Bolt over base in new LMT MRP

[mark5pt56]

If live, it's in the magazine.

My error for not clarifying this.

Bolt over, aka bolt over ride is the live never came out of the magazine, sometimes complete over ride without catching it, others when it catches about half of it, putting that gouge in the body, sometimes shoulder/neck.

Brass over bolt is when you can get the live or spent ON TOP of the bolt between the ch/bolt

If yours is the latter and a live, magazine.

If it's the former, still can be a mag on top of the other issues discussed so far. bottom line, bolt speed is to fast

[Pappabear]

I went through this with a new KAC rifle. It came down to the 20 round Colt mags or older Pmags. I installed a Vltor A5 buffer now it doesn't matter what mag. Not sure this will fix your issue, but an A5 never hurt anything IMHO.

PB

[MistWolf]

MistWolf - anyway I can test this?

Make new springs and install them. That's how I tested it. Don't forget to count the coils of the old springs. The new ones have to be that many coils and maybe a couple more.

[Rifleman_04]

The extractor of the LMT E-Bolt uses two extractor springs. The two springs are smaller in diameter and longer in length than the standard extractor spring. All too often, the LMT springs are under powered, leading to extraction issues that cause bolt overs. To fix the extraction issues with the LMT E-Bolt I have, I had to make new extractor springs from a take down pin retainer spring. If you do make new springs, don't simply cut them to the same length as the originals. Count the coils and compare the lengths. Add a couple of coils if needed to make the replacement springs just a little bit longer. Not too many extra coils or the springs will bind up.

There is absolutely nothing in this thread about failing to extract.

Also this is a ridiculous fix for a non issue. I can’t believe this wasn’t called out earlier. I hope nobody read this and hacked up springs from a clicky pen to “fix” their enhanced bolt.

Eta: and extraction issues don’t cause bolt over base malfs. A bolt over base malfunction is when the bolt carrier group outruns the magazines ability to get the next round up or the bcg short strokes. Overgassed(not likely with LMT), undergassed, magazines, or buffers and action springs are the cause.

[MistWolf]

There is absolutely nothing in this thread about failing to extract.

Also this is a ridiculous fix for a non issue. I can’t believe this wasn’t called out earlier. I hope nobody read this and hacked up springs from a clicky pen to “fix” their enhanced bolt.

Eta: and extraction issues don’t cause bolt over base malfs. A bolt over base malfunction is when the bolt carrier group outruns the magazines ability to get the next round up or the bcg short strokes. Overgassed(not likely with LMT), undergassed, magazines, or buffers and action springs are the cause.

Is that right?

The LMT bolt I had did indeed have failures to extract which manifested as bolt over the base of the cartridge next in the magazine. Why does a failure to extract manifest itself as a bolt over? Because the extractor loses control of the rim of the spent case. When that happens, the ejector cannot eject the empty. When the rifle attempts to feed a fresh round from the magazine but the empty case is still in the action. This brings the fresh round to a sudden halt before it's stripped from the magazine and the bolt rides up over the rim. Usually, the spent case is also caught in the action. Sometimes, it gets pushed out of the ejection port after causing the bolt over.

But couldn't the bolt over be caused by short stroking? No, it cannot. The bolt going forward cannot get a grip on the next round in the mag until it's completely behind the rim.

Ok, what about carrier speeds being so high it outruns the magazine? With modern magazines, it's unlikely, especially in a semi-auto AR. I built a pistol AR that had a grossly oversized gas port. Carrier speeds were so fast that the impact against the hammer sent a sharp sting through the trigger to my finger. Yet the AR never had any bolt overs.

Finally, the extractor springs were the issue with my LMT Enhanced Bolt. It caused failures to extract which lead to bolt overs. The bolt was given to me by a friend because he could not get it to work. He had the same problems. When I looked it over, it turned out the extractor spring tension was almost non-existent. Go read Grant's thread on tuning an SBR to run suppressed and unsuppressed. He had problems with the LMT Enhanced bolt.

Recently I dug the bolt out to see what I could do to fix it. The extractor springs were identical to the take down retainer pin spring except the LMT extractor springs were shorter. If cutting down the take down retainer pin springs to use as extractor springs is a "hack", it's the same hack LMT used without success. No "clicky-pens" lost their lives to fix the extraction problem the LMT Enhanced bolt had.

