Help me dubug my 10.5 LMT.

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[ARCHIVED THREAD] - Help me dubug my 10.5 LMT.

Posted: 3/9/2006 8:37:29 AM EDT

Shot my 10.5 today -- just put it together yesterday.

Has a Wolf heavy extractor spring, no o-ring. Blue insert.

Has a Shooting Systems chrome-silicon recoil spring. Endine buffer. Carbine stock.

With Winchester Q3131, it cycles and will eject the brass about 4 feet (which I think is not very far). If you put in an empty mag, it will lock open.

With Hornady 75 TAP .223, it will not lock open or cycle.

When I put a silencer on it, it seems 100% reliable with both ammo, and ejects 7-8 feet.

What do you think? Open gas port one drill size?

Personally I want to spank all of the people who told me I should be happy with .223 Hornady ammo and that it was 'good enough' and I did not need the 5.56mm NATO load. I think that .223 ammo has a lower margin of reliability, especially in short barrels.

Posted: 3/9/2006 8:50:39 AM EDT

[#1]

If it's an LMT-built 10.5 upper, then don't mess with the gas port. LMTs are correct as is.

TAP is a bit on the unusual side, so I wouldn't use it as a gauge for reliability. You seem to have found a load that will cycle reliably, so use that or investigate other loads. Just stay away from TAP loads.

I would add an o-ring or D-fender to the extractor, it will add life to the spring and give you much better ejection.

Posted: 3/9/2006 9:05:45 AM EDT

[#2]

Ok. So I suggest I should try a lighter buffer and stick to TAP 5.56m and never shoot .223 SAAMI pressure ammo.

Posted: 3/9/2006 9:06:42 AM EDT

[#3]

BTW, people have asked me MANY times if a 10.5 inch upper will work with an AAC flash hider. The answer is yes for LMT 10.5 inch uppers.

Posted: 3/9/2006 9:07:18 AM EDT

[#4]

I remember reading a thread awhile ago about an Australian guy in Iraq that was having problems with his LMT 10.5. It wouldn't hurt to do a search for that thread.

Also, check the troubleshooting forum.

Posted: 3/9/2006 12:13:02 PM EDT

[#5]

Simple: 1) increase barrel length by 1"; 2) leave suppressor on rifle

Just kinding (actually the second idea isn't that bad

From what I understand, you have chamber pressure, gas port diameter, and dwell time. When the bullet dwell time is severly limited by the short (under 3") barrel extension, the port diameter can only do so much. At some point, making it bigger will actually make things worse. I bet yours port diameter is already optimum. That leaves chamber pressure, which is ammo dependent. Bottom line, shorties like yours are picky about ammo. Play with some loads, find one or two that work well, and stick with them.

Posted: 3/9/2006 12:34:29 PM EDT

[#6]

Quoted:

Has a Shooting Systems chrome-silicon recoil spring. Endine buffer. Carbine stock.

Before you screw with the gas port, I would suggest trying a H2 buffer and standard (Colt or CMT) buffer spring.

I recently had a friend who was having simular problems, his gun was dirty and he was using an extra power buffer spring. I cleaned the gun, changed the buffer and spring, and the problems went away.

That is not to say that the gas port may not need to be opened, but try changing out the buffer and spring prior to doing any mods to the gas port.

Posted: 3/9/2006 1:11:25 PM EDT

[#7]

I have some H2 buffers coming. And I will put in a standard spring.

Also note that the Endine buffer has a spring in it which adds extra resistance for the last 1/2 inch of travel -- so that might be the problem.

Posted: 3/9/2006 1:29:42 PM EDT

[#8]

Robert, there have been a few claims on the board here of short stroking when combining the Endine buffer with weaker ammo. I'd try a different buffer first, and definitely lose the heavier buffer spring.

Posted: 3/9/2006 1:41:03 PM EDT

[#9]

So I bought these springs because they are supposed to not take a set and are supposed to be good for more cycles. I considered them lifetime springs.

