Couple of questions for the owners.

Has anyone set up a LM7 or Razorback with an A5 buffer tube? What length did you cut the spacer?

Was lucky enough to pick up both.  Sadly the LM7 bolt does not have a sear trip. I just read an old uzitalk thread that mentioned a bolt length difference necessitating a different trip thickness. Any chance someone could give me the thickness of the LM7 trip?

Sorry. Forgot one thing. The screw that holds the trip. Loctite from the factory? Can’t inspect the firing pin on the Razorback without pulling it off and it won’t budge. 5/64 limits how much ass I want to give it

Thanks.

Made it to the range today.  Colt 614 with a Geissele SSF trigger and an A5 buffer tube. LM7 with Razorback bolt.

Answered one question from above. 3.5 inch spacer worked well. Adequate bolt travel. Could have went a little shorter but didn’t want to risk the charging handle impacting.

Overall it worked well. I had only loaded up 4 belts. It ripped through the first 2. Mix of semi and auto. Then I started having stoppages. All of them were the same. I assume it was firing out of battery. Cases were split and jammed up the t-slot.

At least three possibilities that come to mind.  Tight chamber was hanging up the bullets? Timing is off? Early and releasing the hammer before it is fully seated. Late and it is bouncing when the hammer hits.

Was still way more successful than the lithocore experiment.

Razorback bolt face to leading edge of the trip is 5.15 inches. I will have to go get some feelers to see check the bolt gap at release. The LM7 bolt is .1 shorter than the Razorback. To get the same 5.15 inches the trip would need to be extremely thin. Like .030 thin. Can that be?

Sucks being a decade plus late to the party.

Thanks for any and all help/tips/advice.

The issue. Attached File

Given the age I doubt this gets much interest at all. It looks like lakesideguns forum is still up. Not sure it is possible to register. Would love to be able to just read them.

Would it be possible to get a picture of the back of the casing to determine where the blow-out is happening in relation to the t-slot and firing pin?

I don't think you have an out-of-battery situation here, as the casing seems to be blowing out where it isn't supported by anything when the bolt is fully closed.  A possible cause is build-up of fouling in the barrel, which would increase chamber pressure as you went through belts.  You noted that the first couple of belts went fine and then the problem started.  Please check the bore and clean it aggressively.

It's easy to forget how many rounds you are running down the bore, as the belts go quickly when the gun is running correctly, but I have seen barrels that had long streamers of lead pushed out of them after they got thoroughly leaded up.  Cleaning had to start with a .17 caliber rod as a .22 rod was impossible to insert.

What ammo are you using?  Back in the old Lakeside days the company released glowing reports of CCI Blazer being the PERFECT ammo for the LM7, giving 100% functioning.  I bought a brick and it leaded up the barrel horribly because it was a different lot of Blaser and has a different lube on the bullets.  You may solve your problem just be changing ammo.  A plated bullet might help.

Are you talking about this old thread: http://www.uzitalk.com/forums/showthread.php?49112-Lakeside-Razorback&p=456008&viewfull=1

Those are my posts and pictures in there.

Eric at Lakeside used to advise everyone to check their own timing for the sear trip as to the variances out there.
I used a numbered drill bit set to check the timing.  I can't recall what Eric recommended.

So I personally wouldn't go by anyone's trip recommendations...you need to do that yourself.

I checked my notes and my hammer drops at .033".  However, I have several bolts, trips etc..

I am also using a Colt 614.  I am using a factory Colt fire control group.  Eric used to laugh and say it doesn't make a difference.  I had sent my fire control to Eric for him to hone the bottom of the sear and tail of the hammer, trigger face etc to reduce 'hammer dip'.  I think I've posted about that several times here already.

