Dissapointed in JSB King Extra Heavy 25's

[rsterne]

Since a pellet's rotation slows much more slowly than it's forward velocity.... it is not uncommon for a pellet that is marginal to develop Dynamic Instability as it travels downrange.... IMO that is the most common reason for pellets spiraling, because they tend to shoot well close up and then the groups open up much faster than the MOA cone does.... A barrel that shoots 1 MOA (~1/2" CTC) at 50 yards, should, under ideal conditions shoot close to that same 1 MOA at 100 yards (~ 1" CTC).... However, it is not uncommon for airguns to shoot MOA at 50 to 70 yards, and then have the groups open up to 3-4 MOA (or more) at 100 yards.... Something is obviously happening as the bullet travels downrange, and with pellets, which are primarily drag stabilized, I feel the culprit is likely to be too high a spin rate, which becomes an increasing problem as the range increases.... One more difference between pellets and bullets....

Some of the top custom airgun manufacturers are now using extremely slow twist rates to eliminate spiraling.... AAA now uses a 32" twist in their .25 cal. pellet barrels.... 

Bob

[KnifeMaker]

The success of the FX Smooth Twist seems to hint at this as well.

Knife

[rsterne]

Yep, the original Smooth Twist barrels produced spin rates as slow as 1 turn in 13 FEET (156") by actual measurement of a pellet in flight.... The RPM depended on pellet hardness more than anything (how easily it stripped when going through the rifling at the muzzle at 900 fps).... but I think the fastest spin measured was about 1 turn in 4 feet (48").... even though the pressed in twist was about 1 in 16"....

Bob

[KarlH]

Been a while, lets see if this long post will paste in one or if I have to make more than one post, wrote it in word.

I checked the twist and it is approximately 1 in 17 inches.   I ran over 100 pellets, some H&N's of various sorts and the 34 grain jsb kings through loading from the magazine and then pushing them back out with a rod from the muzzle.  Many of the jsb's had sharp gouges with some shaving on the skirt, hardly any sign at all on any of the H&N's although they still were not what I'd call pretty.  The jsb's definetely load much harder when being pushed into the rifling when loading than anything else.  With the extra effort loading the jsb's, after the head has engaged the rifling fully, the pellet quickly jumps forward until the skirt hits the rifling.  It is difficult to control given the pressure it takes to push the head into the rifling.  Being extra careful, the jsb's had less damage on the skirt, but still looked bad. 

So, for the first time ever, I removed the barrel so I could check it out better.  The beginning of the rifling is a straight 90 degree wall and it definetly was quite a sharp edge.  Using a punch that fit in the base of a selection of pellets, I pushed many into the rifling giving me a direct feel.  It felt rough as heck pushing pellets in, much more so with the jsb's and it really showed on the jsb's after pushing them back out, then I pushed a bunch all the way through the barrel.  The jsb's did not fair well, it's no wonder they were flying all over the place with wild swings in velocity down range.  The jsb's have a much thinner base than the H&N's which held up much better.  All pellets felt wierd going through the choke, not consistent at all.

Since I had the barrel off, I gave it a thorough cleaning and discovered another "problem", whether it is a problem or not it just does not seem right/correct.  After running a brush and patches with solvent, I was surprised how clean it was, I really was expecting more junk.  I put a jag on my cleaning rod and ran a fairly tight patch of lead away down the barrel.  When it reached the choked part of the barrel at the end it came to a screeching halt.  It took one heck of a lot of force to push it through which is when I discovered the "problem".  The choke of the barrel gets tight, then for a quarter to half an inch relaxes, then gets incredibly tight again.  It's double choked and choked harder than I would have imagined.  No lead came out though, so that was a good thing.  Running some solvent patches down the barrel with the jag was not quite as hard to push through the choke as the lead away patch.  Being ready for the choke, I had a good grip on the rod handle and was pushing reasonable fast and hard to go through the double choke, the rod was doing a pretty hard double bouncing sort of jolt each time.  And the 5th time my one piece carbon cleaning rod broke.  That really pi$$ed me off, I just bought it to replace my one piece coated stainless rod I had stepped on stupidly a week before and bent.  The good news is I called the company and told them what happened, literally less than 5 hours after I bought the rod,  and they are sending me a new one, no questions asked, no proof of purchase, just straight up sending me a new one. 

