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View Full Version : HELP! Short stroking?


chunger
10-01-2007, 7:09 PM
So I finally got my 2 California rifles together, and got out to the range to sight in and function test/break in.

I find one of the rifles (multicam one) does not lock the bolt back on empty mag. . . well, it does once out of every mabe 30 or so opportunities.

The pink rifle runs very well. Everything about the 2 rifles rear of the barrel is identical except for the color. I swapped out the bolt carrier groups, and the pink rifle still runs like a top, and the multicam one still fails to lock back.

It also induces a bad jam w/ some regularity. Round fails to strip completely and the bolt does not go into battery. Upon forceable removal of the mag, the partially stripped round has a huge dent across the top of the casing. I chuck the round.

I have all of tomorrow to try and sort this rifle out, but I work all Wednesday and go to shooting school w/ the wife on Thursday. . . so I'm freaking out a bit because I don't know how to further diagnose the problem or if there is anyone in the Bay Area I can take this to on such short notice.

Is it the gas system? Should I try a lighter buffer spring? Is it even possible to adjust the gas system at home?

http://i7.photobucket.com/albums/y274/chungsteroonie/IMG_4933.jpg

C.G.
10-01-2007, 8:33 PM
Sounds like a mag problem. They are not ProMags by any chance?
Without seeing the mags I would check the feedlips, deburr any burrs and "exercise" the mags with a stick a few times.
BTW, what kind of ammo were you using?

chunger
10-01-2007, 9:50 PM
New C-products 10 round mags w/ Magpul Gen II followers. Feed lips have been de-burred prior to any firing. Exhibited same problem with PMC 55 grain FMJ and Winchester white box 55 grain FMJ

C.G.
10-01-2007, 11:12 PM
New C-products 10 round mags w/ Magpul Gen II followers. Feed lips have been de-burred prior to any firing. Exhibited same problem with PMC 55 grain FMJ and Winchester white box 55 grain FMJ

Eventhough C products are supposed to be good, there were some instances of problems. It still sounds like a mag problem, try different mags.

ar15barrels
10-01-2007, 11:15 PM
I forgot to mention on the phone that you should lube these heavily for the first few hundred rounds.
If these are brand new builds, you need to fully break-in the gas rings, carrier and receiver before you can expect perfect function.

If you have a couple hundred rounds through the gun and it was kept really wet, THEN I would recommend opening up the gas port a tad.

Any chance that the INSIDE of the receivers got painted?
That will cause problems too.

The paint on the barrel is going to make FSB removal a problem.
Expect to have to re-paint that after it's put back together.

chunger
10-01-2007, 11:44 PM
Thanks for the call Randall,

There's no paint on the inside of those upper receivers. . . except on the back of the dust cover. I completely masked them prior to painting because my understanding is that the factory teflon coating is excellent for internal parts.

There are presently ~120 rounds through the rifle. . . and I've been running it wet with FP-10. I've not seen any improvement yet through the course of break in. Many of the shots have been 1 or 2 rounds loaded to check for slide lock-back.

RobG
10-02-2007, 3:47 AM
Not sure what upper you are running but, I have a Stag that did the same thing. Sent it back and they resolved the issue promptly and paid for shipping both ways. They opened the gas port and replaced the bcg and now it is flawless. They apparently had a bad batch that caused the issues.

m24armorer
10-02-2007, 10:36 PM
Paint on the barrel is no problem. Just drive the pins out and rotate the sight 180 deg. Now gee, there is a perfect hole right there where the sling swivel was and there is the gas port.

ar15barrels
10-02-2007, 10:55 PM
Paint on the barrel is no problem. Just drive the pins out and rotate the sight 180 deg. Now gee, there is a perfect hole right there where the sling swivel was and there is the gas port.

That's what I'm planning to do.
Sometimes it's fun to get the gas tube out with the FSB painted into place though.

m24armorer
10-02-2007, 10:58 PM
At least you can't see where the hole gets EDM'd when you rotate it back.

ar15barrels
10-02-2007, 11:02 PM
At least you can't see where the hole gets EDM'd when you rotate it back.

Who said anything about EDM'ing it?

You EDM your gas ports?

m24armorer
10-02-2007, 11:09 PM
Every dang one.......

ar15barrels
10-02-2007, 11:11 PM
Every dang one.......

