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All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Big Bore AirGun Gate => Topic started by: Extreme Big Bore on April 14, 2016, 05:19:00 PM
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Turkey season open in Michigan Monday I have built a 28 gauge air shotgun for the challenge I have lots of birds on camera in the back 40 and some good TOMS. I am getting great patterns out to 35 yards 24 inch pattern with no holes in it at 35 yards. I installed a polly choke on it and on extra full it patterns great for the 1 1/8 ounce of number 4 shot. With nitrogen I am getting the 1 1/4 ounce shot at rite at 1000 fps with helium it is 1300 fps sounds crazy but on helium it is faster than a powder burning 28 gauge. I have come up with a new way so loading is easier than ever. Enough said I will post pictures when the hunt is over with results.
Brent Hoag
Extreme
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You're pushing 1 1/8oz., and 1 1/4oz.? Holy smoke that's a huge shot charge for a 28ga.
How are you doing it....inquiring minds gotta know...
Gene
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;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D
photo photo photoooo jejeje
Pau
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WOW! OVER AN OUNCE+ at those 1000 and 1300 fps............INCREDIBLE!
I think air shotguns are soooo cool
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I agree Fazfou...shotguns rock, a workable compressed air shotgun that works well...brilliant!
The shotgun has fed more mouths in the history of mankind than any other...
1 1/8oz is thee most well known 12ga target load...with the 1oz load a close second.
1 1/4oz is one of the most popular high velocity 12ga hunting loads....
You go Brent...
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I gotta see this!
Love my scatter guns and an AG version has my curiosity
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Pictures and more info about the air shotgun
Norm
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How does the noise compare to a powder burner?
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Hearing protection required for sure, I would say just as loud a PB shotgun.
At the Pacific Airgun show a guy shot a 20ish gauge shotgun and it was loud as heck and it was shot indoors of course too...
Everyone froze for a few seconds and then started clapping their hands to applaud him :P
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Hearing protection required for sure, I would say just as loud a PB shotgun
Seriously?
I have shot trap and skeet for years. An airgun with that kind of report is hard to grasp.
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A lot of PCP air guns have powder burner level noise IF they are used without a shroud. And shroudless big bore PCP air guns are definitely that loud.
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I will post pictures of everything even better yet I killed a nice tom turkey yesterday.
Brent
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Congrats Brent! Put the turkey in the hunting gate please
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Ok I will do that. Is it also ok to put it on the dark side.
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I moved it for you, only one thread on a topic anyway ;)
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I'm questioning your numbers. I think your getting false readings or you just can do a shotgun over chrony.
1.25 oz is 547 gr. So 547 gr at 1000 fps is 1214 fpe. 1.25 at 1300 is 2054 fpe.
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I questioned that also dyotat100. I tested it many times with the same readings and if you look at what my 72 caliber shoots for speed with a bullet and a rifled barrel with very close to the same weight the numbers work out. Trust me these numbers are not inflated. You must remember one thing with a shotgun there are no rifling grooves to create friction like there is on the bullet. It is a smooth bore with a plastic shot cup or wad with minimal friction exiting the barrel. Actually it shoots a little quicker than I posted. Example 72 caliber rifle 437 grain or 1 ounce at 920 FPS 28 gauge shotgun 437 grain or 1 ounce of shot well over 1000 FPS.
Brent Hoag
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I just think a few of the shot are getting thru the chrony faster. It's like shooting a big bore to close to a chrony and you get false readings.
It's making a lot more power then the .72 does.
Only way to really know is shoot a solid slug thru it.
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Yes, it does seem like a lot.... 1.25 oz at 1000 fps (1214 FPE) is about the maximum I would expect from a 28 ga. with wide open ports (ie no ports under bore size = 0.55") and a 30" barrel at 4500 psi on air.... However, it is not beyond what should be possible, if all those conditions are met.... It is the mathematical equivalent of hitting 200 FPE in a .257 with a 30" barrel at 3600 psi with a 90 gr. bullet.... Helium at 70% above that FPE is not out of the question, either....
Realistically, the .72 cal is not pushing the limits, but IIRC, it has a much shorter barrel, does it not?....
Bob
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The reason the 28 gauge has more power than the 72 with the same one ounce load is do to no rifling groves. The shot cup is casting the shadow just like the bullet does. Think of it like this when you slug a barrel the bullet is very hard to force through the barrel now the shot cup in the shotgun barrel slides through very easy the gas check in the back also seals the gasses behind the shot cup so it has a better seal then a bullet. Combine these two things together and I %100 agree with 80 FPS faster than the 72 caliber. I do my chronograph testing at the same distance for shotgun and rifles. The way that the shot cup works with the tape holding the shot inside it makes it so the shot has not left the shot cup until after passing through the chroney.
