why would bolt break?

[LRRPF52]

Make sure you're wearing ballistic eye protection when using an inertia puller (looks like a hammer). I had a primer detonate on me once, and it was a surprise.

[dammitman]

Make sure you're wearing ballistic eye protection when using an inertia puller (looks like a hammer). I had a primer detonate on me once, and it was a surprise.

i have thrown that piece of crap away,,,,the RCBS collet puller is the only way to go! no hammering and no damage to anything.

[dammitman]

i have already noticed on some brass that the primer flash hole is considerably bigger on the PPU brass than anything else. now this does mean something as i have loaded rubber bullets before in 44 magnum brass and part of the loading ws enlarging the primer flash hole. included in those instructions was the warning that mixing up these modified brass and loading them with actual bullets and loads could cause extreme pressures and death or worse turn you into a liberal democrat! so looking at these brass with the much larger flash hole and then installing CCI magnum primers i would really lean toward a decent increase in pressure. really isnt ruling out anything else at all but its a start,,,,,my only problem so far is the case capacity being equal and the load really wasnt that hot ,,,,

[mongoosesnipe]

You're using a solid that likely isn't filling the brass consistently. Try using water, all from the same source. You'll just need to tape over the primer hole.

using a solid (powder) to measure volume (powder capacity) is a perfectly acceptable way to cheek case volume as the same solid was used for each sample and it not like said solid is marbles where there could be large voids in it and measure case capacity with water is messy and since the cases don't get loaded with water (liquid) they get loaded with powder (solid)

also what different sources are you getting your water from that it is having that much influence on your measurement the temperature of the water will more likely cause a greater fluctuation in measurement of volume , also taping over the primer pocket allows the primer pocket to fill with water which is not part of the case capacity and the different volume of large and small primer pocket would have more error than different sources of water, but for maximum accuracy you should use pure water at 4 degrees c (maximum density of water)and take all of your measurements at sea level (to prevent errors from variations in gravity) then measure 100+ cases from each head stamp and take the mean volume fore case capacity and obviously you will want to eliminate statistical outliers while keeping to a 95% confidence interval.... if you actually finished reading all that i was being a little facetious differences are more likely to pre present because 2 of the case are fire and one is not and it i t unknown if the 2 fired case have been sized...

[Tedward]

That was a breath full....

[cory]

using a solid (powder) to measure volume (powder capacity) is a perfectly acceptable way to cheek case volume as the same solid was used for each sample and it not like said solid is marbles where there could be large voids in it and measure case capacity with water is messy and since the cases don't get loaded with water (liquid) they get loaded with powder (solid)

also what different sources are you getting your water from that it is having that much influence on your measurement the temperature of the water will more likely cause a greater fluctuation in measurement of volume , also taping over the primer pocket allows the primer pocket to fill with water which is not part of the case capacity and the different volume of large and small primer pocket would have more error than different sources of water, but for maximum accuracy you should use pure water at 4 degrees c (maximum density of water)and take all of your measurements at sea level (to prevent errors from variations in gravity) then measure 100+ cases from each head stamp and take the mean volume fore case capacity and obviously you will want to eliminate statistical outliers while keeping to a 95% confidence interval.... if you actually finished reading all that i was being a little facetious differences are more likely to pre present because 2 of the case are fire and one is not and it i t unknown if the 2 fired case have been sized...

Is it acceptable sure, but when you're comparing cases with minute difference in volume you want to use an incompressible liquid.

Otherwise you get an all but identical measurement as we see has happened.

If we're comparing 5.56, 6.5 Grendel, and 308 case, using powder is a great way to do that and get a good idea of the difference.

I do agree with the PPU large primer pocket throwing the numbers off. I don't know if it give a tight enough fit, but you could use a SPENT primer and put it in upside down. Otherwise, wax will likely be your best option.

Now if you'd like to do a true analysis with 100+ cases be my guest, but I can't say I care enough for that exact of an answer. haha

Mineral content in water can vary relatively drastically, which changes the mass of an inch cube sample. If you ever notice some water tastes different from other water, that's because it is different.

[LR1955]

I just went and measured some case capacities between 3 different types of cases:

* PPU 37.5gr of CFE to the neck (raw capacity, not possible to load)
* Hornady 1 x fired 37.0gr CFE to the neck
* Lapua unfired 37.0gr to the neck

I thought the PPU brass had noticeably less case capacity last time I measured it. Something weird is going on. Maybe your bolt was prone to cracking, especially if the receiver face is off-kilter. Check that before you use the new bolt. It has happened before. The receiver face needs to be true where it mates with the barrel extension flange. Is this a complete Les Baer upper?

LR52:

Nothing weird is going on. There is not enough of a difference between the PPU brass and Lapua brass to shear lugs in six shots. If Alexander still has his load data for the PPU brass posted, you will see the loads are identical to the Lapua brass. Differences are in the .1 grain range.

The problem is the bolt on the Grendel is not strong enough to take repeated poundings from max loads of any powder / bullet combination. Unlike the 5.56, 6.8 etc, there is not enough steel to support the lugs when it is hit over and over again with a strong impulse.