Nice.

I wish I had an EDM.
That's proably one of those things that I would use all the time if I had it.

I got along for years without a surface grinder.
Now that I have one, I use it all the time.
I can't imagine NOT having a surface grinder now.

m24armorer
10-02-2007, 11:19 PM
Kinda funny how we wound up with it. I bought a Sargon DRO for a lathe off Egay. It was a local company so I drove over to pick it up, when I was there I asked if they had anything else that they wanted to get rid of.

In the corner of the shop was a brand new $65K sinker EDM. It was purchased by the former owner and never used.

Cost me a hundred bucks plus trailer rental.

You should be able to find one in SoCal easy. Check Ebay.

m24armorer
10-02-2007, 11:20 PM
Cleanest burr free ports you ever saw....

ar15barrels
10-02-2007, 11:21 PM
You should be able to find one in SoCal easy. Check Ebay.

I don't have the space in my 1-car garage, but it's on the lost of "wants" when I get a respectable sized shop.

ar15barrels
10-02-2007, 11:23 PM
Cleanest burr free ports you ever saw....

I know, quit rubbing it in.

Do you drill them a few thousandths undersized and then plunge straight down with an electrode the proper size, or do you go in with an undersized electrode and work your way around the hole from the sides?

m24armorer
10-02-2007, 11:24 PM
Almost a must have for chrome bores.

m24armorer
10-02-2007, 11:30 PM
We use different size endmills that we grind and finish with the graphite to final size. The milling just saves a little time.

Speaking of time, are you single pointing your threads? You might want to look into a Geometric 3/4 D die head. Threads a AR barrel in about 7 seconds.

chunger
10-02-2007, 11:31 PM
Just wanted to go on record to say ar15barrels is saving my butt on this one. . . I overnighted my complete upper to him after an exhausting day of absolutely no progress on the issue.

Irvington Arms --> no parts, no advice. Got a couple boxes of M193 to see iffn' ammo is the issue.

So I armed myself w/ my big wire cutters and an extra buffer spring and headed directly to Chabot Rod and Gun club --> closed (3 cops blasing away on the range pistol training)

Headed directly to Richmond Rod and Gun club --> closed (earth movers working on the birms)

Headed to Bullseye range in San Rafael --> frangible ammo only.

Went home and there were tears. . . ok. . . mabe not that dramatic. Contacted ar15barrels to arrange emergency service. At least it's in capable hands now if it arrives as promised by USPS. I pick up on my way from Bay Area to Vegas for rifle class w/ the wife Thurs.

But the wife is happy. . . her rifle runs like a top. Mabe I should have painted mine pink too. I'll file that in the brain for future reference. Pink rifles run better.

m24armorer
10-02-2007, 11:35 PM
It's in good hands.....

chunger
10-03-2007, 6:19 PM
Pinging Randall to check if the upper arrived safely.

Also need details on where to meet tomorrow early afternoon. I need an address so I can plan my route and coordinate an acceptable meeting timeframe.

Hopefully everything has arrived and is good to go.


edit:
Well, nothing more I can do right now except stress out. . . Hopefully Randall is working his magic on the gas system as I type. . .relieved some stress by calling and emailing the governor's office a couple more times about AB 1471 and AB 821. . . check the bank account to see if i can allocate some funds to Blackwater's legal fund. . . Now to load up the rest of the gear I need for shooting school. Very excited that my sister in law who has never fired a gun before is coming out for the 4 day pistol course using my wife's pistola . . . get some rest tonight, and hit the road tomorrow for a learning adventure. Hopefully the beginning of a long road of rifle shooting. 6000 Hornady 55 grain FMJBT's arrived in the mail yesterday :) Gotta develop some loads and shoot 'em up.

chunger
10-03-2007, 8:21 PM
All is well :) All is well!!! Randall called with the great news. . . the finish on the rifle was even preserved. The port hole was gauged and determined to be out of spec for the barrel length causing my short stroking. I'm so glad there was a clear, measureable answer to the problem.

Picking up tomorrow! Many thanks to all the outstanding businesses that have gone out of their way to help me in my builds. Ten Percent, Global Tactical Supply, Irvington Arms, Toolbox X (U-15 stocks), Cold War Shooters, Bravo Company, Brownells.

