AR15.Com Archives
 Gas Port Size
smithengineered  [Member]
7/30/2010 4:49:14 PM
Ok so I have a DPMS 7" Kitty Kat upper and a RRA LAR-15 pistol lower. While shooting 55gr .223 ammo since I put this together it short strokes. I have heard that the Kitty Kat barrels are known for the gas ports being too small. The port is a #53 drill .0595. My question is what is a good port size to go with to fix this issue?
Monkey_Wrench  [Team Member]
7/30/2010 4:56:52 PM
TAG as I have a kitty kat upper as well....with no cycling issues though.
smithengineered  [Member]
7/30/2010 5:01:47 PM
Hmmm maybe I should try running some higher grain ammo. I just assumed 55gr I should have no problem with. What kind of ammo are you using?
shadowcop  [Team Member]
7/30/2010 5:06:05 PM
I had to have my KittyKat opened to .078. You may not have to go that big.
What buffer are you using?
What BCG?
I run a 9mm buffer with M16 carrier.
Port size from barrel to barrel can change. I have no explanation for it.
My Rainier 7.5" has a .056 gas port and has run 100% even with Wolf.
I run mostly 55 gr.
Monkey_Wrench  [Team Member]
7/30/2010 5:06:28 PM

Originally Posted By smithengineered:
Hmmm maybe I should try running some higher grain ammo. I just assumed 55gr I should have no problem with. What kind of ammo are you using?

I ran Wolf, Federal, and Prvi through it. Some semi, most FA.
smithengineered  [Member]
7/30/2010 5:15:02 PM
Originally Posted By shadowcop:
I had to have my KittyKat opened to .078. You may not have to go that big.
What buffer are you using?
What BCG?
I run a 9mm buffer with M16 carrier.
Port size from barrel to barrel can change. I have no explanation for it.
My Rainier 7.5" has a .056 gas port and has run 100% even with Wolf.
I run mostly 55 gr.


Im running the buffer that came with the RRA lower and the BCG is the one that came with the Kitty Kat. DPMS offered to take it back and "fine tune" it, but I still have not heard back from them on how much they charge....
shadowcop  [Team Member]
7/30/2010 6:20:03 PM
Well thats real nice of them, considering it's their product and it doesn't run.

Is it ejecting?
Check short stroking by putting one round in a mag, firing it, and see if the bolt locks back on the empty mag. If it does, it's not short stroking.
If you already know this, I appologize. Some have feeding and ejection problems, and think it's because of short stroking.
Dave
smithengineered  [Member]
7/30/2010 6:33:11 PM
Originally Posted By shadowcop:
Well thats real nice of them, considering it's their product and it doesn't run.

Is it ejecting?
Check short stroking by putting one round in a mag, firing it, and see if the bolt locks back on the empty mag. If it does, it's not short stroking.
If you already know this, I appologize. Some have feeding and ejection problems, and think it's because of short stroking.
Dave


Thanks for the heads up I'll check it with one round next time I make it to the range. It is ejecting the round, but then I have to pull the chare handle again. I just assumed it's short stroking because the ejected casings are only coming out and landing approx 2-3' to my right.
LastRites  [Member]
7/31/2010 4:44:25 PM
Oh they should fix it for free if it's short stroking. So when your pulling back the charging handle are you actually reloading a round of ammo or just recocking the hammer?
clintox  [Team Member]
8/2/2010 12:56:05 PM
I have an ASA 7.5" barrel and the gas port diameter is .086. When it was at the range I was running an H2 buffer and brown bear cases were ejecting around 4 o'clock.
smithengineered  [Member]
8/2/2010 1:43:12 PM
Originally Posted By LastRites:
Oh they should fix it for free if it's short stroking. So when your pulling back the charging handle are you actually reloading a round of ammo or just recocking the hammer?


I would think they should fix it as well! When pulling the charging handle I am relaoding another round.



OK so this is the email I recieved from DPMS:

Hello David,

Just to follow up with our previous reply.

That is normally a #53 drill (.0595”), however, with that short of a barrel, there is a very tight window of performance. It is not uncommon for fine tuning to go to a #52 (.0635”).

If needed, we can certainly test it and fine tune it for you.

