30 sherman magnum

[VLD Pilot]

Hey, thinking about going from the 300 PRC to 300SM. Does anyone have barrel twist recommendations? I see the load data lists 1-9. I am currently shooting a 1-8 in my PRC. This is not a hunting a rig, heavy bullets only for competition. Thank you.

8

 

[tyler6593]

8

Thank you, are you guys seeing meaningful performance increases in the SM over the PRC?

 

[VLD Pilot]

Mines a hunting rifle. I wanted an honest and easy (not hot load) 3000 fps with a 225 bullet. The SM gave me that. The PRC did not. Mines a 9 twist. Heaviest I'll shoot is 225. The 208 is my main hunting bullet. The 30SM isn't anything magical but gives the performance edge over the PRC

 

[Taylorbok]

Thank you, are you guys seeing meaningful performance increases in the SM over the PRC?

I comfortably run 250's at 3k from a 32" tube in my 30SM.

 

[VLD Pilot]

I've heard some guys running the 250s at that velocity with long barrels. Mine is 26" and I'm pretty happy with 3000 with the 225s. I think I could see close to 3K with the 245/250s as well but likely it would be a hot load. No desire for that heavy bullet for my needs but for a shooter wanting that big heavy higher BC bullet for target shooting, a longer barrel makes sense. I only run my 208s at around 3000-3100 and that's a light load. They do what I need. When I need the 225 for bigger animals, I'll push it a little more

 

[nkyshooter]

Not here to create any arguments - just responding from my own personal opinion from my own equipment/experience which is definitely not all encompassing/extensive ... I am only at under 200rounds in so far including forming.

@tyler6593

Definitely agree with the 8 twist - and depending on the altitude you will shoot it, you might even consider 7.5 for 250's at sea level ... Probably a good idea to look at Berger's twist calculator with the specs/dimensions of the bullet you hope to use.

IMO ... when comparing like for like pressures in like for like barrel lengths, arguably the performance gain is small but there is a gain. I have experience with other Ackley Improved cartridges (which is essentially what Rich's 30 SM is) and there are distinct advantages ... but also tradeoffs for those. You will have to decide if the additional work is worth the gain you will get.

I built mine to take to 1 mile on the range ... purpose built for that reason while leaving the door open to use it in other ways as well. With the gains I see in mine over PRC unmodified and compared to the extra in dies and forming brass, in hindsight, I would be on the fence about doing it again... not against, but I would be thinking about the reasons I want the extra and is this the optimal way...

If you have quickload or grt (I use GRT) run the numbers in like for like bbl lengths and at like for like pressures. H2O capacities are important for this as the PRC's are in the 94-97g range from what I have seen and the 30SMs are in the 96-99 range from what I have seen. I have found 'mathematically' these cartridges are closer than the community reported velocity gains would indicate. I suspect this is for multiple reasons including:

1. The ackleyization of a cartridge is known to 'hide'/'better handle' pressure so in general I think we tend to try to push these a bit hotter...
2. Most 300 PRC rifles are straight factory vs all 30SMs are custom barrels (unless a factory 30cal was rechambered) and likely to handle higher pressures

My setup doesn't like the pressure ... it taps out sooner than I think it 'should' and the bolt gets stiff even before I see any other pressure signs (typical for ackleyized) ... If I was one of the guys pushing 250's at 3K with no pressure, I'd probably be saying to not even think about a straight 300 . Still, I get PRC or better performance without exception. AND 300prc ammo shoots VERY accurately in mine ... so far, just as accurately as my 30SM loads. Good enough that I'm disappointed if over .5MOA (Savage factory action - SAV2 Trigger)

If you like to tinker and solve problems and really be in tune with your rifle/ammo and enjoy the custom world and the extra work, don't hold back on a 30SM ... I love mine... that being said, the only things I would be leaving behind if I went straight PRC would be a 'bit' of velocity gain and the pros and cons of an Ackley Improved cartridge.

One final thing... I run a 26" 8tw bbl. Something I would definitely do differently regardless of 30SM or PRC (for my purpose of a 1 mile range rig) would be to go to 28" or possibly even longer barrel to get more velocity without going into the unsafe zone.


Have fun with the analysis/decision ... and ... whatever you decide, have a blast with the building/prepping/shooting - I know I have!


Maybe I'll try out a 7PRC next ... hmmm

 

[QuietTexan]

Hey, thinking about going from the 300 PRC to 300SM. Does anyone have barrel twist recommendations? I see the load data lists 1-9. I am currently shooting a 1-8 in my PRC. This is not a hunting a rig, heavy bullets only for competition. Thank you.

