oldmossy
Well-Known Member
I did a build with 1n8 twist to shoot 195 bergers. Is that too fast a twist for 180s?
Rate of twist
- Thread starter oldmossy
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oldmossy
Well-Known Member
7mm rum
sable tireur
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The formula for RPM and twist rate is:
Muzzle Velocity (x) 720/twist rate
Example= 2950 x 720 = 2,124,000
2,124,000/8 = 265,500 RPM
This is perfectly acceptable as an RPM for the 180 class bullets. This will of course depend on the construction of the bullet where a thin skin bullets might require less RPM in order to not destroy itself. Standard Match bullets or Hunting bullets will usually survive easily.
Enjoy!
Muzzle Velocity (x) 720/twist rate
Example= 2950 x 720 = 2,124,000
2,124,000/8 = 265,500 RPM
This is perfectly acceptable as an RPM for the 180 class bullets. This will of course depend on the construction of the bullet where a thin skin bullets might require less RPM in order to not destroy itself. Standard Match bullets or Hunting bullets will usually survive easily.
Enjoy!
oldmossy
Well-Known Member
Thank you.
What FPS do you think the 180 will be going.
As the throat wears is when potential problems can start. I know of instances were a I cant remember a 215 or 220 berger didn't make it to target in a 9 twist in a 300NMAI at 3200
oldmossy
Well-Known Member
Talking to my gunsmith today. He made my rifle specifically for the 195s. He thinks my bullet will be out of the case before bullet hits rifling if I shoot 180s. And doesnt think I will get the one hole accuracy he got me with the 195s. He has the gun shooting a touch slower than id like. But after talking with him, Im thinking accuracy trumps speed. Actually shot my personal best this fall at 767yds with his build. 1.5 inch 2 shot group. Dead center in bullseye to boot. And multiple other 3 inch groups on different days. Plenty good for me.
I like to shoot 2 shots...simulating a potential hunting scenerio. Sometimes only shooting 2 shots total on a given day
I like to shoot 2 shots...simulating a potential hunting scenerio. Sometimes only shooting 2 shots total on a given day
Hugnot
Well-Known Member
Measure the length of the bullet, if not a Berger bullet, then visit the Berger Stability Calculator site:
bergerbullets.com
What would happen if the supply of 195"s ran out? > other bullets would be used. 180's might be satisfactory - sometimes a long running start is not bad.
Twist Rate Stability Calculator
Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.
bergerbullets.com
What would happen if the supply of 195"s ran out? > other bullets would be used. 180's might be satisfactory - sometimes a long running start is not bad.
MagMan
Well-Known Member
Just checked my notes from my 7 RUM days. 180 Berger 3300 fps with a health dose of US869. 200 grain Wildcat 3160 FPS with the same powder. 30" barrel
If you run out of 195s you can always test the Hornady 180 ELD. It has a similar length boattail as the 195 Berger. I wouldn't be afraid to test Berger 180 VLDs or 175 Elite Hunters jumping a lot in your chamber. Long jumps don't always mean bad accuracy.
Friend of mine finished his 300 PRC this past weekend. He had some old Hornady 208 match hollow point. Was going to use these just to get on paper. Hard to get on paper when they all blew up! There was a few tiny pieces made it to 100 yds as there was small holes in the paper. His barrel is a 9 twist IBI. Was only running them just over 2900 FPS. Those bullets must have an extremely thin jacket. I agree with others that the 180 should be fine out of your barrel. I run lots of bullets in the 300,000 rpm range.
If the 180 is going 3300 your right at 300,000 rpms in an 8. Its true long jump doesn't mean it won't shoot but it sure doesn't mean it will either.
If its not broke I wouldnt try and fix it buy enough 195's for the barrel life.
