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50/70 questions - Dave951 - 12-24-2020
I’ve been working on getting a 12.7 Swede to shoot. It has been rechambered to 50/70 and the bore is in very good condition. Slugged, rifling measures 495/515. Twist is 1/42. Brass has been fire-formed to the chamber. So far, the best I’ve been able to get is about 4in at 50yd. For an 8 shot group, 3-4 shots will be almost in one hole with the rest on walkabout.
So this is just to open a conversation on getting this rifle to shoot. I’ve worked through a number of combinations but I’m wondering if I’m missing a variable unique to the 12.7
RE: 50/70 questions - Kurt - 12-24-2020
With the .495/515" bore you will be slightly handicapped and you will get a mould that is .515" diameter plus maybe .516" for a GG bullet if that is your choosing. A PP bullet patched to bore .495" will have to be on the soft side so the obturation is sufficient filling the grooves or you will ge gas cuts and that will start what you called a walkabout. A hard undersized GG bullet will have the same results.
I had a mistake barrel on one of my rifles that had deep grooves that gave me fits and even spending countless hrs lapping the lands to shallow up the grooves using a cut brass lapping slug for just cutting down the land tops showed improvement but never satisfactory results with the bullets and alloy I wanted to use.
I guess this one case were you should do what the rifle wants and not what you want to use.
Merry Christmas All.
Kurt
By the way; Welcome to the forum.
RE: 50/70 questions - Don McDowell - 12-24-2020
What are you doing for fouling control? Sounds like things run pretty good until the fouling builds up.
RE: 50/70 questions - Dave951 - 12-24-2020
I’ve been working with a 400gr and the Lyman 515141. The 400gr is a modified actual 50/70 design where we added a spire point instead of a meplat. The modified bullet drops at 517 and the Lyman at 515. I’ve tried as cast, 516 and sized to 510. The larger sizes give seating problems while the 510 wants to fall out of the case. There is no charnge in grouping. My thoughts there is the rifling is so pronounced that even the 510 bullet has enough material displaced entering the rifling to seal the bore.
So is it possible that the seating depth/wad etc can be the cause? I’m not beyond relining it but would rather not.
RE: 50/70 questions - Dave951 - 12-24-2020
(12-24-2020, 02:42 PM)Don McDowell Wrote: What are you doing for fouling control? Sounds like things run pretty good until the fouling builds up.
At this time wet patch followed by dry patch after each shot.
RE: 50/70 questions - Don McDowell - 12-24-2020
Might need to go to 2 patches.
RE: 50/70 questions - Distant Thunder - 12-24-2020
Dave,
I don't think you mentioned what powder you're using or how much compression, but more compression might help also and with your grease groove bullet some crimp could also help. Soft bullets and as big as will chamber is also good. The .50-70 is a great cartridge and so darn much fun to shoot!
RE: 50/70 questions - Dave951 - 12-24-2020
I’m using Old E 3f since I have a decent supply of it for N-SSA competition. Bullets are pure lead and I’ve tried some wheel weight too. I have a 7/8x14 threaded rod with one end turned to fit inside a case. It’s not the best for precision compression. I do have a purpose made compression die coming that will fix that. I also have a 24” drop tube. I’m thinking the height of the powder column is the issue since I want to try to seat the bullets at the rifling
RE: 50/70 questions - mikeg - 12-25-2020
With that deep rifling you might consider a hollow base bullet, even if you have to hand make a few to test. Works for me in odd size 45-70's.