Harry Fuller, a little help. please

[sgeorge]

Harry,

You posted a picture of a barrel, machined to fit a FX Elite action. The picture showed a number of steps that were machined to reduce the OD of the barrel several times.

Do you think that doing this machining to the outside of the barrel changes the bore in a significant way and how might this affect the barrels potential for accuracy?

 

[Harry Fuller]

Profiled .25 cal BSA/ John Bowkett barrel to fit FX Elite rifle:

Harry,

You posted a picture of a barrel, machined to fit a FX Elite action. The picture showed a number of steps that were machined to reduce the OD of the barrel several times.

Do you think that doing this machining to the outside of the barrel changes the bore in a significant way and how might this affect the barrels potential for accuracy?

I can only go by results Steve.
The FX Elite with profiled BSA barrel, as seen in the picture, shoots extremely well as these pics below will indicate.

Groups shown are single groups and are not chosen from many. They were shot in August .

Just two groups shot in the session: one group of 5 shots was fired at 71 yards with .25 Benjamin 27.8 gr pellets: (That's near the range of your "Extreme Range" yearly competition; I think my barrel would be competitive in that upcoming event?):
CTC 0.40 inches:

http://img.photobucket.com/albums/v392/Kyogle/FXElite25BenjaminsBSAbarrel71yards_zpsbca5f2bf.jpg

And the second group after the one above was at 115 yards (to see how the Benjamin pellet may hold up at longer range from the BSA barrel):

http://img.photobucket.com/albums/v392/Kyogle/aaa7cf80-7d48-4b9d-a1ad-d8e7d70dafd4_zps7597512c.jpg

I do understand that profiling "button rifled" powder rifle barrels relieves stress - and is supposed to change the bore diameter causing it to grow unless stress relieved before profiling:

A supporting quote from Border Barrels:

..."When contouring a barrel, a lot of metal is removed and if there is any stress in the metal then this is relieved by the removal of material. This may result in a barrel that started out as straight ending up as bent. This is not usually a problem when cut rifling a barrel as this does not induce any stress, but button rifling induces a fair amount of radial stress which is relieved by turning the barrel down. What happens then is that as you remove metal from the outside so the dimensions on the inside grow larger. If you turn a sporter barrel with a skinny muzzle from a buttoned blank then you find the barrel is bell mouthed and the bore diameter is a thou' or more bigger at the muzzle than the chamber - definitely, not good! Buttoned barrel blanks have to be stress relieved before profiling to prevent this expansion at the muzzle. " ...
Reference: http://www.border-barrels.com/articles/bmart.htm

But as indicated in the quote, "cut rifling" apparently does not induce any further significant stress; so if you were working with a cut rifled barrel presumably there would be no problem .

However I personally don't know how this phenomenon relates to "hammer forged" barrels such as my BSA Bowkett/ Elite barrel; or whether the BSA barrels were stress relieved in the manufacturing process, or there-after.

So I can only respond to you by way of evaluating the performance of my particular barrel in the light of shooting results as in the groups above. It is a very accurate BSA 16 mm OD barrel, in the FX Elite platform, by any standards.

Best regards, Harry.

 

[mark6869]

No problems with that barrel

Nice barrel,nice shooting regards,mark

 

[sgeorge]

Harry,

Great groups. The question was raised based on reports that Lothar Walther and CZ barrels, after being re-profiled, had changes in bore dimensions that could be felt when pushing a pellet or, even a cleaning felt. Now, if the machining is causing the bore dimension to increase, then we might have additional choke points along the barrel. Not knowing how hammer forged barrels react to this type of machining just poses another question. Thanks.

 

[crb]

Long !!

Here is the bbl that is on my 40X at the moment. I bought a couple of used bbls for a 2013 and this one was said to be a Shilen. It was only about 21" long and it had a .920 OD which was worrisome [ 10/22 normal "match" bbl OD ]. I borescoped it and it did look smooth enough to be a Shilen. I don't like short bbls so I never tried it on the 2013 which was eventually sold.

