PRC twist rate 7,7.5,8?
- Thread starter Gobears16
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Gobears16
Well-Known Member
So it sounds like the 1-8 could/probably work but the 1-7.5 has no downside for shooting 140-156gr bullets. Is that a safe assumption.
Danehunter
Well-Known Member
Yes, a safe assumption. I'd feel fine using a 1:7.5 twist for 6.5 CM 130 gr. up through 160 gr.
My 6.5 PRC X-Bolt Pro with1:7 may not shoot 130 gr. well. I'll have to load some 130 gr. ELD-M bullets that I have and see if there is any load my 6.5 PRC rifle would shoot well.
Eric B.
My 6.5 PRC X-Bolt Pro with1:7 may not shoot 130 gr. well. I'll have to load some 130 gr. ELD-M bullets that I have and see if there is any load my 6.5 PRC rifle would shoot well.
Eric B.
I just can't see too much twist not playing an important role in bullet failure. If a course of fire demands a specific number of shots in a specific period of time then all things being equal everyone's bullets would blow up. Increased twist is increased friction. Add in the torsional stresses and the temperature of a barrel and clearly a threshold has been crossed. Incredible demands are placed on what seems to me to be a relatively fragile component. Even if it is "just shy" of exploding imagine the distortion it must experience. Too much of a good thing is still too much.
So have we as consumers, competitors, and just plain ole folks been so spoiled that we actually expect a "silver bullet"?
I wanna shoot the same bullet (weight) at the same speed and the same twist at a 9500' change in elevation regardless of rate of fire in unknown temps and get the same results. Is this reasonable?
I wanna shoot the same bullet (weight) at the same speed and the same twist at a 9500' change in elevation regardless of rate of fire in unknown temps and get the same results. Is this reasonable?
Gobears16
Well-Known Member
Are you thinking or suggesting that if the bullet spinning so fast would blow up quicker when hitting hide and bone?
Danehunter
Well-Known Member
Dirtrax,
I agree, "increased twists increased friction". And that is why it's likely better to have 5R rifling for faster twist barrels. Fewer lands and grooves, less bullet jacket deformation and radiused groove corners all make for a bit less friction.
Eric B.
I agree, "increased twists increased friction". And that is why it's likely better to have 5R rifling for faster twist barrels. Fewer lands and grooves, less bullet jacket deformation and radiused groove corners all make for a bit less friction.
Eric B.
I would agree that a bullet spinning faster will expand faster. And since I don't shoot monos, it'll be 8 twist at my altitude.
Danehunter
Well-Known Member
I have never seen any science that would confirm any relationship between a faster bullet spin and faster expansion. Got any factual info on this?
Eric B.
Eric B.
William Cameron
Member
I ordered a Pac Nor 30" 5 groove 7 twist should be here tomorrow. I plan on breaking it in with the factory loaded 147 ELD-M's. I'll let you know if if they start breaking up.
Eric, Based on bullets blowing up in flight with fast twists and hot barrels, it would seem they are impacted by RPMs. My opinion though and never blew any up in air.
That said it looks like the Berger twist calculator says the 156 EOL should have a 1.78 SG with an 8 twist. A 140 vld has a 2.03 SG. Those being the SG numbers, I think my 8 twist will be fine.
In looking it sounds like anything over 1.5 or so is considered stable. What would greatly exceeding 1.5 SG provide? Honest question as I have no idea.
Gobears16
Well-Known Member
When I put my numbers for the 156 EOL at 2930fps with 8 twist at sea level I got 1.46 with 7.5 I get 1.76.... both will work but 7.5 has better leeway.
Live at 6,700 foot elevation and shoot from 5,300 to 12,000. Way more forgiving than down at sea level. Read some more on the bullets blowing up and seems like it must be more likely caused by a rough throat then too fast of twist. 8 is working for me where I am, sounds like 7.5 would be better down at sea level.
