Bullpup Design: Why must the hammer be behind the magazine?

[Cableaddict]

Going to the deepest darkest corner of "The Darkside" tonight......   

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When considering the best candidates for my next pcp rifle,  I'm only looking at bullpups since I need the longest barrel in the shortest package
And of course the "overall length to barrel length" ratio is important.

But one thing bugs me constantly:  The problem of high scope mounting due to a high cheek area.  This is always a problem if you need to do pesting at very short distances, then switch to longer range hunting.   Even the "best" bullpups still have cheekrests that are at the level of the top of the breech block, and of course you can't go any lower than that.

Except you probably CAN:
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It seems to me that the back-half of the breech could be significantly lower, if the hammer spring wasn't located back there.   OK, you have to have the pellet probe there,  but that only takes up a few inches.   The hammer and valve simple open a passage for air, so why do they have to be at the back of the gun?  Couldn't the mechanism be turned "backwards," and then located somewhere just behind the trigger area?

If that were done, bullpups could be even shorter for a given barrel length, and / or the cheekweld area could be significantly lower.

I think.   

Does this make sense?

[JungleShooter]

Very interesting observation, Cableaddict! 👍🏼


Here's another thought as I skipped down that same road of "longest barrel in the shortest package":

Some manufacturers seem to reduce the gun's size by placing the action behind the trigger — the foundational bullpup idea.
BUT then they turn around and increase that size again by adding buttstock behind the action.... 🤦🏻‍♂️ 

For me bullpups are bloated if they have a lot of buttstock behind the action — they have a bloat stock!!


🔶 A couple of years ago I made a photo comparision chart of the current bullpups — sorted according to the efficiency of the stock.
➔ I was in for several surprises...! 😄
Some very bloated stocks, and some very efficient stocks!


So, if size matters to you, this chart is for you. 👍🏼

Matthias


❌ Attachment:  Bullpup Bloat Stocks

[Mike -]

The Airmax Caiman and Caiman X rotated the action "down".  The sear is at a 90° angle or vertical rather than horizontal, (parallel to the barrel).  That makes things about as short as they can get.

Short, nice to shoot, accurate as most of todays guns.

Mike

P.s. - I should be receiving a Cricket II tomorrow.  I got the curvier stock.  And yeah, it also has a long "butt" on it vs. the older stock or the "ladder" design.  I'll be cutting / shortening it as far as possible.
I like short guns..!

[bigfoot159]

I just bought the kral puncher knight.  It listed on pa as a rifle but to me it screams bullpup. I only had it for 2 days. Max volsity 972 , over 93 shoots sd was 31. You get best shots 62 shots. The cheek piece is bebind the receiver,  low mounts would easily fit this bullpup. On max power with 18.13 JSB = 37.1 FPE at muzzle.

[Cableaddict]

The Airmax Caiman and Caiman X rotated the action "down".  The sear is at a 90° angle or vertical rather than horizontal, (parallel to the barrel).  That makes things about as short as they can get.

Wow.  There you go!

Sadly, those are IMO about the ugliest rifles ever made.  Lol....    But the design is solid.   
 I think my idea of reversing the spring would allow for a slimmer & thus better looking gun, assuming it can work technically.

Also, with either system, it would probably be a good idea to add some kind of safety shield, to protect the shooter's face from any accidental problems at the breech.  Does the Airmax have something like that?
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I just bought the kral puncher knight.  It listed on pa as a rifle but to me it screams bullpup. I only had it for 2 days. Max volsity 972 , over 93 shoots sd was 31. You get best shots 62 shots. The cheek piece is bebind the receiver,  low mounts would easily fit this bullpup. On max power with 18.13 JSB = 37.1 FPE at muzzle.

Very interesting.   Sort of a compromise design.    Not quite what I fantasize about,   but I like that Kral is exploring such designs.

[Cableaddict]

Some manufacturers seem to reduce the gun's size by placing the action behind the trigger — the foundational bullpup idea.
BUT then they turn around and increase that size again by adding buttstock behind the action.... 🤦🏻‍♂️ 

Yeah I've noticed that as well.   I think the reason is that they haven't placed the trigger far enough forward, so the buttstock has to be artificially extended in order to obtain a decent feel when holding the gun.   You'll notice on some of the best "ratio" guns that their triggers are indeed further towards the front.

Well, at least with a "bloatstock" rifle, you could theoretically cut off the back and then make a quick-attach connector for it. That would make the gun more portable, at least.

I think this whole discussion also points to the fact that HOW TO HOLD a bullpup,  and corresponding design changes based on alternate holds, is still not fully developed.  -  This includes where to put your head.
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Nice work on that list, BTW !

You need to add two more:

1:  The upcoming Reximex Throne II.  (It will look just like the current throne, but with a few major technical improvements.
Barrel:  22.8"  /   Overall length:  34.4"

2:  The Airgun Tech Uragan.  Barrel: 22.4"  /   Overall length 32.6"  (including a very slight bloat stock. lol... )

Of course, one factor that's really hard to figure, when making these comparisons, is factory shroud size.  That of course affects the total length. So what happens if the gun is too loud, and you want to remove the original shroud (they are rarely very efficient) and add an aftermarket moderator?   The numbers change, and comparisons no longer hold.   