Regarding ammo, back in the day, Eric recommended Blazer but later discovered that the Federal made Blazer was problematic while the original CCI Blazer worked properly.   The CCI Blazer had a darker lead and came in the clear plastic seperators.  See this Youtube video on it:


ETA:  Do you have a picture of your spring assembly?  You need to make sure you are using a setup with the anti-bounce weight.  Eric actually made several variants.  I have probably all of them.  He also made several different charging handles.  Polymer was the first, then he made some steel of various weight...some hollowed out and aluminum.  I've got several of those as well.  I had a heavy steel one break on me though.  I think I went back to the hollow steel.

First off thanks for jumping in gentleman.

Regarding the ammo. I only ran CCI Blazer. Clear plastic separators in the 50 packs. The belts were broken in and I used the loading kit to ensure they were uniformly seated.

In the case pic above it is blown out right where the firing pin impacted it. All of the ones I kept were. That is why I was thinking out of battery. No chamber support above and below until completely seated.

But that got me thinking. I never looked at the spent brass for the ones that worked.  Where many more split but didn’t bulge to the point of stoppage? I always thought of the reduced power hammer spring from only cycling the action perspective. Free up a little energy to ensure function. Never really considered how hard the hammer is hitting the firing pin.

Blunting the firing pin isn’t really an option.  Can’t add it back on and zero spares. So I may have to try a reduced power hammer spring.

For the buffer I was using the one with the steel  anti bounce weight.

Attached File

Alright I have loaded up some “tight” belts as well as some seasoned ones. SSF hammer spring swapped for a reduced power one. Did not go all the way to 4 o’clock but I will take with.

Hoping for the best

Due to the nature of the t-slot in the bolt, the top and bottom of the case right in front of the rim will be unsupported even with the bolt fully closed.  The firing pin may be weakening the brass enough to provide a weak spot for a blow-out, but I still think you need to check the chamber and bore for build-up of lead and fouling that would lead to increased chamber pressure.

If you can't remove the firing pin with the FA trip in place, you can try filing or grinding a SMALL angled relief on the top of the trip to allow the firing pin to sneak past it.  The top of the trip doesn't do anything except sit there.  If you can get the pin out, you can check for sharp edges and stone them down.  You wouldn't want to shorten the overall length of the pin, just make it smooth.

Another experiment you can easily try is belting up a short belt (20-50 rounds) of standard velocity ammo.  It might not have enough power to function, but it might and it would have lower chamber pressures.

My initial thought was a tight chamber preventing the round from fully seating. I could not feel any sharp edges. I still spun a chamber brush in there to help loosen it up.

I went through one 50 and one 100 round belt before it started being problematic. Not sure if Eric test fired them. If he didn’t it was the first 150  down the barrel.

Made it back to the range. I had buzzed the chamber to soften the edges to help feeding and swapped to a reduced power hammer spring. I wish I had only done one one at a time to try and figure out what helped and what didn’t matter.

The good news was I only had two stoppages due to blown case rims.

It ran better but I want it to run like it is capable of.  Always loved the thousand round belt video. Mine will be chewing through a belt and then just stop.

One thing I noticed when hand cycling the LM7 is that there is a spot where the bolt catches and locks up tight. This happens with the LM7 and the Razorback bolt. Happens with the top over open or closed. The pin on the feed claw or whatever it is called catches. I cannot replicate this on the Razorback upper.

I can’t see anything obvious but maybe some one else will. Geometry wise are these parts the same between the models? Pain to swap?
LM7 first. Razorback second. Attached File


Attached File

That's the cam that engages the extractor and makes it move up and down at the appropriate times.  As far as I know, there was no reason to change that part between the LM7 and the Razorback so they should be the same.  There's a small stud on the "back" of the extractor that rides in the track formed by the cam and if you can get the bolt to hang up with the top cover open then you should be able to see where the little stud is in relation to the cam.  If there's a rough or damaged spot, you can try to file or stone it away without removing too much metal.

As a test, try removing the extractor from the bolt and then hand-cycling the action.  If it still hangs up, it isn't the extractor or cam.