While I often give praises for people who treat me right, AR15barrels has gone way beyond reasonable expectations in my opinion to resolve this gunsmithing emergency within the tightest of timeframes. I'm one happy guy. Now I don't have to shoot a pink rifle at shooting school :)

ar15barrels
10-03-2007, 10:31 PM
Upon seeing the paint job on this upper, I think I'll just keep it.
You have almost convinced me to paint a gun.
Almost.

chunger
10-03-2007, 11:08 PM
If you need something painted, let me know. I'm happy to horse trade, and I've got extra paint. . . I needed 8 colors to do the multicam. . . plus pink for the wife's. . .you can estimate how much extra duracoat I have lying around. Seriously, I have to re-do the wife's buffer tube and sling plate. (her buffer tube was 1/16" too short Toolbox X sent me replacement parts). I rigged it to work for the class by hogging out some of the the sling plate to make the buffer tube go in far enough to retain the buffer pin.

But this means I have to do the entire cycle of colors again. The only difference between the 2 rifles is basically 1 color (trade green for pink). Painting something that small, I throw away half the paint I mix, so I'm happier if I have more things to spray. The painting is super fast. . . the masking is the bugger.

ar15barrels
10-03-2007, 11:14 PM
I have to re-do the wife's buffer tube and sling plate. (her buffer tube was 1/16" too short Toolbox X sent me replacement parts). I rigged it to work for the class by hogging out some of the the sling plate to make the buffer tube go in far enough to retain the buffer pin.

I have machined the shoulder back on the buffer tubes to make it work properly with a sling plate and still retain the buffer detent.

chunger
10-04-2007, 12:13 AM
I guess that works good to. . . you're probably real good at that turny tool that goes round and round and cuts metal. :)

chunger
10-09-2007, 10:52 AM
Thanks for all the help. . . we got out there and the guns ran. I did however have 2 type 3's that I did not induce on purpose. I wondering if I should get the Crane O-ring and black extractor buffer. We had a great time learning some rifle fundamentals and hope to shoot some local matches. Lots of folks from California asked about the U-15 and legal California configurations. They were surprised that we had functional weapons that were 100% legally configured.

http://i7.photobucket.com/albums/y274/chungsteroonie/RifleClassKeepers-27.jpg

http://i7.photobucket.com/albums/y274/chungsteroonie/RifleClassKeepers-44.jpg

http://i7.photobucket.com/albums/y274/chungsteroonie/RifleClassKeepers-30.jpg

The wife got a lot of attention and people taking other classes kept coming by the range because they heard about "the pink rifle". It also became the preferred weapon platform for instructors to demonstrate all new techniques on.

http://i7.photobucket.com/albums/y274/chungsteroonie/RifleClassKeepers-19.jpg

ar15barrels
10-09-2007, 12:34 PM
I did however have 2 type 3's that I did not induce on purpose. I wondering if I should get the Crane O-ring and black extractor buffer.[/IMG]

Having no formal training on malfunction types, is a type 3 malfunction a failure to extract or a failure to eject?

I would not generally recommend upgrading the extraction force beyond a Wolf extra-power extractor spring.
An o-ring is sometimes detrimental to a rifle-gassed barrel.
On a rifle-gassed barrel, it's quite possible to have too much extractor tension.
This is very different from carbine-gassed barrels, where you almost can't have too much extractor tension.

chunger
10-09-2007, 9:59 PM
The malfunction was a failure to extract I think. . . don't remember very clearly because I was too busy clearing it. From what I remember, the casing did not eject all the way, and another round was trying to get inside the chamber so there were 2 objects deep inside the ejection port. I recall having to lock bolt back, strip mag, and dig out a wedged bullet w/ my fingers from inside the mag well.

The memory is very foggy as it happened so fast. I was shooting steel against the wife, and obviously she kicked my butt on that one.

ar15barrels
10-09-2007, 10:38 PM
The malfunction was a failure to extract I think

That's a failure to eject.
Failure to extract leaves the fired case in the chamber.
Failure to eject leaves the fired case sitting on top of the live ammo in the mag and shows up as a "double feed" (one live, one dead)

chunger
10-09-2007, 11:09 PM
I honestly don't remember which one it was. . . It could have been a failure to eject w/ one live round and one dead round trying to get into the chamber.

