Why bullpups?

[Tony Williams]

I've just updated my web article looking at the pros and cons of bullpups: http://www.quarry.nildram.co.uk/bullpups.htm

I will at some point extend the final paragraph to include an analysis of the benefits of long barrels when designing future ammunition. These thoughts were prompted by some work done by a gun experimenter with a hacksaw, who kept chopping more and more off a barrel of a .300 Win Mag to measure the result in muzzle velocity. Interestingly, he concluded that the MV of the magnum from a 16" barrel would be the same as for the same bullet fired by a .308 Win from a 24" barrel - only at the cost of bigger and heavier ammo developing lots more recoil and muzzle blast.

The significance of the 8" difference in barrel length is of course that this is about the same as the difference in overall length between bull pups and traditional rifles with the same length barrels. Or to put it another way, the performance of a .308 bullpup will match that of a traditional .300WM when the guns are the same overall length.

Now it could be argued that no-one in his right mind would think of firing .300 Win Mag from a 16 inch barrel (though I wouldn't bet against it - you can buy 5.56mm carbines with barrels of around 8") so I did some more digging and discovered that you can more or less match the velocity of 7.62x51 from a 13" barrel (as used in the SCAR H carbine) with the .302 Whisper (7.62 with the case cut short to 38mm) fired from a long rifle barrel.

The conclusion is therefore that deciding to design any new military cartridge (to meet whatever ballistics are required) for a bullpup rather than a traditional rifle allows you something like a 50% increase in barrel length, which means that the cartridge can be smaller and lighter, will develop less recoil, and produce much less muzzle blast, requiring a much smaller suppressor.

Not that I'm expecting the US Army to change it's antipathy towards bullpups, but it does demonstrate that the current fetish for ever-shorter barrels has a significant cost.

[JASmith]

Excellent points!

I think the resistance comes from the semi-pragmatic concern about more complicated trigger groups since the firing pin is a few or more inches behind the trigger and the visceral reaction to having the chamber immediately adjacent to one's face.

Are these valid concerns? Maybe not, but are among the items a bull-pup design would need to satisfy.

[stanc]

I've just updated my web article looking at the pros and cons of bullpups...

I will at some point extend the final paragraph to include an analysis of the benefits of long barrels when designing future ammunition. These thoughts were prompted by some work done by a gun experimenter with a hacksaw, who kept chopping more and more off a barrel of a .300 Win Mag to measure the result in muzzle velocity. Interestingly, he concluded that the MV of the magnum from a 16" barrel would be the same as for the same bullet fired by a .308 Win from a 24" barrel...

Perhaps 20 years ago there was a similar experiment published in a Scandinavian magazine (VAPEN, IIRC), in which the author incrementally cut down the barrel of a 6.5x55 Mauser. I wish now that I'd kept the article, as it might've given good data for comparison to 6.5 Grendel and 6.5 GPC.

[Tony Williams]

Perhaps 20 years ago there was a similar experiment published in a Scandinavian magazine (VAPEN, IIRC), in which the author incrementally cut down the barrel of a 6.5x55 Mauser. I wish now that I'd kept the article, as it might've given good data for comparison to 6.5 Grendel and 6.5 GPC.

Yes, that would be interesting. Is anyone able to calculate the performance of, say, a .260 Rem or a 6.5mm Creedmore from a 16" barrel, to compare with the same bullet fired from a Grendel case in a 24" barrel?

[JASmith]

There is a tool that is useful for estimating the change in velocity resulting from changes in barrel length. One does need to know the baseline barrel length, powder charge and bullet weight, however: Velocity Estimator

[stanc]

Perhaps some of this info can help:

6.5 Creedmoor

26" barrel - 140gr - 2860 fps
22" barrel - 140gr - 2805 fps
http://precisionrifleblog.com/2013/07/16...-velocity/

Last time I chrono'd my 18.5, Hornady factory 140's were doing 2640fps.
http://forum.snipershide.com/snipers-hid...ost2608464

[16.5"] 2,820 fps - 123 Lapua Scenar, 40.5 grains of Varget, COAL 2.83"
http://forum.snipershide.com/snipers-hid...ost2609366

[waveslayer]

The triggers on the bullpups have come a long ways. My Desert Tactical is awesome and so is the new Geissele for the IWI Tavor. I have no issues now with any of my bullpups, they are fun to shoot and have a place. I will have to post my new .338 Norma Mag AI in a 22 inch barrel from the DTA, It is a blast to haul around being so short and maneuverable.

[VASCAR2]

I bought a Tavor in January and so far I really like it. I'm using the standard trigger pack and for CQB/off hand shooting it is fine. I really like the ergo's and the compact size. The Tavor is easily shot from the week side and it is easy to use one handed. The design makes it very easy to use your weak hand to open doors or similar task.

My Tavor has been totally reliable with factory ammo and reloads. The Tavor is not as easy to shoot off the bench as an AR-15 but it can be done. I put a bi-pod on my Tavor along with a 2.5 X 10 scope and shot some reloaded 69 grain SMK at 150 yards. Most groups were 1.5" - 2" but the bolt catch/release can be deactivated if using a rear sand bag.