8 twist for sure, I run 208s with no problem and it leaves the door open for moderately heavy monos and maximally heavy Bergers/A-Tips.

Thank you, are you guys seeing meaningful performance increases in the SM over the PRC?

I'm getting 300 PRC velocities from fireforming loads, so to me there is no downside. I have the option to run faster or at lower pressure going forward. I load the cases as if they were 300 PRC, I shoot them, I run them through a sizing die. There's no difference in the loading and shooting process other than the case comes out looking different after the first shot, and it takes one or two more firings before I have to set my sizing die to bump the shoulders.

If you're putting on a new barrel, I see zero reason to not go 30SM.

 

[Pdvdh]

If you'll shoot heavier copper mono bullets, consider a 7.5 twist barrel.

I just installed an 8.5-twist. I now have an 8-twist ordered to install on my other 30 SM. If it weren't for the insanely long waiting periods to order & receive a specific twist & contour barrel, I'd probably order a 7.5-twist.

But 8-twist seems more available. So a happy compromise.

 

[elkaholic]

For those who aren't aware, the truth is, the 30 SM preceded the PRC by several years and was originally known as the 30/375 SI
Hornady built my dies for it and when the PRC came out, if not for a thicker neck, I could have fired their round in my chamber. The SM has less taper and a 40 degree shoulder which gives the advantages already mentioned. The PRC is a good round, but does leave performance on the table and the SM will shoot factory PRC ammo very accurately, as was also mentioned.
I run the 9 twist in mine which works very well even with the 245 Berger. An 8 is better for the 250 Atips and some of the long monos.

 

[VLD Pilot]

For those who aren't aware, the truth is, the 30 SM preceded the PRC by several years and was originally known as the 30/375 SI
Hornady built my dies for it and when the PRC came out, if not for a thicker neck, I could have fired their round in my chamber. The SM has less taper and a 40 degree shoulder which gives the advantages already mentioned. The PRC is a good round, but does leave performance on the table and the SM will shoot factory PRC ammo very accurately, as was also mentioned.
I run the 9 twist in mine which works very well even with the 245 Berger. An 8 is better for the 250 Atips and some of the long monos.

It's why I built mine on a 9 twist. I won't shoot solids so a faster twist won't matter. Have no reason to shoot 245s but if I did, I could do it with a 9 twist.

 

[Pdvdh]

For those who aren't aware, the truth is, the 30 SM preceded the PRC by several years and was originally known as the 30/375 SI
Hornady built my dies for it and when the PRC came out, if not for a thicker neck, I could have fired their round in my chamber. The SM has less taper and a 40 degree shoulder which gives the advantages already mentioned. The PRC is a good round, but does leave performance on the table and the SM will shoot factory PRC ammo very accurately, as was also mentioned.
I run the 9 twist in mine which works very well even with the 245 Berger. An 8 is better for the 250 Atips and some of the long monos.

I considered mentioning that. Better to hear it from you. Indeed, an example of your orignal wildcat preceding a light-weight Hornady SAAMI 300 PRC.

Hornady techs mighta been on Valium when they finalized their 300 PRC. Leading to an "easy does it" "everything in moderation" decision. Where's the fun in that? Hahaha

 

[JBarton]

Hey, thinking about going from the 300 PRC to 300SM. Does anyone have barrel twist recommendations? I see the load data lists 1-9. I am currently shooting a 1-8 in my PRC. This is not a hunting a rig, heavy bullets only for competition. Thank you.

I am running an 8 twist in both my 30SM's. I am running 230gr and 245gr bullets with zero stability issues.

 

[elkaholic]

I am running an 8 twist in both my 30SM's. I am running 230gr and 245gr bullets with zero stability issues.

No, they shouldn't have any issues. The question becomes, is an 8 necessary or is it just building a little more pressure.
An 8 covers your tail for whatever though!

 

[elkaholic]

I considered mentioning that. Better to hear it from you. Indeed, an example of your orignal wildcat preceding a light-weight Hornady SAAMI 300 PRC.

Hornady techs mighta been on Valium when they finalized their 300 PRC. Leading to an "easy does it" "everything in moderation" decision. Where's the fun in that? Hahaha

Im not saying it was a copy because they had a pretty say guy over there that was playing with a 30/375 early on. Im just saying that it was crazy how close we both ended up if it was an accident because it was considerably different than the original 375 Ruger. Far different than just a neck down job which they normally do.