Ballistics By The Inch!

[187Penguin]

I have a Vorteked B30 22cal that has had a rough life. I purchased it in VERY used condition, but man was it powerful! Well over 22 FPE! It also was not quite as smooth as I had hoped for. When the scope mount finally fell off, I decided to do something about it! I ordered a Vortek RWS48 kit with new seal and dropped it in. There was a little lost power (20 fpe) but the shot cycle improved dramatically. Unfortunately, have lost about 30fps a year for 2 years, but it's still very smooth.

I needed the mount shortened to fit a droop mount for an RWS and re-attached. A buddy heard about it and proclaimed "I'm a welder! I'll fix it up like new!" "What Luck!" I though.... until I got it back.... I learned a valuable lesson. Just because someone HAS a welder does not mean they ARE a welder. I will let the pics speak for themselves. Shortly there after, life got hectic, and the B30 went into the closet. It came out from time to time, but was such an eye sore I didn't even want to look at it, even if it WAS a dream to shoot. Besides, I shot rim fire and center fire enough to keep me happy. Recently, after realizing that this ammunition lunacy is not going away, I decided to revisit my air rifles.

First on the list is the venerable B30! I contacted Mike M. for a replacement receiver assembly. Unfortunately, all new 22 cal bore assemblies were gone.  But not all was lost! He found a used 22 B21 assembly in need of minor repair. But alas, that is a story for another day. Since I had a half mangled B30 receiver with zero collectable value, I decided I would chop the barrel down 1 inch at a time and chronograph it with an array of pellets I typically shoot. All the traditional knowledge I could find said a springer does most of it's accelerating in the first 6 inches. Since this given fact is quite old, I felt it might be a bit outdated with a more modern, magnum rifle.

For the pellets, I selected Crosman Premiers (14.3gr), Gamo Hunters (15.43gr), And Crow Magnums (18.21gr). My reasoning is that I don't like to shoot too light OR too heavy of a pellet. CP's are as light as I go, and CM's are the heaviest. The Gamo Hunters are the closest to the average of the two weights that I had on hand.

Since I was not checking for accuracy, just velocity, I was not overly concerned with a perfect crown. So long as it was burr free, and pretty square it was good enough. I cut the barrel with a heavy duty chop saw. I know that a lathe would have been better, but I do not have one at my disposal. Also, I do not have a crown cutter, so I just used an abrasive grinding ball to de-burr the cut. I had intended to cut it an inch at a time down to 6 inches, but found going that far to be unnecessary.

As far as the data, I shot pellets until a 3 shot trend emerged. I was not looking for the consistency of the individual pellets to see which might group the best. I was looking for something closer to a mode for a given barrel length and pellet weight, give or take a few fps. I began shooting and discredited any obviously low or high values. Fortunately, 85% of the time, consistency was great with only 3 shots needed to get 3 consistent shots. One notable exception was the 13" length with CM's. After 10 shots they were sill all over the place with an extreme spread of over 25 fps and a standard deviation of over 10!  By comparison, this rifle typically has an extreme spread of about 5 and a standard deviation of about 2! One unique observation: The Gamo Hunters we amazingly consistent never needing more that 3 shots to show a trend! By comparison the CP's typically needed 4 shots, and the CM's often needed 5+.

After the data was gathered, I averaged the 3 selected values for each pellet at each length. I then converted the speed to FPE to give me equal units across the board to compare.

Observations with my particular B30:

Surprisingly, barrel length vs. velocity with a springer doesn't appear to be linear, or even proportional. Perhaps piston bounce has something to do with it?

At 9", there was an increase in muzzle blast, some what noticeable velocity drop off, a bit more "sharpness" (but by no means and increase) to the recoil and the ever-so slightest hint of a hint of miniscule piston slam. Am I right at the point of no piston bounce? It was also the most constant when all three pellets' SD and ES are taken into account! Maybe if the piston was just a touch lighter? I felt no need to go shorter out of fear of damaging the piston, and the obviously wasted pressure. Perhaps at <12ftlbs 6" is all you need, but at +17ftlbs, I recommend going no shorter than 9"

Crow Magnums are comparably inconsistent in my rifle, especially at 13". 13" must be the magic length where the pellet transitioned between being pushed and simply coasting. I think the minute tolerances in the pellets diameter really come into play at that length

Cheap Gamo hunters must fit my bore perfect! They often had an ES of less than 3!!!

A 9" barrel is awfully nicely balanced and handy.

So I am thinking that in 22cal, at ~17fpe, a 9" barrel and a moderator to help with the blast would be ideal. With a short barrel it would need a side/under lever..... Remind anyone of any thing???

Final Thoughts:
Between 10" to 17" on a 17ftlb gun the differences were trivial. Report slightly increased but that was it. So, in MY opinion, if you want to chop your barrel, don't get too caught up in the "optimal" length. Go with what you think looks good, then see if it's velocity is consistent with the pellet you like. If your ES is all over, take another ~1/2" off and call it a day! Don't loose sleep over the 1/2ftlb that could have been.

