Broke another bolt.... your thoughts??

[Cajuntransplant]

So went to the range today, was having a great time. Snapped another lug off a bolt in what was my last mag of ammo. Was a Maxim bolt this time so i'm asking if I'm doing something wrong with my setup as I read the Maxim bolts were some of the best. I swapped in my spare bolt head and was able to finish up the day with some shooting and a smile on my face so I've got that going for me. First bolt head I broke was from AlexProFirearms and they swapped it out for me, hoping Maxim might do the same but I'm not worried if they don't. Rifle was dirty, but I run suppressed so no worries there. The upper build is listed below. I shoot handloads... this range trip was 107TMK's and 123ELDM bullets in hornady brass, CCI 450 primers and ARComp powder. 107s are going 2600fps and 123s are going 2515fps. Rounds are loaded to book spec over all length and maybe one of every four or five has a slight ejector mark with new brass. All brass ejects out about 4 o clock. Trying to decide if I am running too hot or need to change something in my setup. What do ya'll think?? Bolt head is breaking same spot as the first one, the lug just next to the extractor.

Upper is aero precision with a satern machine 1-8 twist 5R barrel, 18", Mid-Length Gas
Has an adjustable gas block from superlative arms, silencerco omega suppressor
Bolt carrier group is nickel boron from Alex Pro Firearms
Bolt was Maxim Firearms
Standard buffer and JP flat spring

[A5BLASTER]

Maybe to hot on the handloads?

Maybe the can is creating to much back pressure for where the gas is set, allowing early unlock?

What chamber on that Saturn barrel?

Had a saturn/liberty barrel as my first grendel and it showed high pressure signs with Amax and sst factory ammo.

[A5BLASTER]

Any pressure signs on the ejected brass?

[Cajuntransplant]

I'm thinking it's got something to do with early unlock but how can I tell? Swap springs or adjust the gas block more? Original bolt that came with the barrel and the replacements I've gotten are all type 2. It shoots lights out and from the forum here it runs a little fast cause I shouldn't be seeing some of the speeds I get with 18" barrel and suppressor, but brass shows no pressure signs.

[Cajuntransplant]

Any pressure signs on the ejected brass?

Maybe one of every 5 or 6 off a rapid fire string has a very slight ejector mark is all. I found my pressure limits when I started my handloads and backed off my powder charges a bit to make them safer for year round shooting.

[A5BLASTER]

I'm thinking it's got something to do with early unlock but how can I tell? Swap springs or adjust the gas block more? Original bolt that came with the barrel and the replacements I've gotten are all type 2. It shoots lights out and from the forum here it runs a little fast cause I shouldn't be seeing some of the speeds I get with 18" barrel and suppressor, but brass shows no pressure signs.

You could try adding some tungsten weights to the rifle buffer and make it heavier.

If it is unlocking early going heavier will help stop that.

I would stay with the JP spring as it's a tad stronger then the basic rifle spring.

If that doesn't work let me know I have a spare jp scs you can try and see how it acts with it installed.

You could trying to turn down the gas as well.

[Cajuntransplant]

You could try adding some tungsten weights to the rifle buffer and make it heavier.

If it is unlocking early going heavier will help stop that.

I would stay with the JP spring as it's a tad stronger then the basic rifle spring.

If that doesn't work let me know I have a spare jp scs you can try and see how it acts with it installed.

You could trying to turn down the gas as well.

I might try to get a heavier buffer to try out. I'm running a carbine length buffer and tube with standard carbine weight and the JP flat spring. My first bolt broke when I was using the rifle length tube and standard weight buffer with JP spring though too. So maybe upping to a heavier buffer will help. Couldn't hurt any. Is there a way to tell if it is unlocking early at all? I might just save up a little to replace the bolt head with a nickel boron one from Maxim and get a heavier buffer and tune my gas block some. See if that helps it out. I know there's still a lot of gas coming back in the chamber area cause the brass and bolt carrier group is absolutely filthy even after a hundred or so rounds from a match. You can scoop the carbon out of the bolt carrier group at the end of the day.

[Klem]

Maybe one of every 5 or 6 off a rapid fire string has a very slight ejector mark is all. I found my pressure limits when I started my handloads and backed off my powder charges a bit to make them safer for year round shooting.

Your loads are hot. Both your loads are 100fps hotter than mine.

Too hot is the first things that stands out. It might also be that the bolt lugs are not all resting square against the barrel extensions lugs. That would mean only one lug is taking all the pressure. If this, then you need a new barrel.

I would drop your loads by 100fps and see how that goes before spending any money on the rest of the gun.