I'll make note next time it happens.

captain91
10-13-2007, 2:55 PM
Hope im not thread jacking

The "short stroking " sounds like thats happened to me more than a few times. I have tried all the function testing and I havent figured it out yet. I thought it might be my mags but then one time I used a friends and still had the same problem. Wat can I do about this? It's not easy trying to find anyone willing to take a look at black rifles in central cal.

ar15barrels
10-15-2007, 12:40 PM
The "short stroking " sounds like thats happened to me more than a few times. I have tried all the function testing and I havent figured it out yet. I thought it might be my mags but then one time I used a friends and still had the same problem. Wat can I do about this?

Is the rifle new, or well broken-in?
500 rounds is well broken-in.

Keep it well oiled.
Check for smooth carrier movement in the receiver via the 45 degree angle test.

What type of barrel and gas system?
Sometimes short stroking is actually caused by a hiccup in extraction.
The short stroke test is done with an empty mag and loaded chamber.
Do this ten times and look where the bolt or carrier is being caught by the bolt catch.
If it consistently catches on the carrier (not the bolt), you have a short stroking problem.

Try another known-good bolt carrier group.
If that does not fix it, you may need to open up the gas port to proper dimensions.

I specialize in AR-15 barrels if you need help.

captain91
10-15-2007, 9:27 PM
Is the rifle new, or well broken-in?
500 rounds is well broken-in.

Keep it well oiled.
Check for smooth carrier movement in the receiver via the 45 degree angle test.

What type of barrel and gas system?
Sometimes short stroking is actually caused by a hiccup in extraction.
The short stroke test is done with an empty mag and loaded chamber.
Do this ten times and look where the bolt or carrier is being caught by the bolt catch.
If it consistently catches on the carrier (not the bolt), you have a short stroking problem.

Try another known-good bolt carrier group.
If that does not fix it, you may need to open up the gas port to proper dimensions.

I specialize in AR-15 barrels if you need help.
Upper is well broken in
I do keepit oiled
45 degree angle tests good
the barrel is dpms 16" hbar
gas sysytem..... i dunno.
As far as short stroke test I will not be at a range for about another 2 months.
So I do not know where it is catching. It gets stuck halfway to feeding then I have to pull on the charging handle and bang buttstock on floor for a while. I just may need help with this. Thanks for the info

ar15barrels
10-15-2007, 10:23 PM
the barrel is dpms 16" hbar

So I do not know where it is catching. It gets stuck halfway to feeding then I have to pull on the charging handle and bang buttstock on floor for a while.

Is it failing to fully cycle, or to feed?

DPMS barrels are known for their tight chambers.
What ammo are you using?

m24armorer
10-15-2007, 10:58 PM
When I was younger I short stroked a lot......:p

ar15barrels
10-15-2007, 11:00 PM
When I was younger I short stroked a lot......:p

:rofl2:

My strokes are longer now than when I was 14 too...

m24armorer
10-15-2007, 11:51 PM
14?

My rubber duck was in harms way much earlier....

m24armorer
10-15-2007, 11:55 PM
Stroke Fu?:jump:

Tweak338
10-16-2007, 12:10 AM
tight chambers,short stroking, stroke fu..
oh gawd

m24armorer
10-16-2007, 12:24 AM
Had a failure to extract once....

Child support is expensive.

Tweak338
10-16-2007, 12:41 AM
Had a failure to extract once....

Child support is expensive.
LoL
that is sig worthy right there.

captain91
10-16-2007, 10:23 PM
My problem is the same exact as described by the thread starter. The round sometimes will not go into chamber all the way rather it will end up angled and jam up and then it difficult to remove.

ar15barrels
10-17-2007, 8:46 PM
My problem is the same exact as described by the thread starter. The round sometimes will not go into chamber all the way rather it will end up angled and jam up and then it difficult to remove.

Post pictures.
This is probably NOT short stroking unless you are getting failures to eject which leaves the fired casing in the action while the new one tries to feed into the chamber.

captain91
10-19-2007, 9:05 PM
well I dont get much opportunity to shoot so I cant post pics.