Are you doing the hand-cycling with ammo?  If so, you could also have a tight spot in the t-slot, which would keep the extractor from moving up and down freely and stop the bolt.  The t-slot gets filled with crud as it's right by the opening of the chamber and it's a blowback operating system, so there's plenty of gas and dirt coming out of the chamber.  I use a dental pick to make sure the t-slot corners are clean and a jeweler's file to remove any burrs or rough spots in there.

No ammo just the bolts. I’m certain it is catching on that cam. It does not do it with that piece removed.

So I pulled that little cam piece off. It did have burrs on it.  Stoned it down a bit smoother. Not sure how much it will help. When it locks up the pin on the extractor does not drop down, it tries to go up and over the top.  Not easy to see but it happens right here

Attached File

Is that when the bolt is traveling to the rear?  The extractor isn't supposed to drop down until the bolt has gone all the way to the rear and has started coming forward again.  The cam is spring-loaded with that piece of music wire spring on the outside of the receiver, which I was not impressed with from a design standpoint.  It's supposed to provide enough force to keep the right side (as pictured) down and the left side of the cam up to insure that the extractor follows the top track on the way to the rear and then dips down into the bottom track on the way forward.

The extractor will probably stay in the top track if it's being cycled with ammo or dummies, as the friction of the round in the t-slot will help keep the extractor up where it needs to be.

Finally made it back to the range. Made up a trip for the LM7 bolt. Default trip was as close to zero as I could get. Sacrificed a set of feeler gauges to then shim it to where it ran the most reliably. Complete letdown. Would not even run in semi.

Swapped to the Razorback bolt ripped through a 200 round belt. Weird stoppage with 4 left. Slipped a new belt in and nothing. Sheared the roll pin that holds the plunger on the buffer. What a pain in the ass to get apart after that.

Will have to pull the firing pin and hand cycle some rounds with the LM7 bolt.  Can’t have one that doesn’t work.

Good luck with the LM7 bolt.  It never worked well in full-auto, probably because the nylon body made it too "bouncy".  Most LM7 owners bought a Razorback bolt and never looked back, as it was MUCH more reliable.

Well I think I may have found the issue. An issue at least. When I cut the A5 tube spacers my thinking was to allow for max bolt travel while ensuring the charging handle could not contact the rear of the slot.

The issue with that is approach was when in battery it left a gap between the rear of the bolt and the buffer. Running start at the buffer could not have been good for the roll pin.  It also allows the bolt to bounce back and slip off of the round.

Hope that answers how the pin broke and why the LM7 bolt will not even run in semi. Good thing I had a mile of that size emt laying around.

Well my search has been fruitless. Only Eric seems to be letting go of lakeside parts. On to having some parts made then. I have someone making a few aluminum charging handles already but I’m curious about barrels.

Has anyone had a blank machined to fit a LM7? Looks pretty straight forward. Green mountain blanks are reasonable. Turned to the correct diameter. Mill the end and mill the quick release slot. My guy is backed up with glock slides. Was curious if anyone has had it done.



Thanks.

New question then. Has anyone used a spray silicone or similar on the belts? I have some that run pretty well while others, not so much. Round is normally cocked sideways with belt bunched up. It looks like the extractor claw slipped off before it could pull it free.

I am having to use the tight belts Eric still has left. Pockets were opened up but seem to still be a bit tight.  

Thanks.

Made it back out.  I believe the belts that I regularly use are finally broken in. I didn’t have a single stoppage that was obviously belt related. Never had the belt bunched up with a round half extracted.

I did some experimenting with various parts.  Oddly it seems to run better with an unweighted buffer.  Lots of ten round strings then all stop. Hammer down with no bang.  This was with the LM7 bolt. I am hoping the sear timing is off just a tiny amount and I can get it dialed in. Longest run with zero issues was about a 100.

I tried running the Razorback bolt I picked up from Eric. Could not get a single round to fire. Just the faintest indication of a firing pin strike. I checked it against my other Razorback bolt and it is nearly .015 longer. Not sure what option I have there. Weld a bead on the firing pin head??

Pain in the ass.