Thanks,


Jeff Ostberg

QC/Engineering Mgr

DPMS Firearms, LLC

3312 12th St. SE


So it sounds to me from this email they know of this issue. I asked for a quote on how much they would charge to fix it, but still waiting on a reply.

smithengineered  [Member]
8/2/2010 4:58:15 PM
Ok they emails me back and said they can test it out and fix it at a rate of 55/hr for gunsmithing.... Not sure of typical going rates though.
FIGJAM  [Member]
8/2/2010 5:40:05 PM
Originally Posted By smithengineered:
Ok so I have a DPMS 7" Kitty Kat upper and a RRA LAR-15 pistol lower. While shooting 55gr .223 ammo since I put this together it short strokes. I have heard that the Kitty Kat barrels are known for the gas ports being too small. The port is a #53 drill .0595. My question is what is a good port size to go with to fix this issue?


Put an o-ring on your extractor first.

http://www.bravocompanyusa.com/BCM-Extractor-Spring-Uprade-Kit-p/bcm%20extractor%20spring%20upgrade.htm
shadowcop  [Team Member]
8/2/2010 6:12:24 PM
So it's their build, it doesn't run, and they want you to pay for getting it to run.
You have to loves company' like that.
smithengineered  [Member]
8/2/2010 7:04:04 PM
Originally Posted By FIGJAM:
Originally Posted By smithengineered:
Ok so I have a DPMS 7" Kitty Kat upper and a RRA LAR-15 pistol lower. While shooting 55gr .223 ammo since I put this together it short strokes. I have heard that the Kitty Kat barrels are known for the gas ports being too small. The port is a #53 drill .0595. My question is what is a good port size to go with to fix this issue?


Put an o-ring on your extractor first.

http://www.bravocompanyusa.com/BCM-Extractor-Spring-Uprade-Kit-p/bcm%20extractor%20spring%20upgrade.htm


Just the o ring? I just assumed this kit would help extraction issuses not problems with short styling. It's worth a shot for that price though.
smithengineered  [Member]
8/2/2010 7:05:43 PM
Originally Posted By shadowcop:
So it's their build, it doesn't run, and they want you to pay for getting it to run.
You have to loves company' like that.


My thoughts exactly! I purchased this about 9 months ago and only have approx 40 rounds thru it....
FIGJAM  [Member]
8/2/2010 7:44:41 PM
Originally Posted By smithengineered:
Originally Posted By FIGJAM:
Originally Posted By smithengineered:
Ok so I have a DPMS 7" Kitty Kat upper and a RRA LAR-15 pistol lower. While shooting 55gr .223 ammo since I put this together it short strokes. I have heard that the Kitty Kat barrels are known for the gas ports being too small. The port is a #53 drill .0595. My question is what is a good port size to go with to fix this issue?


Put an o-ring on your extractor first.

http://www.bravocompanyusa.com/BCM-Extractor-Spring-Uprade-Kit-p/bcm%20extractor%20spring%20upgrade.htm


Just the o ring? I just assumed this kit would help extraction issuses not problems with short styling. It's worth a shot for that price though.


Your issue is not just pressure but also timing. The dwell time is so short that the bolt is attempting to remove the case before it's had time to contract fully. A lot of time what happens is the extractor is not strong enough and slips off the rim which gives the illusion of a short stroke. The other thing you can try is increasing dwell time which means heavier buffer, spring, carrier or a combination of the above. But sounds like your close enough that stronger extractor pressure is all you need.

Really, all you need is the o-ring. But if you get the Bravo kit, you can change out the spring, too, if you like.

For now, you can try going to the hardware store and picking up some #60 o-rings and give them a try. They aren't the best material but will last for a while until your other kit comes in. You'll want the extractor upgrade regardless if you end up increasing your port diameter.

shadowcop  [Team Member]
8/2/2010 8:11:42 PM
Upgrading the extractor definetly won't hurt. I would still like to know if the bolt locks back on an empty mag. If not, it's short stroking.
smithengineered  [Member]
8/2/2010 10:08:51 PM
Good info thanks! I'll try this out before I fork out 55/hr.




Originally Posted By FIGJAM:
Originally Posted By smithengineered:
Originally Posted By FIGJAM:
Originally Posted By smithengineered:
Ok so I have a DPMS 7" Kitty Kat upper and a RRA LAR-15 pistol lower. While shooting 55gr .223 ammo since I put this together it short strokes. I have heard that the Kitty Kat barrels are known for the gas ports being too small. The port is a #53 drill .0595. My question is what is a good port size to go with to fix this issue?


