View Full Version : Short Stroking issues
I’m currently having failure to feed issues due to what I assume is short stroking.
Rifle specs:
Rainier Arms match barrel 18” mid length gas, .223 Wylde
BCM full-auto BCG
LMT defender 2000 lower with stock spring and CAR buffer
All mags used are 30 round windowed gen 2 P-Mags.
My rifle had about 900 rounds on it shooting mostly Hornady .223 55 grain soft points, and black hills remanufacture .223 55grain soft points before I had any issues.
On the first range trip I had issues I was shooting Fiocchi 69 grain SMKs for the first time and had switched out my CAR buffer with an H buffer. About half way through my first mag it failed to feed. I cleared the round and two rounds later the same thing happened. I then removed the rounds from my mag and reinserted the empty mag into my gun. For the next 30 rounds I fed one round at a time to see if it would lock back and it did every time. I assumed the issues were from low power ammo, too heavy of a buffer and the fact my gun hadn’t been lubed in a while.
On the second range trip I had gone back to a CAR buffer shooting the same ammo and re-lubed my BCG. This time I got through one mag and half way through the next one before I had a failure to feed. I cleared the round added lube to my BCG and made it about five rounds before the same thing happened. For the next eight rounds or so I kept an empty mag in my rifle treating it like a single shot and seeing if it would lock back, and it failed to lock back once.
I have checked my gas rings, I seen no chips, dings or scores on them and they passed the “drop” test.
My gas key is tight.
I removed my gas block to check alignment; it was perfect.
My buffer spring measures 10 3/8 inches.
I did see evidence of some slight gas leakage were the gas tube goes into the upper but it didn’t look excessive or abnormal.
Where the gas tube seals in the gas block however, I do have a very dark patch that’s about 3 ½ inches long, telling me there might be excessive gas leakage.
I also noted that the Fiocchi 69 grains SMKs are only doing about 2735fps. Compared to federal and Winchester with the same bullet doing 2950fps and 3060fps.
I would like to know if there is anything I could do to get my rifle to reliably cycle the Fiocchi SMKs, or if I missed something to help further trouble shoot what is wrong.
Pics would be nice. I'll also say that an H or regular carbine buffer with an 18" rifle barrel is too light. That Fiocchi seems pretty weak based upon the FPS you gave. Have. You tried any other ammo like M855, M193, BH 77gr., etc....
I have tried Federal xm193 but not much of it and not recently, the recoil impulse was noticeably more but otherwise worked fine.
Ill work on getting some pics up.
I should add that I did check the gas port with a caliper when I first assembled it and if memory serves it was between 0.080 to 0.085. To me that seems like a little big for an 18" mid length.
I am thinking this is an ammo issue. .080-.085 is a pretty big range of difference, but I don't think those numbers are too small.
A normal 16" midlength is around .076-.078. A rifle is .093. A midlength 18" would probably be around what you stated. 18" rifle gas system is larger than a rifle as I recall. Something like .099.
I would try some other ammo and then compare it to the Fiocchi. My money is on that ammo being underpowered.
I have tried Federal xm193 but not much of it and not recently, the recoil impulse was noticeably more but otherwise worked fine.
Ill work on getting some pics up.
I should add that I did check the gas port with a caliper when I first assembled it and if memory serves it was between 0.080 to 0.085. To me that seems like a little big for an 18" mid length.
I would agree that it is most likely the ammo, however I do have a lot of it and would like to use it up.
Here is the pic of my gas block. Quality is not that great, it was taken with my phone. my thumb marks were the bulk of the carbon stops.
http://i1063.photobucket.com/albums/t514/RideTheLightning11/gasleak.jpg (http://s1063.photobucket.com/user/RideTheLightning11/media/gasleak.jpg.html)
K.L. Davis
10-13-13, 16:00
While using calipers to measure a gas port is not that accurate, 0.080 - 0.085 would be on the big side... use a pin gauge or drill bit even to measure.
You are getting a lot of leakage at the gas tube... my opinion. The FSB/Gasblock has some of the tightest tolerances of any parts on the M16/M4 - there should be no leakage at the tube.
Also, your gas block *could* be off a little... I see it is pushed back to the step in the barrel - when I draw up a barrel, the gas port is placed 0.295 forward of the step in the barrel, if the barrel has a long "perch" for a full size FSB. This allows for the handguard end cap to fit behind the gas block.