I wish I had the option of carrying my Tavor on patrol as it is easy to use in and around vehicles. I'm currently using an EO Tech on mine and I feel it is capable out to 300 yards. The only gun I felt handled as well in CQB was a select fire MP5. Everybody gripes about the Tavor trigger but to me it feels like a Glock pistol with NY trigger. The trigger reset is the same as a Glock and I have no trouble getting quick hits with the factory trigger. The new trigger packs will only add to the Tavor popularity.

With modern militaries operating more out of vehicles and in urban areas I can see the rationale of the Bullpup. The AR-15 is a better rifle for precision shooting (DMR) but for LE I could see the Tavor capturing a share of the market. IWI had a press release stating they had sold 20,000 Tavor's in 11 or 12 months.

[Tony Williams]

Perhaps some of this info can help:

6.5 Creedmoor

[16.5"] 2,820 fps - 123 Lapua Scenar, 40.5 grains of Varget, COAL 2.83"
http://forum.snipershide.com/snipers-hid...ost2609366

Thanks for that. Does anyone have an idea of how the chamber pressure of that load would compare with the Grendel's? IMO it's important to compare like with like...

[SHORT-N-SASSY]

Thanks for that. Does anyone have an idea of how the chamber pressure of that load would compare with the Grendel's? IMO it's important to compare like with like...

Hornady 6.5mm Creedmoor Factory-Loaded Ammo Specifications:

120-grain A-MAX, 2.820" COAL, 43.5 grains H4350 = 3020 fps, "under 60,000 PSI";
140-grain A-MAX, 2.820" COAL, 41.2 grains H4350 = 2820 fps, "under 60,000 PSI".
http://bulletin.accurateshooter.com/2007...cartridge/

ETA:

6.5mm Creedmoor Short Barrel (16.5") Load Development:

139-grain Lapua Scenar, 41.6 grains H4350 = 2,578 fps http://www.sincityprecision.com/?p=1503

[Tony Williams]

I don't have data on the Grendel with the 139 grain bullet, but the factory load develops just over 2,600 fps with a 123 grain from a 24" barrel, at a relatively low pressure I believe (nothing like 60,000 psi). So if the Creedmore is c.2,550 fps from a 16" barrel with 139 grains, I presume that it will be in the region of 2,700 fps with the 123 grain (same muzzle energy). So a Grendel bullpup the same overall length as Creedmore carbine will lose c.100 fps in muzzle velocity, or around 4%.

Does this sound reasonable?

[SHORT-N-SASSY]

It's been reported in these Pages that 2650 fps - 2700 fps has been reached in a 22-inch-barreled 6.5mm Grendel-chambered bolt gun, with the 139-grain Lapua Scenar projectile and handloads, no doubt with the bullet extended beyond the 6.5mm Grendel's normal cartridge overall length, and at pressures well beyond the safe limits of the AR-15 breech system.

Extrapolating, it would seem reasonable to expect 2500 fps - 2550 fps from a 16-inch-barreled 6.5mm Grendel-chambered bolt gun --- not much different from the 2550 fps -2575 fps velocity the 6.5mm Creedmoor 139-grain Lapua Scenar projectile leaves the muzzle from a 16.5" barreled bolt gun.

The 6.5mm Grendel is an extremely efficient cartridge, which potential performance is restricted when mated to the limitations of the AR-15 breech system. We're back to square one.

[Tony Williams]

Thanks for that, but what I'm trying to arrive at isn't the maximum possible loads, but a comparison of reasonable working loads (similar pressures for both cartridges) such as the military might choose for a "vanilla" ball round, comparing a Grendel from a 24 inch barrel with a Creedmore firing the same bullet from a 16 inch barrel. The purpose is to illustrate the benefits of long barrels (as in bullpups) in enabling smaller and lighter ammunition to be used.

[Bigfoot]

Outstanding article Tony.

Appreciate the emphasis on shorter action lengths. I have a SU-16 and a Mini-30, both have short actions that would result in bullpup LOPs close to 13" so it's easily done. Kel-Tec RFBs LOP is 14.25" IIRC and that's a 7.62 length action. Can't believe designers keep giving us these awkward bullpups with LOPs over 15".

[Tony Williams]

Outstanding article Tony.

Appreciate the emphasis on shorter action lengths. I have a SU-16 and a Mini-30, both have short actions that would result in bullpup LOPs close to 13" so it's easily done. Kel-Tec RFBs LOP is 14.25" IIRC and that's a 7.62 length action. Can't believe designers keep giving us these awkward bullpups with LOPs over 15".

Thanks for that. I agree with your final comment: surely anyone interested in the military rifle market would look carefully at the M4 - or the AKM for that matter - and ensure that their design could match its LOP, since that is obviously what is wanted.

[stanc]

[video=youtube;R-4G1Bo_jgA]https://www.youtube.com/watch?v=R-4G1Bo_jgA[/video]
https://www.youtube.com/watch?v=R-4G1Bo_jgA

[waveslayer]

Have you guys seen the Desert Tactical MDR? That will be the Bullpup to get!

