I've been toying with the idea of shortening the barrel length of my Crosman G-1 Extreme but still waiting for some additional info from some research that I'm doing. Finally upon convincing myself that I have a definite plan of action I decided to shorten the barrel of my G-1.
I was reviewing the article made by Varming Al regarding barrel tuning using a weighted tuner unit near the muzzle of the barrel to affect the timing of bullet exit at the muzzle and there was this little link (actually a very funny one) about listening to your barrel for vibration and ringing (excessive vibration similar to plucking a string of a guitar). being familiar with audio and sound I decided to see if there is a merit to what it wants to explain. I like the author's preface - "This writer is a reporter, pure and simple (minded). I am no physicist, engineer, metallurgist or scientific type of any sort. Any similarity between the content of this article and scientific accuracy must be attributed to the work of others more qualified. Hopefully, however, some of their findings, valid or invalid, are accurately reflected herein. That said, settle back and, hopefully, you, too, will enjoy an enlightening chuckle or two. That is the intent." I like that. Just a sort of a very enthusiastic rifle fanatic that somehow "discovered" something that affected his curiosity and pursued it.
I am no engineer myself too, just a regular guy who never stops trying to figure out if my idea works or not. Being involved in audio before I thought "probably I can use some of the ideas of room tuning to airgunning. Hahaha!" So this idea came into work! Here goes.
Hoke Kerns (the author of the article from this site:
http://www.precisionshooting.com/psm_2007_09_issue.html) worked with a guy by the call-sign "COLT .45" and experimented on tuning their rifle barrel by "listening" to its resonance sound using just a wooden mallet to excite the barrel when struck and listen to it using a stethoscope placed at the surface of the stock. You would hear 3 sounds actually, the first is a "Bong" with a small tail of resonance into it, the second is a "BOOONNNGGG" that has a more pronounced longer resonance tail of sound into it, and the last one would be the "THUD" a solid type of sound that has a sharp note but without the ringing tail associated with the bong and the booonnnnggg sound. Now their idea was to "move" the THUD sound very near or almost at the muzzle by adding a weight tuner (with a variable weight system). The idea actually works ( I can attest to this).
To mimic or replicate their analysis I decided to just tap the barrel of my Crosman G-1 Extreme (without the muzzle brake attached) using a wooden dowel and listen to it with the diaphgram of the stethoscope touching the synthetic stock at the C.O.G. area of the stock. I can hear the Bong, Bong sound all through the length of the barrel but suddenly shifts to a THUD at around 14" - 14.625" from the end of the breech. I found that interesting. I noted that on a piece of paper and then started to add weights on the end of the barrel using the assorted sockets that I have (from a socket wrench set). I don't have a weighing machine so I just used the heaviest of the sockets and use some rubber bands to put them together and hang them tight to the end of the barrel. What I have noticed upon hanging the added weight was that the "THUD" sound did actually shifted "forward" near the muzzle of the barrel by about 0.75" (similar to what Hoke and Colt .45 noticed too). In my G-1's case this "dead zone" area of THUD sound is about 5/8" in range. After that 5/8" zone it starts to ring again and have that BONG sound.
My G-1 is already too heavy (even without the Leapers 3-9X50 scope) since Crosman makes their airguns mostly with all metal parts so I don't want to gain some additional accuracy into it by adding more weight using a weighted tuner at the muzzle. What I want to find out is that If this "zone of neutrality" exhibited by the THUD area be the right spot to cut the barrel and "therefore" (this is just my analysis) bringing the dead zone at the crown area. Instead of using weight I just "shifted" the dead zone by shortening the barrel (in a theoretical point of view).
So, now I know that the barrel of my G-1 has its dead zone from 14" - 14.625" from the breech, all I need to find out now is exactly "where" will I cut my barrel at this dead zone? So Off I go to my old ideas about room acoustics and come up with this analogy:
"we excite a room with multiple frequencies by putting a subwoofer at a room's corner. It does not matter where, any corner will do (even at the corner ceiling! LOL!). Then to know where you can locate or position your listening is to divide the room into odd multiples like (Length divided by 5, by 7 by 9, by 11, etc....) and plot them in the room using masking tapes. Then by actually moving your chair very near these odd lines or intersections you can actually find a sweet spot wherein most of the frist modal room resonances is actually not that strong" (just like what hoke and colt .45 found out in a barrel of a rifle). Sound like a voodoo science eh? Well, you can think of it like that but in reality there is some truth into it. In audio the axial modes of the rooms resonance are the most notorious to control and they affect the overall frequency response of your speakers (regardless of brand except other design like planar speakers) wildly! The rememdy that we do before room acoustical tuning is to position the listening chair to a sweet spot and from there work on refining the sound by adding some acoustic panels into the room. (Enough of the room acoustics stuff. Hehehe).
Applying this to my G-1's barrel, I am "assuming" that this THUD area (zone of neutrality) would also mean that the main axial modes of resonances of the barrel will be exhibiting the least amount of vertical deflection (a form a first-order resonance mode) and so I'm convinced that this is a good spot to cut my barrel. Now I already know that I can but my barrel anywhere within 14" - 14.625" but where? What I did was to divide the original barrel length of 18.5" (this is the G-1's original barrel length) with odd numbers and find out which among them is within this zone of neutrality area. Here is what I came up:
18.5 inches divided by 9 multiplied by 7 = 14.39"
18.5 inches divided by 13 multiplied by 10 = 14.23"
I opted for the 14.23" length. I don't have the midwayUSA's tool to totally make the crown perpendicular to the barrel so what I have used it to buy this 90 degree metal brackets that I use to attach wooden planks on a cabinet. Using just a regular hacksaw I cut the barrel. That's it. Now off I go to clean it up using a metal file and a 280 grit to clean the new crown. I used a metal countersunk bit to finish the crown and I'm satisfied with the results.
Here are the pics of the final outcome.
The advantages? Well, for one thing I like the way the weight is balanced now on my G-1. I did not notice any additional recoil from shortening the barrel. In my personal experience I kinda like it more now that it is less weight heavy. The only downside is a more pronounced cocking effort but I can live with that. Accuracy? Again in my own personal opinion and experience I gained an additional tighter grouping from my shortened G-1. That's all folks. Hehehe.
Speedturtle
