20BR/20-220 Swift education

[trotterlg]

Here is what I have learned so far. My load of 31.5gr of 4064 which gets me 4,250fps in the 20 BR gets me 3,800 in the 20-220 Swift. Moved up to 34.5gr and only hit 4,150. I have some wide velocity swings with the same load, so I think the empty space in the Swift is giving me problems in both areas. My next try is going to be to drop down to a slower powder (I have Varget and Winchester 760) and try for a fuller case. Looks like the powder that is best in the BR case is too fast for the larger Swift case. Found a similar thing with the 8208 which is really nice in the 204 case but too fast for the BR case. Interesting to me anyway. Larry

[410gauge]

Larry, what you are coming up with is the same thing I've found with the 20WSSM case. RE-15 worked fine for me in three different 20BR rifles with the 9-twist barrel and 55 gr Bergers. RE-15 is too fast for the 20WSSM case with the 55 gr Bergers. Leaves too much space and shows pressure fairly quickly. I changed the 11-twist to a 9-twist Kreiger barrel on the 20WSSM and shot it yesterday for the first time using RE-17. Worked much better in both filling up the case and no pressure. Best four shot group was .250 fireforming cases. The 20-220 Swift case and the 20WSSM case should be fairly close in capacity. I probably will try even a slower powder. 410gauge

[trotterlg]

Thank you for the info. I was fairly sure this was my problem, the primers were starting to get sort of flat with 34.5gr of 4064, the swift case will hold 44 gr of 760 and 42.5 of Varget both of which are slower then the 4064 is. I will just start at the top load of 4064 using the 760 and Varget and move up from there. It is really looking like there is a narrow range of powder speeds suited for the case capacity and bullet weight when you get to the extreme range of things. Larry

[trotterlg]

37.5gr of Varget did 4,440fps and 38.5gr of W760 did 4,180fps. Those were my top loads and I didn't see any real pressure signs with either. I will move up quite a bit on the 760 and a little more on the Varget. Primers were flat but no problem with hard bolt lift or extraction, so I think life is good. Velocity spread also tightened up nicely with both. Larry

[410gauge]

Larry, sounds like you are on the right track. I'm getting 4200 fps out of the 39 gr Sierra BK's in the 20WSSM with no pressure signs...and very good accuracy. I haven't chrono'd the 55 gr Bergers yet. That's next. I'm thinking of trying RE-19 just for grins. 410gauge

[trotterlg]

I think my approach with the really large cases is looking good. Add powder until you get pressure signs, if you have more capacity in the case, go to a slower powder and keep adding until you get pressure signs, keep doing this until you run out of case capacity just when you hit the pressure signs. We will see how this works. I still have case capacity with both powders and I may have to find one more if this won't work out with the two I have. Just from what I am seeing, RL 19 may be a little slow, RL 17 is not too much slower than the W760 is, and I am getting the feeling that the 760 may be a little too slow for my combo. Larry

[410gauge]

Larry, your approach to the large case 20's is exactly what I've been trying to accomplish...arriving with a slower burning powder with little to no case capacity left and acceptable pressures. The main difference I see is that you are staying with a 32 gr bullet with a 12 twist, and I'm trying to accomplish this with the 55 gr Berger and a 9-twist. Another possible issue I see for the 20WSSM, is I get to the desired powder; case capacity; and acceptable pressures...then the 55 Berger goes to fast and never arrives at the target!! I agree with your comparison of the W-760 to RL-17. I believe them to be close. In looking at published data for the .223WSSM round itself between RL-17 and RL-19, RL-19 could definitely be too slow as the velocity falls off over 100fps according to Alliant loading data with the 55 gr bullet in .22 caliber. But necking the case down to 20 caliber does change things in my opinion as far as pressures and amount of powder/case capacity compared to the regular .223WSSM. So I'm considering trying a pound of RL-19 in the 20WSSM just to see what happens. My guess like yours, it will be to slow...but we'll see. Like your 20-220 Swift the 20WSSM has been a real hoot to experiment with! Barrel may not last long, but I've got a couple of more blanks laying around. 410gauge

[trotterlg]

Glad someone else is thinking along these lines. I am going to try to figure out how many grains the 760 is behind the Varget in speed and then load some up a little more. Being a ball powder more will fit in the case, so it may work out just right.

[trotterlg]

I ran some more loads today. I got up to 38.5gr of Varget with the 32 gr Noslers at 4,512fps, the 26gr Varmint Gernades were doing 4,620fps. I still did not have hard bolt lift or any other real pressure signs. The W760 started showing pressure at 43gr and was only making 4,450fps, so I am done using it. Case will hold 41.6gr of Varget, so I have a little bit to go. The groups were tightening up nicely the faster I went. I did have to put the Chrono out at about 10 or 12 yards to get it in the sun today. Larry

[410gauge]

Larry, got out today to the range with the 20WSSM. Tried RL-19 at 100 yards, and was not impressed. Velocity was actually less by 115 fps with 1.5 grains more powder in the case. RL-17 best velocity was a average of 3765 fps average and three shot group of .242". RL-19 best velocity was a average of 3650 fps and a .237" three shot group. My 20BR does 3650 fps with RL-15...so in my opinion not much to write home about. Pressures looked okay with fairly flat primers. No problems on bolt lift or extraction. All rounds were with 55 gr Bergers. This is showing me that the 20BR is "probably" the best all-around large capacity case 20 with the larger bullets...as others have found out. I was hoping for 3800-3850 fps with the 20WSSM, but don't see that happening with these powders. Back to the drawing board! 410gauge