Put an o-ring on your extractor first.

http://www.bravocompanyusa.com/BCM-Extractor-Spring-Uprade-Kit-p/bcm%20extractor%20spring%20upgrade.htm


Just the o ring? I just assumed this kit would help extraction issuses not problems with short styling. It's worth a shot for that price though.


Your issue is not just pressure but also timing. The dwell time is so short that the bolt is attempting to remove the case before it's had time to contract fully. A lot of time what happens is the extractor is not strong enough and slips off the rim which gives the illusion of a short stroke. The other thing you can try is increasing dwell time which means heavier buffer, spring, carrier or a combination of the above. But sounds like your close enough that stronger extractor pressure is all you need.

Really, all you need is the o-ring. But if you get the Bravo kit, you can change out the spring, too, if you like.

For now, you can try going to the hardware store and picking up some #60 o-rings and give them a try. They aren't the best material but will last for a while until your other kit comes in. You'll want the extractor upgrade regardless if you end up increasing your port diameter.



shadowcop  [Team Member]
8/2/2010 10:25:42 PM
Is it ejecting?
Check short stroking by putting one round in a mag, firing it, and see if the bolt locks back on the empty mag. If it does, it's not short stroking.
If you already know this, I appologize. Some have feeding and ejection problems, and think it's because of short stroking.
Dave[/quote]

Thanks for the heads up I'll check it with one round next time I make it to the range. It is ejecting the round, but then I have to pull the chare handle again. I just assumed it's short stroking because the ejected casings are only coming out and landing approx 2-3' to my right.[/quote]
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You stated it was ejecting, so ejection is not the issue.
An extractor upgrade will help insure ejection but will not solve short stroking. Extractor upgrade is always a good idea to me. I have it in all my rifles.

Dwell time is an important factor in getting a 7.5" to run well. I also use a full auto carrier and 9mm buffer. It increases the dwell time which gives the case aextra nano seconds to contract.

This is where a lot of rifles have problems running steel case. Steel case takes longer to contract than brass.
Dave
My 7.5" runs Wolf without an issue.
smithengineered  [Member]
8/3/2010 12:42:17 AM
Yes you are correct it is ejecting. What weight buffer should I use? RRA is rated at 5.6 Spikes is like 4.3 oz. Also should I worry about ever trying to shoot heavier grain ammo with a heavy buffer? Seems like more power with more mass/ heavier buffer may do damage to the BCG??

Thanks






Originally Posted By shadowcop:
Is it ejecting?
Check short stroking by putting one round in a mag, firing it, and see if the bolt locks back on the empty mag. If it does, it's not short stroking.
If you already know this, I appologize. Some have feeding and ejection problems, and think it's because of short stroking.
Dave


Thanks for the heads up I'll check it with one round next time I make it to the range. It is ejecting the round, but then I have to pull the chare handle again. I just assumed it's short stroking because the ejected casings are only coming out and landing approx 2-3' to my right.[/quote]
––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––


You stated it was ejecting, so ejection is not the issue.
An extractor upgrade will help insure ejection but will not solve short stroking. Extractor upgrade is always a good idea to me. I have it in all my rifles.

Dwell time is an important factor in getting a 7.5" to run well. I also use a full auto carrier and 9mm buffer. It increases the dwell time which gives the case aextra nano seconds to contract.

This is where a lot of rifles have problems running steel case. Steel case takes longer to contract than brass.
Dave
My 7.5" runs Wolf without an issue.[/quote]

smithengineered  [Member]
8/3/2010 2:54:31 AM


http://www.spikestactical.com/z/index.php?main_page=product_info&cPath=104_97&products_id=201&zenid=s6j31a4nroh0dn0vmd2ourli55
DaJester  [Member]
8/3/2010 10:42:54 AM
I was given this advise by iNuhBaDNayburhood (he's on this forum) and it was a tremendous help. I ended up upgrading the buffer and drilled the gas port 1 size up on my Kitty Kat. Read this over, hope it helps...