However, cutting down two take down retainer pin springs fixed the extraction problem. No more failures to extract, no more bolt overs during however many hundreds of rounds I've shot through that upper since the fix.

I've had bolt overs in other ARs. Wanna take a guess what fixed the problem in each case? That's right, replacing a weak extractor spring. I've helped other AR owners troubleshoot and fix bolt overs Wanna take another guess as to what the fix invariably was in each case?

Wanna guess what things did not fix the bolt over problems? Smaller gas ports, heavier buffers, new action springs or different magazines.

[Rifleman_04]

Is that right?

The LMT bolt I had did indeed have failures to extract which manifested as bolt over the base of the cartridge next in the magazine. Why does a failure to extract manifest itself as a bolt over? Because the extractor loses control of the rim of the spent case. When that happens, the ejector cannot eject the empty. When the rifle attempts to feed a fresh round from the magazine but the empty case is still in the action. This brings the fresh round to a sudden halt before it's stripped from the magazine and the bolt rides up over the rim. Usually, the spent case is also caught in the action. Sometimes, it gets pushed out of the ejection port after causing the bolt over.

But couldn't the bolt over be caused by short stroking? No, it cannot. The bolt going forward cannot get a grip on the next round in the mag until it's completely behind the rim.

Ok, what about carrier speeds being so high it outruns the magazine? With modern magazines, it's unlikely, especially in a semi-auto AR. I built a pistol AR that had a grossly oversized gas port. Carrier speeds were so fast that the impact against the hammer sent a sharp sting through the trigger to my finger. Yet the AR never had any bolt overs.

Finally, the extractor springs were the issue with my LMT Enhanced Bolt. It caused failures to extract which lead to bolt overs. The bolt was given to me by a friend because he could not get it to work. He had the same problems. When I looked it over, it turned out the extractor spring tension was almost non-existent. Go read Grant's thread on tuning an SBR to run suppressed and unsuppressed. He had problems with the LMT Enhanced bolt.

Recently I dug the bolt out to see what I could do to fix it. The extractor springs were identical to the take down retainer pin spring except the LMT extractor springs were shorter. If cutting down the take down retainer pin springs to use as extractor springs is a "hack", it's the same hack LMT used without success. No "clicky-pens" lost their lives to fix the extraction problem the LMT Enhanced bolt had.

However, cutting down two take down retainer pin springs fixed the extraction problem. No more failures to extract, no more bolt overs during however many hundreds of rounds I've shot through that upper since the fix.

I've had bolt overs in other ARs. Wanna take a guess what fixed the problem in each case? That's right, replacing a weak extractor spring. I've helped other AR owners troubleshoot and fix bolt overs Wanna take another guess as to what the fix invariably was in each case?

Wanna guess what things did not fix the bolt over problems? Smaller gas ports, heavier buffers, new action springs or different magazines.

You are either confused or really don’t know what you are talking about. You have your malfunctions mixed up and your post is a soup sandwich.

[MistWolf]

Yep. That's gotta be it. Enjoy your lunch.

[Rifleman_04]

Yep. That's gotta be it. Enjoy your lunch.

The first malfunction you described is a failure to eject so you still don’t know what a bolt over base malfunction is or what you are talking about. You are spreading mis information on an open forum that used to be known for good info. Go do some research.

[17K]

It comes from the pistol side where most everyone incorrectly calls a FTExtract a double feed.

[sig1473]

The two springs are smaller in diameter and longer in length than the standard extractor spring. All too often, the LMT springs are under powered, leading to extraction issues that cause bolt overs. To fix the extraction issues with the LMT E-Bolt I have, I had to make new extractor springs from a take down pin retainer spring.

I didn't want to chime in but there is some wrong info right here. The 2x LMT extractor springs are not similar to the take down/pivot springs. They do not have the same rigidity. I would advise against making your own out of these. They appear closer/if not exact to regular ejector/safety select springs. I took a pic of the springs in question. I'll let you be the judge.

Top: Ejector/Safety select spring
Middle: LMT enhanced extractor springs
Bottom: Take down/pivot spring
Attachment 54138