Being generally pi$$ed off and generally stupid at times like this, I went looking for something that would fit freely into the bore before the rifling but not get through the rifling itself.  Turns out a 1/4 inch drill bit, the smooth end not the cutting end, slipped right in and stopped on the rifling.  The non working end of the drill bit was also nicely chamfered.  So I dive right in, find the valve grinding compound, and get to work.  Dropping the drill bit down the air port is just at the rifling and let me easily coat the back side of the drill bit with compound, this allowed me to leave the breach oring in keeping the bit centered and not bugger up the oring.  Using no pressure but the weight of the bit itself, and while watching tv, I just started twirling the bit back and forth every no and then pulling it up a hair and adding a touch more compound.  Rather all of a sudden, the bit dropped down a couple inches.  Turns out the beginning of the rifling was actually tighter than just a few thousandths past, and the bit fit through the bore at that point but with the grinding compound it kind of bit into it pulling it out.  Put some good scratches on the lands up to half an inch into the riflling.  Oh well, in for a penny in for a pound.  I have a bunch of old mops and cut one down to only a quarter inch, loaded it up with grinding compound and worked the first half inch of rifling using a cordless drill.  Then I got another mop, cut it down, and did the same thing with a much finer compound I had around.  Then took a full length mop and using simichrome, polished the first inch and a half or so, however long that mop was, then followed that up again with flitz.
Not content to stop there, using a patch and rod, reduced to using multi piece brass rod,  i measured from the muzzle where the choke started.  Using a q-tip I put grinding compound in from the muzzle to cover the choked area and then started running clean patches down the barrel with a jag.  After every 5 or so, grabbed the q-tip and put some more compound on the choke.  When I could feel the double bump of the choke starting to get a little less, I switched to the finer compound and continued a little longer before moving to semichrome and then flitz.  The barrel is still choked, and it still is double choked, but the two tight parts of the choke are much closer to the center part of the choke now.  After much more cleaning, I pushed a bunch of pellets through the barrel again, and none were damaged/bad looking, even the jsb's.  Although the base of the jsb's did not always appear to be perfect. 

The jsb's load much much much more smoothly now even though I still have to push them in with a little force.  The H&N barracudas have almost no resitance loading, and the grizzlies just a little less than the jsb's.

Off to shooting, and realise I really don't have any pellets left except for jsb's.  I litterally only had 15 H&N grizzlies, no barracudas, and maybe 50 baracuda hunters which never shot well at range, they are 28 grain.  The jsb's shoot better than they did, but still s&ck balls.  The baracuda hunters shoot like they always did, not good but a long shot better than the jsb's.   With only 15 grizzlies, I can only say they may or may not be marginally  better, with so few left I did not sort them as I normally throw out any of them that don't look perfect and they shot just like I expect the sorted ones to shoot. 

Bad day for the chrono, sunny day but it was giving more failures to read than normal, even with a fresh battery.  The jsb's still scaring 100fps variation at 113 yards, out of 60 i ran accross the chrono only 42 registered(4 did not go through the skyscreens, they flew wide) with extreme spread of 91 fps.  For the barracuda hunter  just under 30 of the 40 I  shot registered on the chrono had an extreme spread of 28 fps, if i throw out one pellet of those, the lowest velocity of any of them,  the extreme spread was just 19fps at 113 yards, I recall those had a much larger extreme spread at long range in the past, closer to 40 fps.   11 of the grizzlies registered on the chrono at 113 yards with an extreme spread of 17 fps, still cooking along at 711 fps average, pretty much what they always did.  Both my tanks are down to 3500 psi now, I normally fill them at 3700, just a number I chose to fill my cricket to and get lots of recharges before having to fire up my compressor.