Whenever I deal with short-stroking, the first things I do are:
1.) Check the bolt, carrier, gas tube, gas block, and gas rings for proper fit & tightness. Test Fire with low-pressure ammo (WOLF).
2.) Replace gas tube & gas rings with a new ones. Check tightness. Test Fire with low-pressure ammo.
3.) Replace muzzle device with a Noveske Flaming Pig. Test Fire.
4.) If STILL short-stroking, I'll take off the gas block, and measure the gas port size in the barrel, and shine light into the gas block - to ensure it's not plugged/blocked. If you see light escaping, it's almost certainly a fine gas block - the problem is likely the gas port size.
5.) Install H2 Buffer, and if gas port is out of spec, Drill the gas port one increment wider. Test fire.
6.) Repeat Step 5 until functioning.

I'm not 100% sure what your specific barrel's gas port should be drilled to... There are FIVE main considerations that need to be measured:
1.) Distance to muzzle (Crown of barrel, not end of muzzle brake/flash hider).
2.) Diameter of the barrel where the gas port is drilled (Usually 0.625" or 0.750").
3.) Length of Gas Tube (Carbine? Mid-Length? Rifle? or Custom?)
4.) Length of Barrel.
5.) EXISTING diameter of gas port.

Many are surprised to learn that even Carbine & Rifle length gas systems can both suffer from short-stroking due to improperly drilled gas port sizes.

The easiest way to try fixing it is to add the Noveske FH, but even that may not work reliably... Another muzzle device some try to add is a .223 caliber Krinkov AK style muzzle brake, which also has a small chamber for gas expansion, but this doesn't work as effectively for gas cycling as the Noveske Flaming Pig. Krinkovs were designed with incredibly short barrels, and that was the Russian's solution to their short stroking problem with their short-barreled AKs. It may not work very well in an AR though.

Depending upon the above measurements, it could likely (but not certainly) require a diameter anywhere between 0.081" to 0.094". That's a WIDE range of potential gas port sizes, and the best way to do this with HIGH certainty that you're not over-drilling your gas port is to send your upper receiver assembly to an AR-15 Armorer, or do it yourself.

The only things you need are:
1.) Small drill press with Vise, or Handheld power drill (with workbench vise). With variable speed (either setting (drill press) or the ability to squeeze the trigger lightly & drill slowly)
2.) Oil for drilling.
3.) VERY GOOD drill bit set with 1 Gauge to 60 Gauge drill bit sizes.
4.) (Optional) Hammer & Small diameter Pin Punches.

Honestly, there's not much to it other than making a few measurements above, and most notably checking the existing gas port diameter... The MOST ACCURATE way to check the diameter of your gas port - is with Drill Bits. The proper set of drill bits to open up a gas port can be purchased from Northern Tool:
http://www.northerntool.com/shop/tools/product_200326944_200326944" target="_blank">http://www.northerntool.com/shop/tools/product_200326944_200326944
It has Gauge sizes 1 to 60 (for drilling gas ports or small precision holes), and it also has A through Z gauges, and standard "English" fraction-inch sizes.

As a certified AR-15 Armorer, this is the same bit set that I use for drilling gas ports - both in AR-15's and AK-47 custom builds, and a few belt-fed weapons. There's not much to it, really... With the above measurements you can closely calculate approximately how wide the port should be drilled, but that's still just an approximation, and the best way to ensure reliable results is by Trial & Error.

1.) Measure existing gas port with drill bit. Turn the bit around, put the shank-end of a drill bit into the gas port, starting with the 54 Gauge drill bit shank, and working your way up toward 46 Gauge... One bit will probably get very snug, and be difficult to enter, and the next won't fit. The previous one that went in - that's the diameter your gas port was drilled to...
2.) From there, it's really just trial & error!

Although, your barrel should be drilled anywhere between 46 (0.0810") and 42 (0.0935") gauge sizes, you DO NOT want to drill it any wider than is necessary to cycle the least-reliable ammunition which you intend to fire regularly. I'll admit, I DO use Wolf polymer coated ammo as a low-pressure benchmark for the guns I work on... A gun should reliably eat all SAAMI spec ammunition, including Wolf, although I DO NOT recommend its regular use - a reliable gun should be able to cycle with it.

SO, how do you make sure you don't over-widen your gas port? Trial & Error is the only way to be sure.

