Design of bolts for ARs

[LRRPF52]

From my understanding, the extensions are the same dimensions, but held to tighter tolerances so there is no intrusion into the ID with the teeth.

I don't remember what method was used to cut the ramps. I talked with Bill about it, and I know it's something he has worked out to avoid the extractor binding issues.

I also learned something about extension dimensions that I didn't know was there all along. It helps to have the TDP when navigating parts sourcing.

[SHORT-N-SASSY]

. . . If AA was to have used a different upper, different extension, etc., it would have placed the Grendel in an even less accessible manufacturing posture, and these parts would be bottle-necks in the supply chain.

The decision to use as many AR15 parts makes the cartridge more accessible to consumers. Keeping the pressure at 50,000 psi mitigates the issues one would run into if they were exceeded. In the end, the BC and SD does more than enough to make up for initial muzzle velocity, which is fine where it is. . . .

First things, first: Nice Elk! One shot, one kill --- a responsible hunter.

LRRPF52, re your statement, above, you'd make a great car saleman. Personally, I prefer the model you were selling in the "Grendel Evolution" Thread, Reply #44, ". . . What needs to happen is for a new gun to be built around the cartridge, rather than trying to stuff .260 performance into a rifle that was literally built around the 50,000 psi .222 Remington. . . ." --- not to mention the increased Bolt Thrust resulting from the larger case diameter of the 6.5 Grendel cartridge.

[woohoo]

Are you saying the feed ramps have something to do with the extractor binding? The feed ramps are at 6 O'clock and the extractors pass through 45 degrees off TDC or 1:30. How do they effect anything to do with the extractor?

I have a feeling you have a big 55 gal drum with AA stenciled on the side as a coffee table. A straw stuck in there and your computer on top. Possibly a red phone with a direct line to the bat cave. Long term exposure to certain elements can cause heath issues. lol

[LRRPF52]

That was under the premise where people were trying to get .260 performance out of the AR15. At the end of the day, there are significant trade-offs.

* More muzzle velocity = more case volume necessary, as you can only do so much with pressure, which has diminishing returns in performance, with increasing returns in penalties that aren't worth it.

* The 6.5 Grendel as it is finds a balancing place between performance (name me one factory chambering that out-classes it in the AR15), and ability to be manufactured

* As soon as you expect more performance from the cartridge that very few have even pushed to the limits currently, you sacrifice the benefit of parts commonality.

I'll give you a personal example. I have always considered my little 16" Grendel carbine a 700yd maximum effective range system with the 123gr Hornady A-MAX, 123gr SMK, or 123gr Scenar, for hitting man-sized targets. Only because of a dare, I realized that I was short-changing it by 500yds in summer conditions here in the mountains. I found that I was able to predictably and consistently hit such a target at 1200yds, as fast as I could break the trigger.

I already knew that I smoked 5.56 77gr at 600yds, but didn't realize I was staying supersonic out to over 1300yds until a situation led me to stretch the legs way farther than I normally would have. Granted, at sea level, I would be limited to 1050yds at 59 F. That's with the factory Hornady 123gr A-MAX from a 16" carbine, going 2470fps.

What kind of performance are you needing again, and what are you willing to sacrifice to get it?

[SHORT-N-SASSY]

. . . * The 6.5 Grendel as it is finds a balancing place between performance . . .

Why is the word, "Balance," used so often on the 6.5 Grendel Forum? It's hardly seen on others. Isn't it just possible that Colt Competition Rifle and others prefer not to do the balancing act?

LRRPF52, you should know that you've earned my respect long before I became a 6.5 Grendel Forum Member. Indeed, most of what you advocate makes good sense --- but, it also keeps us from seeing over the horizon!

[Tedward]

Are you saying the feed ramps have something to do with the extractor binding? The feed ramps are at 6 O'clock and the extractors pass through 45 degrees off TDC or 1:30. How do they effect anything to do with the extractor?

I have a feeling you have a big 55 gal drum with AA stenciled on the side as a coffee table. A straw stuck in there and your computer on top. Possibly a red phone with a direct line to the bat cave. Long term exposure to certain elements can cause heath issues. lol

Woohoo, I think the answer is being avoided or can not support the comment that was made. Thanks for your input.

[LRRPF52]

Are you saying the feed ramps have something to do with the extractor binding? The feed ramps are at 6 O'clock and the extractors pass through 45 degrees off TDC or 1:30. How do they effect anything to do with the extractor?

I have a feeling you have a big 55 gal drum with AA stenciled on the side as a coffee table. A straw stuck in there and your computer on top. Possibly a red phone with a direct line to the bat cave. Long term exposure to certain elements can cause heath issues. lol

Harrison, I've been dealing with AR15's since the 1980's. You know that I know where the feed ramps are. The broaching of the feed ramps before heat-treating can warp the part, because you don't have equal distribution of heat throughout the mass, now that two large chunks are removed from it.

