How often do you replace your bolt?

[hatt]

After looking this (http://www.dtic.mil/ndia/2006smallarms/taylor.pdf#search=%22sopmod%22)it appears after 3000-6000 rounds a bolt could potentially go at any time.


Most Bolts Subjected to Harsh Firing Schedules Will Show Initial
Cracking Around 3,000 to 6,000 Rounds

On Milder Schedules, Nearly All Bolts Will Show Initial Cracking at
6,000 to 10,000 Rounds

Once the Crack Is Initiated, the Bolt May Fail at Any Time, or May
Last for Thousands of Rounds, Depending on Crack Propagation

[Robb Jensen]

I replace mine when they fail. I run my hard but probably not as hard as a selective fire Mk18.

[Don Robison]

Same here, I keep a spare on hand and run them till they fail.

[Harv]

Run them till they puke...and always keep a spare....
last bolt I had ran 12K before it broke...buy decent bolts that follow the TDP and you minimize the chance of premature failure....EVERYONES BOLTS WILL FAIL..... the trick is getting the ones that have a lower percentage of breaking....;)

[hatt]

I was thinking about duty/self defense guns with this thread. Waiting for the bolt to break sounds OK for fun/comp guns. It sounds a little late for a defensive weapon.

[mactastic]

Then go ahead and replace it every thousand rounds just to be sure, lol.


Replace it when it dies. Actually in my short, very boot-like, newbie amount of experience in the last 100k rounds or so I haven't seen one go down.

[Don Robison]

I was thinking about duty/self defense guns with this thread. Waiting for the bolt to break sounds OK for fun/comp guns. It sounds a little late for a defensive weapon.

I don't own any game guns. Every time you clean also give everything a good inspection. I've never had a catastrophic failure of a bolt. I've always found them cracked while inspecting and replaced them at that time.

[ddemis]

If you want a bolt to last a long time make sure you get a Lewis machine & tool bolt that has been Mag particle inspected. One of those babys should last you a good 20k rounds. If your buying a average one it will probaly puke out at 5k.

[hatt]

If you want a bolt to last a long time make sure you get a Lewis machine & tool bolt that has been Mag particle inspected. One of those babys should last you a good 20k rounds. If your buying a average one it will probaly puke out at 5k.

At the end of the report I cited there are numbers and e-mail addresses for the people who run Crane. You should contact them with this information on the LMT bolts.

[Safetyhit]

If you want a bolt to last a long time make sure you get a Lewis machine & tool bolt that has been Mag particle inspected. One of those babys should last you a good 20k rounds. If your buying a average one it will probaly puke out at 5k.


Sounds like good advice. Was recently wondering who was the best to go to for a new bolt. Thanks.

By the way, what does "mag particle inspected" mean?

[Stickman]

People aren't firing under "harsh" conditions with their semi-auto AR15s, and those people who are training and running real world conditions where "harsh" is routine, are having their unit armorers replace parts as needed.


On a side note, I would be interested in seeing what, if any units are replacing bolts at 3k as a matter of routine PMC.

[Heavy Metal]

It should be noted that longer gas system weapons do not have the proclivity to eat bolts the carbine gas system does.

That noted, I wonder how much of the .mil's harsh firing schedule issues are related to the uber-high pressure frangible ammo used for MOUT training?

[Don G.]

Content deleted.

[III]

It is best to replace a bolt and bbl. at the same time. Heavy suppressed and or short bbl. wear much harder but the bolt wears with the bbl extension and if you get up over 10,000 rounds I would recomend replacing both of these parts at the same time. If you get a premature bolt breakage checking headspace is always a good idea.

[Heavy Metal]

Mr. Knight,

You folks obviously have found a solution to the carbine bolt breakage issue. Can you share your observations on the issue of bolt breakage in the AR series and why it seems to happen so much sooner in the carbine length gas systems than the longer ones?

I assume you must have developed some useful observations during your years of testing and evaluation and would be grateful for any insight you might provide.

