30 Nosler & 300 PRC vs 30-28 Nosler & 300 PRC SI Wildcats
- Thread starter BoatTail
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BoatTail
Well-Known Member
In order to consider one of these four cartridges for a custom long-range rifle build, I need to consider the neck, throat and freebore of the chamber. My goal is to select or request a case and reamer that promotes small velocity standard deviations (SD) standard deviations and limited extreme spreads (ED). It also needs to limit the bullet incursion into the case, to maximize powder volume while fitting in the magazine.
Here are the reamer, neck, throat and freebore dimensions of two of our focused cartridges.
Of the two, we are told that the 300 PRC was designed to have a custom chamber and that the case was designed at the same time. While I'm not an expert, lets see if we can validate which might be better. It will help me decide what to end up with.
The SAAMI version of the 30 Nosler has a neck of 0.346. I've been taught you need a minimum of 0.003 clearance on the neck of the loaded round to the chamber. Too much clearance and I found I get larger SD's, inconsistent velocities and the alignment to the throat and then to the rifling is challenged which affects accuracy.
30 Nosler - The new Nosler case necks I measured varied between 0.0156 and 0.0162. Without turning the necks for consistency, this means there is between a 0.0023 to 0.0013 extra gap. This is an example of too much slop in the neck
300 PRC – I don't have any 300 PRC cases to check neck thickness. I thought I read where someone provided the thickness on new brass. Without it, what I believe is as Hornady said, they designed the case and the chamber at the same time so it makes sense that the 300 PRC case neck thickness has a tighter tolerance and that the average is likely slightly smaller but no greater than 0.0155. This would then limit the slop when the bullet leaves the case and provide better alignment to the throat and into the rifling.
I'll stop her and we can discuss throat size advantages next time.
Here are the reamer, neck, throat and freebore dimensions of two of our focused cartridges.
Of the two, we are told that the 300 PRC was designed to have a custom chamber and that the case was designed at the same time. While I'm not an expert, lets see if we can validate which might be better. It will help me decide what to end up with.
The SAAMI version of the 30 Nosler has a neck of 0.346. I've been taught you need a minimum of 0.003 clearance on the neck of the loaded round to the chamber. Too much clearance and I found I get larger SD's, inconsistent velocities and the alignment to the throat and then to the rifling is challenged which affects accuracy.
30 Nosler - The new Nosler case necks I measured varied between 0.0156 and 0.0162. Without turning the necks for consistency, this means there is between a 0.0023 to 0.0013 extra gap. This is an example of too much slop in the neck
300 PRC – I don't have any 300 PRC cases to check neck thickness. I thought I read where someone provided the thickness on new brass. Without it, what I believe is as Hornady said, they designed the case and the chamber at the same time so it makes sense that the 300 PRC case neck thickness has a tighter tolerance and that the average is likely slightly smaller but no greater than 0.0155. This would then limit the slop when the bullet leaves the case and provide better alignment to the throat and into the rifling.
I'll stop her and we can discuss throat size advantages next time.
Pooley dont know were your getting your info but 30 Nosler saami neck is.344.
As far as neck clearance, again theres alot of opinions on that also so here goes mine .004-.005 is just about right for what your wanting. Worrying about reamer spec is also a non issue if you get your own or find the right Smith who does it doesnt matter as long as the reamer has the .225 freebore neighborhood. Nosler screwed the pooch on there freebore.
I've shot factory chamber neck clearance of .008 and they have shot pretty good right at .5 m.o.a
Like I stated in an earlier post I'm making my decision on brass quality and availability.
As far as neck clearance, again theres alot of opinions on that also so here goes mine .004-.005 is just about right for what your wanting. Worrying about reamer spec is also a non issue if you get your own or find the right Smith who does it doesnt matter as long as the reamer has the .225 freebore neighborhood. Nosler screwed the pooch on there freebore.
I've shot factory chamber neck clearance of .008 and they have shot pretty good right at .5 m.o.a
Like I stated in an earlier post I'm making my decision on brass quality and availability.