The 40X was my first bbl fitting project and it's normal bbl is an Anschutz Match blank that Numrich sells. These blanks are 1.25" OD straight , no taper. The bore is SMOOTH. It is also straight with choke at the muzzle. A pulled bullet slides with almost no resistance after you get beyond the leade.

I shot the bbl as a straight cyl for quite awhile. It would shoot good groups but threw too many fliers. Eventually I bought the borescope and discovered what I call 'boat paddle' burrs on the rifling which turns out is normal from what I have seen with other bbls I have looked at. I used a split arbor and 600 paper to eliminate the burrs and then the bbl would really shoot some great groups. Still would throw the occasional ammo induced small flyers but no more 7s or worse.

I then turned the OD down to .825 so I could use a tuner on the bbl. I left a full dia torque shoulder and when slugging I could feel a constriction at the shoulder. Hmmm. I then turned off the shoulder and extended the tenon threads and now use a Pacnor nut to secure the bbl. This also gives adjustable headspace.

Now back to the .920 bbl. I turned down the 2013 bbl tenon to .645ish to use in a 40X bbl tenon that I extended the threads on for use with the Pacnor nut and I bored the ID to .645ish. I used Loctite 609 to secure the bbl to the tenon. I did NOT slug the bbl. When I had borescoped the bbl earlier I did notice that the leade looked perfect which was surprising and encouraging. I did not slug the bbl. The gun shot extremely poorly so I removed the bbl and ignored it for a few weeks. Then while slugging other bbls I decided to slug this bbl. The slug had slight resistance all the way down which tells me the bore is slightly tapered as is the norm on state of the art rf aftermarket bbls.

When the slug got to the muzzle it STOPPED. It had to be hammered on through. Obviously the person that did the original bbl work did not cut off enough of the blank. I cut off 1/2" and tried it again. Still too tight. I cut off another 1/4" and redid the crown.

In thinking about this set up I decided I didn't like having the weight of the full .920 bbl hung off that .645" dia tenon. I also wanted to induce a bit more taper to the bore so I came up with the dimensions needed to have equal length sections with equal diameter change for each segment. Basically the segments are 3" long and enlarge by .050" OD segment by segment. This ends up with the last 3" segment at the muzzle being the original .920" OD so I don't end up with the bore dimension growing at the muzzle. In other words I retain the smallest possible ID in at the muzzle.

When slugging the newly turned bbl it did seem to have slightly more drag on the slug. Not a tremendous amount but some more than the original straight contour. The constriction at the muzzle still seems tight to me but not excessive as before.

I shot the rifle after our last match and the thing showed a lot of promise in the short time I had available. I shot one group of 8 to 10 shots at one RBA sighter bull and all shots were clustered around the 10 ring. Not a tiny group, but all solid 10s. This is with no tuner.

I came home and made a sleeve [ about .010" wall thickness ] to allow the mounting of a Fudd tuner I have. I will shoot the gun some more on Thursday morning if the weather cooperates.

I have a couple of Benchmark bbls that came with a rifle and both shoot very well with Center X. One of these bbls is a short 3 groove, RF BR reverse taper sporter bbl that is about 21.5" long. It shoots very well even though it is short for my tastes. It is VERY draggy when slugging as is the other Benchmark reverse taper. I was trying to duplicate this draggy slugging feel with the 'telescope' turning of the bbl in the pic.

 

[Dennis D.]