[III]

On a short bbl and with a can the pressures are much higher during the unlock phase of operation. As you remember the vietnam era carbine had a booster on the front to make the gun run.This booster was deemed a suppressor by ATF.14.5 was deemed the shortest bbl to give acceptable reliability without a booster. To get the 10in guns to run the gas port has to be opened up too far. The distance from port to bbl. end is also crucial becuase this is when all the work is being done.I feel it is stupid to design a gun around ammo that was made for an 18in bbl. We need 10 in bbl ammo first and then the gun can be properly designed around that ammo.
Many things can go wrong with a bolt during manf. especially during heat treat. We have gone to great efforts to make our E3 bolt as durable/reliable as possible .Changing this has made our bolt not backwards compatible. Any sharp edge on a part can lead to cracking so getting rid of as many sharp edges as possible helps. Material choice and manufacturing process is still the key.We have reports of 50,000 round life with certain materials . This is probobly overkill. A bolt does not really need to last longer than a bbl. (15,000 to 20,000 rounds). If a bolt lasts twice as long but costs twice as much is it really better?
I still think if we wan't a short gun we should start with a clean sheet of paper. "Hacking" up Mr. Stoners original rifle design and calling it flawed is not fair. We will never get optimum performance from the staight AR style mag. Building any system around this flawed magazine is a mistake. It is always such a conflict to make something new and still deal with the logistics of "in the system" (mags,ammo,etc.)
I know that is a lot of info and kind of rambling but I hope it helps in some way.

[Heavy Metal]

Thank you Mr. Knight,

I am sure you have seen the old saw about how the width of Roman roads determined future rail guages and rail tunnel widths thus limiting the diameter of the Space Shuttle's SRB's.

Once a standard becomes set and somewhat functional, it tends to become entrenched, sometimes in ways the original designers could never have imagined. We are, at times, prisoners of our previous successes.

[Failure2Stop]

III-

Your little insight there has greatly boosted my perception of your company and of your intent.

Thank you.

[watchluvr4ever]

Can switching from an AR15 bolt to a m16 one extend life?

[Robb Jensen]

Can switching from an AR15 bolt to a m16 one extend life?

The bolts are the same, the carriers are different.

[III]

I think you would have a hard time telling the difference between Colt parts used for military contract and those put into comercial/LE guns. Does Colt put a HF/CL bbl in say a 6920? I still think a company like Colt who builds 5000+ full auto US gov't guns a month is going to have a better handle on what it takes to do it right. One bad batch of bolts cost them alot as far as reputation and you can be sure they pay attention more than most companies. A company that does not build full auto rated parts doesn't even know what they don't know.
One thing I don't see many people doing is porting a bbl for suppressed fire only. If you run a can on a short bbl all the time the port size could be greatly reduced and the pressure curve foward of the port would last much longer . You could probobly cut a 14.5 in bbl down and leave the port size the same. I would like to be more clear about chamber pressure ;the pressure is not higher but opening the bolt while these pressures are still high is what causes the problems. Too fast of a cycle rate is also a big part of the problem. I have seen regular M4s go way over 1000 RPM(1100-1200) with a supressor installed. If someone is experiencing bolt breakages on a semi-auto non suppressed weapon under 5000 rounds something is very wrong.

[Safetyhit]

I have seen regular M4s go way over 1000 RPM(1100-1200) with a supressor installed.


I had no idea an M4 could run that fast. How do they hold up at rates like that, assuming the gun and parts are tier 1? I would expect you would see a slightly shorter life expectancy, but how much shorter?

[III]

Anything over 1000 Rpm is way too fast 750 is a good target range.Typically a can will add 100 RPM. The gun doesn't run well if slowed down too much either.I think 500 RPM is a perfect rate of fire but a AR type design will not run right if slowed down this much. I have never done it but there is an old wives tale that you can put a bolt in a lathe and spin it at a certain RPM the extractor will move out from centrifigal force. That is one reason we changed the pivot point on the E3 bolt to maintain more extractor spring pressure while the bolt is turning.Carrier velocity is the real thing to measure RPM is just an easy way to get a rough idea of carrier velocity; diff buffers can effect this in a way unmeasurable by RPM.

