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< 20fpe BC comparison

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Franklink

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Sep 3, 2017
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@Arzrover did some extensive ballistic coefficient testing and posted his results in the projectiles section.

Difficult choices

A little history... A friend contacted me and asked if I would shorten a barrel on a BRK Commander to make it legal for pistol EFT. He was interested in that one because of the solid construction and bottle, which meant a good number of shots at the 20 ft lb level, vs the Atomic, which gets only...
www.airgunnation.com www.airgunnation.com

Just wanted to share it here since it's so relevant for field target and perhaps some ft diehards only follow the FT section.
 
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Solo1 said:
Interesting that the 13 gr’s didn’t show to be much better than 10.3
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Yep, we discussed this a bit as well. Many have moved over to the .177/13.43 but they're maybe only a tiny smidge higher BC than the 10.34s.

Top three pellets at a field target legal fpe, and based on BC were:
  • .20/13.73
  • .177/13.43
  • .177/10.34
And pushing the .177s from a polygonal rifled barrel seems to net yet another small increase in BC (versus a 12 land and groove).

If the trend we saw from better BCs in .177s from polygonal barrels extrapolates to the .20.... 😙 (Whistle)!!!! THAT could be field target magic. One big really unfortunate problem....there isnt a .20 polygonal rifled barrel.
 
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Franklink said:
Yep, we discussed this a bit as well. Many have moved over to the .177/13.43 but they're maybe only a tiny smidge higher BC than the 10.34s.

Top three pellets at a field target legal fpe, and based on BC were:
  • .20/13.73
  • .177/13.43
  • .177/10.34
And pushing the .177s from a polygonal rifled barrel seems to net yet another small increase in BC (versus a 12 land and groove).

If the trend we saw from better BCs in .177s from polygonal barrels extrapolates to the .20.... 😙 (Whistle)!!!! THAT could be field target magic. One big really unfortunate problem....there isnt a .20 polygonal rifled barrel.
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Very good/useful compilation. As far as trends…there is some anecdotal data that indicates that the 10.34gr BC is improved a little more when using a choked slow twist poly.
 
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Airgunoregon said:
Thanks for sharing this info Bobby and Frank..

I've been really happy with the slow poly in my USFT and the 10.34 Air Arms. I think I'm at .035 BC.

Another thing to consider is the trajectory path... which is much better with the lighter 10.34s

Did you compare the Air Arms 10.34 verses the JSB 10.34?

Wayne
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Wayne, my .177 USFT with slow poly and 10.34s is in that chart but BC was down around 0.032 using the less-accurate two chrono method. Caveat to that is that I need the same 0.035 (that you cite) in Strelok for predicted to match actual. And that's been confirmed through the many shooting sessions, so Id have to say the 0.035 is more accurate than that one session of two chrono distances bc collecting I did.

And yes I agree, the 10.34s trajectory is less of a 🌈 and for that reason, my preferred pellet and rig. That slow twist poly with 10.34s is what I shoot when I want to win.

As for the Air Arms versus JSB labeled tins of 10.34....I don't know if Bobby did any comparisons there. I personally have not. Are they slightly different shapes?
 
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Franklink said:
Wayne, my .177 USFT with slow poly and 10.34s is in that chart but BC was down around 0.032 using the less-accurate two chrono method. Caveat to that is that I need the same 0.035 (that you cite) in Strelok for predicted to match actual. …
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Regular or slow twist on the last two USFT 23” chart entries? They show BCs of 0.0370 and 0.0388.

I have a Delta Wolf with a 17” .177 (non-poly). It’s accurate but BC is coming in around 0.029 to 0.030. I probably should have gotten the 23” .177 barrel kit, but did not know/understand the differences at the time. I have two 24” poly blanks, one regular and one slow twist. So now I need to make a decision to either buy a 23” Daystate barrel (relatively expensive) or prep one of my LW poly blanks for the Delta Wolf. I’m going to shoot with the 17” barrel at a couple more matches and see if the BC deficit continues to bother me.
 