[Rallyshark]

The design issues of a bullpup that lead to the high scope mounting generally has nothing to do with where the hammer is or most anything else in the breech block.  It has to do with sight picture.  They don't have the long upward angled butt stock to bring the action/barrel higher  and closer to eye level.  The high rails and rings are needed to get the scope up to eye level, so you don't strain your neck trying to get a sight picture. 

In other words, you'd have to have a rather wonky looking stock to get the breech block/barrel high enough to use a scope that is closer to the bore, and still be comfortable to shoot.  It just boils down to ergonomics  and function more than the ability to trim down the action etc... As far as length goes, there some guns that are designed to get the magazine/probe as far back as possible to trim the length even more.  That's fine, but you're still only going to be able to decrease the length an inch or two at best.  Is that design compromise worth the 2" shorter length?  It isn't to me, but it may be to others.   I try not to get to bogged down on specs like length and scope height.  I just look at is as:  Is the gun pretty short and accurate?  If so, I'll work around the rest  

I used to get concerned about the high off bore scope mounting of the pups, but now, I couldn't care less about it.  It used to drive me nuts that I couldn't get the scope closer to the barrel.  You will get used to it though, and know where your holds are for various distances.  Of course, a good reticle makes a world of difference in that regard too.  There's also a benefit to the high off bore scopes, which is long distance shooting.  You can effectively hold/dial for longer distances with the high mounts, because the angle between where the scope sight in and the line of fire from the barrel meet is a greater angle.  It just takes practice, and then you're good to go.  15 yards or 150 yards doesn't matter to me, because I know the gun can make the shot, I just have to practice enough to know how to make that shot.

I think the bullpup design is very developed, but the shooters haven't adapted to them as well, because it is a different way of shooting compared to a traditional rifle.  The fact is, there isn't a whole lot more that can be done with a pup to make it shoot like a rifle.  It's just a side effect of the design.  We can adapt, or shoot rifles.  Sure, some are better than others, and that is a lot of the reason we have "semi-bullpup" designs like the Brococks and Vulcans to name a few.  I'm not trying to discourage innovation or anything like that, but I'm afraid it just is what it is. 

[CableStop]

The main issue I see with reversing the hammer set up is cocking the rifle.  If I'm following correctly you mean kind of like an airforce style hammer that fires towards the back of the gun.  Airforce limits their guns to single shot and the cocking lever goes forward instead of back which would be hard to replicate on a multishot rifle.  Also the geometry of the air path with such a set up may be less than ideal.

[Cableaddict]

The design issues of a bullpup that lead to the high scope mounting generally has nothing to do with where the hammer is or most anything else in the breech block.  It has to do with sight picture.  They don't have the long upward angled butt stock to bring the action/barrel higher  and closer to eye level.  The high rails and rings are needed to get the scope up to eye level, so you don't strain your neck trying to get a sight picture. 

To change what you wrote, " They don't have the long upward angled butt stock to lower the cheek weld position."

A regular rifle has the exact same height limitation, if you remove the long butt stock and move the trigger forward.

I just don't see your point.

[Cableaddict]

The main issue I see with reversing the hammer set up is cocking the rifle.  If I'm following correctly you mean kind of like an airforce style hammer that fires towards the back of the gun.  Airforce limits their guns to single shot and the cocking lever goes forward instead of back which would be hard to replicate on a multishot rifle. 

Yes, you'd have to cock the hammer forward, but why would that prevent using a mag?  As long as the probe pushes a pellet out, then pulls back, the mag's spring will still do its thing.    So, you'd push the arm forward, tensioning the hammer spring and pushing a pellet into the breech, then you'd pull the arm back & lock it, so the magazine advances & the next pellet is ready to be loaded by the probe.

The only possible problem is that it might be possible to fire the gun without pulling the lever back, so the next round wouldn't load.   It wouldn't hjurt anything, and eventually you'd get used to it.     I think ......   

Also the geometry of the air path with such a set up may be less than ideal.

That's a good point.  Experiments would have to be done.   However,  I think ~ 2600 psi wants to go where it wants to go.  I doubt s 180º turn would matter much. Still, it is a good point & something to consider.

[CableStop]

The main issue I see with reversing the hammer set up is cocking the rifle.  If I'm following correctly you mean kind of like an airforce style hammer that fires towards the back of the gun.  Airforce limits their guns to single shot and the cocking lever goes forward instead of back which would be hard to replicate on a multishot rifle. 

Yes, you'd have to cock the hammer forward, but why would that prevent using a mag?  As long as the probe pushes a pellet out, then pulls back, the mag's spring will still do its thing.    So, you'd push the arm forward, tensioning the hammer spring and pushing a pellet into the breech, then you'd pull the arm back & lock it, so the magazine advances & the next pellet is ready to be loaded by the probe.

The only possible problem is that it might be possible to fire the gun without pulling the lever back, so the next round wouldn't load.   It wouldn't hjurt anything, and eventually you'd get used to it.     I think ......   

How would it seal if the probe retracted again?

