PDA

View Full Version : under gassed issue


croc4
07-01-2012, 11:58 AM
Hey guys,

Just got back from the range trying out a new upper, and sadly its under gassed, I was using Tula 75 and 55gr ammo. This ammo works great in all previous uppers I have tried it in, so I don't think the ammo is a problem.

The rifle ejects the spent round, but does not come back enough to strip a new round, on the last shot the bolt carrier locks on the bolt catch, not the bolt face as it should, so it needs about 3/4" more rearward travel.

So on the drive back I was tossing around two options.
1. a lighter spring
2. a lighter buffer

Which would be the best route to go?, or does it not make a difference?

Croc4

TKM
07-01-2012, 12:09 PM
Pull the gas block and check the carbon pattern on the barrel. Is it centered on the gas port?

If it's not misaligned check the size of the port. Is it the same size as on your other barrels? Opening it slightly could get you up and running.



http://www.calguns.net/calgunforum/showthread.php?t=402217

Mossy Man
07-01-2012, 12:17 PM
i've had issues with underpowered tula causing these type of problems

Mongoblack23
07-01-2012, 2:27 PM
im gonna go with TKM here. check your existing parts first before you buy more parts, the gas hole may be too small or misaligned. my supervisors AR was short stroking because the gas block was canted a couple degrees. it happens. also check your gas tube, make sure its not kinked or jammed up with something....

FMJBT
07-01-2012, 2:48 PM
What configuration is your new upper? Tula is notoriously underpowered. My SPR wont run at all with the 75 grain Tula, it's rifle length gas system with 18" barrel is designed for higher pressure ammunition like the NATO spec 77 grain Mk 262. Even my 16" mid length gun has a hard time running Tula. About every 4th or 5th round is a FTE or FTF. Easy way to solve this problem is to switch ammunition, rather than tailor a rifle to run on underpowered ammo. Running a lighter buffer and spring combo to accomodate the Tula ammo could cause it to be pretty hard on the internals when running NATO spec ammo.

Carsgunsandchics
07-01-2012, 3:00 PM
It being a new upper with all new and heavy finish it might be a bit of extra drag that is causing part of your problems. Oil it a little on the heavy side and cycle it till it smooths out as I'm sure you can feel the machine marks left behind and they just need to be smoothed out.

croc4
07-01-2012, 3:07 PM
Its a 16" dissipator, with rifle length gas system, maybe it is just the ammo, but I've never had a problem with Tula in any of my other uppers. but the bullet has more time in the bore after the gas port to on those.

As a highly scientific (cough, cough) test, I plugged the chamber with a paper towel, then placed a small section of paper towel in the muzzle , then used a can of air in the gas tube (chamber), it blew it out with some decent speed.

Unfortunately I didn't have any other ammo with me to compare, I'll have to try that next trip.



Croc4

FMJBT
07-01-2012, 3:18 PM
Its a 16" dissipator, with rifle length gas system, maybe it is just the ammo, but I've never had a problem with Tula in any of my other uppers. but the bullet has more time in the bore after the gas port to on those.

As a highly scientific (cough, cough) test, I plugged the chamber with a paper towel, then placed a small section of paper towel in the muzzle , then used a can of air in the gas tube (chamber), it blew it out with some decent speed.

Unfortunately I didn't have any other ammo with me to compare, I'll have to try that next trip.



Croc4

I think the configuration is the problem, rather than anything mechanical. Even on the best of days, the 16" dissys are undergassed with most ammo. Most dissipators solt by manufacturers are the moc dissipator style, with a concealed carbine or mid length gas block under the handguard just to ensure reliable functioning. Rifle length gas on a 16" barrel simply wont have enough dwell time to function reliably with Tula ammo.

MXRider
07-01-2012, 3:29 PM
What upper are you using? What buffer? Spring? Not every configuration will like crap ammo, and that is what you are shooting, crap.

Sent from my PC36100 using Tapatalk 2

croc4
07-01-2012, 3:52 PM
The upper is from delton, midway had it for a decent price, I had the funds, my bday was coming up and it was 'different' from my other uppers(yeah I'm a gun junkie), the buffer and spring are standard carbine types.

Delton noted that those would be fine. I'm under no illusions that tula is top quality ammo, I use it for plinking, I reload when I'm going for groups/more serious shooting. This is the first time I have run into this issue with it.

Croc4

Josh3239
07-01-2012, 4:24 PM
Tula is underpowered, it is notorious. I'll bet money right now if you use full power 5.56mm it'll run right. You could try changing different parts but a box of 20 5.56mm will be cheaper than playing with springs, buffers and other parts.

USM0083
07-01-2012, 9:47 PM
Break it in with some full power stuff. Once broken in it might function with Tula.

crazychinaman
07-02-2012, 6:59 AM
On that version of the Dissy.You need to enlarge the gas port on barrell.I have the same Dissy.I did this years ago and have not any problems with it.The problem is that is not enough gas pressure to move the bolt back all the way,because of the distance from the gas port to the end of the barrell.I suggest that you buy a new gas block that can be taken off at the range and enlarge the gas port at the range .This way you can enlarge the port little by little.Instead of going back and forth to the range. I even use as a 22lr conversion for my kids.

croc4
07-22-2012, 4:21 PM
Just thought I would update this thread. I installed a YHM front site / gas block and I open the gas port to 7/64" and that was not quite enough based on testing, then opened up to 1/8" and that did the trick. Gun functions flawlessly now.

Thanks for all the replies / help.

croc4

WReyth
07-22-2012, 4:51 PM
I have the same upper, and same problem. Thanks for posting