I'll go through an example of how I've done the last two AR-15's:
1.) Gas port measured 0.052" (55 Ga.), and it should have been between 0.070" (50 Ga.) to 0.086" (44 Ga.) (14.5" barrel, 0.750" diameter at gas port) Clearly drilled out of spec and under size.
2.) Drilled to 52 Ga. (0.0635"), reassembled, and test-fired with H2 Buffer & Wolf 55 grain ammo - USGI Cprod magazines. Still short stroking.
3.) From that point (0.0635") on, I drilled it up just ONE bit size increment at a time, then reassemble & test-fire...
4.) Surprisingly, the next bit size up (0.067") was all it needed! With the H2 Buffer, 0.067" gas port, the gun ran 100% reliably through 120 rounds (4 mags) of 55 grain Wolf ammo! It didn't NECESSARILY have to be drilled up to 0.070" which is the "Mil-Spec" minimum diameter, and at that point it ran fine with Wolf, and 100% of all other ammunition I've run through it!

The gun has since fired over 4000+ rounds of all sorts of ammo, and has run 100% reliably after bringing the gas port up CLOSER to spec. Although it's not drilled 100% within spec, it's still 100% functional, and since I didn't OVER-drill the gas port, the bolt carrier cycles reliably, but LIGHTLY! Meaning there's VERY LITTLE felt recoil from using the H2 buffer during testing & drilling.

NOW, how do you drill it? Well, I have a small drill press & vise that can hold the entire upper receiver & barrel clamped in nice & tight. However, MOST drill presses have a 'chuck' that's too large to hold such TINY bits! Although I don't do this, I've seen another Armorer just clamp a barrel into a $20 workbench vise from Home Depot, and use a DeWalt power drill, and just went SLOW, & Carefully with his drilling!

I use a small drill press, and plenty of cutting / machining oil, but honestly, a little bit of Kroil, or even basic motor oil will do just fine with a power drill, workbench vise, and a VERY STEADY hand while going slowly!

The one armorer I saw who DID drill the gas port by hand wound up breaking one of the bits off in the gas port. A small set of pin punches, and he punched it through the gas port hole with no problem. That is why you only drill ONE SIZE UP at a time... If you break off a bit in the barrel, it's not IMPOSSIBLE to remove the piece if you're just going one size up at a time... Once he got the metal chips out of the barrel, he just went on to drill up to the next size, and so-on.

It's SLOW, and time consuming to drill them, and you have to frequently take the bit out part way through the drilling to clear chips & metal shavings/dust. That helps to keep from breaking off your bits. Go slow, take your time, and it can be done yourself - just remember - only one size up at a time! Don't get hasty, or you'll ruin the barrel.

That could save you A LOT in shipping it off to an Armorer and paying for his work, plus range fees for testing it.

Hope this information helps you out in some way...

-inuhbad
shadowcop  [Team Member]
8/3/2010 11:41:26 AM
As stated above, there is no magic gas port size.
My Rainier 7.5" has a .056. My 10.5 has a .078.
H2 buffer is a good buffer to use. Not as heavy as a 9mm. I've had good luck with both.
I don't know of a heavier buffer causing damage to a BCG. Just gives you more dwell time.
I believe H2 is what the MK18 uses. I use one in my pistol lower with the 7.5"
Good advise to check the gas system. I had a gas block that was clogged with red locktite. I had mounted a clamp on gas block and somehow the locktite seeped into the gas port and tube.
Make sure your gas rings are good. Pull the BCG, pull the bolt to the end of the carrier and stand it on end(bolt end). If the bolt does not slide back in from the weight of the carrier, it should be good.
I use a small piece of rubber tubing to check gas block alignment. Remove the BCG, put the tubing on the gas tube(inside the upper receiver) and blow through it. If air passes freely, you know the gas tube/block are aligned.
Dave
smithengineered  [Member]
8/3/2010 10:39:16 PM
Not sure how comfortable I feel about drilling out a gas port. Is a Noveske FLamming Pig legal on a AR pistol? I assumed it would only be legal on a SBR. How would one of these FH help? I just ordered a Spikes 4.3 oz buffer and a new extraction kit and am going to try the hose to test gas port alignment and make sure it's free.
shadowcop  [Team Member]
8/3/2010 11:37:16 PM
The Pig definetly works. I had one on my 10.5" entry rifle. It ran fine until I took it off. I wanted to run a suppressor, so I had to be able to use the mount.
The Pig creates back pressure. It helps with cycling SBR's and was designed to do so. It also directs the blast down range
The Pig is heavy and almost 3" long.
I use the Levang comp now. It creates enough back pressure, is lighter, shorter, and much less expensive. I don't know that it will create as much BP as the Pig, but it has worked for me on my 10.5" and 7.5".
And yes, it is legal on a pistol or anything else for that matter.
Dave