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Scotchmo said:
Regular or slow twist on the last two USFT 23” chart entries? They show BCs of 0.0370 and 0.0388.

I have a Delta Wolf with a 17” .177 (non-poly). It’s accurate but BC is coming in around 0.029 to 0.030. I probably should have gotten the 23” .177 barrel kit, but did not know/understand the differences at the time. I have two 24” poly blanks, one regular and one slow twist. So now I need to make a decision to either buy a 23” Daystate barrel (relatively expensive) or prep one of my LW poly blanks for the Delta Wolf. I’m going to shoot with the 17” barrel at a couple more matches and see if the BC continues to bother me.
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BC Deficit to what ?
 
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Scotchmo said:
Regular or slow twist on the last two USFT 23” chart entries? They show BCs of 0.0370 and 0.0388.

I have a Delta Wolf with a 17” .177 (non-poly). It’s accurate but BC is coming in around 0.029 to 0.030. I probably should have gotten the 23” .177 barrel kit, but did not know/understand the differences at the time. I have two 24” poly blanks, one regular and one slow twist. So now I need to make a decision to either buy a 23” Daystate barrel (relatively expensive) or prep one of my LW poly blanks for the Delta Wolf. I’m going to shoot with the 17” barrel at a couple more matches and see if the BC deficit continues to bother me.
Click to expand...

Those last two in the chart are from Bobby's USFT. That barrel actually came from @Airgunoregon Wayne years ago. I can't remember if Bobby has ever told me if it's slow twist or normal twist rate.

You've probably already read my comments in the BRK Ghost review, but for those that haven't.....I've shot two matches with a likely similar to your DW barrel, a 17" .177 (non-poly) but in the Ghost. Since both our barrels (DW and Ghost) come from same parent company, and are even swappable from One gun to the next, I doubt we'd be able to tell the difference between them if they were next to each other. So with that Ghost barrel, in one match I scored 47/48 and the other was 39/48. The higher score was with hardly any wind, the lower score was windy. Very accurate barrel, but I felt at a disadvantage with the 17" non-poly in the wind, compared to how much I felt I would have needed to hold off with what I'm used to seeing from the poly barrel in my USFT.

My take, from anecdotal experiences, but also somewhat supported by Bobbies chart is the following....for wind resistance: slow twist poly is better than standard twist rate poly and standard twist rate poly is better than 12 land and groove rifling.
 
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Motorhead said:
BC Deficit to what ?
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0.029 BC is a deficit (shortfall) compared to what I’ve been using the last few years (0.033 BC).

Wind threshold for what I can feel is about 3mph. At BC=0.033, when I detect light wind, I can hold just inside the KZ edge for s 55yd shot, and be OK. At 0.029, I need to hold slightly outside the KZ. Just outside the KZ bites me sometimes, so I’ll likely lose a couple more points.
 
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Scotchmo said:
0.029 BC is a deficit (shortfall) compared to what I’ve been using the last few years (0.033 BC).

Wind threshold for what I can feel is about 3mph. At BC=0.033, when I detect light wind, I can hold just inside the KZ edge for s 55yd shot, and be OK. At 0.029, I need to hold slightly outside the KZ. Just outside the KZ bites me sometimes, so I’ll likely lose a couple more points.
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I agree that BC values seem to have a pretty strong correlation to how much hold off is necessary in a given (read: educated guess) wind speed.

Further a guy has to hold off, the sketchier it gets, resulting in more misses when the wind abruptly changes or wasn't guessed correctly in the first place.
 
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Airgunoregon said:
Now, I'm wondering two things... why did I sell that barrel to Bobby:) and

How much does barrel prepping effect the BC of the pellet? The barrel I sold to Bobby and the one I shoot now were both prepped by Larry Durham, who in my mind knows the most about barrel prepping of anyone on the planet.