I have sheared seven or so lugs off of bolts ranging from very well made 7.62 X 39 through Grendel bolts. My theory is 30 grains of 2520 and a 120 grain range bullet is too much for the lugs after maybe 1K rounds. Back it off to 28 grains and the bolt will probably last a long time but the velocities will suck so badly that any wind will be big problems at distances from 300 and beyond.

So, no need to give much thought to this issue. It is common and is the single biggest weakness to the Grendel. A bigger, more stout bolt is needed if someone is to shoot max charges exclusively.

LR1955

[Tedward]

I guess the next question is what kind of Bolt was being used? Was is a Carpenter 158 Steel Bolt or the 9310? I think that might make the difference in life too. I think the new and improved A.A. bolt is made from 9310.

Please correct me if I'm wrong but I think that was one major request made to Maxum for his bolts he is making now.

Thanks

[cory]

Hence forth the need for an AR12. To bad woohoo won't make us anymore of those beefed up bolts and extensions.

[dammitman]

I think lr1955 is right on. As i said i have 2 more bolts coming from les baer. Just too hot a load for the bolt. I would love to chrono graph what it is. I wonder what the bolts made from? Would a titanium bolt be better?

[pinzgauer]

too many variables to declare this a defective bolt design...

- Seating depth? Is the bullets to far in the lands and increasing pressure? This can make much more of a difference than .5 grain case capacity difference
- Bolt steel & mfg? Not all bolts are the same. Even 5.56 bolts have a fixed service life carpenter 158 lasts longer than 9130 or lesser steels
- The Barrel/Barrel extension machining can also make a difference. Was it also LBC?

Not saying it was not a hot load, just that there are many grendels shooting full power loads with reasonable bolt life. Shoot too-hot loads, and you will reduce that service life. Have a machining or alloy issue and it can be much shorter.

There is a reason the TDP (gov spec) requires Carpenter 158 with Mag Particle Inspection. (and proof test, though that actually reduces bolt life).

[Tedward]

too many variables to declare this a defective bolt design...

- Seating depth? Is the bullets to far in the lands and increasing pressure? This can make much more of a difference than .5 grain case capacity difference
- Bolt steel & mfg? Not all bolts are the same. Even 5.56 bolts have a fixed service life carpenter 158 lasts longer than 9130 or lesser steels
- The Barrel/Barrel extension machining can also make a difference. Was it also LBC?

Not saying it was not a hot load, just that there are many grendels shooting full power loads with reasonable bolt life. Shoot too-hot loads, and you will reduce that service life. Have a machining or alloy issue and it can be much shorter.

There is a reason the TDP (gov spec) requires Carpenter 158 with Mag Particle Inspection. (and proof test, though that actually reduces bolt life).

Agree to your post except the last part. The Govt does not use the Grendel therfore has no need for the 9310. if it is better or worse I have no clue but AA uses it for some reason.

[cory]

... Would a titanium bolt be better?

I think the question your asking is whether a titanium bolt would be a viable solution. Maybe, but you'll pay at least as much for that bolt as you will for your barrel, likely more.

Titanium is much stronger than steel and therefore incredibly difficult to machine.

IMHO you'd be money ahead to redesign the bolt and extension to round off the sharp edges on the bolt. Have you ever wondered why the bolt always fails at the lugs? It's because they designed it with the 90 degree angles. That's the weak point in the design.

A round structure is stronger than a square structure. I believe it was the Romans who discovered this. Since then we've come to learn that stress concentrations are significantly higher in sharp edges.

All that being said the locking feature in the bolt and extension is critical to operation. I'm not sure how large of a radius is possible, but I assure you it's greater than the r~0 in the design as it stands.

[bwaites]

I think the question your asking is whether a titanium bolt would be a viable solution. Maybe, but you'll pay at least as much for that bolt as you will for your barrel, likely more.

Titanium is much stronger than steel and therefore incredibly difficult to machine.

IMHO you'd be money ahead to redesign the bolt and extension to round off the sharp edges on the bolt. Have you ever wondered why the bolt always fails at the lugs? It's because they designed it with the 90 degree angles. That's the weak point in the design.

A round structure is stronger than a square structure. I believe it was the Romans who discovered this. Since then we've come to learn that stress concentrations are significantly higher in sharp edges.

All that being said the locking feature in the bolt and extension is critical to operation. I'm not sure how large of a radius is possible, but I assure you it's greater than the r~0 in the design as it stands.

Interestingly enough, Titanium has been tried. Its not so prohibitively much more cost wise that it would make much difference, and machining Ti has come a long way, thus you now see flashlight bodies made from the stuff! However, its mechanical properties are such that it really isn't any huge improvement. The very hardness that makes it so good for some uses makes it not so great for bolts.

There are probably some Ti alloys that would work, but for the cost of researching those alloys and testing them, it doesn't make much sense economically.

The rounded lug design has been used, and I think it may be patented. I remember there was some controversy over that a few years ago.

[dammitman]

I really didnt think ti was needed. I like the suggestion about touching up the sharp edges on the bolt lugs. Anyone have more on this as to dos and donts.
By the way this is a shilen built barrel and i had the origional bolt sent to shilen. I hope these replacements will drop in for use