'm definitely inconsistent though...not the greatest shooter...avg joe for sure.

    but i've heard the gun shoots well with quality 55gr flats also...i have yet to try.
     
  19. Liberty4Ever

    Liberty4Ever Moderator Supporter

    May 19, 2006
    Lexington KY
    I'd also drop some of those Armscor rounds into a .223 cartridge gage.
     
  20. NeilFromSeattle

    NeilFromSeattle Member

    25
    Oct 7, 2010
    Luckily my brass container is almost full. So while I can't say 100% that all this brass was from the last two visits, it should be since I grabbed from the very top. So yes, it looks like all the brass had some degree of charring:

    20170712_151610.jpg

    Sadly I didn't save the actual targets, just pictures. I'll have to print a few out when I send the rifle in.

    Thanks for all the suggestions!