High velocity accuracy

[Cableaddict]

Thanks, guys.

There's an awful lot to digest here.  ( ! )

Personally I think I'll leave it up to the manufacturers to get all this right, but this is great info for choosing the right model and options, down the road.  I know that FX has been experimenting a lot along these lines.  Not sure about any other companies as of yet.

It's also not easy to get details like twist rate, magazine length, etc for most rifles, but maybe that will change as awareness increases over time.

[K.O.]

so been thinking a (dangerous thing) what are the trade offs to K.O.ing a 30g BBT   decking the boat tail  off... Why to lose some SD/weight...get the velocity up out of my Buccaneer... and it likes the JSB K.O. ...

currently not turned up all the way... 675 fps with 30g BBT... 725 25g w/K.O. 

so sacrifice the Boat tail  from the BBT... hollow-pointed  should be down around 25g 

so debate becomes... how effective is the short rebated boat tail..?  Me I like the clean base it provides because the rear of the round steers... but also a short gas check or short rebated Boat tail can help divert the muzzle blast evenly...and that can help prevent yaw at the muzzle...  that can be significant in shorter barrel... and the Bucc

so losing those things and gaining maybe 85 total fps leaning on the hammer spring... Hmmm.... 760 ish fps flat base(? B.C. .065 ish )  vs 700 ish fps 30g .08 ish B.C.     

I do know BSA has always been 1:19   twist for all their barrels... it was in the meteors owners manual... it's in this vid... so have to respect that they do care to share...plus have wanted a BSA since  a friends BSA/Martini tilt block 22
so will compare the two rounds as shot out of my Buc .22 first...yep Like my BSAs

 then as out of My .22 Max and .22 AT44 L they about match fpe...
yep Like my BSAs

   


so blue is 30g .08 BC at 700 fps and green is 25g .067 BC 760fps

[K.O.]

Ok now out of my Max And AT44...looks a bit more worth the effort... only becuese the 30g is just a touch to heavy for the Maximus... so it make 5 fpe more with the 25g jsb K.O.

 50 fpe with  the K.O.'d .25g (green)... 45 with 30g BBT Blue

[K.O.]

so about what would look like and a Cg and weight check

http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=inches&weight_unit=grains&bullet_name=.338+air&re_calculate=yes&boundary_layer=L%2FT&entry=return&diameter=.217&length=.325&nose=.114&meplat=.152&drive_band=.217&base_diameter=.170&angle=0&boat_tail=0.074&secant_radius=&weight=147.2&density=11.4 

looks like ~h 24.6  just from decking...  so ~23g as  hollow point...

http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=inches&weight_unit=grains&bullet_name=.338+air&re_calculate=yes&boundary_layer=L%2FT&entry=return&diameter=.217&length=.251&nose=.114&meplat=.152&drive_band=.217&base_diameter=.217&angle=0&boat_tail=0.&secant_radius=&weight=30.9&density=11.4   

[rkr]

so been thinking a (dangerous thing) what are the trade offs to K.O.ing a 30g BBT   decking the boat tail  off... Why to lose some SD/weight...get the velocity up out of my Buccaneer... and it likes the JSB K.O. ...

currently not turned up all the way... 675 fps with 30g BBT... 725 25g w/K.O. 

so sacrifice the Boat tail  from the BBT... hollow-pointed  should be down around 25g 

so debate becomes... how effective is the short rebated boat tail..?  Me I like the clean base it provides because the rear of the round steers... but also a short gas check or short rebated Boat tail can help divert the muzzle blast evenly...and that can help prevent yaw at the muzzle...  that can be significant in shorter barrel... and the Bucc

so losing those things and gaining maybe 85 total fps leaning on the hammer spring... Hmmm.... 760 ish fps flat base(? B.C. .065 ish )  vs 700 ish fps 30g .08 ish B.C.     

I do know BSA has always been 1:19   twist for all their barrels... it was in the meteors owners manual... it's in this vid... so have to respect that they do care to share...plus have wanted a BSA since  a friends BSA/Martini tilt block 22
so will compare the two rounds as shot out of my Buc .22 first...yep Like my BSAs

 then as out of My .22 Max and .22 AT44 L they about match fpe...
yep Like my BSAs

so blue is 30g .08 BC at 700 fps and green is 25g .067 BC 760fps

I tried H&N slug testpacks in .217 and .218 from two .22 BSA barrels at 12 fpe and at 36 fpe and the accuracy was poor. That kind of makes me cross BSA barrels off the list of slug shooters.

[K.O.]

wonder if N.O.E. would be interested in making it... seems could just use the 30g BBT cherry just with less plunge depth...he  did shorten the .172 round...

