LMT upper issue

Gothmog

Gothmog

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I just purchased an LMT upper off the EE. I put it together with a lower and bolt assembly and tried to function test it and found that a standard notched hammer will not work in this setup when function tested. I am unable to pull the bolt back more than a cm or so before the action locks up.

There seems to be insufficient clearance, or perhaps the shape of the hammer is striking the back of the bolt in an odd way ... when the hammer is replaced with an early , non notched hammer, all seems well and I can rack the action. However, I have concerns about slam fires with the use of this type of hammer.

Any ideas or suggestions guys? :confused:
 
I mounted it to two different lowers (known to work) with notched hammers and the problem was the same with both. I attached it to a lower with the early style hammer and the problem disappeared. The seller says that a full auto bolt was used with it before (one of these 'bolt not included' deals) and that it worked then.

I don't have any experience with f/a bolts and so don't see how that might fix the issue. I also don't have one available to me to experiment with.
 
pic of your bolt?
Bottom of it

But first assemble the lower with the hammer cocked,safety on.
can you rack the bolt then?
 
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Gothmog said:
If the hammer is cocked, the bolt can be racked ... I'll try it while having the safety on as well.
Click to expand...
That's good enough,let us see the bottom of your bolt carrier
We've established it's not the lugs getting caught,might just be a bad edge on the carrier.
I polished mine and rounded it off at the edge.Maybe that is the issue

Only other thing i can think of that would stop the bolt coming back would be crud built up in the forward assist.
But since it racks with the hammer cocked it must be the mating surfaces of the hammer/carrier not getting along.
Some file work/polishing should sort it out
 
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Bolt bottom pic

IMG_3923.jpg
 
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(Ronin) said:
But since it racks with the hammer cocked it must be the mating surfaces of the hammer/carrier not getting along.
Some file work/polishing should sort it out
Click to expand...

I should tell you that I've used this bolt/lower combination before with another upper ... its their use with an LMT upper that causes the issue.

PS - the carrier is marked with a 'C', it may be a Colt carrier. The other carrier I have does no better, though.
 
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I think i see it.Pics coming

Ok..i see a wedge shape there were the hammer could be getting binded in after firing.
A difference of a couple thou in fit closer between the upper and lower can be enough to make this an issue.
IMG_3923.jpg


My M16 carrier,note the squareness were the hammer would come in and hit the firing pin
Picture184.jpg


I'd grab a file and run it over the sides were it tapers in a V and widen it just a hair.
Or as an alternative file the sides of the hammer and polish them smooth.
I'm betting the problem will be solved.
 
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The two shiny marks on the carrier in the center of the pic?

Yes, I suspected that the hammer is making contact there. The question is why? I've used it with other uppers and never had a problem.
 
Gothmog said:
The two shiny marks on the carrier in the center of the pic?

Yes, I suspected that the hammer is making contact there. The question is why? I've used it with other uppers and never had a problem.
Click to expand...
Well if the fit was tighter,or a difference in tolerances could bring the hammer up further into that groove.So your hammer is striking even a couple though higher on the firing pin.
Than could be enough to get it wedged in there and bind it up.

It looks like the carrier is at fault due to the design

Hit it with a file or polish the sides and the top of the hammer.
$5 says problem solved ;)
 
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Problem solved, I think ...

... and no filing necessary, but thanks for the input.

I was looking at your pics and noticed that the firing pin was missing from my pic. I never thought much of it as I regularly run that bolt without a pin for use in a teaching gun, and without any problems.

Now here's the tricky bit ... I always use the lower with the old style hammer in combination with that bolt as a 'trainer'. It appears that the non notched (old style) hammer works happily without a firing pin. The notched hammers do not!

Case closed, I think ....

IMG_3925-1.jpg


Old style hammer ...

IMG_3926-1.jpg


Newer style hammer, notched to prevent slam fires ....
 
(Ronin) said:
lmao..Yeah that could do it
I was looking so deep i didn't see the obvious :redface:
Click to expand...

Yes, you and me both ... :redface::D

I suspect that it was the 'notch' in the hammer that was binding things up. Well, I just learned something new. Now to get a worn out AR15 firing pin and chop it down for use in my training gun.

Thanks again, now I can happily try this sucker out! :dancingbanana:
 
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Just remember not to pull your firing pin out if you want to practice dryfire or make you weapon inoperable. Your cam pin will rotate and you won't enjoy trying to get it unstuck from inside your receiver.
 
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