[A5BLASTER]

I might try to get a heavier buffer to try out. I'm running a carbine length buffer and tube with standard carbine weight and the JP flat spring. My first bolt broke when I was using the rifle length tube and standard weight buffer with JP spring though too. So maybe upping to a heavier buffer will help. Couldn't hurt any. Is there a way to tell if it is unlocking early at all? I might just save up a little to replace the bolt head with a nickel boron one from Maxim and get a heavier buffer and tune my gas block some. See if that helps it out. I know there's still a lot of gas coming back in the chamber area cause the brass and bolt carrier group is absolutely filthy even after a hundred or so rounds from a match. You can scoop the carbon out of the bolt carrier group at the end of the day.

Yea it's unlocking to early that's why it's so dirty.

Ok go to KAK website they sell the tungsten buffer weights two should bump your buffer weight up to H2 level and that will slow the unlock time down and let pressure drop to a safe level.

I would see if you can tune the gas down some more first before spending the 20 bucks for the weights and shipping.

I run lowmass parts with tuned gas from adjustable gas blocks and can put alot more rounds throw my set ups without coming close to being as dirty as what your' s is getting.

The can could be causing some of the dirty action as well, don't know for sure as I don't own any cans.

This is what I would do.

1. Try to turn the gas down more, if it still isn't working then
2 Add tungsten weights and bump the buffer weight up to h2 or h3 level
3. Maybe take the load down bout .03 grains and see what it does, if the first two things don't fix the issue.

[VASCAR2]

Did you lap the receiver face to ensure the barrel is square with the upper receiver? It has been speculated not being square can contribute to early bolt failure. More Velocity usually equates to more pressure, AR Comp hasn’t been used as much as other powders.

Another forum member broke a couple bolts running IMR8208XBR with 107 grain SMK. His loads exhibited the same trait as yours so it is possible with the chamber heat plus suppressor your adding additional pressure/bolt thrust.

I’ve never used any rifle length gas 18” barrels and I don’t know if this gas system plays well with suppressors. Others on the forum have more experience than I do with suppressors and maybe they’ll chime in.

[A5BLASTER]

Your loads are hot. Both your loads are 100fps hotter than mine.

Too hot is the first things that stands out. It might also be that the bolt lugs are not all resting square against the barrel extensions lugs. That would mean only one lug is taking all the pressure. If this, then you need a new barrel.

I would drop your loads by 100fps and see how that goes before spending any money on the rest of the gun.

Klem feel free to correct me but his speeds don't seem high at all when compared to my 18 inch jp barrels when shooting 123 grain eld-m factory and PF loaded 100 grain nbt ammo.

I have never shot the 107 smk or tmk in any caliber so not sure if his load is fast for it in the grendel.

[Cajuntransplant]

Your loads are too hot. Both your loads are 100fps hotter than mine.

Don't bother tinkering with the rest of the gun, just take your foot off the accelerator.

You have the same setup as mine?

Not trying to sound cocky but why is that your assumption? Using the shared quickload data here i'm under the powder charges for the bullets but i'm close to the velocities listed and I have no pressure signs on my brass except for the occasional swipe when it's hot and the gun is run hard. What speeds do you think I should be seeing then with a supressed 18" satern barrel for those bullets then that are safe? I should be 2400 and 2500 for the 123s and 107s? You think I just have a tighter chamber(?) maybe and the loads are too much?

[Cajuntransplant]

Yea it's unlocking to early that's why it's so dirty.

Ok go to KAK website they sell the tungsten buffer weights two should bump your buffer weight up to H2 level and that will slow the unlock time down and let pressure drop to a safe level.

I would see if you can tune the gas down some more first before spending the 20 bucks for the weights and shipping.

I run lowmass parts with tuned gas from adjustable gas blocks and can put alot more rounds throw my set ups without coming close to being as dirty as what your' s is getting.

The can could be causing some of the dirty action as well, don't know for sure as I don't own any cans.

This is what I would do.

1. Try to turn the gas down more, if it still isn't working then
2 Add tungsten weights and bump the buffer weight up to h2 or h3 level
3. Maybe take the load down bout .03 grains and see what it does, if the first two things don't fix the issue.

Thanks A5... Appreciate all the help!!

[Cajuntransplant]

Did you lap the receiver face to ensure the barrel is square with the upper receiver? It has been speculated not being square can contribute to early bolt failure. More Velocity usually equates to more pressure, AR Comp hasn’t been used as much as other powders.

