Is bolts beaking still a big concern now days with the 6.5 grendel?

[SG4247]

Properly made Grendel bolts are no problem.

Grendel extractors...is another discussion...

[LRRPF52]

Properly made Grendel bolts are no problem.

Grendel extractors...is another discussion...

Grendel bolts with .136" face depth and proper metallurgy/processes will last.

.125" bolt faces with whatever extractor is used will see early failure due to lack of lip material.

We even see that on the DPMS LR-308/AP4 which has a much wider extractor/more lip material.

You especially see it on poorly-designed bolts meant for 7.62x39 use, where the people specifying the bolt dimensions don't have complete guns in house to test in fleet.

There just isn't enough lip material there to pull the thicker case rim.

[The Profit Joseph Sith]

Grendel bolts with .136" face depth and proper metallurgy/processes will last.

.125" bolt faces with whatever extractor is used will see early failure due to lack of lip material.

We even see that on the DPMS LR-308/AP4 which has a much wider extractor/more lip material.

You especially see it on poorly-designed bolts meant for 7.62x39 use, where the people specifying the bolt dimensions don't have complete guns in house to test in fleet.

There just isn't enough lip material there to pull the thicker case rim.

I follow what your saying about the case rim but I'm a little confused about the lip reference. I don't get how a .125/.136" depth would change the thickness of the bolt material supporting the case head. bolts don't have a slight taper to their walls do they?

I'm also a noob here and had a few questions along these same lines so I'll ask them here as well. I guess first off I'll start with a new question I thought of reading all this. it's slightly off topic but related.

has anyone ever heard of barrel extension lug failures or is it standard practice to make the bolt weaker so it fails before that can happen? ive hardly hear people even mention barrel extensions at all. from what little research I did or could even find online from mfg's it looks like the majority are made from barrel steel's CrMo. and a couple may have been 9130. by in large though it's not advertised what people use on their barrels.

because of this very topic last week I emailed a local shop who sells a enhanced S7 bolt a lot like the SRC relia bolt and tried to sell them on the idea of making a saami spec grendel bolt for us. maybe kick off a GB if that would help convince them. anyway I realize this is a grendel forum but what do people think of those style of ”enhanced bolts" to me having a full profile lugs all the way around adds some stiffness and support to the bolt walls and help manage pressure.
has anyone seen or heard of those SRC relia-bolts breaking even though S7 is supposed to be significantly (somewhere around 30% I think it was) stronger?does running a piston setup exacerbate the lug breaking issue? seeing how there is no gas to aid in unlocking... I see tons of reputable makers suck as hk running pistons not to say they are directly comparable. seriously considering the superlative arms piston kits with AA bolt.

also does anyone use a SRC Relia bolt and have they had any issues with misfeeds/failure to feed? I would especially like feedback from high volume shooters who have more experience but all is welcome. while watching forgotten weapons on the HK-SL8 and how they modified the ONE bolt lug very similarly to that of ALL of the lugs of the relia bolt.
this modification of the lower bolt locking lug WAS SPECIFICALLY DONE TO FURTHER PREVENT WORKING WITH A DOUBLE STACK (STANDARD) MAGAZINES if anyone tried to circumvent the other magazine limiting features.
would be very ironic if the relia bolt turned out to be the unrelia-bolt.

interesting about the SR25 bolts... sounds accurate. shock is never good. and man those faxon bolts are SEXXXY!!! gotta bite my lip every time I see those.

sorry I'm perceptive and suck at writing so my posts are long and kinda hard to read.

[The Profit Joseph Sith]

I work for the DOD in the Small Arms development and modernization..... In fact I have some of the highest round count M9 pistols and M4s in the Army inventory right down the road on the wait list for swapping out.

I know the 5.56 bolt breakage numbers are vastly lesser than other caliber ARs... but, again I am new to the 6.5 Grendel arena.
I guess I was just looking for reassurance that 6.5 Grendel bolts now days are built to better specs than years past.
Thanks for the reply... good to know.

sounds like a fun/interesting job. answer is it's GTG, ready for DOD approval I'll call lake city for ya! would love to see the US lead the way and be the best equiped. we owe it to those protecting... I hope Russia doesn't beat us to it. not a fan at all of .223/5.56 7n6 is considerably better IMO. nice to see a few new grendel ammo flavors from shotshow this year as well.

anyway glad to see your here, welcome a'hoard captain!

