PDA

View Full Version : 10.5" AR pistol w\ midlength gas


gr86ss
12-06-2011, 11:04 AM
I just finished putting together a 10.5" midlength gas system AR pistol. I'm getting some FTF problems. What would you recommend that I do to tune the timing??

thanks in advance

Nathan Krynn
12-06-2011, 11:05 AM
buffer weight?

h0use
12-06-2011, 11:08 AM
lube it up. are you using a pistol buffer tube with the right weight. i had the same problem with mine. i am using the spikes pistol buffer tube kit and it works fine now.

Nathan Krynn
12-06-2011, 11:09 AM
Doesn't help you but both my 10.5's are carbine gas.

gun toting monkeyboy
12-06-2011, 11:15 AM
Yeah. The most likely cause is that you have a gas system that is too long for the barrel. Monkey around with the buffer weight or spring. Try to decrease the resistance that your gas system has to fight. You are working with less gas pressure than you need to cycle the action. Your other option is to take it to a smith and have them open up the gas hole on your barrel to up the amount of gasses vented into the system, like they do on disipator carbines. Mid-length is wonderful for carbines. Not so much for pistols.

-Mb

tomd1584
12-06-2011, 11:50 AM
Curious as to why you went midlength for such short of a barrel. Typically, carbine gas system is the choice for 7.5"-12.5" barrels. Especially if you're going with something from DD, BCM, Colt, or Noveske- as they have their gas port sizes dialed in.

gr86ss
12-06-2011, 11:52 AM
Just ran home to check the buffer, it's a standard buffer that came on the PWS pistol lower. The barrel is a custom cutdown midlength gas barrel. The previous owner said that it worked fine on his set up, but I don't know what other components he used on his build. He said that the longer gas tube length helped buffer felt recoil on his build.

gun toting monkeyboy
12-06-2011, 12:31 PM
Did you just get the barrel from him? Or did you get the upper from him? And he may say it worked for him, but you have no real way of knowing for sure. As for what he says about the longer gas tube, take that with a grain of salt. Not firing because of a FTF would definately have less felt recoil than actually shooting a round... I hope you can get it working, but realize that you may end up having to either take it in to get it fixed, or replace the barrel with one that has a regular carbine-length gas system. You might also give Randall at AR15Barrels.com a call. He is very good with these kinds of things.

-Mb

MrPlink
12-06-2011, 1:48 PM
never heard of a middy 10.5. Interesting.

Agent Tikki
12-06-2011, 2:08 PM
JP LMOS carrier, and a lightest spring and buffer you can find...........

Also a Noveske KX3 would definitely help you.

gr86ss
12-06-2011, 2:30 PM
never heard of a middy 10.5. Interesting.

It's a custom cut barrel.


JP LMOS carrier, and a lightest spring and buffer you can find...........

Also a Noveske KX3 would definitely help you.

I'm using a Troy Claymore on the end

gr86ss
12-06-2011, 2:31 PM
You might also give Randall at AR15Barrels.com a call. He is very good with these kinds of things.

-Mb

I have sent email to Randall. thanks for the recommendation

HK35
12-06-2011, 2:35 PM
never heard of a middy 10.5. Interesting.
Yah, there's good reason why: not enough dwell time to cycle the action correctly.

FeuerFrei
12-06-2011, 2:42 PM
Too long gas tube system without enough space between the muzzle and gas port.
Timing this will be a PITA.
Gas port size/location, length of gas tube and buffer weight will play havoc with your dwell time etc.. Barrel profile will affect gas port size choices too.
KX3 will help push up back pressure and use full power ammo might help.
You may end up with a picky eater.
Good luck.

gr86ss
12-06-2011, 2:49 PM
Too long gas tube system without enough space between the muzzle and gas port.
Timing this will be a PITA.
Gas port size/location, length of gas tube and buffer weight will play havoc with your dwell time etc.. Barrel profile will affect gas port size choices too.
KX3 will help push up back pressure and use full power ammo might help.
You may end up with a picky eater.
Good luck.

I was hoping not to read a post like yours.. :) I have an email to Randall at AR15barrels.com and awaiting a response to see if he can salvage this barrel and make it work. If not, I guess that I will be purchasing another barrel...

wash
12-06-2011, 2:53 PM
The carbine gas system was designed for "commando" length ARs back in the day, the mistake was using that gas system on the 14.5" carbines.

Now you've taken a barrel whose length is perfect for carbine gas and put a mid-length gas system on it...

