.50 Beowulf necked down to 6.5?

[Sticks]

Would it be possible to neck down a .50 Beowulf to 6.5, and would the chamber handle the pressure in an AR15 or for the sake of argument, a Howa mini action?

[JASmith]

There will be three challenges.

The serious challenge is being sure you stay within recommended pressures for the Beowulf. The large base diameter suggests you will be working at 35 ksi to keep the bolt thrust about teh same as the Grendel at 52 ksi.

Second, and less serious is ability to feed. One get a preliminary check by comparing the angle of a line drawn between the nose and shoulder with that of the WSSM cartridges. They presumaably feed OK.

Last, and easiest, is case capacity. Use QuickDesign, a companion to QuickLoad to draw up your canidiate design. Start with tihe Beo, a near match, or start from scratch. The software will tell you the resulting case capacity. Then yiu can jump into QuickLoad and explore loads with different bullets!

[LRRPF52]

I know guys who have done it, as well as .458 SOCOM necked down, and they had all kinds of problems over more than a year of testing, but could never get it to work.

They were using a larger barrel extension diameter, larger tunnel in the upper receiver, and a different bolt.

They were exceeding .260 Remington speeds, but I don't think either of them knew what they were doing regarding pressure containment.

One of the alarming comments was, "I think bolt thrust is bullish*t."

Bolt thrust is a well-known behavior in locked breeches, fundamental to high pressure/centerfire firearms design.

Another problem trying to stuff .50 Beowulf into the Howa Mini Action is the diameter of the barrel tenon and receiver.

Alexander Arms had a .50 Beowulf bolt gun at SHOT this year, which I think was based on somewhat on a Remington 700 type action.

[video=youtube_share;bwJB99MyLB0]https://youtu.be/bwJB99MyLB0[/video]

[Kswhitetails]

LOL - "I think keeping my face in tact is baloney."

A "here - hold my beer" moment if ever I read one... Exactly the type I want convincing me his data is absolutely rock solid and safe. "Look here fella, it worked for me, so it's fool proof!" No thanks, I'll place my trust in God, not feeble experimentation.

At first blush, I would think you'd need an extra heavy barrel, larger receiver, etc. You'd need more metal in that chamber to handle the forces of that much fast powder in a short case. Look at what they did with the WSSM, SAUM, RUMs. It'd be a similar - though not on the same scale entirely - situation. Sounds like fun though, if it could be made financially viable.

[bj139]

The Weatherby Vanguard which is a Howa 1500 is chambered in 375 H&H mag which has nearly the case diameter of the 458 SOCOM so it would probably work.
You could run higher pressure loads in a bolt action than in a AR-15.
My first question is why? With the 6.5 Creedmoor and 260 Remington better solutions already exist.
I just bought a 260 Remington barrel for a Savage action since it was a good deal for a match grade barrel.
I don't really need it since the 6.5 Grendel is still the best combination of all factors but the quest for small groups continues.

[JASmith]

So, we should ask ourselves "How is a Beowulf Upper different than a Grendel upper?"

We know that the WSSM cartridges worked but they seem to have a larger bolt and purpose-built receiver.

The second implementation question is "What needs to be done, other than swapping barrels, to convert a .50 Beowulf to a 6.5-.50 Beowulf?"

LRRPF has it right -- bolt thrust has to be considered in looking at potential performance. That is why I speculate we are looking at closer to 35,000 psi than 40,000 psi as a max pressure.

[LRRPF52]

The other problem using the big bore AR15 parent cases is that they are engineered with FoS for very low working pressures compared to center-fire rifle cartridges.

Think 35ksi region for working pressure, vs 50-65ksi. That has significant considerations for the brass metallurgy and yield. What's the top end on the Beowulf brass?

As you neck down the gasket, the pressure increases due to choking the funnel for gas expansion.

The whole idea behind a necked down big bore in the AR15 is to stay in the AR15 frame size without having to go to the larger AR10 frame.

I saw a build recently where a guy wanted to be as lightweight as possible with a .308 Winchester AR10-sized 16" blaster.

He used a 2A Xanthos receiver set and handguard, lightweight 16" .308 pencil barrel, a lightweight BCM stock, and still ended up over 10lbs once he put glass on it (Leupold in Leupold mount) and loaded magazine.