Another forum member broke a couple bolts running IMR8208XBR with 107 grain SMK. His loads exhibited the same trait as yours so it is possible with the chamber heat plus suppressor your adding additional pressure/bolt thrust. Curiours where your spent brass is landing. If the brass is landing at 1-2 O Clock it sounds like you could still be over gassed.

I’ve never used any rifle length gas 18” barrels and I don’t know if this gas system plays well with suppressors. Others on the forum have more experience than I do with suppressors and maybe they’ll chime in.

No never did any lapping of any of my builds.... could be a hiccup with it I suppose but i've had this rifle a few years now I think and this has only started happening since I started running suppressed. But first bolt broke after a couple thousand rounds. This one after about 500-600 I think. I tried 8208 and didn't get the same consistency as ARComp and got a lot more pressure and didn't get same velocities without bad pressure signs.

All the brass lands at 330-4 oclock consistently.

[Klem]

Yea it's unlocking to early that's why it's so dirty.

Ok go to KAK website they sell the tungsten buffer weights two should bump your buffer weight up to H2 level and that will slow the unlock time down and let pressure drop to a safe level.

I would see if you can tune the gas down some more first before spending the 20 bucks for the weights and shipping.

I run lowmass parts with tuned gas from adjustable gas blocks and can put alot more rounds throw my set ups without coming close to being as dirty as what your' s is getting.

The can could be causing some of the dirty action as well, don't know for sure as I don't own any cans.

This is what I would do.

1. Try to turn the gas down more, if it still isn't working then
2 Add tungsten weights and bump the buffer weight up to h2 or h3 level
3. Maybe take the load down bout .03 grains and see what it does, if the first two things don't fix the issue.

With respect, it's dirty because he is running a can, not because it's unlocking early. Cans maintain barrel pressure for longer and as soon as the pressure drops enough for the case to contract all the smoke and crud is forced around the case back into the receiver. Even if you run a piston with a suppressor your receiver will be filthy. There is nothing he can do to prevent this apart from trying different suppressors and/or powders to lessen it.

Buffers springs and weights are not going to affect the peak pressure on the bolt lugs. They only influence the motion of the BCG when the lugs have unlocked and are no longer in contact with anything, including pressure.

He's tried two different bolts which means it's not a weak bolt. Sure, it could also be the lugs are not lining up properly but that ignores the obvious and simple reason...His loads are too hot.

[Klem]

You have the same setup as mine?

Not trying to sound cocky but why is that your assumption? Using the shared quickload data here i'm under the powder charges for the bullets but i'm close to the velocities listed and I have no pressure signs on my brass except for the occasional swipe when it's hot and the gun is run hard. What speeds do you think I should be seeing then with a supressed 18" satern barrel for those bullets then that are safe? I should be 2400 and 2500 for the 123s and 107s? You think I just have a tighter chamber(?) maybe and the loads are too much?

Cajun,

It's my assumption because I have an 18" barrel and have never cracked a bolt. You have cracked two. Your loads are 100fps more than mine. I am also familiar with reloading and suppressors. Sometimes the most obvious and irresistible inference is the right answer. My experience is that loads on this website are on average hot, in part encouraged by the Grendel having a relatively small boiler room for a 6.5. Let's also not forget that the AR15 is a relatively fragile action compared to bolt guns. It's less forgiving to pushing the envelope.

I have not used AR-Comp. When I read your post I opened QL and looked at what pressure it takes to reach your numbers and it is what it is, a hot load. What more can I say?

[Cajuntransplant]

Cajun,

It's my assumption because I have an 18" barrel and have never cracked a bolt. You have cracked two. Your loads are 100fps more than mine. I am also familiar with reloading and suppressors. Sometimes the most obvious and irresistible inference is the right answer. My experience is that loads on this website are on average hot, in part encouraged by the Grendel having a relatively small boiler room for a 6.5. Let's also not forget that the AR15 is a relatively fragile action compared to bolt guns. It's less forgiving to pushing the envelope.

I have not used AR-Comp. When I read your post I opened QL and looked at what pressure it takes to reach your numbers and it is what it is, a hot load. What more can I say?

Klem

Thanks a ton for the replies and your input. I was under the quickload load data info from the forum and without pressure signs I thought my loads were safe. If I only started popping the bolts since I started running suppressed what do you think? When I first built the rifle I ran a brake but tax stamp cleared and now it’s always suppressed. I run 27.5g of ARComp with the 123s and 28.3g with the 107s. Quickload shows those as too much pressure? I know the AR is definitely more fragile than a bolt gun for sure. And with the way the bolt head is cut out to make a grendel case fit makes it even more delicate. Might I ask what powders you run and velocities you get? Maybe I’ll just have to redo my ammo.

