Decided I'd post some info for others to reference now that the rifle is together. So far, very happy with it, and hope to go on another 4 day squirrel blasting trip in about 2 weeks after the first alfalfa cutting.
Using LC 223 brass formed to 20VT, case capacity after firing is 21.77gr H2O
Barrel is 26", 10 twist, 0 freebore reamer.
24gr Hornady NTX seated to 1.805" OAL (throat measured 1.815" to the initial soft touch on the lands, and if I shove hard on the OAL tool the bullet hits a hard stop at 1.875" OAL.) 1.805" puts the ogive of the 24gr NTX right about even with the case neck and the base about even with the start of the case neck, so it's not eating up excess case capacity seated to 1.805".
Vihtavuori N120 & CCI 450
Initial rounds out of the barrel and first round of testing to figure out velocities, these got popped into the burn pile out in the orchard before loading some up to head to the range...
16.5gr 3711 fps
16.8gr 3780 fps
17.1gr 3850 fps
17.4gr 3900 fps
17.7gr 3975 fps
18.0 gr 4035fps -- very, very slight drag on the bolt handle on bolt open, but primer radius and firing pin indent looked perfect like all the other charges.
Loaded up 100 at 17.25gr to settle the barrel down, and after shooting up all of those loaded up the second round for testing at 300Y.
Second round of testing:
17.20gr 3800 fps
17.35gr 3835 fps
17.50gr 3885 fps
17.65gr 3910 fps
17.8gr 3960 fps
N120 wasn't happy at the lower charge weights, the ES/SD especially at 17.2gr but also at 17.35gr was high and groups at 300Y weren't great, about 1 MOA. Groups tightened up substantially and ES/SD came way down at 17.5gr and above. 17.5, 17.65, and 17.8gr were all very good at 300Y, about 1"-1.5" 5 shot groups. 17.5 & 17.65 were about on the same elevation on the target while 17.8 was impacting about 1.5" higher.
Decided on 17.58gr, now need to load some up and put a final zero on the rifle but it should end up about 3890fps. Temps were 80-85F the day I was testing, so hopefully 17.58gr leaves some margin for shooting on 100F days since I'm not sure about the temp sensitivity of N120; this is the first time I've used it.
Running the numbers for a 24NTX at 3890fps vs a Nosler 32 BTLF at 3575fps (my initial bullet choice, but as of now still unavailable); looks like the 24 NTX drops less and they're both nearly identical for wind drift at 400Y. The 32 BTLF does start with more energy and retains more energy than the 24 NTX. If the Nosler 32 BTLF's become available again I'll certainly try some, but since the 24 NTXs are less expensive, shot accurately, and are readily available, if they do a good job blowing up squirrels I'll probably just end up sticking with the 24 NTXs.
2 things stood out when I was doing load development on the 20VT next to my 223AI; the 20 VT has very little recoil, and after the same amount of shots the 20VT barrel was barely warmer than ambient while the 223AI was getting pretty warm. Why didn't I build one of these things earlier? My friend who was with me that day and also goes on the squirrel blasting trips with me took a few shots and now he wants to build one...
Using LC 223 brass formed to 20VT, case capacity after firing is 21.77gr H2O
Barrel is 26", 10 twist, 0 freebore reamer.
24gr Hornady NTX seated to 1.805" OAL (throat measured 1.815" to the initial soft touch on the lands, and if I shove hard on the OAL tool the bullet hits a hard stop at 1.875" OAL.) 1.805" puts the ogive of the 24gr NTX right about even with the case neck and the base about even with the start of the case neck, so it's not eating up excess case capacity seated to 1.805".
Vihtavuori N120 & CCI 450
Initial rounds out of the barrel and first round of testing to figure out velocities, these got popped into the burn pile out in the orchard before loading some up to head to the range...
16.5gr 3711 fps
16.8gr 3780 fps
17.1gr 3850 fps
17.4gr 3900 fps
17.7gr 3975 fps
18.0 gr 4035fps -- very, very slight drag on the bolt handle on bolt open, but primer radius and firing pin indent looked perfect like all the other charges.
Loaded up 100 at 17.25gr to settle the barrel down, and after shooting up all of those loaded up the second round for testing at 300Y.
Second round of testing:
17.20gr 3800 fps
17.35gr 3835 fps
17.50gr 3885 fps
17.65gr 3910 fps
17.8gr 3960 fps
N120 wasn't happy at the lower charge weights, the ES/SD especially at 17.2gr but also at 17.35gr was high and groups at 300Y weren't great, about 1 MOA. Groups tightened up substantially and ES/SD came way down at 17.5gr and above. 17.5, 17.65, and 17.8gr were all very good at 300Y, about 1"-1.5" 5 shot groups. 17.5 & 17.65 were about on the same elevation on the target while 17.8 was impacting about 1.5" higher.
Decided on 17.58gr, now need to load some up and put a final zero on the rifle but it should end up about 3890fps. Temps were 80-85F the day I was testing, so hopefully 17.58gr leaves some margin for shooting on 100F days since I'm not sure about the temp sensitivity of N120; this is the first time I've used it.
Running the numbers for a 24NTX at 3890fps vs a Nosler 32 BTLF at 3575fps (my initial bullet choice, but as of now still unavailable); looks like the 24 NTX drops less and they're both nearly identical for wind drift at 400Y. The 32 BTLF does start with more energy and retains more energy than the 24 NTX. If the Nosler 32 BTLF's become available again I'll certainly try some, but since the 24 NTXs are less expensive, shot accurately, and are readily available, if they do a good job blowing up squirrels I'll probably just end up sticking with the 24 NTXs.
2 things stood out when I was doing load development on the 20VT next to my 223AI; the 20 VT has very little recoil, and after the same amount of shots the 20VT barrel was barely warmer than ambient while the 223AI was getting pretty warm. Why didn't I build one of these things earlier? My friend who was with me that day and also goes on the squirrel blasting trips with me took a few shots and now he wants to build one...