If I use a short perch (just over an inch) I usually spec the port at 0.265 and allow no room for the handguard cap that is not going to be used anyway...
Most of the time, there are enough over tolerances to allow for you to push the gas block all of the way back on a "295 ported" barrel, but you are really better off spacing the gas block forward 0.030 - you will notice that most barrels that have a set screw divot opposite of the gas port will have a gap between the gas block and the step on the barrel.
One of the first things I checked when I was having issues on the second range trip was to see if the lack of a gap between the gas block and shoulder was closing off part of the port.
It was not. In fact the burnt carbon ring was dead center over the port and the dimple for the set screw lines up just right.
When I assembled this rifle I noticed that the gas tube sort of just slid right in with little resistance. I had DD gas block before and the gas tube was noticeably tighter.
Is there any way I could get this to seal without permanently attaching gas block and tube?
K.L. Davis
10-13-13, 16:42
If the set screw dimple lines up you are golden... some barrels are designed for the gap, some not - same goes for gas blocks; just something I noticed.
Of course loctite will seal the gas tube, but is semi-permanent.
For a quick fix, just to see if it helps, you can set the gas block "face down" in a press or on a mill table... so the hole for the gas tube is facing up... put a 1/4" or so ball bearing in the hole (like a golfball on a tee) and press it down like you are trying to force it in the hole... this will swage some metal down into the hole and make the very first part of the hole tighter... but not a permanent solution.
You can tap the ball with a hammer if you can not press it... harder to control the "depth" of the press of course... but this method is far more amusing to watch. Best bet is to make the hole too small and open it a little with a 0.180 reamer or a #15 drill bit if you don't have the reamer.
All in all... way more work than just replacing the gas block, but it is a quick way to see if that is your problem.
Is that gas block home made? I have never seen one like that. There does appear to be some leakage and I think I would get a BCM or Vltor block and swap it out.
I would agree that it is most likely the ammo, however I do have a lot of it and would like to use it up.
Here is the pic of my gas block. Quality is not that great, it was taken with my phone. my thumb marks were the bulk of the carbon stops.
http://i1063.photobucket.com/albums/t514/RideTheLightning11/gasleak.jpg (http://s1063.photobucket.com/user/RideTheLightning11/media/gasleak.jpg.html)
K.L. -I will try to tighten up the fit between the gas bock and gas tube using the way you described.
As a second idea could I use locktite RC if I cant get it to seal up correctly using the ball bearing? The only problem I see it that when it's in there it may be a little difficult to remove.
IG- Haha no it is not home made, it's a just a basic Stag gas block.
https://www.rainierarms.com/?page=shop/detail&product_id=911
K.L. Davis
10-13-13, 17:12
As a second idea could I use locktite RC if I cant get it to seal up correctly using the ball bearing? The only problem I see it that when it's in there it may be a little difficult to remove.
Loctite will seal it up right quickly... and if you use the right sealer it will be a major pain in the ass to remove - but if it fixes it, you don't have to worry about changing it before you rebarrel anyway !
As a second idea could I use locktite RC if I cant get it to seal up correctly using the ball bearing? The only problem I see it that when it's in there it may be a little difficult to remove.
Loctite 620 may do the trick. As far as the clearance between parts, it could be a barrel dimension as easily as it could be the gas block.
K.L. Davis
10-13-13, 17:43
I use the term "loctite" as a generic term for thread locking compounds - I do not use the Loctite brand name products, 620 cooks at 500 degrees and the gas block can get a lot hotter than that.
Green loctite will seal it up and let you know if that is the problem... but if you want to use a sealer as a permanent repair, I would argue that it is not the right choice for the job.
I Think my plan is to temporarily band aid the gas leak between the gas tube and gas block and see if it helps. If the gas block is an issue I will then replace it.
Loctite 620 may do the trick. As far as the clearance between parts, it could be a barrel dimension as easily as it could be the gas block.
The gas block is snug on the barrel, I needed to use a brass punch and a small hammer to get it to move.
I Think my plan is to temporarily band aid the gas leak between the gas tube and gas block and see if it helps. If the gas block is an issue I will then replace it.
The gas block is snug on the barrel, I needed to use a brass punch and a small hammer to get it to move.
I meant to say gas tube to gas block...
Gotcha, and yeah it very well could be.
Looks to me like a cheap, low quality gas block.
Its hard to get proper cycling with all that gas leakage.
I'd get a quality replacement and be done with it.
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