I did not mean to get a 'heavier' spring.

But I can see they are considered 'extra power.' That would seem bad. I want 'normal' power but longer life.

I was brainwashed into thinking all springs were junk unless they are chrome-silicon. I still can't get it out of my head.

"These flat wire, high-quality action/buffer springs from champion shooter David Tubb will perform flawlessly and are duty rated for 500,000 compression cycles at maximum performance. Made to “extra power” specs without the extra material, these springs are surprisingly lightweight, yet extremely durable. Gives correct timing and resistance on the recoil stroke and a controlled rebound ensures reliable feeding with consistent forward thrust on every shot. Keeps the bolt locked a little longer to allow pressures more time to subside for perfect cycling."

Posted: 3/9/2006 2:26:14 PM EDT

[#10]

The spring may not be bad in and of itself, but perhaps causes problems when used in conjunction with a really heavy buffer.

Posted: 3/9/2006 2:28:06 PM EDT

[#11]

The buffer is 4.3 ounces. Tomorrow I am trying a 3.8 ounce H buffer and I will use a normal spring.

Posted: 3/9/2006 2:31:48 PM EDT

[#12]

Quoted:
The buffer is 4.3 ounces.

I would have thought that it was heavier than that, as it is always being compared to the 7.2 ounce MGI buffer.

Posted: 3/9/2006 3:20:57 PM EDT

[#13]

Quoted:
So I bought these springs because they are supposed to not take a set and are supposed to be good for more cycles. I considered them lifetime springs.

I did not mean to get a 'heavier' spring.

But I can see they are considered 'extra power.' That would seem bad. I want 'normal' power but longer life.

I was brainwashed into thinking all springs were junk unless they are chrome-silicon. I still can't get it out of my head.

"These flat wire, high-quality action/buffer springs from champion shooter David Tubb will perform flawlessly and are duty rated for 500,000 compression cycles at maximum performance. Made to “extra power” specs without the extra material, these springs are surprisingly lightweight, yet extremely durable. Gives correct timing and resistance on the recoil stroke and a controlled rebound ensures reliable feeding with consistent forward thrust on every shot. Keeps the bolt locked a little longer to allow pressures more time to subside for perfect cycling."

As the great American philosopher Flava-Flave said in the later 1980's "DON'T BELIEVE THE HYPE"

Springs are cheap and like tires need to be replaced from time to time. Some springs are better than others. For the price I prefer CMT carbine buffer springs.

Can't go wrong with either Colt (from Brownells) or CMT.

Posted: 3/9/2006 7:43:41 PM EDT

[#14]

www.ar15.com/forums/topic.html?b=3&f=14&t=153425

Posted: 3/10/2006 5:12:32 AM EDT

[#15]

I´m using these springs on my M4. Stock number 078-000-087, Chrome Silicon, standard power.
I change them after 6000 rds.

Buffer is 5.65 oz steel buffer. No hickups, FTE, FTFs or short strokes, works like dream.

MN

Posted: 3/10/2006 5:36:22 AM EDT

[#16]

Sweet. Thanks. I will order some.

Posted: 3/10/2006 11:42:29 AM EDT

[#17]

It works now.

I put in a Colt spring and an H buffer. Fired 150-200 rounds full auto. No failures.

The rate of fire seems on the slow side without the can, and very fast with the can. I bet if I use an H2 buffer it will become too slow without the can (by too slow I mean, to the point where it is less reliable).

Posted: 3/10/2006 1:28:11 PM EDT

[#18]

Quoted:
It works now.

I put in a Colt spring and an H buffer. Fired 150-200 rounds full auto. No failures.

which is what it should have been since the beginning..don't believe the hype..

Posted: 3/10/2006 2:29:44 PM EDT

[#19]

try putting the parts back in one at a time and mixed around so you know what is causing it not to work either or both.

im using the mgi buffers in all of my rifles/pistol and have not had a single problem.

[ARCHIVED THREAD] - Help me dubug my 10.5 LMT.

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