[SHORT-N-SASSY]

[video=youtube;R-4G1Bo_jgA]https://www.youtube.com/watch?v=R-4G1Bo_jgA[/video]
https://www.youtube.com/watch?v=R-4G1Bo_jgA

It would appear that the FB Radom MSBS Bullpup has a removable left-side-ejection port cover (http://bullpupforum.com/index.php?topic=...3#msg53663). However, a right-side-ejecting Bullpup requiring even partial disassembly of the weapon to achieve left-side ejection is old hat, today.

[stanc]

Tony has recently updated his article.

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[COLOR="blue"]Some final thoughts: the current interest in the possibility of a new general-purpose long-range cartridge to replace both the 5.56x45 and the 7.62x51 enhances the case for the bullpup solution. It could be argued that a 7.62mm rifle, being intended primarily for long-range fire, need not be compact, while a 5.56mm carbine, being optimised for relatively short ranges, is not greatly disadvantaged by a short barrel. However, a general-purpose rifle in a general-purpose calibre would need to be short for urban fighting but have a long barrel for optimum long-range ballistics. This can only be achieved in one gun by using the bullpup layout, unless soldiers are to be expected to carry two barrels of different lengths and keep swapping them as the range changes.

Furthermore, the design of a new general-purpose calibre could be influenced by which layout is chosen, if the bullpup's compactness is used to provide a longer barrel rather than a shorter gun. This is because there is an inverse relationship between the barrel length and the size and power of the cartridge required to achieve any given ballistics: other things being equal, the shorter the barrel, the more powerful the cartridge needs to be. This is illustrated by the two notional 6.5mm cartridges shown below (courtesy of Joe Smith). Both of them are designed to develop a muzzle energy of 2,500 J (1,850 ft lbs): the shorter cartridge (basically the 6.5mm Grendel) will achieve this from a 24" (c.600mm) barrel; the larger cartridge, around 9mm longer, is required to accommodate enough propellant to achieve the same muzzle energy from a 16 inch (c.400mm) barrel.



To put it another way, there is a choice between two rifles of the same overall length and ballistic performance: a bullpup using the short cartridge, or a traditional carbine using the long cartridge. The bullpup solution allows the selection of lighter ammunition, developing less recoil, and with a much smaller firing signature in terms of muzzle flash and blast, thereby needing a significantly smaller and lighter suppressor to achieve any given decibel level.[/COLOR]

http://quarryhs.co.uk/bullpups.htm

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[SHORT-N-SASSY]

Tony has recently updated his article.

===========================================

[COLOR="blue"]Some final thoughts: the current interest in the possibility of a new general-purpose long-range cartridge to replace both the 5.56x45 and the 7.62x51 enhances the case for the bullpup solution. It could be argued that a 7.62mm rifle, being intended primarily for long-range fire, need not be compact, while a 5.56mm carbine, being optimised for relatively short ranges, is not greatly disadvantaged by a short barrel. However, a general-purpose rifle in a general-purpose calibre would need to be short for urban fighting but have a long barrel for optimum long-range ballistics. This can only be achieved in one gun by using the bullpup layout, unless soldiers are to be expected to carry two barrels of different lengths and keep swapping them as the range changes.

Furthermore, the design of a new general-purpose calibre could be influenced by which layout is chosen, if the bullpup's compactness is used to provide a longer barrel rather than a shorter gun. This is because there is an inverse relationship between the barrel length and the size and power of the cartridge required to achieve any given ballistics: other things being equal, the shorter the barrel, the more powerful the cartridge needs to be. This is illustrated by the two notional 6.5mm cartridges shown below (courtesy of Joe Smith). Both of them are designed to develop a muzzle energy of 2,500 J (1,850 ft lbs): the shorter cartridge (basically the 6.5mm Grendel) will achieve this from a 24" (c.600mm) barrel; the larger cartridge, around 9mm longer, is required to accommodate enough propellant to achieve the same muzzle energy from a 16 inch (c.400mm) barrel.



To put it another way, there is a choice between two rifles of the same overall length and ballistic performance: a bullpup using the short cartridge, or a traditional carbine using the long cartridge. The bullpup solution allows the selection of lighter ammunition, developing less recoil, and with a much smaller firing signature in terms of muzzle flash and blast, thereby needing a significantly smaller and lighter suppressor to achieve any given decibel level.[/COLOR]

http://quarryhs.co.uk/bullpups.htm

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[SIZE="3"]I think it's ironic that while, on another Thread (http://www.65grendel.com/forum/showthrea...post102073), we're discussing Load testing for the 6.5mm Grendel bolt-action CZ527 (effectively, removing the constraints imposed on the Grendel-AR-15 marriage, by the laws governing Bolt Thrust), here, the emphasis is on the benefits of the shorter Bullpup configuration, using a longer (24") barrel (". . . allows the selection of lighter ammunition, developing less recoil, and with a much smaller firing signature in terms of muzzle flash and blast . . ."), compared to the traditional longer configuration, using a shorter (16") barrel ---



[/SIZE]