Too much of a good thing is still too much.

If you want to save the barrel, I would suggest drilling it for pistol gas and cutting it down to 7.5" to get back in to a known good configuration.

MrPlink
12-06-2011, 3:09 PM
Yah, there's good reason why: not enough dwell time to cycle the action correctly.

kinda what I was thinkin. Im no expert on AR tuning, but just looking at my 10.5 and imagining a middy system, my head started to hurt with all the problems I started to imagine!

Agent Tikki
12-06-2011, 3:12 PM
It's a custom cut barrel.




I'm using a Troy Claymore on the end


Conical Brakes brakes lengthen the gas system, I'm not quite sure if Troys is the same as the KX3, but you might want to look into that.

Colt-45
12-06-2011, 7:23 PM
The carbine gas system was designed for "commando" length ARs back in the day, the mistake was using that gas system on the 14.5" carbines.

I understand that 16" barrels look horrendous with a carbine length gas system because of too much naked barrel, but why is the carbine gas system a "mistake" in the 14.5" barrel?

My 14.5" is a midlength and my 16" is also. Thinking about putting a 14.5" carbine build together.

wash
12-06-2011, 8:43 PM
The mistake is that adding 3 more inches of barrel gave it too much dwell time and the pressure at the gas port is higher than it has to be leading to faster carrier speeds, cyclic firing rate and the increase in weapon failures that go with that.

When manufacturers started making 16" AR uppers to avoid both SBR issues and pinned muzzle devices, the problem got even worse along with looking weird. The Mid-length gas system was the fix to bring the gas system in to a better balance, then people started putting them on 14.5" barrels which is still not right (not enough dwell) but maybe less wrong than 14.5" with carbine gas.

Using a mid-length gas system on a 10.5" barrel is wrong in the almost no dwell direction.

tomd1584
12-06-2011, 8:56 PM
I would personally just buy a new barrel.

MrPlink
12-07-2011, 4:14 AM
The Mid-length gas system was the fix to bring the gas system in to a better balance, then people started putting them on 14.5" barrels which is still not right (not enough dwell) but maybe less wrong than 14.5" with carbine gas.



I was always under the impression people went with a middy and 14.5in to get softer recoil (sissys!) ?

The 14.5in carbine IMO is at least a bit easier to tune, as opposed to having a 16in carbine.

Tuning issues aside (I hate to sound like a poser) I just cant bring myself to own a 16in with a carbine system, it just looks so WRONG to me.

shadow65
12-07-2011, 5:21 AM
Have the mid length gas port welded and have a carbine length gas port drilled. ADCO can do it.
Dave N

Nathan Krynn
12-07-2011, 5:46 AM
!!!!WARNING!!!!WARNING!!!!OPINION!!!!


I'm going to be honest I don't like the KX3. I really feel the PWS CQB Comp is SO much better. It works so well as a flash hider for short barrels. It is like sparks coming out as the KX3 is called the flaming pig for a reason. It helps tune short barrels just as much as the KX3 too.

gun toting monkeyboy
12-07-2011, 7:06 AM
!!!!WARNING!!!!WARNING!!!!OPINION!!!!


I'm going to be honest I don't like the KX3. I really feel the PWS CQB Comp is SO much better. It works so well as a flash hider for short barrels. It is like sparks coming out as the KX3 is called the flaming pig for a reason. It helps tune short barrels just as much as the KX3 too.

And you will be getting fireballs. My 10.5" can have fireballs up to 5 feet wide, depending on the ammunition. I have a little Cav Arms comp on mine, so the blast goes out almost as much to the sides as it does out front. :D

-Mb

jgraham15
12-07-2011, 10:34 PM
And you will be getting fireballs. My 10.5" can have fireballs up to 5 feet wide, depending on the ammunition. I have a little Cav Arms comp on mine, so the blast goes out almost as much to the sides as it does out front. :D

-Mb

Just a guess but I think you are confusing the PWS CQB with the PWS FSC.

This is the CQB

http://primaryweapons.com/store/pc/catalog/PWS_CQB_556_L_1.jpg

http://primaryweapons.com/store/pc/viewPrd.asp?idproduct=90

marktse
12-15-2011, 8:27 AM
you only have 1 inche between the gas port and muzzle you have the same problem with most pistol ars. I woudl recommend that you get a carbine gas system. or get a kx3 pig or the cqb pws compensator.

xxINKxx
12-15-2011, 9:29 AM
Not sure why people buy midlegths because they are told it is "less recoil" I've never felt any difference in recoil between carbine or middy in any AR.

