12ga Big Bore



Author Topic: 12ga Big Bore  (Read 2276 times))

Offline fpjeepy

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12ga Big Bore
« on: January 25, 2019, 01:21:29 PM »
I think the Airforce Texan is the most popular air gun right now, imo based off youtube views. But personally, I would like a more compact gun.

I think a 73 Cal Bullpup rifle with a shroud would be ideal. I think by going from 45 caliber to 73 caliber you can get faster accelerations and use shorter barrels with equal weight bullets. Switching to non-expanding bullets should provide similar penetration to the smaller caliber expanding bullets. (i.e. copper, brass, steel, aluminum)

The goal is a very quiet gun under 40" that shoots a 300gr projectile at 1050 fps. And does it all with 3500psi of air. I know higher pressures and helium make this easier, but sticking with basics here.

Do you think this is feasible? Do you think there would be a market for a gun like this?
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Offline MJP

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Re: 12ga Big Bore
« Reply #1 on: January 25, 2019, 01:37:49 PM »
Well you can hunt with far less than 800fpe, what is the purpose of said gun?
Not that there is nothing wrong with power.

That is the length of the elusive hammer if I'm not mistaken, do you want to create that or something similar.

.73 and 30" barrel tou could get pretty close to your goal with that pressure but the bullet is very short. And its bc going to be low so not a long range gun.

My small projectiles are pretty short for 20mm caliber and they weigh around 1600gr
Cant imagine how short 300gr ~18.5mm would be.

Marko
« Last Edit: January 25, 2019, 01:42:09 PM by MJP »
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Offline T3PRanch

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Re: 12ga Big Bore
« Reply #2 on: January 25, 2019, 02:04:51 PM »
A very similar gun to the one you describe is already manufactured by XP-Airguns in Kansas. It is called the Quigley - Scorpion .72

https://www.xp-airguns.com/photo-gallery.html

Taming the bark of a .72 will be the trick.

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Offline dmeguy

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Re: 12ga Big Bore
« Reply #3 on: January 25, 2019, 02:37:59 PM »
A very similar gun to the one you describe is already manufactured by XP-Airguns in Kansas. It is called the Quigley - Scorpion .72

https://www.xp-airguns.com/photo-gallery.html

Taming the bark of a .72 will be the trick.


They even had a prototype bullpup version on their Facebook page.


But I have to agree, taming the bark of a .72 to something that could be considered "very quiet", is going to take a magic wand or some pixie dust!
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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #4 on: January 25, 2019, 03:16:54 PM »
Well you can hunt with far less than 800fpe, what is the purpose of said gun?
Not that there is nothing wrong with power.

That is the length of the elusive hammer if I'm not mistaken, do you want to create that or something similar.

.73 and 30" barrel tou could get pretty close to your goal with that pressure but the bullet is very short. And its bc going to be low so not a long range gun.

My small projectiles are pretty short for 20mm caliber and they weigh around 1600gr
Cant imagine how short 300gr ~18.5mm would be.

Marko

The intended purpose would be to hunt deer and hogs in the US at close range. But also to be used for backyard target shooting, ideally.

The BC would be terrible. But my logic is this... 1050fps is the max speed that you can push a bullet that you want to keep quiet. Maximum point blank range (MPBR) on a 4" target for a bullet with .1 BC at 1050fps is 92 yards. MPBR for .5 BC at 1050fps is 100 yards. Basically, at close range, BC doesn't have a ton of an effect.

My idea for a bullet is attached below. Just a rough model, but it's showing a steel disc that would weigh 264gr. (301gr in copper) The tan color is a plastic of some sort that is mechanically fastened to the bullet so it doesn't destroy the shroud. There to hopefully keep the bullet flying straight.


« Last Edit: January 25, 2019, 03:24:12 PM by fpjeepy »
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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #5 on: January 25, 2019, 03:23:51 PM »
A very similar gun to the one you describe is already manufactured by XP-Airguns in Kansas. It is called the Quigley - Scorpion .72

Taming the bark of a .72 will be the trick.

Yeah, XP one of the few making .72 cal guns. I think it would have to be a bullpup style, because like you said taming the bark is going to be difficult. I'm thinking the shroud might need to be at large as 3" around and 15-20" long. And adding that to a gun that is already 40" long makes it impractical for a lot of hunting styles.
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Online rsterne

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Re: 12ga Big Bore
« Reply #6 on: January 25, 2019, 04:05:43 PM »
I presume you have already done the math, as a .73 cal lead roundball would weigh 583 gr.... and yet only have a BC(G1) of less than 0.1.... BC doesn't affect trajectory much, but it sure affects the downrange velocity and energy retention.... For simplicity I would go with a .58 cal, and shoot roundballs, which weigh 292 gr. and have a BC of about 0.08.... Keep the velocity at around 950 fps, the wind drift is less than it is at 1050, although admittedly the MPBR would be less for a 4" target, 84 yds. instead of 92 yds....  You should be able to get that velocity on 3000 psi, and you will find that reaching 950 is a lot quieter than 1050, unless you have a really long barrel.... If you have your heart set on 1050, that should be possible using 3500 psi.... With a MV of 950, that .58 cal roundball will arrive at 100 yds. with over 400 FPE of energy.... The size of valve you will need for a .58 cal will be much smaller, which means less hammer strike, easier to cock, less air used per shot, easier to quieten it down, etc.etc.etc…. Just a suggestion....