Where are you at in KY? If you send it back, I'll let you try one of my Levangs before you buy one.
shadowcop  [Team Member]
8/3/2010 11:46:32 PM
Check your IM's
smithengineered  [Member]
8/4/2010 12:23:06 AM
Originally Posted By shadowcop:
The Pig definetly works. I had one on my 10.5" entry rifle. It ran fine until I took it off. I wanted to run a suppressor, so I had to be able to use the mount.
The Pig creates back pressure. It helps with cycling SBR's and was designed to do so. It also directs the blast down range
The Pig is heavy and almost 3" long.
I use the Levang comp now. It creates enough back pressure, is lighter, shorter, and much less expensive. I don't know that it will create as much BP as the Pig, but it has worked for me on my 10.5" and 7.5".
And yes, it is legal on a pistol or anything else for that matter.
Dave

Where are you at in KY? If you send it back, I'll let you try one of my Levangs before you buy one.


I may look into this as well if the buffer and extractor kit don't do the trick. I am in Louisville. How hard is it to remove the gas port?

shadowcop  [Team Member]
8/4/2010 8:23:57 AM
I assume you mean how hard is it to remove the flash hider. It's easy If you have an armorers wrench, use the square notch. If not, just use a box end wrench. It shoulkd be about 30 lbs per square inch torqued.
The Levang does not have flats to tighen it. No idea why. Just use a strap wrench. I just hand tighten mine while at the range. I switched it out for a can. If I plan to leave it on, a strap wrench works.
Dave
Monkey_Wrench  [Team Member]
8/4/2010 8:45:03 AM
I'll vouch for the pig's operation.

For example: Last machinegun shoot, I ran my Kitty Kat upper with a 4-piece Bulgarian Brake on it on my M16, running Wolf like a raped ape.
For some reason, the locking ring on the brake worked it's way loose, and we ended up shooting the internals out of it.
After that, it was short-stroke city. The upper runs fine on the M16 with Federal, but not so much with Wolf, without the brake.
smithengineered  [Member]
8/15/2010 2:49:26 PM
Ok So after putting a New Extractor kit in, Spikes Heavy buffer and Dave was nice enough to let me borrow his Levang FH its still not acting right. I first tried the Extractor and New buffer. Loaded one round of Remmington 55g and fired. Bolt did NOT lock back same result with Wolf 55g Steel and Black Hills 60gr. It would still fire like this putting about 2-3 rounds average between the three types of ammo even though on one round the bolt does not lock back. I tried the Levang FH and it improved a little going thru about 3-4 rounds of the 55gr and I managed to get 5 rounds from the Black hills 60gr. My testing came to an end when a round of Wolf that I got to fire caused the Extractor to get stuck and I had to use a pry bar to get it unjammed! There were a couple of time where the new rounds would jam while being extracted from the mag. A step in the right direction though! Sound more like Gas Port size??
shadowcop  [Team Member]
8/15/2010 3:18:09 PM
I would open the gas port. I believe my KittyKat had to be opened to .078.
HeavyDutyDude  [Member]
8/15/2010 6:29:41 PM
I'm using a 7" kitty Kat barrel as well, the gas port is as delivered. I'm using a Midwest industries gas block. I played a bit with loads and I'm sold on 23.8 grains of Accurate 2015, 55 grain Mid-South soft points. LC brass with crimps reamed, and Wolf 223 primers, it shoots flawlessly! I'm using the Spikes Tactical Buffer tube with the stiff Spikes buffer spring and HEAVY Spikes 135 gram buffer (an OEM carbine buffer weighs 95 grams)

I tried faster powders to help with the fireball, starting with BlueDot Contender loads and kept going slower until hitting on H4198 and I shot H4198 for awhile but it would try to double feed about every 20-30 rounds or so. Installing a Noveske Pig as it's basically a funnel increasing the gas pressure that the gun needs to operate and was a HUGE help, plus chilling out the fireball.

