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No more estimating velocity by calculating weight and velocity of another pellet

April 15 2017 at 11:18 AM
Quinton Lewis  (Login Domer_Pyle)
YF

I've been doing some testing for BC in my basement these past couple days and decided to finally finish sighting in my Summit by running some JSB Express through her instead of what I've always considered "break-in" pellets, CPHP. Just for kicks I threw a few over the chrony and was pretty confused that a pellet the same weight would be 30-40 fps slower so back to the CPHP and still holding true in the 830s. Back to the JSB and still down to 790-800 fps, including a huge amount of dieseling not present with the Crosmans that I've washed. Weird because I thought the slightly looser head fit of the JSB would help velocity compared to the tighter fitting pellet but no complaints about the rifle shooting cheapie pellets quick and dead on at 30 yards.

Anyway, lesson learned on trying to rely too heavily on mathematics instead of hands-on experience.

BTW the .22 Polymags had a MV of 771ish fps (estimated average) and came out with a BC of .024

 
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Jeff D
(Login jcdx25)
YC

I'm with you. I always test/chrony with the pellets I'm trying.

April 15 2017, 2:48 PM 

To go along with your saga, I have also seen significant differences between boxed cps ( which were consistent on their own) and several other brands (not explained by the weight difference).

I even have 2 rifles in particular that shoot AA and JSB at notably different speeds over a chrony (with very different POI so they are not interchange at att.


 
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Lonnie S.
(Login AirSmithCA)
YF

Different pellets almost never fit the barrel exactly the same....

April 15 2017, 10:09 PM 

It's hard enough for the "same" branded pellet to fit the barrel exactly the same everytime.
"It doesn't get done til someone does it"

 
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Quinton Lewis
(Login Domer_Pyle)
YF

I kinda figured the skirts were to blame

April 16 2017, 10:01 AM 

Didn't push any through but would bet the JSB will take less effort. The cavity inside the pellet of the JSB is also noticeably deeper than the Premier so maybe that factors in as well

 
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Lonnie S.
(Login AirSmithCA)
YF

pretty much every aspect is a factor ...

April 16 2017, 7:06 PM 

Skirt diameter, skirt pocket, thickness of the skirt, head diameter , shape, weight, material properties... It all plays a roll. Plus once the pellet leaves the barrel then there's the aero dynamics.

Take the JSB diabolo, H&N FTT, CPH, and Barracuda match all are very good quality dome pellets and even at when I have 4.52 head diameter they fit the barrel a little more or less snug as the other. And you are correct in your observation that internal pocket of those skirts are noticeably different in each.

The good news is usually one of them are consistantly accurate. happy.gif I suppose that all the minute variables in the pellets is what makes up for the barrel variations as well.


"It doesn't get done til someone does it"

 
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Jerry
(Login JCTX)
YF12

pellet head size can vary...

April 18 2017, 9:46 AM 

enough to affect POI, especially at distance (past 30 yds). Even with the top brands, there are tins shipped with 2 sigma varance of 0.02 mm or more from nominal. There are also shifts of 0.02 mm or more in the nominal, and this would also give results as you describe. Cliff Tharp was one of the early adopters of the Pelletgage, and he wrote about his pellet selection and experience on several of his "Varmintair" BLOG posts. Cliff has retired the BLOG, but this link will take you there. I understand Cliff is still doing well, and shooting, but spends less time at the computer these days.

It may be useful to be certain your pellets are consistent, and that they are the best size for your rifled barrel.

http://web.archive.org/web/20160717233743/http://varmintair.typepad.com:80/varmintairs_blog/pellets/

See also:
http://www.pelletgage.com

 
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