Now you know why my large frame components sit in pieces.

To do a short, fat 6.5mm cartridge in the AR15 that exceeds Grendel case capacity, you need some serious re-designs to the critical components of the AR.

The next case size up from Grendel is the 6mm BR, which has a .473" head diameter like a .308 Win.

Next up is the .30 Remington AR.

Since the engineering and component development has been done for the 30 RAR (upper receiver, bolt, barrel extension, mags, barrel nut), I really feel this is your best bet to chase .260 Rem performance from the AR15 frame, but the rifle will not behave very well in the recoil department.

Best bet is to get a 30 RAR upper receiver and mags, as much ammo as possible while it's in production, and have a competent smith work with you on a reamer and new barrel.

The 30 RAR has only a slightly longer case, so you will still have a good selection of 6.5mm projectiles for it if one were to do a 6.5-30 RAR.



Grendel in the middle, 30 RAR on the far right






In the end, you go through a lot of trouble to get an extra 150-200fps.

Working pressure is still limited to 55ksi because of bolt lug length, even with the larger diameter bolt and extension, like on the 30 RAR.

[JASmith]

One other consideration regarding pressure: One may be hard presed to find a slow burning powder that works well at 35ksi.

[Schrambo]

I'll stick with my .375 SOCOM, it works... Not as fun as my .458 SOCOM suppressed with a subsonic 500gr pill, but still fun...

[Sticks]

Thank you all for the input.

This has just been something I have been pondering for a few weeks given all the thoughts on necking down the Grendel cartridge to a smaller pill, I was thinking the other direction, neck a larger case down to a 6.5 since the amount of powder to push the heavier pills seems to be the challenge given the length taking up case capacity. It would be nice to push a 130 or 140 at 2700 in an AR15 frame or mini action.

[LRRPF52]

Thank you all for the input.

This has just been something I have been pondering for a few weeks given all the thoughts on necking down the Grendel cartridge to a smaller pill, I was thinking the other direction, neck a larger case down to a 6.5 since the amount of powder to push the heavier pills seems to be the challenge given the length taking up case capacity. It would be nice to push a 130 or 140 at 2700 in an AR15 frame or mini action.

What I notice in my large frame .260 Remington rifles is that recoil is very similar to a .308 Win., and both of mine were with heavy barrels.

The DPMS LR-260 has one of the heaviest barrels I've ever owned.

I had GA Precision build me one using a 22" Bartlein barrel after that experience, on DPMS receivers and BCG. That rifle is a laser, but it's a pig too. 140s will do 2660-2740 from it, but 2740 is pushing the gas system pretty hard using RL-17. I've literally bent at least 3 firing pin retaining pins due to the pressures generated in that thing, so I really had to be careful with what loads I run through it. I settled on 130gr VLDs going 2800fps, which is an awesome load for external and terminal performance. The rifle weighs 14lbs with optics and bipod, unloaded. If I load to anywhere near book max with it, brass life is lucky to make it past 3 loadings and then primer pockets are toast.

When I think about the recoil one would experience from the much lighter AR15 frame pushing a 140gr 6.5mm even at 2600fps, there is going to be a lot going on with the gas system, bolt carrier inertia, action spring, and buffer. It will really require a lot of gas system tuning and more forward port placement to behave well.

If I was doing it, I would use a +2" Gas System.

Another thing to look at is how .308 Win., 7mm-08, and .260 Rem are graduated downwards in SAAMI working pressure. My understanding is that this is due to bolt thrust, where the narrow flow path for the gas bottle-necks and creates more back pressure inside the actual case, shoving it as it expands against the bolt face harder.

So while the 30 RAR has a SAAMI MAP of 55ksi, a 7mm version would be less than that at ~54ksi, and a 6.5mm at ~53ksi.

.308 Winchester is 62ksi MAP, 7mm-08 is 61ksi, and .260 Remington 60ksi.

A 6.5CM has 52.5 gr H2O case capacity, whereas the 30 RAR has 44 gr H2O.

So we would end up somewhere between a 6.5 Grendel and a 6.5CM in terms of performance, leaning a little more towards the Grendel when you accept the case capacity and working pressure limitations.

