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Old 04-27-2012, 05:48 PM   #1
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Default SU-16B Malfunction

Hi! Fairly long time KT owner, but just registered recently. Sadly it's to report a puzzling series of malfunctions and hopefully get some advice on what to do with them.

I had taken my SU-16B out to the range yesterday with the intent of putting it through its paces for a reliability check. Ironically enough it decided to fail massively. My written records from the range note:
1st 10 round magazine loaded, fired, extracted without incident.
2d 10 round magazine, first round failed to fire when chambered, no sign of a primer strike. When rechambered a second time, round fired. No further incidents.
3d 10 round magazine, same incident as the 2d magazine. Brass shavings observed, though recovered casings did not show signs of mangling. No further incidents.
4th 10 round magazine, same incident as the 2d magazine. First round then failed to eject. Fifth round failed to eject. Sixth round failed to eject.

At this point the bolt carrier was held back by the bolt stop. The bolt stop seemed to be stuck and would not let the bolt carrier ride forward. Naturally testing had to stop after less than 40 rounds fired. Very sad.

Some further notes about the rifle's condition:
Had been cleaned fairly well before heading out to the range.
Ammunition used was Federal XM193.
Magazines used were Magpul PMags limited to 10 rounds (poor Californian).
Bushnell red dot mounted to top rail.
Kel Tec compact foreend installed.
Red Lion trigger installed.
DPMS chromed extractor installed.
Bill Springfield trigger job.
Older SU-16B model, without chromed barrel or spec rails.

I would have tried to switch out magazines except that the rifle became inoperable after a mere 35-ish rounds. It's also possible that the DPMS extractor might have something to do with the FTEs, though it hasn't happened in the past and wouldn't really account for all the other things gone wrong. Past performance of the SU-16B over roughly 500 rounds and in its current configuration (minus the DPMS extractor) has been stellar and flawless with impressive accuracy.

Any ideas on what I should do? Normally if there was just a single problem I'd have no issue troubleshooting it (like changing back to the Kel Tec extractor) but in this case there just seems to be a variety of issues cropping up, seemingly unrelated.

If I do have to return the rifle to Kel Tec for work, would it matter that I had done a few modifications to the rifle? I know that in the manual it states that Kel Tec won't cover unauthorized modifications, but in these forums it seems like most people do at least something to their rifle, and Kel Tec did sell me the foreend.

Thanks for your time!

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Old 04-28-2012, 01:42 AM   #2
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Not ignoring your plea for some help. I have no experience in this and was just waiting for someone who has. I assume you are using mags that have shot well in the past and have started out a full mag by seating the bolt well. Push hard on the bolt to rotate the locking lugs, and enable the firing pin.

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Old 04-28-2012, 03:31 AM   #3
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I'm new with this gun..50-60 rounds through is all..got it yesterday...

I had the same type of thing happen today, put a mag in with only 2 rounds in it...FTF twice...I determined that I had slowed the forward progression of the bolt when I was chambering the rounds...put them back in the mag, mag back in the rifle, pulled the bolt back and let it slam forward...bang bang...my fault I think by not leting the bolt slam forward on its own...
No other mishaps...

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Old 04-28-2012, 03:49 AM   #4
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Originally Posted by A.O. View Post
I'm new with this gun..50-60 rounds through is all..got it yesterday...

I had the same type of thing happen today, put a mag in with only 2 rounds in it...FTF twice...I determined that I had slowed the forward progression of the bolt when I was chambering the rounds...put them back in the mag, mag back in the rifle, pulled the bolt back and let it slam forward...bang bang...my fault I think by not leting the bolt slam forward on its own...
No other mishaps...

This!!! Try and make sure you don't "ride" the charging handle when first chambering a round. 2nd, clean under the extractor claw and make sure no brass shaving are hiding under there which will cause the extractor to slip on a case and not extract it. Also make sure you lightly oil the piston rod and spring/tube assm, this could slow down the bolt carrier too.
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Old 04-28-2012, 04:32 AM   #5
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Wow, thanks for the quick replies!

Quote:
Originally Posted by Kent1955
I assume you are using mags that have shot well in the past and have started out a full mag by seating the bolt well.
Yup, these magazines have all worked well before with no issues. Although I have kept them loaded for maybe 2 months now. Would it be possible to weaken the springs that way in that time?