[toddackerman]

This is a great thread! Makes me want to go to Armorers School.

Since the discussion of preventative maintenance came up a few weeks ago, I have really started to pay attention to the details of "Wear and Tear" on my MRP upper. I always logged my rounds, but now have added "Other Categories" to my log I.e., Head Space checking etc. every 500 rounds because I am over the 3,000 round mark on the current bolt, and 6500 rounds on the current barrel.

One thing I noticed is that there has been no "Appreciable" wear as far as I can measure on the bolt/ barrel lug surfaces. The "Field Gauge" is far from being able to close on the bolt. I have always been very anal about the bearing surfaces of the lugs since being an Ex Benchrest shooter, and I have always used a high quality "Grease" (MD XF-7" on the bolt face where it contacts the barrel, and all of the lug surfaces, on the bolt and inside the barrel. I think this is working to prevent premature wear, but admittedly...It's my first serious endeavor to make the bolt and barrel last as long as I can, and measure the progressive wear. (MRP Barrels are $466...without a new bolt!)

I agree with everyone that "Quality Parts" are the way to get ahead of the "Wear and Tear" replacement/ failure issue. Both bolts I have are LMT. One in the gun, and one in the TD VFG. When the bolt in the gun goes, I will run the spare bolt making sure that it passes the Field Gauge test first. If it does, I'll run that bolt until it doesn't. I would hope that both bolts will pass the "Field Gauge" test for a combination of 15,000 rounds. I always check for stress cracks in the bolt since owning a BM upper years ago.

After that I will probably have to replace the barrel. I'm not as concerned about throat, land and groove wear as it relates to accuracy for this CQB setup as I am about excessive head space and the safety concerns involved. I hope the barrel, and chamber lugs will hold up to 15,000 rounds. I use mainly reduced practice loads (2900 FPS out of this 16" mid-length upper.) I am doing this to help preserve the life of the upper as well.

Thanks to the IP's who post here. It's grat that you share this knowledge with us.

Tack

[kidcoltoutlaw]

Does changing a bolt require re zeroing ? Is there a shift in your zero ?

Thanks, Keith

[RVTMaverick]

Does changing a bolt require re zeroing ? Is there a shift in your zero ?

Thanks, Keith

Hey Keith

I'm NO expert by any means, so I'll say this now that you know that, I do not see any possible way why a "Bolt/BCG" could change anyones ZERO....

Peace Jeff

[scooter22]

Does changing a bolt require re zeroing ? Is there a shift in your zero ?

Thanks, Keith

Jeebus. Thanks for the necro post.

And no, it does not.

[kidcoltoutlaw]

Thanks

[Doc Safari]

This is a good thread to bump to the top.

I've been searching some past threads and I don't remember if it was this forum or some other medium but I remember someone stating that changing the cam pin every 3,000 rounds or so (or more often if it's beat to heck) tends to lengthen the round count before you get cracks in the bolt.

Somebody help me out here....

[wanderson]

This is probably overkill. A bolt does not really need to last longer than a bbl. (15,000 to 20,000 rounds). If a bolt lasts twice as long but costs twice as much is it really better?

This^

[tom12.7]

I hate to add to old threads, but lifecycle testing is very much a real thing. If a component fails excessively early then that's obviously bad. What most folks do not consider is that a component that fails excessively past the lifecycle is also bad. Some say "how so?", that means the potential of more of the base cost could be attributed to this and it doesn't help the customer in any way. The component will not be reused and offers no value in the end to anyone, potentially higher manufacturing costs and higher user price aren't really good considerations for components in business. I would tend to prefer components that make the projected lifecycle pretty consistently, the way to do that is with a safety factor built in that satisfies the end user requirements without going overboard.
Requirements can be very different depending on many things. Meeting the expectations is the requirement, exceeding those may be out of the scope of the user.
The criteria demands certain results, excessively exceeding that criteria means that the cost of getting to that point could be too high compared to another that just meets the users criteria, it's a balance.