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 Post subject: Re: AR gurus, help needed.
New postPosted: August 29th, 2015, 5:01 am 
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AZS; Woohoo!
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slap a low pro block on it and align the port see if it makes a difference

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 Post subject: Re: AR gurus, help needed.
New postPosted: August 29th, 2015, 6:22 am 
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elheffe wrote:
slap a low pro block on it and align the port see if it makes a difference

Likely not going to make any difference. At this point I'd absolutely be looking specifically at the diameter of the gas port assuming first everything else is in spec.


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 Post subject: Re: AR gurus, help needed.
New postPosted: August 30th, 2017, 11:51 am 
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AZS; Woohoo!
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Joined: October 8th, 2005, 10:48 pm
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Lets cogitate on this for a few.

I took off the front sight. The gas hole is gigantic compared to my regular carbine so I don't thing that's the problem. I'm assuming its due to the "dissipater" configuration with the 16 inch barrel and rifle length gas system. I guess they needed a heavier gas impulse as the port is so far down the barrel and so close to the muzzle.

Front sight came off, everything looks good there. It appears to line up with the gas port. I took out the gas tube to make sure it wasn't clogged or I didn't goober it during install. everything appeared fine there too.

SO... WTF???

It's not cycling with a full mag. Take some of the resistance off of the bolt by having less tension on the mag spring and it runs fine. With a full mag the extra drag causes failure to chamber. It goes back far enough to eject the spent casing but not far enough to strip off the next round.

SO.... How do I improve the reliability of the extraction?

Cut coils off the spring till it works? Put in a carbine spring instead? I lightweight bolt or buffer?

I had a dissipater carbine before and it had no problems. This is the first AR ive had that is giving me fits.

Any thoughts? I know its hard as hell to diagnose over the net but its not like this is my only rifle. I'm willing to try anything.

Since Photobucket users got f***ed I don't have an imagine site any more so I cant put up photos until I can find a decent webhosting site.


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 Post subject: Re: AR gurus, help needed.
New postPosted: August 30th, 2017, 12:44 pm 
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AZS; Woohoo!
AZS; Woohoo!

Joined: June 4th, 2011, 7:48 am
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Location: NW Valley
Try using an adjustable gas block. Since the gas port is large, you may need to tune it to get just enough gas. Doing so also helps tone down recoil by not having too much gas.
When adjusting the gas block, shoot .223 which has less gas than 5.56 so it will work on both. Still a little more recoil on 5.56 but more reliable.


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 Post subject: Re: AR gurus, help needed.
New postPosted: August 30th, 2017, 2:26 pm 
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He said his problem is short stroking after it gets a little dirty.

Isn't this the gun that was built by one person and he was going to take somewhere else to have fixed?

What kind of magazines is the OP running? Try it with some GI ammo and mags. I recall he was using XM193 equivalent at one point. Also, try a different BCG and see if you can duplicate the results.


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 Post subject: Re: AR gurus, help needed.
New postPosted: August 31st, 2017, 8:43 am 
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AZS; Woohoo!
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It's only had GI mags in it. And IIRC, military XM193 is hot stuff compared to commercial .223. I know Ive shot commercial hollow points out of it as it was my patrol rifle and we would expend older rounds for new on range days. It had the same problem and I had to load my mags light to get it to run.

For some reason it's not getting enough oomph to strip off new rounds. Yes, it happens when it's a bit dirty, say after ten or fifteen rounds. Again, as the mag depletes and the pressure on the underside of the bolt reduces it seems to clear up. Its just ever so slightly under gassed with a full mag. I can see no reason for this.

Do they make reduced power main springs? Is there a such thing as a lightweight bolt? I believe I also read somewhere that a slightly longer gas tube that more deeply engages the gas key might be beneficial. Anyone else know of such a thing?

Its accurate as hell, runs great otherwise. I have an ACOG reflex on it and it's death on a stick at police use ranges. I can just see no reason for this to happen. It's like having an AK47 that wont run. It simply doesn't happen. Its just ever so slightly under gassed or over inertia-ed. Is a dissipater supposed to have a different bolt in it?

I'm stumped, which isn't saying much.


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 Post subject: Re: AR gurus, help needed.
New postPosted: August 31st, 2017, 2:24 pm 
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Let's try this again:

1. take the upper, in its entirety, and put it on another rifle. Does the problem follow?
2. take the BCG, buffer, and buffer spring from the problem rifle and put it into a working rifle. Does the problem continue?
3. take the BCG, buffer, and buffer spring from a working rifle and put it into the problem rifle. Does the problem continue?

Eventually we will dumb luck into what the real problem is. You've already stated on a cleaned and lubed rifle it functions fine for the first few rounds and then short stroking starts. Under that description you gave the rifle is not undergassed. Something else is going on.

XM193 is ball ammo. It's hot. You're getting plenty of gas. So that begs the question of "WTF does this mean?"

Quote:
.....It had the same problem and I had to load my mags light to get it to run.