I then caught a few pellets at range, last time I can do that unless I build or buy something else, my catcher is now destroyed.  There was a large tote in my barn when I bought my place that was in rough shape.  A little gorilla tape and it was water tight.  I cut a 3.5 inch square hole half way down and have been using heavy freezer bags and gorilla tape to cover up the hole making it water tight and shoot through, the heavier H&N's still smack the back of the tote a bit after going through 26 inches of water but not enough to break through.  I generally can catch 3 pellets before the water gets to low.  I knew the jsb's were going to sometimes miss the hole but the tote is in rough shape and getting brittle any way so I did not care.  I loaded a magazine with 4 jsb's and 4 of the barracuda hunters and shot very fast.  2 of the jsb's missed the hole and finished off the tote, 2 of the barracuda's made it in while the water level was still high enough.  The two clean jsb's that I recovered both had a bit of lead shaving on the skirt, no wonder they fly funny, the two barracuda's that made it into the water looked great.  So, a combination of the jsb's being tighter in the bore of my cricket, and having a thinner base just isn't going to work, they cannot make it through my rifle without damage, maybe if the barrel had no choke or at least much less than it does.  I have no intention of working on it any more, kind of feel like I got lucky not to do anything bad and ruin the barrel as it is.  The jsb's will obviously never shoot out of my cricket, anyone live close to blacksburg/york/rock hll sc or charlotte nc want 11 unopened 300 count tins of jsb 34 grain 25 calber pellets?  I'm not going to ship them, don't ask. by the time I paid shipping I'd lose too much money on them.  I'm guessing someone here lives close and wants them cheap.  10 dollars a tin and we'll meet up, I'm losing over 3 dollars a tin at that, don't ask to pay less.

[KnifeMaker]

You are making me feel at least a bit better, as you are only the second person I have known of to use an electric drill and polish to smooth a bore. LOL!!!

I have a .257 barrel here that leaded badly, (10-12 rounds) even with 20-1 lead tin cast bullets. And they were only .003 over bore dia. Accuracy was not what I could accept, and flyers were common from this barrel.

 The barrel was far too rough so I used a 1/4 dia. oak dowel rod, split at the end and put very-very fine crocus cloth in it and polished the heck out of it.  the rotation was both clockwise, and anti clockwise to give both sides for the rifling edged the same effect.  Following this, I used a wheeler fire lapping kit, and finished off with flitz.

The gun, went from 10-12 shots, (what is normally required to re-season a typical bbl. after cleaning), to up to 200 shots.

Accuracy went from 2 1/2 average at 80 yards to a touch over 1/2" at the same range.

It pushes an 80 gr Ranch Dog HP at 980, as  backed her down from 1090. Accuracy is now outstanding.

A good polishing can do wonders when a bbl. is in poor shape with rough lands and groves.

I did finish off by re-crowning and extra attention applied to the leade. Flyers are non-existent with this barrel now. 

Of note, is the fact that the lands are now slightly rounded, or domed in appearance, (Only very slightly), rather than very sharp edged,  looking much like older BSA barrels, bullets are less upset by it.  Accuracy not only improved, but flyers disappeared. Happily, fps increased more than expected, as did the lesser need for cleaning. A real win-Win for me. 

Knife   

[KnifeMaker]

As an interesting note, this bbl was sent to me by one of our suppliers who had it returned for bad accuracy. It was tight for a .257.

Now after the work, it will shoot cast bullets very well, and it will  so somthing I had stated in writing that a .257 would not do. It shoots JSB Kings, and does so with stellar performance.
I would like to try the new heavier MK-II's to see what they can do.
But in truth, being set up for casting for the .257, is is so much lest costly to cast, and get superior long range results, not to mention effectiveness on game, that the expense of pellets is not needed or wanted in this gun. 

Knife

[skorec]

Very interesting information’s  .
What about to use softer and also much lover diameter pellet’s for large distance’s  shooting from standard twist rate  barrel’s?

[KarlH]

While waiting for more pellets that I know work to come in, I opened another tin of 300 of the jsb's to play with.  There is a t-post in honeysuckle on the hillside at 135 yards that I know from the past I can watch pellets fly easily every time in the evening.  Just shot 3 mags worth and watched the all of them fly through the scope.  Not one spiralled, they all flew a nice clean straight arc.  I guess polishing the barrel had some affect.  I started playing with barrel harmonics by putting the barrel under tension.  That made the groups (I use that term lightly, still a big shotgun pattern) more consistent, still bad.  So I addded a small bit of foam between the shroud and air tube which damped the ping a bit when I whacked it with my fingernail.  Groups no worse or better that way, about a minute of angle higher.  Next I will play with adjusting tension more on the barrel, that at least made a difference in consistency. My adjuster is marked, so I then tried cranking it up, which apparently is something my rifle will not do.  A half turn on hammer spring and no change in velocity, another half turn and maybe average velocity dropped one or two fps.  Another full turn and a half and velocity actually dropped almost 15 fps.  Back down to a turn less then starting point and velocity was down maybe 10 fps from initial.  So back to original setting and velocity back to where it started in the low-mid 890's.  I remember Earnest Rowe telling me it was maxed out and running as efficient as it could at that power level, now I know he was serious about it being maxed out without a lot more work than he already did.