[Cableaddict]

I used to get concerned about the high off bore scope mounting of the pups, but now, I couldn't care less about it.  It used to drive me nuts that I couldn't get the scope closer to the barrel.  You will get used to it though, and know where your holds are for various distances.

You must not do a lot of pesting, (or you have a second gun for that)  in which case I agree with you.

But fo me,  trying to go from a 6 yard target to a 50 yard target is practically a nightmare, using a bullpup.   I ran the numbers for if I get the MTC 12X SAWT scope that I'm lusting after.   Unless I'm calculating wrong (I'm not sure, and no one here has been able to help with this)   wiith a 21 yard zero,  the holdover at 6 yards is 10.5 mil dots !    That's simply not workable.   Even if I used the turrets, it would be ridiculous.

What I might do is mount a cheap red dot on offset mounts, just for sub-20y shooting.  But I'm having a very hard time figuring what red dot would be best for that, short of a super expensive prismatic / holograpphic type.  It's bloody confusing......

[Cableaddict]

How would it seal if the probe retracted again?

Good point.

But then that makes it easier.  You just push forward to both lock & load.

Prepping the next pellet would mean pulling all the way back, then pushing forward to the locked position again.

Simples, no?

[Scotchmo]

...I'm only looking at bullpups since I need the longest barrel in the shortest package...


...But one thing bugs me constantly:  The problem of high scope mounting due to a high cheek area. ...

On a conventional rifle layout, the barrel and breech is in front of the users face, so the cheek rest can be below the bore line if that's what the designer wants.

In a bullpup layout, the barrel/breech extends all the way to the butt end (ideally). At the lowest, the cheek will need to rest on the barrel. No way around it.

[rsterne]

You can place the hammer and valve underneath the barrel (like in a conventional PCP, but turned around), and have the breech right at the back.... However, your cheek line is still limited by the top of the barrel, plus the thickness of the top of the receiver above that, as Scott says....

Bob....

[Cableaddict]

You can place the hammer and valve underneath the barrel (like in a conventional PCP, but turned around), and have the breech right at the back.... However, your cheek line is still limited by the top of the barrel, plus the thickness of the top of the receiver above that....

Yes, but the area behind the breech doesn't have to be as high.  That's my entire point. 
Assuming internal air volume is maintained, you only need enough "back breech" to enclose the pellet probe.

[rsterne]

I thought you wanted the shortest possible LOA?.... That would mean the breech must be touching your shoulder (so there is no "area behind the breech").... You can't have it both ways.... 

The shortest possible bullpup, with the lowest sightline, would have the bolt sliding inside the barrel itself, with a loading port machined on the top and a barrel port machined on the bottom....



Like the old Crosman 1400, above....

Bob

[Cableaddict]

I thought you wanted the shortest possible LOA?.... That would mean the breech must be touching your shoulder (so there is no "area behind the breech").... You can't have it both ways.... 

Ah, I see your point.

I wasn't thinking quite that radically.  Just take a good existing design and lower the CURRENT cheekweld area.
My goal is to have a lower scope, not the absolute shortest rifle.  I didn't make that clear.

[JungleShooter]

But fo me,  trying to go from a 6 yard target to a 50 yard target is practically a nightmare, using a bullpup.   
I ran the numbers for if I get the MTC 12X SAWT scope that I'm lusting after.   
Unless I'm calculating wrong (I'm not sure, and no one here has been able to help with this) with a 21 yard zero,  the holdover at 6 yards is 10.5 mil dots!
That's simply not workable.   Even if I used the turrets, it would be ridiculous.

Allan, 😊

you might be right with your calculations — but that elevation adjustment at 6y just seem way high....

If you send me your numbers, I'll give them a spin in Strelok Pro:

▪Muzzle energy
▪Pellet caliber, brand, and model
▪Scope mounting height (measured from the centerline of the barrel to the centerline of the scope tube — you'll have to estimate that somewhat, and take into account the mounts you plan on using). 
For kicks, what gun are you mounting this on?

👍🏼 Matthias

[Cableaddict]

you might be right with your calculations — but that elevation adjustment at 6y just seem way high....

If you send me your numbers, I'll give them a spin in Strelok Pro:

Thanks, Mathias.  That would be fantastic.
-  And maybe post the results in that other thread, since it's s;lightly off topic here.


36 gr  .25 caliber slug.  BC 0.1
Muzzle velocity 900 fps  (I don't have that yet, but it's my goal.)
21 yard zero, for now.
6 yard minimum target distance.
60 yard maximum target distance

Current scope: Lowly Bugbuster.  2.75" above bore-center  (to the center of the front element.) 
Click Value:  1/4 MOA.  Total clicks for 1 rotation:  74.
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New option #1:  MTC SWAT 10x30.   3" above bore center.   
Click values:  (This is where it gets confusing, and where I might have screwed up the calculations)  MTC says
"1 click = 1 cm @ 100 yards      Total clicks per rotation:  42.  Mils per rotation:  6.    (I guess 1 click = 1/7th of a mil.  So what is that in MOA?)
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New option #2:  MTC SWAT 12x50.   3.25" above bore center.   
Click specs identical to the other.