Lessons Learned for next time:
Get a lathe!
Get an 11 degree crown cutter!
Do some high speed photography with the rifle free to recoil as it wishes against a grid backdrop! (I have a 1200fps camera but forgot all about it )
Get a 3 axis accelerometer and check out those G forces and vibrations! You can get OK ones as cheap as $80 nowadays!
Get someone to proofread my stuff before I post it!

[187Penguin]

After a rough crown was put on via a die grinder ball I shot a group for science! The top most and left most hole were my fault  ... it coulda been better! 15 CPHP's @ 15 yards, seated on a pillow. I wonder what it would do with a proper crown?

[amb5500c]

Looks like you have it headed your way.
Richard

[187Penguin]

Looks like you have it headed your way.
Richard

Hi
I assume you mean the B21 assembly... and it's already here! Plus my steel picatinny blank! But as I said before, that's a story for another day

[HYspd]

somebody with a mill could clean that weld up a whole bunch

[187Penguin]

somebody with a mill could clean that weld up a whole bunch

I agree, but the rail is so crooked, the scope cants about 15 degrees to one side! It wouldn't be worth finding a shop to pay to do it! But man o man, I could make this thing sweet if I had access to a machine shop! Unfortunately I am limited to hand tools.

My original plan was to just trash this receiver and replace it with the B21 chopped to 12", but that was before I handled it with the 9" barrel! Now I am contemplating removing the boogered rail, replacing it, lightening the piston just a bit, re-crowning and refinishing it! And probably adding a carbon fiber shroud so it doesn't look quite so goofy with that short stub! Then I will have both a nice, powerful, factory looking B21 or a 9" B-30 Vortek wanna-be TX200 Bubba frankengun to drop into the stock. Maybe I could even get an old beat-up RWS stock and trigger guard and have two whole guns! But that will be for another day in another gate!

It's hard to say. Too many ideas, not enough money, no access to proper tools

[Sandspike]

Too many ideas, not enough money, no access to proper tools

The story of my life.

[rsterne]

Interesting how the velocity seems to increase  snd decrease in an almost rhythmic pattern as you shortened the barrel.... faster, then slower, then faster, then slower again.... and then finally dropping at about 9".... Although the variation in velocity wasn't huge, it was an interesting phenomenon....

Bob

[187Penguin]

Interesting how the velocity seems to increase  snd decrease in an almost rhythmic pattern as you shortened the barrel.... faster, then slower, then faster, then slower again.... and then finally dropping at about 9".... Although the variation in velocity wasn't huge, it was an interesting phenomenon....

Bob

I agree! I guess that are far more dynamic forces at action than one might think. My guess is a "second wind" from piston bounce if the barrel is long enough to capitalize on it. I also found it interesting for each weight, there seemed to be a 2-3" range with a "velocity plateau", each happening at progressively longer lengths as the pellet weight increased. 13-15" for CM's, 12-14" for GH's, and 10-11" for CP's.

[187Penguin]

I also theorize I will get more consistent velocities from the shorter barrel. My thinking is that the minute diameter tolerances in the pellets have a trivial impact on pellet velocity during the first big push of acceleration. After the first bounce the pellet "coasts" for a bit while the piston stops rebounding and begins compressing again. Here, friction comes into play. I think minor diameter differences are enough to have an effect at how far down the bore the coasting happens, how dramatic the friction losses are, and the distance traveled during that period. If the pellet is still in the bore after the first wave of "equilibrium", then it gets a smaller, second "shove" which boosts it back up to a more standard speed. I noticed closer to the "velocity plateau" I could guarantee that the velocity would be higher or lower based on how tight the pellet was, and the ES opened up as result. With longer barrel length, it was less apparent, but still there. Perhaps the long barrel is a "buffer" of sorts? The exception was at 9", where the pellets must have been under that initial "push" and then out of the barrel before any other forces could act on them. Therefore the friction forces, and distance traveled in the bore before and during piston bounce, could not be further exacerbated by pellet tolerance and resulting friction differentials. The issue now is walking the fine line of having the pellet release the bore right before the piston bounces, but after enough pressure is created to cancel out slamming. But that's just my theory anyway.

Fwiw, I just shot 10 CPHP's of slightly differing chambering resistances over my chrony out of the 9" barrel. The ES was 4! SD was <2!!! The closest things I can equate the shot to would maybe be swinging an axe and getting it stuck in a solid stump, or maybe slapping a sopping wet beach towel on a sidewalk.... if that makes sense...?

I think testing hold sensitivity is my next area to investigate.

[^^artin]

Thanks for the effort you took here.
That adresses some of the questions I currently asked myself - also the outcome was not as plain as one might wish.

[Horatio]

Thanks for the effort you took here.
That adresses some of the questions I currently asked myself - also the outcome was not as plain as one might wish.

Old post. I think OP no longer here.