If you wanted more working pressure, you could step up to the CMMG Anvil action and push 60ksi, but that Remington brass life is going to suffer.

You kinda start to see why I don't have one.

[Djgrendel]

As an owner of grendel's and a wulf, I have thought about the idea as well. After a ton of hypothetical thinking I came to the conclusion it is not worthwhile. Mainly because of what everyone else has stated. The brass was not intended to work at higher pressure. To me, it would be easier to just go with a bolt action WSM or SAUM. You can burn all the needmores, 260's and x47 lapua. It costs money to go fast. That being said, I really do like shooting the 6.5x47 lapua.

[pajasonc]

What I notice in my large frame .260 Remington rifles is that recoil is very similar to a .308 Win., and both of mine were with heavy barrels.

The DPMS LR-260 has one of the heaviest barrels I've ever owned.

I had GA Precision build me one using a 22" Bartlein barrel after that experience, on DPMS receivers and BCG. That rifle is a laser, but it's a pig too. 140s will do 2660-2740 from it, but 2740 is pushing the gas system pretty hard using RL-17. I've literally bent at least 3 firing pin retaining pins due to the pressures generated in that thing, so I really had to be careful with what loads I run through it. I settled on 130gr VLDs going 2800fps, which is an awesome load for external and terminal performance. The rifle weighs 14lbs with optics and bipod, unloaded. If I load to anywhere near book max with it, brass life is lucky to make it past 3 loadings and then primer pockets are toast.

When I think about the recoil one would experience from the much lighter AR15 frame pushing a 140gr 6.5mm even at 2600fps, there is going to be a lot going on with the gas system, bolt carrier inertia, action spring, and buffer. It will really require a lot of gas system tuning and more forward port placement to behave well.

If I was doing it, I would use a +2" Gas System.

Another thing to look at is how .308 Win., 7mm-08, and .260 Rem are graduated downwards in SAAMI working pressure. My understanding is that this is due to bolt thrust, where the narrow flow path for the gas bottle-necks and creates more back pressure inside the actual case, shoving it as it expands against the bolt face harder.

So while the 30 RAR has a SAAMI MAP of 55ksi, a 7mm version would be less than that at ~54ksi, and a 6.5mm at ~53ksi.

.308 Winchester is 62ksi MAP, 7mm-08 is 61ksi, and .260 Remington 60ksi.

A 6.5CM has 52.5 gr H2O case capacity, whereas the 30 RAR has 44 gr H2O.

So we would end up somewhere between a 6.5 Grendel and a 6.5CM in terms of performance, leaning a little more towards the Grendel when you accept the case capacity and working pressure limitations.

If you wanted more working pressure, you could step up to the CMMG Anvil action and push 60ksi, but that Remington brass life is going to suffer.

You kinda start to see why I don't have one.

couldn't you just use the anvil action and push the grendel to 60k. That would get you half way to where you want to be but still allow you to use off the shelf ammo in a pinch.

[sarky]

Hearing all of this, makes me wish they had increased the diameter of the AR upper to be able to take a .308 case head/bolt in the AR-15 platform

[bj139]

Hearing all of this, makes me wish they had increased the diameter of the AR upper to be able to take a .308 case head/bolt in the AR-15 platform

The 458 SOCOM has the same case head size as a 308 and an even bigger body diameter than 308. It needs the ejection port widened to fit the case on ejection.
The 458 SOCOM operates at around 35K psi so the bolt can handle the thrust. At 60K psi it would fail. The case head size determines the rearward thrust so go larger and you must operate at lower pressure. Nothing is free.

[LRRPF52]

Hearing all of this, makes me wish they had increased the diameter of the AR upper to be able to take a .308 case head/bolt in the AR-15 platform

One of the Army Ordnance engineers wanted to use the .25 Remington case necked down to .224, with a total re-engineer of the AR15 receiver set and magazine, but it would likely have killed the design in its early stages as Army Ordnance worked hard to put nail after nail in the AR15 coffin so they could promote the M14 and SPIW. We're talking 1957-1960.

The POF Revolution uses a 7.62 NATO bolt head and new barrel extension with a missing lug so it can have a larger extractor. Bolt carrier is still AR15, as is the upper. The bolt is made from AerMet.