This post is the most commonsense response I've read in a while. But........"where does the 6.5 CM fit into this equation!!!!!!!!!!!!!!??????????
About 50 FPS under the 260 Rem and waaaaaay behind my 7-08 a.i.This post is the most commonsense response I've read in a while. But........"where does the 6.5 CM fit into this equation!!!!!!!!!!!!!!??????????
adam32
Well-Known Member
But........"where does the 6.5 CM fit into this equation!!!!!!!!!!!!!!??????????
At the Girl Scouts camp.
BoatTail
Well-Known Member
L.Sherm,
The information on the 30 Nosler neck size came from the SAAMI Reamer drawing by Nosler and approved by Dave Kiff from PTG. The drawing is available from PTG.
Pooley I must apologize the saami drawing does show .346. All the 30 Noslers I have loaded for with there brass had been right about .340 loaded round.
.006 clearance is getting up there and that doesnt leave anything to clean up necks if you want to.
Again I apologize.
.006 clearance is getting up there and that doesnt leave anything to clean up necks if you want to.
Again I apologize.
BoatTail
Well-Known Member
I wanted to talk about throat diameters today and would like your input. Few years ago I started working with a gunsmith in Colorado Springs Colorado. He's done all my builds for the last 3 rifles. For my reamers I'd always worked with Dave Kiff on the designs and expert for the chamber dimensions. My gunsmith always talked about using his reamers because they had a parallel throat that would better align the bullet as it entered the rifling. He said with his reamer designs bullet seating depth were less important. I had a hard time with that because I didn't understand and it always held my CAOLs 15 to 20 thousands off the lands with good success. I finally understood it this year that what he was talking about was the throat diameter from where the case mouth ends, to where taper to the rifling starts. This I realized was a parallel section . Most of the match chambers I've seen and built to have a throat diameter of the caliber plus 0.0005. So for 0.308 caliber match chamber, the parallel throat diameter would be 0.3085. However, on the 300 PRC they use 0.3088. I was wondering why they went with the larger throat when it's touted to be a match chamber. I assume they did it to avoid liabilities and the difference between 0.3088 is not much from the 0.3085. Your thoughts?
I'm no expert on the throat dia. by know means
Guys like Alex, Rian and JE maybe better people to ask but hers my guess and please somebody correct me if I'm off track I think it has to do with building pressure, I think the smaller dia the caliber you may be able to get away with .0005 remember that's overall so its .0002.5 per side. I think on these bigger cartridges you gotta have a little more like the .0008 my 30 Nosler has.0010. I havent experimented with dia.or bore riders. I'm just now getting a pretty good grasp on freebore and starting to understand the lead angles a little better. I still have alot to learn. With a very small throat dia. And you get some bullets that are a little large could be not good, I know not all are the same. These are good questions though bspooley hopefully I can learn something from the responses also.
Guys like Alex, Rian and JE maybe better people to ask but hers my guess and please somebody correct me if I'm off track I think it has to do with building pressure, I think the smaller dia the caliber you may be able to get away with .0005 remember that's overall so its .0002.5 per side. I think on these bigger cartridges you gotta have a little more like the .0008 my 30 Nosler has.0010. I havent experimented with dia.or bore riders. I'm just now getting a pretty good grasp on freebore and starting to understand the lead angles a little better. I still have alot to learn. With a very small throat dia. And you get some bullets that are a little large could be not good, I know not all are the same. These are good questions though bspooley hopefully I can learn something from the responses also.
BoatTail
Well-Known Member
Interesting. That makes sense. I was struggling with that and may have experienced that with my two 28 Nosler's. The one with the SAAMI chamber has lower pressures but higher velocity standard deviations, while the match chamber one will reach pressure sooner but has low velocity standard deviations. Interesting! Both however seem to shoot equally well. That doesn't seem like it should be the case but perhaps with some more load work I'll see a difference between the two.
