It's made by Muller for Alamo Precision Rifles.
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It's made by Muller for Alamo Precision Rifles.
Ucsdryder
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That's perfect. Same as mine.
Nope. Get the 1:8.4. It works well
@Colin78
I dont know about spinning a 140 gr bullet at 1 in 8, but I'd say if your spinning 180+ go 1 in 8. If your spinning 180- go 1 in 8.4 or so. Honestly your probably fine running 1 in 8 on a 140 unless it has a known history of poofing mid flight.
Look at what people are ordering for fast twist barrels in 6.5 cm/prc/saum rifles and that will answer your question.
I dont know about spinning a 140 gr bullet at 1 in 8, but I'd say if your spinning 180+ go 1 in 8. If your spinning 180- go 1 in 8.4 or so. Honestly your probably fine running 1 in 8 on a 140 unless it has a known history of poofing mid flight.
Look at what people are ordering for fast twist barrels in 6.5 cm/prc/saum rifles and that will answer your question.
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Why would what someone is running in a 6.5 CM/SAUM/PRC give him the answer about a 7 SAUM for twist rate.
Twist is twist. 6.5 class bullets tend to be in the 140 territory. He is wanting to run as low as 140 class 7mm bullets. If a 6.5 prc is running a fast twist barrel for a 140 grain bullet at 1 in 8 he's good. If they run a 1 in 9 then there is something to think about.
I don't subscribe to that thinking but okay. A 6.5 is 2 caliber designations below a 7mm. Bullet construction is completely different which results in a change of the bearing surface of the bullet or bullets. A140 bullet is actually kind of the norm in a 6.5 as guys are running 130's, 123's, 120's in PRCs. Comparing what a 6.5, 8 twist barrel, does to a 140 6.5 bullet vs what a 7mm, 8 twist barrel does to a 140 7mm bullet, is a apples and oranges type comparison.
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Colin78
Well-Known Member
I don't know who is right here but if Raffy is right then I'm good as I just sold a 6.5 SAUM with a 1:8 twist that shoots the 130's lights out. Never got around to trying the heavies in that one like I had hoped.
So I should change my 7 Sherman Short barrel to a 12 twist as Berger recommends a 12 twist for the 180 gr 30 cal bullets? Using other calibers to choose a twist rate doesn't make sense at all.
I think I will stick with the 8 twist I ordered.
Your partially right. The factors that I know of that determine needed twist to stabilize a bullet in flight are bullet construction, weight, diameter, and length. The .5mm difference is important to factor, but minimal relative to the other bullets you are comparing when jumping from a .264 to a .308 as you referenced above. A 7mm 140 gr bullet is similar enough to a 6.5mm 140 gr bullet that my example, though not perfect, is valid. If you stray too far between calibers, like you did, your likely to get in to trouble here. It's just a guideline. Not a hard and fast rule of nature. If you don't believe me go play on the berger bullets stability calculator. I did some of the work already for you. Here, take a look-
Stabity of .284 berger 140 vld vs. .264 berger 140 vld @1 in 8 twist. They both even share the exact same stability factor of 2.42.
Case in point is: Run an 8 twist in a 7 cal shooting both 140 gr and 180 gr bullets. It will do fine! And so will 6.5 shooting 140s.
Stabity of .284 berger 140 vld vs. .264 berger 140 vld @1 in 8 twist. They both even share the exact same stability factor of 2.42.
Case in point is: Run an 8 twist in a 7 cal shooting both 140 gr and 180 gr bullets. It will do fine! And so will 6.5 shooting 140s.
Attachments
I was more referring to over spinning as you somewhat referred to in your original post, "poofing", not stability. The likely hood of 7SAUM shooting a 140 at 2650 are slim to none. The entire idea of a 140 in a 7SAUM was to push it hard. This entire thing gets more complicated with Monos. Anyways….. moving on.
You can pick it apart if you want. The speed is irrelevant since he can load it down if he needs to. Monos really are a totally different beast. But I agree, lets move along.
In my 7 SS I will shoot Berger 180 Hybrids with an 8 twist. A 180 Hybrid 308 cal requires a 12 Twist, a 180 Hybrid 284 cal will not shoot in a 12 twist barrel. Using your suggestion would prove totally wrong. In regards to your bullet diameter, it is virtually the same difference as your example.
You got lucky with your 6.5 sample, but it is not even close to being an accurate way to guide someone to determine twist needed to stabilize a bullet.
That's all I'm saying.
Steve
You got lucky with your 6.5 sample, but it is not even close to being an accurate way to guide someone to determine twist needed to stabilize a bullet.
That's all I'm saying.
Steve
Your probably right. However the principle I am trying to point out is the situation of leaning towards overtwisting a bullet, if it can handle it. With a 12 twist, then you are erring on too slow of a twist, but if you would have a 10 or a 9.5 twist it would work for both of your calibers with both of your bullets. That is the other side of the coin. If I am picking a twist rate and I have to choose fast or slow, I will choose faster. However I lean towards heavy for caliber bullets and therefore benefit more often by faster twist rates. We are both right, it's just two opposite sides of a coin.