For some reason it's not getting enough oomph to strip off new rounds. Yes, it happens when it's a bit dirty, say after ten or fifteen rounds. Again, as the mag depletes and the pressure on the underside of the bolt reduces it seems to clear up. Its just ever so slightly under gassed with a full mag. I can see no reason for this.


So what is it? When it is clean and freshly lubed does it run fine with a full mag or not? What kind of springs are you running in the mags and what mind of follower?

There are differences in bolts and bolt carriers. An M16 carrier weighs more than a commercial AR15 carrier. The standard M16 BCG weighs 11.6 ounces. A standard AR15 carrier weighs in at around 10.25 ounces. Try switching to a lighter BCG and buffer and see if that helps.


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 Post subject: Re: AR gurus, help needed.
New postPosted: August 31st, 2017, 4:30 pm 
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AZS; Woohoo!
AZS; Woohoo!

Joined: December 4th, 2007, 1:22 pm
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John Kuhns wrote:
Let's try this again:

1. take the upper, in its entirety, and put it on another rifle. Does the problem follow?
2. take the BCG, buffer, and buffer spring from the problem rifle and put it into a working rifle. Does the problem continue?
3. take the BCG, buffer, and buffer spring from a working rifle and put it into the problem rifle. Does the problem continue?

Eventually we will dumb luck into what the real problem is. You've already stated on a cleaned and lubed rifle it functions fine for the first few rounds and then short stroking starts. Under that description you gave the rifle is not undergassed. Something else is going on.

XM193 is ball ammo. It's hot. You're getting plenty of gas. So that begs the question of "WTF does this mean?"

Quote:
.....It had the same problem and I had to load my mags light to get it to run.

For some reason it's not getting enough oomph to strip off new rounds. Yes, it happens when it's a bit dirty, say after ten or fifteen rounds. Again, as the mag depletes and the pressure on the underside of the bolt reduces it seems to clear up. Its just ever so slightly under gassed with a full mag. I can see no reason for this.


So what is it? When it is clean and freshly lubed does it run fine with a full mag or not? What kind of springs are you running in the mags and what mind of follower?

There are differences in bolts and bolt carriers. An M16 carrier weighs more than a commercial AR15 carrier. The standard M16 BCG weighs 11.6 ounces. A standard AR15 carrier weighs in at around 10.25 ounces. Try switching to a lighter BCG and buffer and see if that helps.


Good explanation John...This problem should have been sorted out in 10 minutes...not 3 pages of posts. [smilie=icon_eek.gif]


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 Post subject: Re: AR gurus, help needed.
New postPosted: September 1st, 2017, 2:17 am 
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Joined: February 3rd, 2010, 8:13 pm
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Location: Ahwatukee, AZ
Cleaned and lubed is how I keep em.

Lubed like wet all the time.


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 Post subject: Re: AR gurus, help needed.
New postPosted: September 6th, 2017, 1:00 pm 
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AZS; Woohoo!
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I don't like a finicky rifle. If at some point lube simply isn't available I don't need a club as opposed to a functioning rifle. It should run in any condition. If it gets a bit dry or dirty and refuses to run I don't want anything to do with it.

I found a bolt with a bigger cut out on the bottom. Assuming it's lighter. Put the upper on a cav arms lower. It has a carbine length spring in it.

We'll see if that cures it.


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 Post subject: Re: AR gurus, help needed.
New postPosted: September 6th, 2017, 2:59 pm 
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AZS; Woohoo!
AZS; Woohoo!

Joined: June 4th, 2011, 7:48 am
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Location: NW Valley
Don't give up on it. Problem solving is very satisfying. Once you solve the problem that is!


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 Post subject: Re: AR gurus, help needed.
New postPosted: September 6th, 2017, 3:03 pm 
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AZS; Woohoo!
AZS; Woohoo!

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That seemed to be the magic. I ran it completely dry, shot five rounds out of a full thirty round mag then reloaded. It continued to run and was flinging brass quite a distance. Combo of lighter spring and lighter BCG seemed to cure its ills.


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 Post subject: Re: AR gurus, help needed.
New postPosted: September 6th, 2017, 7:39 pm 
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Me seems to think I said to do this. Now, have you gone back, lubed the rifle, and tried it again? Bet it runs just fine.


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 Post subject: Re: AR gurus, help needed.
New postPosted: September 10th, 2017, 11:52 am 
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AZS; Woohoo!
AZS; Woohoo!

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Yeah, it was just one of those weird things where an AR just didn't like the way it was assembled. The combination of a lighter bolt and a presumably lighter carbine spring gave the bolt much more speed in it's rearward travel. It ran great dry, no reason to suspect it wouldn't run as well or better lubed. My rifles have to work in all conditions or I'm not happy. I'm form over function every time. That's why I like AKs so much. Say what you will but those bastards will run no matter what and all you need is a good size rock to keep em running in adverse conditions. A gun that won't run in adverse conditions is a possible liability. Not so important now that I'm no longer on the job but old habits die hard.


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