Brent
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I disagree that the rifling, or lack thereof, has much to do with the velocity.... Very little energy is taken up in imparting spin to the bullet (on the order of 1-2 FPE), and the friction is mostly a matter of fit in the bore.... However, I have found it more difficult to get accurate and consistent Chrony readings with my .410 Hayabusa, loaded with three OOO buck in a shot cup.... However I didn't try taping the shot cup closed, that might make the difference....
I assume, Brent, that you are using a barrel of about 30" or so?.....
Bob
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No disrespect intended Bob. I have to disagree on your calculation of 1 to 2 FPE. I have taken bullets and ran them through barrels before and have broken off many hardwood dowel rods trying to get them through the barrel even having to hit the dowel rod with a hammer to get them through I have no way of measuring the FPE to get the bullet through but it is a lot. I have even seen velocity increases by going to a slower twist rate on my 40 caliber I went from a 1 in 14 twist rate to what I have now for the 40 caliber which is a much slower twist rate and saw 50 to 60 FPS different with the same rifle and bullet just different twist rate also I have great accuracy with it. I understand sizing of the bullet is important but even with the perfect sized bullet the rifling still must deform the lead taking FPE away. With the plastic shot cup I will agree with 1 to 2 FPE to get it down the barrel. One other thing that proves my theory the shotgun will use more air per shot with the same spring as the rifle do to less resistance in the barrel trying to close the valve so a lighter spring is needed. Again I have no scientific proof for any of this but do have the test results and can only speculate why the shotgun performs different than the rifle.
Brent Hoag
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You said 1000 fps with 1.25 oz. That's 547 gr.
Your saying 80 fps with 435 gr diffence between .72 and 20 gauge. That's a lot more then 80 fps difference shooting 435 gr at 1000 and 547 gr at a 1000.
Yes I know first hand how a faster twist slows the fps down. I have done 2 guns where going from 1:14 to 1:10 was a 40-50 fps loss. This happened in .257 and 7 mm.
How hard would it be to shoot a solid slug or is the choke permanent?
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If you have to hammer a slug through the bore, it's too tight a fit, IMO.... As to twist rate and muzzle velocity, here is what Brian Litz has to say on the subject....
http://bulletin.accurateshooter.com/2015/02/does-barrel-twist-rate-affect-muzzle-velocity-litz-test/ (http://bulletin.accurateshooter.com/2015/02/does-barrel-twist-rate-affect-muzzle-velocity-litz-test/)
The math says.... " In the case of the .30 caliber 175 grain bullets, the math predicts a loss of 1.25 fps per inch-unit of barrel twist".... and his live fire tests showed more variation shot to shot than from an 8" twist to a 12".... and an actual variation in velocity of 1.33 fps per inch.... (5 fps slower for an 8" twist than a 12")....
Anecdotal evidence is just that, and I would suggest that if you lost a lot of velocity with a faster twist, you need to look at the bullet fit / bore diameter.... I'll prefer to believe the math and the experts, but that's OK, we're allowed to disagree and still get along....
Bob
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I used one ounce or 437 grain in both rifle and shotgun for this test and the shotgun will do better than 1000 fps I was down to 4000 psi in my tank and my booster is screwed up. So the old data I have for the 72 cal is based off 4500 and the 437 grain shotgun was based off 4000 psi so it will get faster at 4500 PSI. So I believe we agree a faster twist rate can and does slow the bullet down do to more restriction and it only makes sense that no twist and a plastic shot cup will only increase velocity. As for putting a bullet in this shotgun I really do not want to because it has a poly choke on the end the people at poly choke told me that slugs can be shot through it but it is hard on the poly choke and this shoots such a nice pattern that I don't want to risk it ultimately this shotgun was to shoot shot of some sort not slugs. I try my best to only put information on here that I believe is accurate and if I find that any information I post on here is not accurate I will be the first to correct it. There is nothing good about anyone whether it be the gun builder or a shooter posting false or inaccurate information.
Brent Hoag
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Brent, what is the barrel length on the 28 ga. and on the .72 cal?....
Bob
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Bob the barrel on the 28 gauge with poly choke installed is 28 1/2 inches and the barrel on the 72 I tested was 27 1/2.
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At 28.5", on 4500 psi, your 1214 FPE is right at the limit of what my spreadsheet predicts as a "lofty goal" for a PCP, closer than anything I have seen in the past, so congratulations.... The .72 cal, at 27.5" on 4500 psi would have to reach 2100 FPE to duplicate that relative level of performance, however.... Incidently, these power levels are exactly 50% of the theoretical maximum that can be achieved with that barrel length, bore area, and pressure, regardless of the gas used, just to put things in perspective....
Bob
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Sorry about the delay but I will post pictures later this week.
Brent