Quote:
Originally Posted by A.O.
my fault I think by not leting the bolt slam forward on its own...
I think that's an interesting point, since at least in the beginning only the first round in each magazine that was manually chambered had issues, with the rest being fine. It would be reasonable that the manual chambering might have had something to do with it. Only problem with that theory is that I think I've always shot the same way and it would be a little strange if I was doing something a bit different since there were no problems before yesterday.

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Originally Posted by Bam_Bam
2nd, clean under the extractor claw and make sure no brass shaving are hiding under there which will cause the extractor to slip on a case and not extract it.
This is also good advice since I was observing brass shavings after the 3d magazine. In fact I'm probably going to just ditch the DPMS extractor altogether and go back to the Kel Tec one (I can also examine the extractor for brass buildup when I take it out).

Quote:
Originally Posted by Bam_Bam
Also make sure you lightly oil the piston rod and spring/tube assm, this could slow down the bolt carrier too.
To clarify, you're saying that if I oil the piston rod too much then it would slow down the bolt carrier? Would wiping it down with a paper towel "unoil" it sufficiently?

The good news is that I managed to get the bolt stop down, though I don't know how. All I did was hold the rifle vertically with the barrel down, and the bolt carrier just slid forward. Which means that I can now change the extractor out and hopefully field test the rifle with these new suggestions.

So is it still worth sending in the rifle to Kel Tec or is it likely I can work out these problems myself? And what did cause the bolt stop to get stuck?

And for the help, here's a video of my rifle on the one magazine that did work. Beautiful 10 for 10 at 100 yards with a simple red dot. Not bad for a little carbine!
http://www.facebook.com/v/10101239651644973
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Old 04-28-2012, 11:28 AM   #6
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That is exactly correct...I "rode" that charging handle forward...learned an easy lesson..

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Old 04-28-2012, 11:49 PM   #7
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Quote:
Originally Posted by Bam_Bam View Post
Also make sure you lightly oil the piston rod and spring/tube assm, this could slow down the bolt carrier too.


Quote:
Originally Posted by Grotz View Post
To clarify, you're saying that if I oil the piston rod too much then it would slow down the bolt carrier? Would wiping it down with a paper towel "unoil" it sufficiently?

No, I mean if you don't oil the rod/spring it will cause it to cycle to slowly or not at all. Someone posted on here awhile back about NOT lubing this area, WRONG, you must lightly oil it, but not too heavy or the oil will carbon up the piston making cleaning it a PITA!



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Old 04-29-2012, 12:43 AM   #8
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And for the help, here's a video of my rifle on the one magazine that did work. Beautiful 10 for 10 at 100 yards with a simple red dot. Not bad for a little carbine!
http://www.facebook.com/v/10101239651644973


The video says its private and I/we cant watch...
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Old 04-29-2012, 01:53 AM   #9
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Quote:
Originally Posted by Bam_Bam
No, I mean if you don't oil the rod/spring it will cause it to cycle to slowly or not at all. Someone posted on here awhile back about NOT lubing this area, WRONG, you must lightly oil it, but not too heavy or the oil will carbon up the piston making cleaning it a PITA!
Bam Bam
Oh, okay. I think I had read somewhere before that the spring had been pre-oiled at the factory and that I shouldn't touch it. I guess that's misinformation?

Quote:
Originally Posted by A.O.
The video says its private and I/we cant watch...
Sorry about that! Ought to be fixed now.

So I did exchange the extractor back to the original one, lightly oiled the spring, lightly oiled the ejector (don't think that was part of the problem since it wouldn't even extract much less eject), and polished the bottom of the bolt carrier. Still pitted but much smoother. The bolt carrier now slams forward very rapidly (and loudly) so I hope that helps fix the issues I've been having.

Now to get some range time to test out these fixes again!
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Old 05-25-2012, 03:36 AM   #10
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Just wanted to do a follow-up report after the latest range trip with the SU-16B.

After polishing the bolt carrier bottom, switching out the extractor to the Kel-Tec factory extractor, and oiling the ejector I took my rifle out to the range today.

Fired 330 rounds of Federal XM193, Privi XM193, and a few random rounds I had lying around. Not a single failure or abnormality of any kind. Truly the best range reports are the boring range reports.

A big thank you to Bam_Bam and A.O. for the advice, and I encourage anyone else who's having problems with a SU-16 to try it!

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