Feedback wanted: 1:7 twist and/or progressive twist for 300 PRC

[nkyshooter]

I recently ordered a 30 Sherman Magnum barrel ... it is to be a dual purpose rifle - 85%+ range rifle in attempt to achieve a goal of a 1 mile hit ... <15% hunting if opportunity/need arises that my sporter 300 winmag can't handle ... I have Hornady 230gr A-Tips that I'll start with - mostly because I can't find ELD-M's ... but also because of the .823 G1 BC (wow)

I ordered it with an 8 twist - not a gain - just a straight 8 (AND a threaded muzzle for the biggest brake I can find! lol)

At first, I was second guessing myself - did I go too fast? - because I see most other guys shooting the heavies are shooting 9 twist ... with some (at elevation) shooting 10tw's. Then, when I was looking at Hammer's website, I saw some of their heaviest 30's (mono's) require faster than 8.

Savage lists their 300 PRC's as 8.5twist ... I feel confident my choice of 8twist is right for me, my application, and within my anticipated environmental factors (elevation of 600-1200 feet around here, summer temps and humidity at the "icky" level, winter temps usually in the 20's-50's often gray/rainy)

BTW - when we talk about twist, what really matters is the RPM ... the twist, combined with the velocity at the muzzle, is what dictates the RPM's ... so, a faster muzzle velocity could stabilize a bullet at a given twist that at a much slower muzzle velocity with same bullet and twist would fail to stabilize ...

I'll also add this - I have first hand experience shooting a rifle with a twist that is too fast for some of the lighter bullets ... My Savage 223 Wylde with 1:7 twist, as the barrel warms a but, has a tendency to spin 50gr vmax bullets apart after 150 or 200 yards. I literally watched 2 impacts - one on each side of a p-dog - on more than a couple of shots in Montana a few years back ... we were around 3000ft elevation and the 7twist and 50vmax was not a wise choice ... that being said, there are way more p-dogs that met their demise than there were those now living their extended life .

 

[VLD Pilot]

I recently ordered a 30 Sherman Magnum barrel ... it is to be a dual purpose rifle - 85%+ range rifle in attempt to achieve a goal of a 1 mile hit ... <15% hunting if opportunity/need arises that my sporter 300 winmag can't handle ... I have Hornady 230gr A-Tips that I'll start with - mostly because I can't find ELD-M's ... but also because of the .823 G1 BC (wow)

I ordered it with an 8 twist - not a gain - just a straight 8 (AND a threaded muzzle for the biggest brake I can find! lol)

At first, I was second guessing myself - did I go too fast? - because I see most other guys shooting the heavies are shooting 9 twist ... with some (at elevation) shooting 10tw's. Then, when I was looking at Hammer's website, I saw some of their heaviest 30's (mono's) require faster than 8.

Savage lists their 300 PRC's as 8.5twist ... I feel confident my choice of 8twist is right for me, my application, and within my anticipated environmental factors (elevation of 600-1200 feet around here, summer temps and humidity at the "icky" level, winter temps usually in the 20's-50's often gray/rainy)

BTW - when we talk about twist, what really matters is the RPM ... the twist, combined with the velocity at the muzzle, is what dictates the RPM's ... so, a faster muzzle velocity could stabilize a bullet at a given twist that at a much slower muzzle velocity with same bullet and twist would fail to stabilize ...

I'll also add this - I have first hand experience shooting a rifle with a twist that is too fast for some of the lighter bullets ... My Savage 223 Wylde with 1:7 twist, as the barrel warms a but, has a tendency to spin 50gr vmax bullets apart after 150 or 200 yards. I literally watched 2 impacts - one on each side of a p-dog - on more than a couple of shots in Montana a few years back ... we were around 3000ft elevation and the 7twist and 50vmax was not a wise choice ... that being said, there are way more p-dogs that met their demise than there were those now living their extended life .

The 8/9 twist barrels are best for conventional bullets. The 7 twist is for the solid lathe turned bullets primarily. If someone is shooting primarily solids and also 245/250 jacketed bullets, the 7 twist wouldn't be an issue. I wouldn't get it if my plan was to shoot 215-250s. The 8 twist would be my choice and I'd have to selectively chose which solids the 8 twist barrel would stabilize and make my choice based on that.

 

[Jeff Heeg osoh]

With any gain twist it has to either smear or twist the bullet as the twist gets tighter. It is common knowledge that a barrel that slightly gains twist will shoot better than one that the twist is slowing. IMO 7 is too fast for a 30. The ruger precision guns are twisted at 8. I put together prc,s with a 9 twist. We do not shoot the 250 Atip bullet but you lose so much speed is it worth it? I guess if you are in the 2 mile shoot. A 9 stabilizes the 230,s . All I need.

Dave
Whats opinion on the 375 cal bullet from a 32" barrel, twisted or damaged? Just asking after seeing your info.

Thanks

 

[milo-2]

Dave
Whats opinion on the 375 cal bullet from a 32" barrel, twisted or damaged? Just asking after seeing your info.

ThanksView attachment 247674

I have never even seen a pic of a bullet design like that. Tell me about it. By looking at it, my level of thinking says it would fight the air all the way to the target.
I think I was the first in this post to express concerns of over engraving a bullet with gain twists. But it was a non issue in my experience, limited as that may be.

