March 30, 2015 at 1:14 am #18973genetParticipant
Started getting serious about collecting data now that I’ve converged on a general configuration. Attached data on Eunjins and JSB Kings with and without o-ring and with and without insert.
(well I guess not – no pdfs for some reason). Here’s a quick summary:
18″ bbl Condor SS, 25 cal with TT Hammer and ‘QC’ Top Hat. Shooting from ‘full’ (2850-3000) down to 1500 or so:
Wide open top hat (no inserts) shot Eunjin 43.2’s best between 1500 and 1300-ish, with a spread from 679.5 to 709.8 – things got dismal after that pretty quick.
Add the Talon Tunes large insert and the best 10 occur from ~2950 to 2650 (734.5 – 730.6) (much tighter, eh?) Taking the best 15 the spread is still less than 3 fps. 20 the spread is 8fps. (The best 20 shot spread of anything I’ve tested).
Now tuck an o-ring behind the tophat (1/4″ id, 3/8″ od) and best 10 are from 731.8 – 724. Best 15 ar from 730.7 to 724 and best 20 are 728.2 to 716.3.
With the Eunjin’s the tophat with insert was a huge improvement. The o-ring made a slight unimprovement.
On to JSB Exact Kings (25.39gr)
With insert, no o-ring:
Best 10: 852.8-853.8 <— This is the tightest 10-shot distribution I’ve achieved!
Best 15: 852.8-848.5
Best 20: 852.8 – 847.7
(Bonus that all the best strings start at the same place!)
Add an o-ring:
Best 10: 843.7-838.1
Best 15: 841.8-838.1 <— This is the tightest 15-shot distribution I’ve achieved!
Best 20: 841.8-833.2
The o-ring isn’t magic, but seems to be benign to marginally beneficial. Adding the o-ring costs ~1fpe.
The o-ring gives you about 2 more shots within a given velocity band than without.
The TT tophat with insert is a must!
Except for running wide open the best results occur very close to a max fill on down.
Except for running wide open, the best results occur above 2200 psi, suggesting that it’s not worth testing much below that point. (Wide open there was a sweet spot for the Eunjin’s at ~1200 down to a little over 900.
50 fpe is achievable without sacrifice. 77fpe is achievable but only for a few shots.
I still need to match these with some accuracy tests.
It’s a work in progress – I’d be happy to share raw numbers if someone can point to a good format to do so…
GsTMarch 30, 2015 at 2:03 am #223067lurker-1Participant
I stopped testing the 43 gr. EJs at 2250 PSI
From 2500 – 2250 i had 7 shots with steady drop of 7 to 8 FPS.
I am amazed at yours tightening up from 1200 to 900 ❗
That gives me something more to do at home.
I too need to follow up with group shooting but it was 20° last might and cold drizzle rain today.
We have similar rifle setups except mine is a 24″ .
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