Wayne
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I've also wondered about what effect leades, level of polishing, and choke characteristics can have on a BC....ie. if a barrel/pellet/speed combo averages say, 0.032 for example, prior to being touched by a master, can it be made to produce BCs higher than that after knowledgeable massaging?
 
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Airgunoregon said:
Now, I'm wondering ...

How much does barrel prepping effect the BC of the pellet? .

Wayne
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Doubtful if said barrel/s are of good quality and have a good crown and symmetrical leade.
Always have found the barrel itself as to the Land / Groove diameter differential playing the bigger part.
Tall lands disrupt the pellets outer most diameter head & skirt more so than shorter height lands .. similar to a poly barrel.
* In other words: have a smaller differential to land / groove diameters.

My primary FT rifle has a "HW" barrel purchased out of country. I have prepped and shot many LW barrels of similar caliber that a pellet appeared to be of similar fit etc ... Shot in the wind as well calculated BC is not similar having the HW barrel better overall.
* Push threw a pellet in either, the rifling impression / grooving is less so on the HW than the LW even tho BOTH show minimal groove contact.
keeping a loose track on BC values at @ 800fps the LW was D.O.P.E. calculated BC at @ .035 where as the HW runs @ .040 to .044

Just info ... not sure anyone even knows ? .... but those of us who shoot competitively well know that some barrels for what ever the reason are simply STELLAR shooters.
 
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Scotchmo said:
0.029 BC is a deficit (shortfall) compared to what I’ve been using the last few years (0.033 BC).

Wind threshold for what I can feel is about 3mph. At BC=0.033, when I detect light wind, I can hold just inside the KZ edge for s 55yd shot, and be OK. At 0.029, I need to hold slightly outside the KZ. Just outside the KZ bites me sometimes, so I’ll likely lose a couple more points.
Click to expand...
I've been shooting field target since 2007 and I've never shot an air gun even close to as accurate or with less wind hold off than the USFT 169 LD built and shot at 2021 Nats... and I talked him into selling to me. It's got the slow poly.

The light to medium winds are sometimes harder than the stronger winds, because you are wondering do I hold outside or not? In my early days with USFT 169 about 80% of my misses were from getting burned holding off the kill zone and hitting right where I was aiming. It took me a long time to have confidence not to hold off in mild winds like I had to with prior air guns.

Wayne
 
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thane said:
There is an endorphin rush when you hold off KZ an inch or more and drop the target.

Knowing when not to take the gamble is a tough urge to overcome... at least for me.
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Out at the Nevada State / GP we have at times been OVER a foot outside KZ and knocking em down .... You never get comfortable doing so, tho know any less and you won't even hit face plate !
 
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Airgunoregon said:
I've been shooting field target since 2007 and I've never shot an air gun even close to as accurate or with less wind hold off than the USFT 169 LD built and shot at 2021 Nats... and I talked him into selling to me. It's got the slow poly.

The light to medium winds are sometimes harder than the stronger winds, because you are wondering do I hold outside or not? In my early days with USFT 169 about 80% of my misses were from getting burned holding off the kill zone and hitting right where I was aiming. It took me a long time to have confidence not to hold off in mild winds like I had to with prior air guns.

Wayne
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These types of reports (I have one that I feel the same about) always makes me ask the question: WHY?!?!?!?!?!

What is it about that particular barrel that is so special, in comparison to many, many others. This question has often come up in discussion with Bobby, before and during all his testing.
 
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thane said:
There is an endorphin rush when you hold off KZ an inch or more and drop the target.

Knowing when not to take the gamble is a tough urge to overcome... at least for me.
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Like Scott said, the Nevada St GP is full of endorphin rushes... except success is not often enough:)

It is a super rush to hold off 8-12" and often 4-6" low as well and knock down the target..
It's a very steep canyon that narrows a lot where we shoot field target... forcing the wind thru a 3 sided funnel of sorts. The wind speed increases and is also forced up.

It's the ultimate field target challenge.. do it if you can! June 9th -11th Battle Mt NV.
 
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