20 Practical AR and gas port size

[bbassi]

Anyone out there shooting a 20P with a rifle length gas port KNOW what your gas port hole diameter is? I think mine is mis-drilled.

Back story - I recently received a barrel back for the second time from a respected barrel manufacturer who will remain nameless, for now. I had to send this barrel back because the chamber was apparently mis-cut. I was having problems with including stuck bullets in the throat and short stroking the BCG . The shop said their reamer was the issue and they would order a new one, but insisted that the gas port dia. was correct for the smaller caliber. 2+ months later I get the same barrel back and while the chamber seems better, the gun is still short stroking. I've run 2 different powders up to book max and repeated with 2 different primers and the results are the same every time. It will kick the spent case but fail to pick up a new one.

BTW - I've tried 2 different proven BCG, 2 diffent proven lowers, and 3 different proven magazines. I've made sure the gas port and block are lined up correctly and the gas key is not binding on the tube. This isn't my first rodeo with an AR but it is my first sub .224. Any help would be appriciated.

 

[bobcat93]

Have you chronograph your reloads.. perhaps there not hot enough.
Would you mind sharing powder and charge wieght , bullet wieght, brass, primer combo
Also have you considered changing to a lighter buffer.

Do you have a simple millspec buffer spring in the gun, or is it something different..I ran in to the same issue with a tubs spring..changed it out and the gun ran good.
Have you tried different magazines.
You could put a wood rod in the barrel this will protect the barrel then open up the gas Port to the next size use a quality drill bit and oil..go slow..it's supposed to be done with a reamer but a drill but will work.. and switch to an adjustable gas block..
But that is last resort..

 

[Hotshot]

Had this problem with a 20Practical barrel from X-caliber.
The gas port was only .080 so we used the next bigger carbide bit that we had and it was some better in the
.092 but still not right. Went the next size to
.114 and it's great except won't catch the bolt all the time on last shot in the magazine. Afraid the next bit might be too big so stopped there. This barrel shoots tiny little groups and I'm a big X-caliber fan. I don't know where they got the info for that hole.

 

[Jdne5b]

I used a .089 on my recent build and it cycles fine so far. I ran from 3450 up well into 3900+ (too hot) with a 40gr v-max and nothing short stroked. Ended up with 3730ish being the sweet spot. 25.5gr Benchmark and a WS2 coated 40 vmax, CCI450n Lake City Brass

I run a 24 inch, rifle gas, A2 buffer and tube, X-caliber blank that my smith turned, chambered and drilled.

Make sure your shoulder to port distance is the same on the barrel and gas block. Some blocks are different to allow for handguard mounts or something?

 

[jepp2]

Anyone out there shooting a 20P with a rifle length gas port KNOW what your gas port hole diameter is?

I run a White Oak Armament 24 inch 20 Practical with a rifle gas system on it. 10T with the gas port being 0.086" measured with a pin gage, so really accurate. I'm shooting it on an A2 stock. Originally used the rifle buffer, but since have converted to the J P Enterprises silent capture spring. I have NEVER had a single issue of being under gassed with any load. Just a standard gas block.

 

[IPSCNUT]

Does x-caliber know what they are doing in regard to AR .20 Practical barrels?
Hopefully someone from x-caliber will chime in. Gotta know where the gas port is located and how large port must be in order to succeed!!!!!!!

 

[bobcat93]

IPSCNUT; good one...BAM!!!..

 

[bbassi]

jdne5b and jepp2, thanks for the input. My gas port is somewhere between .078 and .093 based in the bits I have. My smith thinks the port should be at least .093 for a rifle length. I'm going to try a different gas block and tube just to make sure it's not one of those before I send it to my smith to be bored.

 

[Fast14riot]

I run a .093 on my 24" BHW, I use it on two different rifle lowers, non adjustable gas block.

Have you double checked the gas block itself? The gas tube? I've seen the ports on GB mis drilled, the hole in the gas tube 30° off, etc.

Next step, is this a brand new build? How many rounds through the upper? Do you use an accu-wedge between the upper and lower?

Many times a new upper needs to be cycled a couple hundred times dry to break in. I've also seen an accu-wedge stick up enough to drag on the bcg and cause short stroking.

Where are the rounds ejecting now? Barrel being 12 o'clock, they should land between 3:30 and 5 o'clock. Too much gas can cycle the bcg too fast and cause short stroke symptoms by cycling forward before the next round can be pushed up enough.

A bad bolt catch can cause some symptoms as well.


I've built a few specialty ARs and have had to do the tuning tango before...

 

[msalm]

18" and longer barrels with rifle length gas system standard spec for 5.56 is .093". A 20 Practical, tactical, 17 remmy, etc should all be at that or LESS. While making barrels for a lot of the sub cals, I would start at .070ish and work up while test firing. If I remember right, a lot of them ran very well in the mid .080's, maybe .088". Clean the buffer tube, use a very light oil and lightly oil the buffer tube and spring. Lube the bolt carrier contact areas with a little more viscous lube and it should work. With the gas port alignment, the distance from the shoulder varies and you may be 'on' left and right, but be too far rearward and cutting off half of the port. Slide off the block and see that there is a carbon ring centered on the port. Hand cycling should be smooth with no dry 'scratchy' sounds. Double check during hand cycling that you can even retract the bolt all the way back and nothing is hanging up... There are a lot of little things that COULD go wrong, but seldom do...

 

[bobcat93]

http://www.6mmar.com/site/mobile?url=http://www.6mmar.com/20_Practical.html#2550

Not many powders listed ..also I could see how the light bullets could not create enough back pressure for the gun to cycle correctly..
Please keep us in the loop on your findings..sorry your having issues man that sucks after all that waiting ..but you know we are both in the same boat..maybe give the guys at the link above and chat with them..
I'm sure they will tell you what's up..I should have gone there to begin with..
There load data is showing h-335 used with .25,26 gr..that is alot more then I was using..loaded up maybe they will shoot

 

[bobcat93]

Did you get your rifle running yet?

 

[bbassi]

Did you get your rifle running yet?

No, been real busy but got back to it a little today. I'm waiting on a replacement gas block to try on the 20. That's the only thing left to replace.
The 18" mid length barrel is running like a champ though, even with the lowest powder charges given in the book. As a matter of fact every load that would not cycle in the 20 cycles just fine in the 18. Same lowers(s), same BCG(s). swapped them back and forth just to amuse myself. Go figure.

 

[bobcat93]

Well that's good news!! Im just impressed with the accuracy of the .20 practical.. Pretty amazing even with the loads that won't function my AR ..there still accurate..
Working on loads now
LC brass
Rem. 7 1/2 br primer
Hornady 40 gr. V-max
IMR. 8208 xbr powder..starting at 23.5 gr.
And
Going to work on some loads with
N-133 starting at 23 gr...
Hope it all comes together
Hoping the 8208 works better because it's cheaper then the VihtaVuori powder that's for sure..haha

 

[bobcat93]

I forgot to ask on your 18" barrel you have a mid length gas system? What size is your gas port?
Did you open it up, I'm very curious ..
I've made up quite a few reloads mine will only cycle properly when I'm pushing bullets above 3600fps..
Anything slower forget it....