[EPeterson]

I've never seen any broken AA bolts. I'm not worried about it personally either if you stick to fac loads or handloads that are within the load data like what's presented in the 6.5 reloading handbooks. I've broken a AA extractor though around the 1200ish count though. Some of those rounds were warmer handloads however, 123gr pills over 32gr of CFE. Used a can a lot as well.

[The Profit Joseph Sith]

so it's kinda sounding like a piston setup might actually help manage the robust gas impulse perhaps. definitely help with a can. not that I ever plan on running one unless hearing act passed along with maybe another bill or two. I'd love one, but I'd also love to be able to afford one!

[LRRPF52]

I follow what your saying about the case rim but I'm a little confused about the lip reference. I don't get how a .125/.136" depth would change the thickness of the bolt material supporting the case head. bolts don't have a slight taper to their walls do they?



has anyone ever heard of barrel extension lug failures or is it standard practice to make the bolt weaker so it fails before that can happen? ive hardly hear people even mention barrel extensions at all. from what little research I did or could even find online from mfg's it looks like the majority are made from barrel steel's CrMo. and a couple may have been 9130. by in large though it's not advertised what people use on their barrels.

because of this very topic last week I emailed a local shop who sells a enhanced S7 bolt a lot like the SRC relia bolt and tried to sell them on the idea of making a saami spec grendel bolt for us. maybe kick off a GB if that would help convince them. anyway I realize this is a grendel forum but what do people think of those style of ”enhanced bolts" to me having a full profile lugs all the way around adds some stiffness and support to the bolt walls and help manage pressure.
has anyone seen or heard of those SRC relia-bolts breaking even though S7 is supposed to be significantly (somewhere around 30% I think it was) stronger?does running a piston setup exacerbate the lug breaking issue? seeing how there is no gas to aid in unlocking... I see tons of reputable makers suck as hk running pistons not to say they are directly comparable. seriously considering the superlative arms piston kits with AA bolt.

also does anyone use a SRC Relia bolt and have they had any issues with misfeeds/failure to feed? I would especially like feedback from high volume shooters who have more experience but all is welcome. while watching forgotten weapons on the HK-SL8 and how they modified the ONE bolt lug very similarly to that of ALL of the lugs of the relia bolt.
this modification of the lower bolt locking lug WAS SPECIFICALLY DONE TO FURTHER PREVENT WORKING WITH A DOUBLE STACK (STANDARD) MAGAZINES if anyone tried to circumvent the other magazine limiting features.
would be very ironic if the relia bolt turned out to be the unrelia-bolt.

interesting about the SR25 bolts... sounds accurate. shock is never good. and man those faxon bolts are SEXXXY!!! gotta bite my lip every time I see those.

sorry I'm perceptive and suck at writing so my posts are long and kinda hard to read.

A shallower bolt face doesn't allow room for an extractor that has enough material in the lip, which is why .125" bolt face depths with 7.62x39 or 6.5 Grendel are prone to failure.

Extractors undergo a lot of stress as they try to pull the case from the chamber, so even a great design will suffer when processes aren't QC'd tightly in any self-loader.

The S7 tool steel used on the Relia-bolt encountered multiple failures in their first production run because they didn't have a handle on processes. S7 also is not a good choice for AR15 bolt alloy because of the elasticity modulus in extreme low temps, like in the Arctic or wind-chill encountered on your 4 wheeler when hunting up here in the mountains.

[LRRPF52]

so it's kinda sounding like a piston setup might actually help manage the robust gas impulse perhaps. definitely help with a can. not that I ever plan on running one unless hearing act passed along with maybe another bill or two. I'd love one, but I'd also love to be able to afford one!

An external piston is even harder on the gun and is a really bad approach to mitigating bolt stress.