RKR Buccaneer slug test 40 yards at bottom link reply 17 KO and H&N .217 bout 30-32 fpe...

 honestly I think the KO shoot more accurately out of my .22 Buc than the 30g BBT because of harmonics and not the velocity outside the barrel...

But could be the Nose shape of the K.O. is better suited to the choke... but then I look at the behavior of the H&N slugs at 40 yards... and need to figure out why they are behaving the way they do...

the 25g H&N slug does not do well at all... the JSB 25g slug does... why..?

the 21 g and 23 g are all over the place(over spun + harmonics +?)

the 27g and 30g H&N slugs do ok but hit way higher... BBT 30g and H&N 30g are shooting about the same... same general pattern in multiple test...

 maybe I will make some measurements/drawing and think about it some more...

it seems hard to know right now... So still seems like a bit of voodoo at times...

would 24 twist of some of the .22 short barrels help the light slugs... seems that would be the sweet spot for a light slug/pellet barrel..? 

https://www.rimfirecentral.com/threads/rate-of-twist-the-22-short.593288/


in the end we have to test what we have available and compare notes...this is pretty new stuff still...and in the end your rifle/barrel will like what it likes...

I do think I will go for more fpe in the long run Probably with a 26"-28" barrel tho... more efficient and less muzzle blast than trying to do it with a 19"-22" in barrel... 

https://www.gatewaytoairguns.org/GTA/index.php?topic=199308.msg156325640#msg156325640

[K.O.]

My.177 Buc really likes the .177 13.4g K.O. ....

30g BBT out of the Urban are not pin point but are near the same as the 30g BBT and 30g H&N from my 22 buc... just 50 fps slower... I consider that something that will get you dinner... so worth doing... best/optimum no...

[K.O.]

Riku sorry forgot to ask if you lubed them..?

right now I Am shooting only outside wind away from me only... am using a nano abrasive lube right now... trident divers grease which pretty sure is fumed silica and silicone oil...will clean and switch back to just 30 weight silicone after next session... 

I imagine there is more lead in the blast than normal and safe but it does seem to have worked... no leading yet... only about 450 slug thru mostly BBT... about 80-90 with the silica the rest just 30 weight... still like the JSB 16 and 18g best and still same pellet friendly... a lot of cleaning 1/4 the time with goo gone... pull  moderator crown protector in tight wet patch then 2 to 3 patches to dry...

have been lazy at times and just pushed a dry patch thru...  cause sometimes it is just a few shots that day...but yep cleaned bout twenty times maybe even 30  for those 450 or so lubed slugs... it does not seem to matter to pellets accuracy wise if I clean after a lubed slug session(have mixed pellet/slug sessions)...but I at least drag one patch thru... I also clean out the moderator. saw no sense in putting out nano particulate when not needed...do not clean when sending pellets... just remembered  I have some of the 18g Cudas forgot to try..   think I will wait till next week.... It is a touch warm out...  s' posed to be cooler then...

do plan on trying to move to a lard/beeswax type lube soon also... be cool if I can get home made more edible 30w to work... but am worried pellets might object...

[K.O.]

my Buc .177  ran ~30 abrasive K.O.  in one sitting...cleaned well and since have sent bout 60 in a couple session  just 20w silicone oil... no leading still loves the Sniper mags and CPUM and AA 10.3...

[Tomygun1]

Kirby,


Boy do I like the testing you are doing, as it tends to separate various factors that detract from accuracy that might otherwise be overlooked.    It’s my belief that attention to cleaning, leading, and lubrication done properly is the final step towards ultimate accuracy.    Hopefully you are able to work with the best bores available and nicely polished.    I base this on all the work done with single shot black powder muzzle loading bench slug rifles from the early 1900’s with their fouling problems.     I have done this in the distant past but am now to old to pursue it with pcp rifles.     


One approach was the use of false muzzles when loading from the front, a 2”section of bbl was cut off and centered with four pins to the muzzle.    The loading end was slightly enlarged to allow the gradual engraving of the projectile following the rifling when loading with a rod.    The bore was always cleaned in exactly the same way between shots for consistency.    In later days using cartridges cleaning and loading was done the same but from the breach end.    But the projectile was always seated and engraved before inserting the powder filled cartridge case after the bore was cleaned.    The best of these long range rifles often called ‘Creedmores’ on occasion would produce a 10 shot ‘string’ at what we now call moa to 1000yds.   


Various lubricants made a difference.    For me allox and bees wax 50/50% worked best including comparisons to more modern lubes of the time.     Better lubes seem to be available now so you decide what works now.   


What you seem to be doing closely follows what was done with early target bench rifles but now with modern pcp rifles.    From what I read it seems many are content with the accuracy and velocity already achieved and you seem to be looking a step beyond.    Cudos, and I wish you well..


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