Bob
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Offline MJP

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Re: 12ga Big Bore
« Reply #7 on: January 25, 2019, 04:13:26 PM »
Bob has very good points there, taming down .73 is going to be down right impossible.
 The volume of air needed to push the projectile around 1050fps is quite substantial.

I have pretty good understanding of bigger end of the bigbore rifles and the air volumes involved.
Taming something so big to backyard friendly would require can the size of a bucket.

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Offline rkr

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Re: 12ga Big Bore
« Reply #8 on: January 25, 2019, 04:26:47 PM »
Having made 150 fpe .357 very quiet and 270 fpe .45 backyard friendly, I would say that you need one enormous can to make that powerful .73 very quiet. In general it takes more air to get more power and more can volume to quiet it down. A good .357 can is 2" in diameter and over 10" long back vented model.
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Re: 12ga Big Bore
« Reply #9 on: January 25, 2019, 05:26:45 PM »
So would 0.2 CI per FPE be a good starting point for a "can" ?.... If so, then for 300 gr. @ 1050 fps, maybe 3" in diameter and 2 ft. long....  :o

Of course a .58 cal at the same FPE would need the same size....  ::)

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Offline Back_Roads

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Re: 12ga Big Bore
« Reply #10 on: January 25, 2019, 08:06:58 PM »
So would 0.2 CI per FPE be a good starting point for a "can" ?.... If so, then for 300 gr. @ 1050 fps, maybe 3" in diameter and 2 ft. long....  :o

Of course a .58 cal at the same FPE would need the same size....  ::)

Bob
So a basic straight flow high performance car muffler to quiet it down < back roads terms>  ;)
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Offline rkr

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Re: 12ga Big Bore
« Reply #11 on: January 26, 2019, 06:58:10 AM »
So would 0.2 CI per FPE be a good starting point for a "can" ?.... If so, then for 300 gr. @ 1050 fps, maybe 3" in diameter and 2 ft. long....  :o

Of course a .58 cal at the same FPE would need the same size....  ::)

Bob

Just for the fun I checked the volumes of different good cans I have and considered at which power level they were quiet etc (ranging 12-270 fpe). It seems that it takes very roughly about 4000mm3 (rounds up to around 0.25CI) volume for each fpe to make a gun "quiet". By quiet I mean you can hear the shot but it would be a quiet one, not disturbing neighbors - bullet flight noise is about the same level as the shot noise. No action only quietness, that would take 3-4 times more volume for each fpe. It is also worth noting that the bigger the caliber the more flight noise and efficiency varies etc. - still perhaps that is a useful guideline - at least for reality checks. As for the upper limit, my biggest can is 50mm in diameter and 440mm long reflex type. It makes a 270 fpe .45 gun about backyard friendly. Same can in a 230 fpe .357 I would call normal backyard friendly. 300mm version of that can in a 150 fpe .357 is very quiet and so on.
« Last Edit: January 26, 2019, 07:10:35 AM by rkr »
Huub Viking Mk2 .177/.22 bullpup - grab'n go gun
BSA Scorpion SE .177 - plinker/training gun
BSA Scorpion .25 - 100M BR gun at 60 fpe
BSA Scorpion .224 - 100M BR gun at 100 fpe
Evanix Blizzard .357 bullpup - 230 fpe silhouette gun
Exanix Sniper X2 .45 - 270 fpe silhouette gun
Drozd Blackbird HPA - 1200 rpm full auto fun gun / meat grinder
Evanix AR6 carbine/pistol
+ a couple of springers

Offline fpjeepy

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Re: 12ga Big Bore
« Reply #12 on: January 26, 2019, 11:48:20 AM »
I'm assessing this more as a viable product for a company to produce than something to have built for myself.
I presume you have already done the math, as a .73 cal lead roundball would weigh 583 gr.... and yet only have a BC(G1) of less than 0.1.... BC doesn't affect trajectory much, but it sure affects the downrange velocity and energy retention.... For simplicity I would go with a .58 cal, and shoot roundballs, which weigh 292 gr. and have a BC of about 0.08.... Keep the velocity at around 950 fps, the wind drift is less than it is at 1050, although admittedly the MPBR would be less for a 4" target, 84 yds. instead of 92 yds....  You should be able to get that velocity on 3000 psi, and you will find that reaching 950 is a lot quieter than 1050, unless you have a really long barrel.... If you have your heart set on 1050, that should be possible using 3500 psi.... With a MV of 950, that .58 cal roundball will arrive at 100 yds. with over 400 FPE of energy.... The size of valve you will need for a .58 cal will be much smaller, which means less hammer strike, easier to cock, less air used per shot, easier to quieten it down, etc.etc.etc…. Just a suggestion....