Since you're my elder, and I was taught to respect my elders, I'll refrain from the personal attacks. Either there is merit to my statements, or there isn't. If I am missing something technical that you care to enlighten us on, please feel free to. I suspect that you would not speak to me in this manner if we were face to face.

I make it a point to treat other forum members with the adult respect that any reasonable person would anticipate in gentlemanly discourse. Anyone on the forum can attest to that.

[LRRPF52]

Woohoo, I think the answer is being avoided or can not stand up to the comment that was made. Thanks for your input.

I can do my speaking and thinking for myself.

[Tedward]

I can do my speaking and thinking for myself.

thanks LRRPF52, I just wanted the answer to who makes cheap extensions as you said. Not poking.


The topic went from inadequate parts to single shot takes Elk story.

[cory]

...* As soon as you expect more performance from the cartridge that very few have even pushed to the limits currently, you sacrifice the benefit of parts commonality...

An AR12, at least as I envision it would sacrifice little in parts commonality with what's on the market for ARs now.

There's no reason an AR12 shouldn't utilize the same LPK. Maybe, just maybe it'll need a longer mag release latch.

I see no reason it shouldn't utilize the AR15 carrier. Therefore it should utilize the AR15 charging handle, unless you want to redesign it to utilize a slick side charging handle.

It should be able to utilize AR15 rifle and carbine buffer system. However, I think it's likely that it would greatly benefit from an VLTOR midlength buffer system or something similar.

Essentially a weapon could be designed around the Grendel (& the 6.8 to make it a more profitable investment) that would only require a specifically built lower, upper, bolt, & extension. Oh and magazines.

[LRRPF52]

The Elk hunting story illustrates what happens when you are able to practice with a low-recoiling cartridge that has good projectile selection with bullets that have high sectional densities. In this case, the guy ventured off to find an elk to shoot early in the morning, only to hear his wife make a shot, then he finds that she DRT'd it in his absence.

There are some people who are suggesting that we need more and more muzzle velocity, when the currently-available system is able to harvest game as documented above. These performance demands require a different bolt and extension to be made, so that one can chase the .260 Remington out of the AR15 platform, which you will never reach unless you increase case capacity and pressure, since the .260 Rem is a 60,000 psi SAAMI-rated cartridge.

Even my heavy 22" target-barreled .260 Rem AR10 can be stiff on the shoulder. I wonder what other parts would start to give if I stuffed that much pressure into an AR15, even if the bolt and extension were able to handle it. There are some engineering considerations that need to be accounted for when asking for .260 Rem performance in the AR15 receiver set. The DPMS LR-308 bolt isn't really adequate at dealing with .260 Rem pressures, since it has a rather large firing pin hole.

[cory]

The Elk hunting story illustrates what happens when you are able to practice with a low-recoiling cartridge that has good projectile selection with bullets that have high sectional densities. In this case, the guy ventured off to find an elk to shoot early in the morning, only to hear his wife make a shot, then he finds that she DRT'd it in his absence.

There are some people who are suggesting that we need more and more muzzle velocity, when the currently-available system is able to harvest game as documented above. These performance demands require a different bolt and extension to be made, so that one can chase the .260 Remington out of the AR15 platform, which you will never reach unless you increase case capacity and pressure, since the .260 Rem is a 60,000 psi SAAMI-rated cartridge.

Even my heavy 22" target-barreled .260 Rem AR10 can be stiff on the shoulder. I wonder what other parts would start to give if I stuffed that much pressure into an AR15, even if the bolt and extension were able to handle it. There are some engineering considerations that need to be accounted for when asking for .260 Rem performance in the AR15 receiver set. The DPMS LR-308 bolt isn't really adequate at dealing with .260 Rem pressures, since it has a rather large firing pin hole.

I think most of us here in the discussion of pushing the Grendel to higher MVs recognize that the Grendel will never get .260 performance.

I for one just want to see the Grendel fully utilized. I believe the AR15 is selling the round short.

[LRRPF52]

An AR12, at least as I envision it would sacrifice little in parts commonality with what's on the market for ARs now.

There's no reason an AR12 shouldn't utilize the same LPK. Maybe, just maybe it'll need a longer mag release latch.

I see no reason it shouldn't utilize the AR15 carrier. Therefore it should utilize the AR15 charging handle, unless you want to redesign it to utilize a slick side charging handle.

It should be able to utilize AR15 rifle and carbine buffer system. However, I think it's likely that it would greatly benefit from an VLTOR midlength buffer system or something similar.

Essentially a weapon could be designed around the Grendel (& the 6.8 to make it a more profitable investment) that would only require a specifically built lower, upper, bolt, & extension. Oh and magazines.

AR15 and AR10 mag catches are the same. The main lower parts differences are the pivot and take-down pins, then bolt catch. The question is, what are we achieving if we make this slightly larger receiver set? It would certainly be welcomed by some of the people who like to wildcat, but most shooters will not be capable of or care to exploit the extra 150-200fps. Then we move into the business decision aspect of it.