Slugging fired barrels

Ray, when you slug fired rimfire barrels it can be very difficult to tell if the barrel is tight or if your feeling the extra drag created by the roughening of the bore from firing. The only way I know to tell is to slug up into the spot that feels tight then push the slug back out the way it came and remeasure. Machining the breach of a button rifled barrel should let it open up a bit. Machining a hammer forged barrel is suppose to tighten it up. Of course that's IF the bore is uniform to begin with. Of the eight or so LW air gun barrels I've slugged none have been very uniform. Most have been tight at the breach then looser in the middle and then of course tight at the choke. A couple have shot quite well and I suspect it's only because of the choke. Just as an experiment I took one LW barrel that didn't shoot very well and reversed it as it had about a 2 inch tight spot at the breach end. I cut off the choked end first of course. It shoots better this way than it did though still not up to BR standards. I also suspect that to tight or to abrupt of a choke is the cause of some of the flyers in airgun.
When slugging I've noticed that some pellets will come out with a little bit of shaved lead attached to the skirts. At first I thought this might be from the throat but when pellets are pushed only up to the choke then back out the breach it is less apparent so I'm concluding it's from the choke itself. Most of these I'm sure are blasted off when firing but some must occasionally stay attached and be another source of flyers. Unfortunately I'm not very skilled at lapping barrels but I suspect that a more gradual taper into the choke would help.

Dennis

 

[crb]

The question is; is a tapered bore going to work for airgun ?

I would almost think you would want a straight bore with choke. Of course the 'telescope' turning of the bbl like I did the one in the pic only induces a tiny bit of taper which might work out fine for airgun. I have one more of the Annie 1.25 OD bbl blanks that I could mess with but turning the bbl down to a smaller dia is a swine of a job. I should order some JCB 22 cal pellets to use as slugs for my various 22 lr bbls. It would be very interesting to 'telescope' turn the Suhl 19t bbl and try to induce a bit of taper. As a 22 the Suhl shoots great when it's hot outside. Keyholes when it's less than hot.

What are you guys using for chambering reamers ??? I am totally lost on airgun building . It would be cool to adapt a 22 bbl to my CRX if possible. The 'bolt' might not work in the larger bore. The CRX shoots so well that I don't want to fool with it.

 

[crb]

The other thing I wanted to question was what effect pulling the trigger has on the pellet vs what happens in a firearm. Does the pellet skirt get blasted into full contact by the sudden application of pressure. I assume that on a 22rf that the gas pressure is like a hammer applied to the back end of the bullet which blasts it into full contact with the bore. I would love to be able to safely stop a bullet in the bbl and then be able to push it out backwards and have a good look at it.

 

[Harry Fuller]

The other thing I wanted to question was what effect pulling the trigger has on the pellet vs what happens in a firearm. Does the pellet skirt get blasted into full contact by the sudden application of pressure. I assume that on a 22rf that the gas pressure is like a hammer applied to the back end of the bullet which blasts it into full contact with the bore. I would love to be able to safely stop a bullet in the bbl and then be able to push it out backwards and have a good look at it.

I have just read your query Ray.

Ray, it depends upon the power of the rifle and the thickness of the pellet's skirt as to what the pellet's form/profile is like after being shot. If present, that change in form profile can then cause some of the difference (not necessarily all such difference) in drag coefficient (and BC) noted between the same pellets shot from different rifles. Here is an example:

.22 cal JSB pushed through a smooth twist FX barrel with a freely rotating rod:

http://img.photobucket.com/albums/v392/Kyogle/STElite22JSBpushedthrough_zps7755a5c9.jpg

Same pellet style shot through the same barrel:

http://img.photobucket.com/albums/v392/Kyogle/STElite22shotJSB_zps02275ff4.jpg

I think you will detect the change in form and can surmise that there will be a difference in flight dynamics of the above pictured shot pellet compared to one that may have been shot at a much lower power or one with much thicker skirt lead.

Kodiak with thick lead skirt pushed through the barrel:

http://img.photobucket.com/albums/v392/Kyogle/STElite22Kodiakpushedthrough_zpsd23fe5a1.jpg

Another Kodiak shot through:

http://img.photobucket.com/albums/v392/Kyogle/STElite22shotKodiak_zpsaee18b5d.jpg

The difference is not so marked as with the JSBs with their thinner skirts.

Kind regards, Harry.