Bob

That being said I think you are right that a .58 round ball might be the simplest way to get what I'm looking for, but it's not very exciting. When was the last time that any modern gun product was released that used round balls? Modern arms use pellets, bullets, sabots, and discs. A .58 at 400 fpe works great, but I don't think anyone would consider it the latest and the greatest. Daisy Red Rider and flintlock muzzleloaders are the only ones I can think that use a round ball.

 
Bob has very good points there, taming down .73 is going to be downright impossible.

Marko

Marko, you are quick to say it is impossible, but from what I am hearing... a 3.6" x 18" can would suppress a 300gr 72 cal at 1050fps and 735fpe to be backyard friendly. I would say that is far from impossible. If you think a can that large is goofy. That is merely another problem to solve. A possible solution is not making the can round. See the example below.
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Offline rkr

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Re: 12ga Big Bore
« Reply #13 on: January 26, 2019, 01:22:23 PM »

Marko, you are quick to say it is impossible, but from what I am hearing... a 3.6" x 18" can would suppress a 300gr 72 cal at 1050fps and 735fpe to be backyard friendly. I would say that is far from impossible. If you think a can that large is goofy. That is merely another problem to solve. A possible solution is not making the can round. See the example below.


This is 50mm diameter 440mm long can, it's not too bad from practical point of view. Whether it looks goofy or not is then another thing.

Eva-ldc_zpsmgm4kafa by abbababbaccc, on Flickr
Huub Viking Mk2 .177/.22 bullpup - grab'n go gun
BSA Scorpion SE .177 - plinker/training gun
BSA Scorpion .25 - 100M BR gun at 60 fpe
BSA Scorpion .224 - 100M BR gun at 100 fpe
Evanix Blizzard .357 bullpup - 230 fpe silhouette gun
Exanix Sniper X2 .45 - 270 fpe silhouette gun
Drozd Blackbird HPA - 1200 rpm full auto fun gun / meat grinder
Evanix AR6 carbine/pistol
+ a couple of springers

Offline TPL

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Re: 12ga Big Bore
« Reply #14 on: January 26, 2019, 01:28:20 PM »
fpjeepy, Yo're right, it is quicker to say than do.



You only need to tame this. Ok, it is bigger but you get the idea. It is not a steam engine, cold weather is condensing the most of air coming out from 20mm.

There are only laws of physics against you unless you invent something to close the door right after elvis left the building...

I'm not saying it is impossible but is it handy or practical? NO.
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Offline TPL

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Re: 12ga Big Bore
« Reply #15 on: January 26, 2019, 01:32:19 PM »
Before someone says, it was wrong said. Compressed air burst is condensing the moisture of surraunding air to visible cloud...
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Offline MJP

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Re: 12ga Big Bore
« Reply #16 on: January 26, 2019, 02:46:41 PM »
Well if you have not shot one then i would recommend to try just to let you know what kind of air volume you are dealing with.
By all means build it and let me know how backyard friendly you can get it.

One thing I might add please don't try it a residential area, there are other safety factors to consider than just the sound.

Marko
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Offline fpjeepy

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Re: 12ga Big Bore
« Reply #17 on: January 26, 2019, 03:02:07 PM »
fpjeepy, Yo're right, it is quicker to say than do.

You only need to tame this. Ok, it is bigger but you get the idea. It is not a steam engine, cold weather is condensing the most of air coming out from 20mm.

There are only laws of physics against you unless you invent something to close the door right after elvis left the building...

I'm not saying it is impossible but is it handy or practical? NO.

Is rkr's can practical? What if it was 75% larger in diameter? Do you disagree with 0.25 in^3/fpe?
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Offline Sbak

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Re: 12ga Big Bore
« Reply #18 on: January 26, 2019, 03:31:16 PM »
Why just cans? Have it vent back into a reasonable diameter shroud. A lot of free volume provided along the barrel length
« Last Edit: January 26, 2019, 03:43:18 PM by Sbak »
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Offline TPL

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Re: 12ga Big Bore
« Reply #19 on: January 26, 2019, 03:42:06 PM »
Is rkr's can practical? What if it was 75% larger in diameter? Do you disagree with 0.25 in^3/fpe?
What is rkr's caliber? Air quantity?

By all means try it, I am not resisting.
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