The reason is that you have instantaneous carrier movement with an early 1900s op-rod piston design, compared to the superior Stoner Internal Expansion system of the AR15, which uses gas to fill a chamber formed by the back of the bolt, the gas rings, and the carrier to create carrier inertia. This slightly delays the rearward movement of the carrier.

On a primitive piston gun, the gas volume immediately hits the piston cup at the gas block, which then moves rearward with the carrier. The HK design steps backwards in many ways, all of which require an additional feature or gadget to counteract the change, which results in a complicated gun-the exact opposite of the Stoner Internal Expansion system.

Colt Canada's engineers have a lot of high speed camera evidence to justify sticking with the Stoner design.

[The Profit Joseph Sith]

awesome thank you VERY much for your input. something's you just don't think of but I love it when you hear stuff that makes absolutely perfect sense. the BCG's gas expansion chamber is what made me seriously start wondering about the piston systems. glad I asked these questions before wasting any money. never thought of the timing delay. awesome design when you realize it's brilliance. also makes things a lot easier for me as I'll just get all DI setups now.

I had a feeling that's what you were talking about with the "lip" I guess you were talking about the lip of the extractor. I figured you'd call the case rim the rim and the bolt face rim as such or something. it was just worded a little weird for me. I know you know your terminology slot better than me. thanks for clarification.

interesting about the S7 bolt, I was also curious if that "enhanced" shape they used causes any failures to feed/failure to strip from mags. it's funny how much hype there can be in this Industry.

[LRRPF52]

Here's what I mean about lip material and bolt face depths:

[mdewitt71]

awesome info ^^^^. Thanks

[Bisley]

I find it very odd how originally it was all about the bolt lugs breaking. And there was a bad batch that were incorrectly heat treated, and did have problems. Now that it is really no concern, we have gone to it being an extractor thing. All the while thousands and thousands of 7.62x39 chambers are sold every year with no problems.

At $80 just for a bolt, I will stick to the 7.62 bolt, which an entire BCG can be bought for $80, and continue to send thousands of rounds out of both my 7.62x39 as well as the .264LBC with zero problems. I prefer whiskey, and drink the "Kool-Aid" thanks.

[NugginFutz]

Well, I think it could be that two separate issues are being discussed, here. Broken lugs are the result of one issue, while the merits of the .125" vs .136" bolt face are another. Not mutually exclusive, but still two distinctly different issues. One does not necessarily predate the other, either. The bolt lug issue can (and has) still rear its head when someone comes across a defective bolt or has an alignment issue with their upper receivers and barrel extensions. The broken extractors have been an ongoing occurrence, but that is not to say that all of the x39 extractors are failing.

Several shooters here are using the .125" bolts to good effect, same as you. Good. Glad to know it. Not everyone has been as lucky as you, though. Reloaders, in particular, have borne the brunt of breakages.

But to level the "Kool-Aid" reference to Jim Jones, one of the worlds most notorious cult leaders, at someone like LRRPF52 is both unwarranted and thoughtless. There is a substantial body of evidence that has been presented here and on other boards which support the reasoning of both Colt and Alexander Arms decision to utilize the bolt and extractor geometry they did. This goes way beyond simple tribal support of one's chosen brand.

There is, as far as I can discern, no Kool-Aid being served in this thread.

[LRRPF52]

I find it very odd how originally it was all about the bolt lugs breaking. And there was a bad batch that were incorrectly heat treated, and did have problems. Now that it is really no concern, we have gone to it being an extractor thing. All the while thousands and thousands of 7.62x39 chambers are sold every year with no problems.

At $80 just for a bolt, I will stick to the 7.62 bolt, which an entire BCG can be bought for $80, and continue to send thousands of rounds out of both my 7.62x39 as well as the .264LBC with zero problems. I prefer whiskey, and drink the "Kool-Aid" thanks.

The after-market 7.62x39 bolts and extractors break on a regular basis because very few of the companies making them have ever tested the system in pyramid fashion with 10 rifles and 100,000rds in a developmental program. That costs too much money, so they just make bolts with an incorrect face depth, and resulting weak-lipped extractors that will break on you.

The only 7.62x39 bolts that have good longevity to them without peer are the LMT enhanced versions, but they still have .125" face depth and a thin lipped extractor.