Again, before redesigning the gun, try a Spikes Tactical Buffer assembly and load up some of those 2015 loads, I think you will be pleased!
I've got roughly 600 rounds threw the pistol and I'm in the process of loading 1000-1500 rounds of that 2015 load, I'm that pleased with it and it shoots pretty good in carbines and rifles as well. Per Sierra AR .pdf you can go as hot as 25.2 grains of 2015 but since i'm using military brass I down load a little. 23 grains would shoot but wouldn't catch on the bolt catch on the last round. 23.8 grains shoots perfect.
HDD

http://accurateshooter.net/Downloads/sierra223ar.pdf

shadowcop  [Team Member]
8/15/2010 7:12:54 PM
Uhm, not everyone has the equipment to reload.
smithengineered  [Member]
8/15/2010 7:44:27 PM
Originally Posted By HeavyDutyDude:
I'm using a 7" kitty Kat barrel as well, the gas port is as delivered. I'm using a Midwest industries gas block. I played a bit with loads and I'm sold on 23.8 grains of Accurate 2015, 55 grain Mid-South soft points. LC brass with crimps reamed, and Wolf 223 primers, it shoots flawlessly! I'm using the Spikes Tactical Buffer tube with the stiff Spikes buffer spring and HEAVY Spikes 135 gram buffer (an OEM carbine buffer weighs 95 grams)

I tried faster powders to help with the fireball, starting with BlueDot Contender loads and kept going slower until hitting on H4198 and I shot H4198 for awhile but it would try to double feed about every 20-30 rounds or so. Installing a Noveske Pig as it's basically a funnel increasing the gas pressure that the gun needs to operate and was a HUGE help, plus chilling out the fireball.

Again, before redesigning the gun, try a Spikes Tactical Buffer assembly and load up some of those 2015 loads, I think you will be pleased!
I've got roughly 600 rounds threw the pistol and I'm in the process of loading 1000-1500 rounds of that 2015 load, I'm that pleased with it and it shoots pretty good in carbines and rifles as well. Per Sierra AR .pdf you can go as hot as 25.2 grains of 2015 but since i'm using military brass I down load a little. 23 grains would shoot but wouldn't catch on the bolt catch on the last round. 23.8 grains shoots perfect.
HDD

http://accurateshooter.net/Downloads/sierra223ar.pdf

http://i980.photobucket.com/albums/ae285/HeavyDutyDude1911/DSC04220sm.jpg


Sweet gun, but yes I do not have the ability to load rounds. A am debating on trying to argue the fact that I bought the barrel 9 months ago new from a supplier of DPMS and see if they can help me out any with the price of gunsmithing to open the gas port, and order a new FH since that seemed to help out a bit.
Thanks for the info though!
David

HeavyDutyDude  [Member]
8/15/2010 8:40:26 PM
Shadow cop, okay I'll give you that, many non-shooters or wealthy people don't reload. But AR 15's were designed to function a specific way under specific conditions. And most factory and mil-spec ammo is designed for that configuration. AR pistols don't know they have a 7" barrel attached, all they know is they need GAS PRESSURE to operate. So when you assemble a one off gun that wasn't intended to be when the gas operated action was on the designing board, some times you must tweak things, and ammo with faster powder is the most logical way. Common Remington green box 223 is intended for a 22"-24" heavy barrel varmint bolt action rifles. Will it be the best choice for a 7" barrel AR? Uh no... It doesn't take a rocket scientist to figure that one out. A 7" Kitty Kat barrel only has 2" of barrel past the gas port to capture our needed gas pressure.

Operating pressure happens after the bullet passes the gas port hole and ends once the bullet leaves the barrel, a civilian carbine with a 16" barrel has the most barrel past the gas port than any other AR and it's the easiest AR to find ammo that functions well in it, even a 20" rifle has less barrel after the gas port than a 16" carbine.

When your shooting a one off gun and you expect the most out of it (like reliability), it will probably take some one off ammo. You need a faster powder than a normal AR uses... its just simple physics. One to limit the amount of un burnt powder still exploding past the muzzle, and two is to get a pressure peak right in the sweet spot just before the bullet is exiting the barrel.

My pistol shoots just fine with cheap black box wolf, but there is so much still exploding powder after the muzzle you look like a fool shooting it, also the Pig flash hider attempting to contain all that still exploding and expanding powder gets hotter than hell and transfers that heat to the hand guard. The 2015 load I just spoke of generates far less heat... actually a ton less. Again adding to the usefulness of the firearm.