I actually think the market is only going to increase for different calibers, as hunting with AR15's becomes more and more the norm. When the market will bear regular sales of such a receiver set and series of cartridges, along with mitigating the safety precautions of ammunition commonality, then we'll start to see larger case capacities that are somewhere between a Grendel and a .308, as well as some of the short fatties that hold more capacity than a .308, moving into 6.5-06 performance territory.

I think most of us here in the discussion of pushing the Grendel to higher MVs recognize that the Grendel will never get .260 performance.

I for one just want to see the Grendel fully utilized. I believe the AR15 is selling the round short.

Tell that to my 16" Grendel with the 123gr. If most shooters aren't capable of exploiting the performance edge the Grendel has, why throw out the AR15/Grendel combo when it works so well? Without the AR15, there would be no Grendel.

I think a lot of this is driven by an arbitrary desire to just have more muzzle velocity, not fully realizing what you already have. I was guilty of that until I took it out to 1200yds. I can't say this enough; it honestly surprised me.

[Tedward]

I know there are some that want more and more but I think the Grendel in the AR-15 is great and do agree with the low recoil. And yes, you want more beef, get the AR-10 and go 260 or something.

i just wanted to know about the Grendel Extractor and barrel extension issue if there is one. I don't think there is. If someone goes for more and more hotter loads, yes they will cause issues or premature failures. I like the round as it is and feel to just drop back on the load to make it reliable, not get that extra 5fps. Just want to make sure I'm not missing something using the standard safe, 50k/55k psi round. If the 60k psi is the breaking point or early failure loads.

The AR-10 and AR-12.25 is a different subject as far as I am concerned.

thanks for the info

[SHORT-N-SASSY]

. . . I for one just want to see the Grendel fully utilized. I believe the AR15 is selling the round short.

+1

[LRRPF52]

+1

What are your experiences with this cartridge in the AR15? There are tons of people who are stacking their freezers with meat every hunting season, and taking animals that people would have said were unethical if you told them that you would be hunting elk, caribou, feral hogs, mule deer with an AR15.

I think the AR15/Grendel is a wonderful match, based on shooting and loading for it since 2009. When I take new shooters who have never shot at distance, put them behind a little 16" Grendel, and they are ringing steel at 300-600yds as if it was normally easy (in full value winds at 12-20mph speeds), it clearly is a highly-capable system that takes the AR15 to performance levels that are closer to the .308 Winchester, with less wind drift, 50% less recoil, and 85% of the .308's energy at distance that can clearly be witnessed when shooting steel.

[cory]

LRPF52 I didn't realize that about the mag cathces, as I've yet to own or build an AR10. I don't believe you'd need different takedown or pivot pins from the AR15 utilizes. I could be wrong, but I don't think that'd be a failure point if we left it at the current spec.

who said anything about throwing out the Grendel/AR15 combo. You'd still have that option.

It'd be like the forged vs billet choice. You can still go cheaper forged option that's more than adequate or you can go the more expensive billet route and get a better fit. Just an analogy.

We certainly don't NEED an AR12 that fully utilizes the Grendel, but can tell me you wouldn't be one of the first to build one if a company offered it at a reasonable price? I'd have one preordered!

[SHORT-N-SASSY]

. . . Without the AR15, there would be no Grendel. . . .

I think it's fair to state that if the 6.5 Grendel was initially designed to work with a robust platform, such as the Remington R-15 30AR or the ARPerformance Big Bolt, instead of "shoehorning" it into the weaker AR-15, we wouldn't be having this Discussion.

[Tedward]

Cory, We all understand making another AR like a AR-12 would cost millions and the propitiatory parts from the upper receiver itself (longer to fit the longer lower due to the longer magwell), lower receiver and mags. You are right that it would let you use a longer COL. Then the next guy would want a AR-13 so the COL can be 2.45 or 2.55. It is a never ending of wants.

When I hit the lottery I'll make one of each and you will be first on the list. Or just figure out how to lighten up the AR-10. I do like the small compact AR-15 Grendel and if it were to go to an AR-12, the recoil would increase with heavier bullets and more powder, then your back to breaking bolts and then need an AR-12 extension and bolt. One change leads to another and another and proprietary product.

anyhow we can all dream and mine is to hit the Lottery.

[cory]

Tedward, yes???

Hornady lists the max col for the 308 at 2.81". I assuming that's the max col for the AR10. Either way at a COL of 2.7" or greater then your well into AR10 territory. Not to mention that much COL would be useless to the Grendel and likely useless to the 6.8 too.

Once an AR12 is built your max pressure would be derived per the case limitations, which I'm assuming would be around 58ksi. You're right in recoil would increase for heavier projectiles. There's nothing to stop you from loading to 52ksi if lower recoil is what you seek. At 56-57ksi we're looking at an ~5% recoil increase. I don't think it'd be that significant.

To design and build a new FORGED AR, yes it would costs millions. A billet AR12 could be machined in existing CNC machines once the design is CADed.