That's what muzzle brakes are for.

Nathan Krynn
12-16-2011, 6:42 AM
Not sure why people buy midlegths because they are told it is "less recoil" I've never felt any difference in recoil between carbine or middy in any AR.

That's what muzzle brakes are for.

I know a lot of people just sit at a bench for most or all their shooting and they feel a slight difference in recoil but you are right it is a soft recoiling round as is. You do have people that have injuries though. Mostly I think people buy into the stuff they read on the web that for the average AR owner who sits at a bench and shoots 100 rounds a month or even year it will make no difference at all.

I rarely shoot at a bench at all anymore and really just when I am stressed and need to relax or right before hunting season or a special hunt. I really only use my AR's for action shooting and at different distances with strings of fire engaging different targets. With this I can get faster follow up shots with mid vs carbine and have more A zone hits with cloverleafs. However I do just fine with carbine too just that mid does improve it. Rifle goes further and that's why you see most pro shooters use rifle 18".

However I know most people are not lucky enough to have ranges with action bays and do not have places to shoot like this. Or that they just don't participate in local match's which is where you will see the difference IMHO timed against other people.

gr86ss
12-16-2011, 9:10 PM
Well Randall of ar15barrels.com never got back to me. So as most of what I've read about his being a flake is somewhat apparent. He should take down his website if he doesn't do business any longer.

I'm going to try a heavy buffer and different BCGs that I have before I give up on this upper. The previous owner of the barrel assures me that he had absolutely no issues so I'll try and tune the current setup prior to forking out for a new barrel.

wash
12-16-2011, 9:35 PM
A heavy buffer is going the wrong direction, you need it light so that the little gas you have can get things moving.

As far as the previous owner goes, start thinking about not listening to him so much.

Your story sounds like a guy wanted an AR pistol so he cuts down a barrel and then sells it once he figures out it doesn't work.

Unless your first move was to throw in a heavy buffer and change everything you possibly could, it should be working the same for you as it did for him.

I don't like seeing people get taken for a ride because they don't fully understand how their gun operates.

There are very few absolutes and "midlength is better" is not one of them.

Mr_Monkeywrench
12-16-2011, 10:06 PM
Thats kinda strange. All the rifles if fired (with the exception of a few) have been 16 with carbine gas systems. Never had a problem other than the hand guards being too short for my Neanderthal length arms.arms. id like to try a mid length to see the difference

Mr_Monkeywrench
12-16-2011, 10:13 PM
Also, op if you don't wanna hassle wit tuning your pistol upper, you can sell it with full disclosure and use whatever revenue you get for it and buy a new one. Palmetto has some good deals.

FeuerFrei
12-16-2011, 10:14 PM
Still not working?
...Question to OP.
Is the gas block attached via set screws?
FailureToFeed after the first round goes bang and won't feed another round?
I have seen set screw gas blocks come loose. Slight enough to choke gas to carrier. Won't cycle.
This may explain why the upper worked for seller but now not you.
Check gas block for being off center or canted. Check w/compressed air.
...or the seller is a lying sack of crap and it never worked?

freonr22
12-16-2011, 10:22 PM
Have you pm ' d Randall at Caprc?

vta
12-16-2011, 10:24 PM
Before you buy a new barrel, try to open up the gas port incrementally until it will cycle and go from there. I between that and using an appropriate muzzle device would be the direction I would go. I good luck.

VytamenC Tactical
12-16-2011, 10:32 PM
Still not working?
...Question to OP.
Is the gas block attached via set screws?
FailureToFeed after the first round goes bang and won't feed another round?
I have seen set screw gas blocks come loose. Slight enough to choke gas to carrier. Won't cycle.
This may explain why the upper worked for seller but now not you.
Check gas block for being off center or canted. Check w/compressed air.
...or the seller is a lying sack of crap and it never worked?

agree i have also.

i have a new 10.5 inch barrel i will sell you for $115 carbine length gas system.
also from what i have heard ar15 barrels is really busy and getting anything from him is hard

Seesm
12-16-2011, 11:36 PM
I took a 10.5 and cut to 8.5 and took the carbine gas system and cut it even shorter... Made my own gas tube... Functions just like a carbine once I got the gas port larger enough...

I would put a carbine gas system on that barrel you have and plug the old gas port. Or cut it down and re gas it again as a carbine... YOu have a few options.