I gave you a key to the lock, but you just tossed it in the weeds, I still love you neighbor. Just continuing the discussion.
HDD

Matthew 22:39 And the second is like unto it, Thou shalt love thy neighbour as thyself.


HeavyDutyDude  [Member]
8/15/2010 9:18:25 PM
David, I wish you all the luck on your pistol. I'm sorry you don't reload as I find as much enjoyment finding that just right load for each gun as much as I enjoy shooting. In fact I find I shoot to test loads more than I shoot to just shoot.

As a note I found that the 14" barrel contender guys use Blue Dot in their 223 loads, Blue Dot is 357 Magnum powder and it's designed to do everything it's suppose to do with in a 6" barrel. Even still it's a 2900 fps load and I then discovered that varmint shooters with 24" heavy barrel bolt guns like it because they can shoot at a prairie dog town all day long (like 500 rounds) and not have to swap out guns or let it cool down. (Something I can't do with my 220 swifts) Less powder means less heat. Anyway I tried like hell to make that Blue Dot load function in my AR pistol, same deal as you the bolt would short stroke. I played with Wolff reduced power buffer springs, common carbine 95 gram buffer, even taking it apart and removing weights, clear to trying it empty. NO-GO, the gun requires GAS to operate.

You could have a burr in your gas port hole, or even in the gas block itself, I would explore that system, because in stock form your gun should function with mil-spec ammo. along with fresh gas rings make sure they have a drop or two of oil on them. Good ole cheap black box Wolf ammo shot fine when I was putting my pistol together but with a A2 flash hider I had about a 55 gal barrel sized fire ball in front of me. Fun for a magazine, but then got old quick.

Here is a picture of how my pistol looked when assembled for the first time.
I hope you find the answer, It's something simple.
HDD
shadowcop  [Team Member]
8/15/2010 9:52:54 PM
HeavyDutyDude.
Just to be clear I wasn't trying to offend you. Most guys want a firearm that will shoot readily available ammunition.
I agree, check for an obstruction. We covered that earlier in an IM.
I would like to start reloading myself, just not there yet.
Information is always good to know.
HeavyDutyDude  [Member]
8/15/2010 11:04:04 PM
Shadow Cop, we're all good. I have a bunch of guns and I reload for most of them, but I'm not going to jump on a box and call myself an expert, I'm just an enthusiast. I built my AR pistol mainly because I had left over parts from other guns, the upper on my pistol started out as a DPMS DCM/CMP National Match upper and one trip to the range was all it took for me to realize that iron peep sights, 600 yard targets and my 45 year old eyes was a mistake. That gun now wears a DPMS Low-Pro upper and a target scope. And is a pleasure to shoot from the bench.

Then with extra parts in the safe I thought it might be fun having an AR pistol, so I put one together. I will admit it was a challenge making the thing shoot to my satisfaction. They aren't really beginner guns. And to my satisfaction means hand loads. But they still operate with store bought ammo and hopefully David will find the ailment with his.

My Kitty Kat barrel wasn't machined for the end cap, it came with the front sight tower installed and there was no room for a forend cap. In my first configuration I had .025" machined from the back of the sight tower so I could fit a round forend cap and have the sight tower pins line up. All to give the gun a more finished look. So if David has a clamp on gas block and is using a forend cap like I did the gas block might be covering half the gas port hole. Toss the end cap and push the gas block on as far as possible and give it a test fire, it might be something that simple.
HDD
wildturl1  [Team Member]
8/23/2010 6:11:30 PM
My 7" KK and my 10.5" both run fine with whatever port size the came with.
edit to add: I use the Ace Pistol buffer kit on both......
Jparks29  [Member]
8/25/2010 6:06:34 AM
I used .093 per Colts spec on 10.5"... it's a #42 drill bit.

For 5.56mm
Colt's gas port sizes are:
* 10.5" - .093
* 11.5" - .081
* 14.5" - .063
* 16" - .063

shadowcop  [Team Member]
8/25/2010 8:48:06 AM
Thats the funny thing about gas port size. My Rainier has run 100% with the stock .056 port size.
CircleT  [Member]
9/27/2010 12:25:36 PM
Can somebody please explain the O-ring to me. Im not sure where it goes or what it does. Thanks in advance all the info you guys provide has been most useful.
shadowcop  [Team Member]
9/27/2010 3:09:22 PM
The o-ring goes under the ejector, around the spring. It adds more tension to the ejector.