Broken bolts- thing of the past?

[LR1955]

I broke two bolts on the same day loading 27.2 grains of 8208XBR behind a 123 grain Lapua Scenar with a CCI BR4 primer and Lapua brass. After that I pulled the bullets and checked the power weight. That load had been fine for me all summer but spiked badly on a hot afternoon in August. I've seen posts on this forum with hotter loads that that on this site. If you push the pressure in a grendel you are bound to break a bolt eventually.

rwh;

Personally, I believe it is basically not enough steel on the bolt when using a fat cartridge like a Grendel. Wish it wasn't so but you get to the point where you can't remove any more metal or even the slightest variation in something breaks the part. So guys spend a lot of effort ensuring everything is absolutely perfect when they build a Grendel upper and those uppers work but I dare say that no matter what you do with one, it will not last half as long as a average rack grade 5.56 bolt. I have come to the conclusion that those are the facts and if you want to enjoy a Grendel, have a spare bolt ready to go.

LR55

[sneaky one]

CMMG came up with the larger bolt concept for the Grrr. It's called the Anvil. Re designed upper inside dimensions.

They use a version of the AR 10 bolt. I think DTech uses a version of that bolt in his WSSM calibers also.

Mike Milli, owns Dtech. I'm still looking to go visit him while he makes me a 6.5 WSSM.

He's a 1 man show at his shop in Northern Minnesota.


Gotta find some brass.


For the Grrr, stay just under max loads for bolt longetivity, and accuracy.

[montana]

Colt made a larger variant for the Yemeni military back in 2014 in 7.62X39. The comparison between a standard 5.56 bolt and the larger 7.62X39 bolt starts at the 5.2 minute mark.https://www.youtube.com/watch?v=xovdRJYg_-o

[montana]

Here is a new desighn for the AR bolt:

Young Manufacturing is the licensed manufacture of the HMB bolt.https://youngmanufacturing.net/product/hmb-bolt/ [url]
The HMB Bolt by HM Defense eliminates the pass through cam pin hole and replaces it with a cam pin socket and radiused cam pin design. The new patented design eliminates the natural weak point of Mil-Spec bolts by significantly increasing the amount of metal (and strength) at the cam pin location. The result- NO MORE BROKEN BOLTS!

The HMB Bolt also reduces contact between cam pin and firing pin, enabling smoother operation of firing pin, bolt lugs and aft gas rings. The new cam pin socket also retains lubrication for extended operations.

And not staking the gas key:

https://youngmanufacturing.net/staking-the-gas-key-on-the-ar-15-and-m-16-carrier/

[A5BLASTER]

Here is a new desighn for the AR bolt:

Young Manufacturing is the licensed manufacture of the HMB bolt.https://youngmanufacturing.net/product/hmb-bolt/ [url]
The HMB Bolt by HM Defense eliminates the pass through cam pin hole and replaces it with a cam pin socket and radiused cam pin design. The new patented design eliminates the natural weak point of Mil-Spec bolts by significantly increasing the amount of metal (and strength) at the cam pin location. The result- NO MORE BROKEN BOLTS!

The HMB Bolt also reduces contact between cam pin and firing pin, enabling smoother operation of firing pin, bolt lugs and aft gas rings. The new cam pin socket also retains lubrication for extended operations.

And not staking the gas key:

https://youngmanufacturing.net/staki...-m-16-carrier/

That's perrty cool thinking. But how would that make the bolt lugs stronger and less prone to breaking?

I think what they mean is it helps prevent bolt problems at the cam pin hole.

[montana]

That's perrty cool thinking. But how would that make the bolt lugs stronger and less prone to breaking?

I think what they mean is it helps prevent bolt problems at the cam pin hole.

That's what it meant, it would take a bigger bolt to stop the lugs from breaking.

[SHORT-N-SASSY]

rwh;

Personally, I believe it is basically not enough steel on the bolt when using a fat cartridge like a Grendel. Wish it wasn't so but you get to the point where you can't remove any more metal or even the slightest variation in something breaks the part. So guys spend a lot of effort ensuring everything is absolutely perfect when they build a Grendel upper and those uppers work but I dare say that no matter what you do with one, it will not last half as long as a average rack grade 5.56 bolt. I have come to the conclusion that those are the facts and if you want to enjoy a Grendel, have a spare bolt ready to go.

LR55

And, in addition to the CMMG Anvil, as pointed out by sneaky one, the up-coming Faxon Firearms ARAK-21 6.5mm Grendel:


< https://www.65grendel.com/forum/show...l=1#post108197 >

[centerfire]

I've said it before but it bears repeating, once you take the Grendel out of the AR15 the cartridge loses its appeal quickly. Either make it work in the platform or find another cartridge. Redesigning the platform around the Grendel is a fool's errand. The Anvil might be the exception but unless they make the barrel extensions open source you're stuck with low quality barrels. My AR308 shoots every bit as well as my AR15 Grendel, 6.5CM is very workable in a platform close to the size of a Grendel without any proprietary parts.

[LR1955]

And, in addition to the CMMG Anvil, as pointed out by sneaky one, the up-coming Faxon Firearms ARAK-21 6.5mm Grendel:


< https://www.65grendel.com/forum/show...l=1#post108197 >

SAS:

Does this mean that one can now take the Grendel above the '55k' level without something blowing apart or breaking? If so, this is a major improvement.

LR55

[A5BLASTER]

SAS:

Does this mean that one can now take the Grendel above the '55k' level without something blowing apart or breaking? If so, this is a major improvement.

LR55

Link is dated 2015.

[SHORT-N-SASSY]

rwh;

Personally, I believe it is basically not enough steel on the bolt when using a fat cartridge like a Grendel. . . .

LR55

LR55,

The respective Bolt designs of the CMMG Anvil and upcoming ARAK-21 satisfy the larger Bolt concept for the 6.5mm Grendel cartridge (Case Rim Diameter: 0.447"), compared to the 5.56x45mm cartridge (Case Rim Diameter: 0.378").

[brian y]

Getting close to 4k down my Odin Works barrel with an Odin Works bolt and no problems.

[biodsl]

Broke a bolt yesterday. I was shooting my usual loading of 31.2grs of CFE223 under a 123 Nosler CC @2.245"

I don't know the manufacturer of the bolt. I've been using it so long I just can't remember where I got it. I have at least 4,000 rounds on it.

It has been replaced with a Monster Mk136 bolt!

BrokenBolt.jpg

[lazyengineer]

Broke a bolt yesterday. I was shooting my usual loading of 31.2grs of CFE223 under a 123 Nosler CC @2.245"

I don't know the manufacturer of the bolt. I've been using it so long I just can't remember where I got it. I have at least 4,000 rounds on it.

It has been replaced with a Monster Mk136 bolt!

[ATTACH=CONFIG]19300[/ATTACH]

Thanks for the update. I'm not familiar with the 4 radial grooves cut into the bolt body, that go around it like that. Does anyone else know what brand that likely is?

[41bear]

Thanks for the update. I'm not familiar with the 4 radial grooves cut into the bolt body, that go around it like that. Does anyone else know what brand that likely is?

That's a Maxim Bolt, pictured here.

http://www.maximfirearms.com/online-store/complete-6mm-arc-advanced-rifle-cartridge-bolt/