Short cycling

Talk about them here.

Moderators: mpallett, bakerjw

Post Reply
User avatar
strom19
Silent Operator
Posts: 79
Joined: Sun Jun 03, 2007 2:54 pm
Location: Central Florida

Short cycling

Post by strom19 »

I Finished a blackout build awhile back and seem to have a short cycling problem that is puzzling. Built on a carbine length with a spike adjustable gas block I have used spikes T2 buffer with carbine spring. On the last rd It seems to lock open between the bolt face and the carrier,just short of the bolt catch. I have ran the gas adjustment from one extreme to the other and the bolt still cycles short of the bolt catch. I have tried a standard buffer and even cut the buffer spring one inch and still the bolt would not lock wide open on the last rd fired. Tried several different mags also..

I have reached a point where I'm ready to convert it to 5.56 and pretend I never heard of a 300 Blackout
lol......If anyone could make a suggestion It would be most appreciated... Thanks
User avatar
chrismartin
Silencertalk Goon Squad
Posts: 4226
Joined: Sun Mar 12, 2006 7:18 pm
Location: Tidewater, VA

Re: Short cycling

Post by chrismartin »

So, here is what is left to test:

1. Bolt Carrier Group could be leaking gas. Test with working BCG from a 5.56 AR that works properly.
2. Gas port on barrel could be too small
3. Could be an ammo issue. What ammo are you using? Make sure you are testing with 115gr Remington ammo.
4. Gas block could still be restricting gas flow, either through misalignment or just tuned for less gas. Check for carbon fouling that's oval or "off" around the gas port on the barrel.
5. Gas tube could be dragging on carrier causing it to slow down.

Is this running on a new lower? Carrier/buffer could be dragging in receiver extension if it's not straight (grasping for straws on that one though)
User avatar
strom19
Silent Operator
Posts: 79
Joined: Sun Jun 03, 2007 2:54 pm
Location: Central Florida

Re: Short cycling

Post by strom19 »

All those things mentioned has entered my mind and I believe more testing is required. I'm using Rem 115 i also failed to mention I'm running a nickel boron bolt from Midway well lubed. I kinda feel it is a gas problem so I tore down the barrel and doubled checked the gas block alignment. thanks for the extra
things mentioned in your reply I hope to resolve this problem eventually.....
Smokecloud
Member
Posts: 28
Joined: Mon Mar 08, 2010 12:48 pm
Location: Oregon

Re: Short cycling

Post by Smokecloud »

I recently went through this with a 16" build that my brother put together. After lots of testing, the gas block was out of spec and was not sealing properly on the barrel. He ended up purchasing a Seekins Precision adjustable block and we replaced it, finally got it to stop short stroking, and run reliably, but still would not lock back on the last round. funny thing was that it would lock back 9 out of 10 times with one magazine, but not 10 others that were perfect, no matter how much gas put to it. He had installed a complete DPMS carbine stock kit on it right out of a sealed package. I ended up doing a complete tear down and Armorer level inspection on the entire gun and found that the carbine length spring was way too long (closer to 12") and was experiencing coil bind. After swapping it out with an 10 7/8" spring I had laying around, the gun runs perfect with all loads.
User avatar
strom19
Silent Operator
Posts: 79
Joined: Sun Jun 03, 2007 2:54 pm
Location: Central Florida

Re: Short cycling

Post by strom19 »

Do your self a favor as I did...... Get rid of that Adjustable gas block. As soon as I decided to replace the adjustable gas block with a small standard novenski block all my problems disappeared. I'm sure any gas block would work fine but not adjustable ones. If you compare the gas intake hole in a standard block to that of an adjustable one you should see the difference. Standard has a larger hole. Wish I still had my photo's to show you but I deleted them....I have played with springs, buffers, even tubes etc. for over 6 months with no results. changed the gas block and everything worked fine. even with or without a 7.62 sdn suppressor. Adjustable gas blocks SUCK! Don't need them.......Good Luck
Smokecloud
Member
Posts: 28
Joined: Mon Mar 08, 2010 12:48 pm
Location: Oregon

Re: Short cycling

Post by Smokecloud »

Thanks for the heads up. I have never owned an adjustable block, the Seekins on my brothers build was my first experience with one, it has worked fine for him so far. I have used a switchblock that comes on Robinson Armaments XCR or whatever acronym they have, it has a switchblock that worked very well on .223 when switching from suppressed to non suppressed. The addition of the suppressor radically changed the ejection of the spent brass from 6ft to 15ft. Turn the lever and like magic, the ejection was about 8 feet and ran 100% reliable. I am interested in running something like that in the future.

I have built dozens (over 75) of AR's, both .308 and .223 flavors and am very familiar with them and troubleshooting them, but the 300 blk is a new cartridge that I have limited experience with in relation to the others.

I wasn't advocating that you run out and purchase an adjustable block, just sharing that during the troubleshooting of my brothers rifle, the factory FSB was out of spec and was not sealing against the barrel like it should. We both knew that a new block was in order after measuring it, he opted to try an adjustable in anticipation of any problems he might encounter when adding a suppressor to it after it was complete.
User avatar
strom19
Silent Operator
Posts: 79
Joined: Sun Jun 03, 2007 2:54 pm
Location: Central Florida

Re: Short cycling

Post by strom19 »

That's one of the main problems with the 300 blackout, not enough gas, especially with heavy projectiles and low powder volume. I use a AAC 7.62.sdn 6 and with out the suppressor I have no problems with my reloads 110 Vmax or 125 sierra. when I shoot my suppressed 208 V max or 220 Sierra's ( low Velocity) with a can it provides enough back pressure to eject and run the bolt normally.It took me awhile but I have done my home work when it comes to reloading that little bastard even so much as figuring out the subsonic loading for Remington 220 loading and HMS 208 V max proprietary loads.

Unless someone figured it out by now,this is why there is no company developing the 300 Blackout in Gas Piston drives..... not enough gas to operate the system.
User avatar
strom19
Silent Operator
Posts: 79
Joined: Sun Jun 03, 2007 2:54 pm
Location: Central Florida

Re: Short cycling

Post by strom19 »

One more thing on the Adjustable gas block issue. If anyone own a gas block that has a nipple or small button that needs to be depressed before turning it with an Allan key Beware! These kinds of adjustable blocks will fowl up with carbon no allowing the button to be depressed thus rendering it useless. It then has to be removed and soaked in solvent to loosen the detent ball in the unit.
saigatechusa
Silent Operator
Posts: 63
Joined: Wed Jun 12, 2013 10:29 am

Re: Short cycling

Post by saigatechusa »

unless your building a 9" 50 wulf that cycles 500gr xtp's at 900fps or 350's at 1750 without beating itself to death :)

Image

Image

I opened up the gas port, built my own gas tube with .146" ID

I still have to run a 2.5Oz buffer with carbine spring

I'll do the same thing with my 300 BLK
Post Reply