[Klem]

Cajun,

Pressure signs like ejector swipes and flattened/cratered primers are clumsy indicators of overpressure. When I used to shoot F-Class those of us shooting .223 would run pressures of around 95K lbs (SAAMI peak for 223 is 55K lbs). We could not get bullets to the furthest targets at 1,000yards and still be supersonic without it. The bolt gun actions we used were typical big, solid REM700's and upwards. The cases did not look too bad coming out after that amount of pressure and were fine to reload. We used 450primers because they were extra thick and hard. The firing pins were thinner and the holes were tighter than normal so no tell-tale cratering signs. The cases were supported by properly headspaced chambers so no bulges. My point is, the signs of overpressure in spent cases are subtle, and by then in an AR it's too late.

That suppressor adds a bit to the pressure but if it's cracking bolts it likely means you were already on the raggedy edge before you fitted it.

I use 8208 for bullets under 120 and H4895 for 120 and over.
For the 107SMK it's 28.5/8208 which is 2,513 - 2,527fps (depending on the ambient temperature).
For the 123ELD it's 27.8/H4895 for 2,429 - 2,434fps.

Lapua brass
2.24" OAL
CCI450 primers.
Radar chronographed.

I'm thinking if you can match those pressures in whatever powders you have it's not going to cost you any money. It's also the solution with the least effort. See how that goes and if it cures the symptoms (chipped bolts) then whatever the problem is, or was, is moot. If you get another chipped bolt then my money is on the lugs not being square, and that is a new barrel.

[Cajuntransplant]

Cajun,

Pressure signs like ejector swipes and flattened/cratered primers are clumsy indicators of overpressure. When I used to shoot F-Class those of us shooting .223 would run pressures of around 95K lbs (SAAMI peak for 223 is 55K lbs). We could not get bullets to the furthest targets at 1,000yards and still be supersonic without it. The bolt gun actions we used were typical big, solid REM700's and upwards. The cases did not look too bad coming out after that amount of pressure and were fine to reload. We used 450primers because they were extra thick and hard. The firing pins were thinner and the holes were tighter than normal so no tell-tale cratering signs. The cases were supported by properly headspaced chambers so no bulges. My point is, the signs of overpressure in spent cases are subtle, and by then in an AR it's too late.

That suppressor adds a bit to the pressure but if it's cracking bolts it likely means you were already on the raggedy edge before you fitted it.

I use 8208 for bullets under 120 and H4895 for 120 and over.
For the 107SMK it's 28.5/8208 which is 2,513 - 2,527fps (depending on the ambient temperature).
For the 123ELD it's 27.8/H4895 for 2,429 - 2,434fps.

Lapua brass
2.24" OAL
CCI450 primers.
Radar chronographed.

I'm thinking if you can match those pressures in whatever powders you have it's not going to cost you any money. It's also the solution with the least effort. See how that goes and if it cures the symptoms (chipped bolts) then whatever the problem is, or was, is moot. If you get another chipped bolt then my money is on the lugs not being square, and that is a new barrel.

Klem

Thanks again for all the info. I love learning from people that know more than me and have been doing this longer than I have. I looked through my load data and without suppressor I was actually even faster, by about 25fps on average depending on time of year. I’m guessing that adding the suppressor is compounding everything with the speeds and pressure I’m getting. Also to note I’m running faster than my friends rifle with almost same load data and he’s got a 20” barrel. Interesting to know about the pressure signs and how that when pressure shows at the casing it’s already too late. Never thought about it that way. Hoping I don’t have a bad barrel but I’m thinking the pressures are the cause and suppressor is adding to it and making the problem known.

[Klem]

Cajun,

Two more points...Unless your friend has drilled holes in his barrel it is physically impossible for your shorter 18" barrel to be faster than his 20", with the same ammo. At 18/20" we're talking about 50fps difference (roughly 25fps/inch). If your shorter gun is faster with the same ammo something is wrong with the measuring equipment or regime. You did say it's similar so it's not the same batch loaded by the same person. I am thinking for him to be slower than you his ammunition is milder and definitely not 'almost similar'. A grain or two makes a big difference when you are at the limit of the equipment. BTW, the loads I quoted above are not mild loads, they are on the edge of what I would call maximum.

Suppressors will never lower the velocity of your gun. Typically they add a few fps more due a phenomenon called 'freebore boost'. Suppressors are a containment vessel which allows expansion and cooling but still contains it. Even though the bullet is no longer sealed against the barrel walls there is still a bit more pressure behind the bullet as it passes through the suppressor than if it was the open air. This adds about 5fps more.