 

[Jeff Heeg osoh]

Milo-2
I don't use this bullet anymore do to the fact its great for short range say out to a mile but the bands strip to much BC off for anything in the 2 mile +. I think its like 5% for every band you will loose.
The bullet above of course does not have the dark coating on it anymore because of being fired and retrieved in a large snow bank.
But I don't think the bullet looks bad as far as the questions of getting all twisted and or a aggressive smear because of twist barrels - this bullet was shot from a very-very aggressive twist starting at a easy 16 twist and ramping to a fast 7.7 twist as seen earlier in this post with the barrel cutoff showing all the specs side by side with the fired bullets

GS customs 414 grain 375 cal. from back in 2014.

 

[milo-2]

Milo-2
I don't use this bullet anymore do to the fact its great for short range say out to a mile but the bands strip to much BC off for anything in the 2 mile +. I think its like 5% for every band you will loose.
The bullet above of course does not have the dark coating on it anymore because of being fired and retrieved in a large snow bank.
But I don't think the bullet looks bad as far as the questions of getting all twisted and or a aggressive smear because of twist barrels - this bullet was shot from a very-very aggressive twist starting at a easy 16 twist and ramping to a fast 7.7 twist as seen earlier in this post with the barrel cutoff showing all the specs side by side with the fired bullets

GS customs 414 grain 375 cal. from back in 2014. View attachment 247852

Thanks for that. My initial thought of over engraving was probably more of an overactive imagination. I have yet to go downrange and try retrieve a bullet fired from my gain tw. As I said, there hasn't been any indication as to why I should.

 

[David Emerson]

Dave
Whats opinion on the 375 cal bullet from a 32" barrel, twisted or damaged? Just asking after seeing your info.

ThanksView attachment 247674

 

[David Emerson]

It looks fine. But I stand by what I say. With a gain twist the bullet has to twist or smear. Years ago a man by the name of Morrison was a gain twist barrel maker. He posted photos of bullets. The groove at the back of the bullet was clearly widened. Most of the barrel makers do not offer gain twist. Controvercial? Yes. The germans did a lot of experimentation in WW11. The paris rail gun. WW1? maybe. Choked the bullet down in diameter as it went down the bore. Even now smith and wesson. The 460 s&w is a gain twist. But pistol bullets are pretty short. But if you look at precision shooting I think a straight twist that does not damage the bullet is best. My opinion. Opinions are like Aholes. Everyone has one. When gain twist barrels are winning matches I will perk up.

 

[Gamesniper19]

My 2 cents - gain twist has been tested by many a barrel manufacturer. My sense would be if it was a significant leap forward, we would see more of them. Not saying it won't work but the ability to make a gain twist barrel consistently with current manufacturing is much more difficult and time consuming for not much - if any gain in performance.
Rifling twist = bullet stability. Many twists will run almost any bullet, there is a sweet spot though and finding the sweet for what you want to shoot should be a consideration, especially if you want to run big giant long bullets. Run a stability calc, like the one found in Berger or the JBM http://www.jbmballistics.net/cgi-bin/jbmstab-5.1.cgi
There is a stability optimum as well as an overspin area where you aren't gaining any more by spinning the bullet more. In some cases you may actually give up some speed.
What has worked for me in my wildcats and ELR rifles = stability from 1.7 - 1.9

 

[longestrange]

OK, here is a detailed technical article (for non-commercial use) for determining required twist rate.
Stability and Twist Doc

 

[Gamesniper19]

OK, here is a detailed technical article (for non-commercial use) for determining required twist rate.
Stability and Twist Doc

Or click this

JBM - Calculations - Stability

www.jbmballistics.net

 

[Capt RB]

THere were quite a few 9,9.25 to 8.7 gain twist 7mm barrels for f-class made. I shot a few all were either Barts or Rock creek not sure they were not my rifles. They all seem to produce a bit more velocity than the straight 9 or they all shot accurately a bit faster meaning the node was 30-50fps faster than the 9twists shooting the 7/300wsm or the 284 improved don't know which flavor of improved. My 308 is a rock creek and it has 5/8" or so of gain twist from 12.5 to less than 12. It has been measured so many times I still don't know if it is 11.875 or 11.775. That barrel has 5600+ rounds on it and it is still under 1/2 moa. It has always been cared for with not alot of hot strings. It has been fast since day 1 running box ammo 100-150fps faster than the box stated speed.
FOr the 300PRC stick with an 8 for 230 serrias , 245 Bergers and 250 atips. FOr the 230 a tips 230 Bergers 225eldm and down cup and core 8.5 or 9. My 10 does fine with the 225 eldm and 230 Bergers around 3020fps. I am not done with load development due to a shortage of brass. I also have a 30" barrel vs a 24 or 26" so my speeds are a bit higher than normal. If you are going to run a solid like the GS or icbm from badlands. The198 flatline bullet would pick up some transonic stability with a 7 however an 8 is the recommended twist. With a G7 over .400 and the ability to push it around 3300fps it would be a neat way to spend some money on bullets