300 Norma Mag (Standard Version)

[7.62 Gunner]

I'm gathering parts for a short barreled build in 300 NM, and I'd like to avoid fireforming but am concerned about excessive neck growth with the 20 degree shoulder.
Those of you with experience how often are you having to trim the necks, and hows case life with Lapua brass?

 

[tim_w]

Frankly, I find, if you want the most stable cases and consistent load development always do a first loading in virgin brass as a fireform load using a med pressure load. If you subscribe to that it's no extra work to fireform to a sharper shoulder and less body taper. Why not then get the added benefits of the changes. If improvements are kept moderate, in a bolt gun, IMO, there are no downsides in terms of function or performance.

Neck growth for a given shoulder angle is tied to the peak chamber pressure of the load you run. Also if you anneal vs not can effect this. I subscribe to annealing every firing or not at all.

Even 33-35° will reduce neck growth. Add a bit of reduction in case body taper and the combo allows cases to last longer at a given pressure. It decreases over all brass flow. There is a reason it's called "improved" after all.

With the cost these days of these large cases like the NM/LM I do not want 10 loads I want 30+ loadings. 50 cases should outlast the barrel.

My favs 300 NM Imp designs which have proved to be wickedly accurate, easy to tune with multiple powders and bullets, has dies instock and available are:
@Alex Wheeler 300NM Wheeler and @rpierce Ryan Pierce's 300NM Pierce.

There are numerous guns in the wild with those chambers over a stretch of years now so any bugs have been throughly worked out.

 

[tim_w]

Out of curiosity, how short are you planning for the barrel?

 

[QuietTexan]

I'd like to avoid fireforming

X2 on you'll be best served shooting all the cases through at least once anyways. The barrel will need ~100 rounds also, so doing the improved chamber and shooting a set of 50 cases twice through will set you up perfectly for load development.

If you're new to the chambering you won't have anything to start off of anyways, the 100 forming/break-in shots will let you use then rule out a couple of powders and/or bullets up front.

 

[7.62 Gunner]

Out of curiosity, how short are you planning for the barrel?

20"
I'm looking to send 225/230s around 2850 with H1000.
One thing I'm certain of, if I go through the hassle of fireforming and getting custom reamer and dies it'll be 40 degrees.
With a center feed DBM setup its silly not to..

 

[Ucsdryder]

20"
I'm looking to send 225/230s around 2850 with H1000.
One thing I'm certain of, if I go through the hassle of fireforming and getting custom reamer and dies it'll be 40 degrees.
With a center feed DBM setup its silly not to..

I want the same rifle. 20" to run suppressed in a 300nmi. Very curious to follow along with this build!!!

 

[QuietTexan]

Call 4D, they might stock the reamer and save you the money of ordering your own. NMI is a very popular design.

 

[7.62 Gunner]

I want the same rifle. 20" to run suppressed in a 300nmi. Very curious to follow along with this build!!!

Yes sir I think all things considered it's the way to go with a short barrel, origally I planned on a RUM but Lapua brass and proper bullet seating pushed me to the NM.
I'm having Manson Reamers design me a 40 degree version with .015 case taper specd with Lapua brass.

 

[tim_w]

20"
I'm looking to send 225/230s around 2850 with H1000.
One thing I'm certain of, if I go through the hassle of fireforming and getting custom reamer and dies it'll be 40 degrees.
With a center feed DBM setup its silly not to..

To me more critical than a few extra degrees more on the shoulder that are really adding nothing significant (talking 35 instead of 40. Not std vs imp) it would be a reamer die combo that is spec-d and proven to work perfectly together. The Wheeler version has the steeper shoulder and he generously made it all publicly available. His reamer print is on file at JGS and dies are in stock at bullet central.

Here is a link in a thread about Ryan Pierce's version also extremely good but its a shallower shoulder. On the subject of dies Alex comments and gives info on his chamber and dies etc. I would recommend, if you haven't yet look thru the entire thread. Performance of both are very close. It will get you a good idea on load data and vel numbers as well the amazing accuracy this case gets. Ryan builds very accurate guns.

300 Norma Improved. Load testing, info, and builds

What’s the difference between your design and Alex wheelers design?

www.longrangehunting.com

The 300 NM Imp IMO is a sweet spot. Fits with the longest cup/core in a dbm. Can hit the 3k+ vel with 245-250gr but has best throat and case life at mid-high 2900s. Great nodes. Great brass. Works well with all the slow powders i.e. H1000, Retumbo, N570, N170, RS LRT, H50BMG, RL50, RL33 all with good to ideal case fill. Brass that will last 20+ loading if you keep psi max@ 70k. What's not to like.

 

[7.62 Gunner]

To me more critical than a few extra degrees more on the shoulder that are really adding nothing significant (talking 35 instead of 40. Not std vs imp) it would be a reamer die combo that is spec-d and proven to work perfectly together. The Wheeler version has the steeper shoulder and he generously made it all publicly available. His reamer print is on file at JGS and dies are in stock at bullet central.

Here is a link in a thread about Ryan Pierce's version also extremely good but its a shallower shoulder. On the subject of dies Alex comments and gives info on his chamber and dies etc. I would recommend, if you haven't yet look thru the entire thread. Performance of both are very close. It will get you a good idea on load data and vel numbers as well the amazing accuracy this case gets. Ryan builds very accurate guns.

300 Norma Improved. Load testing, info, and builds

What’s the difference between your design and Alex wheelers design?

www.longrangehunting.com

The 300 NM Imp IMO is a sweet spot. Fits with the longest cup/core in a dbm. Can hit the 3k+ vel with 245-250gr but has best throat and case life at mid-high 2900s. Great nodes. Great brass. Works well with all the slow powders i.e. H1000, Retumbo, N570, N170, RS LRT, H50BMG, RL50, RL33 all with good to ideal case fill. Brass that will last 20+ loading if you keep psi max@ 70k. What's not to like.

Appreciate it
I've read through that thread and it's good stuff.
I've worked with Manson in the past with improved reamers, while I appreciate what Wheeler and others have done, I really don't get all the variations of 32, 35, 37, and even 35 with the shoulder bumped forward..
I know reliable feeding from a BDL setup is the focus of those designs, but I'm going center feed and 40 degrees requires almost 0 trimming while 35 needs it every 5-6 firings.

It's pretty simple to have a reamer and dies designed correctly, in this case I'm designing everything around lapua brass which is .006 shorter than Norma, add a .004 crush fit for fireforming and it's .010 shorter than CIP length.
I'm adding .005 clearance above the web to avoid clickers, .005 neck clearance, and throating it for 225s .025 above the neck shoulder junction

 

[Mike D Texas]

I had a 40° shoulder 300 NMI drawn up in Quickdesign and was about to send to Manson. The I got to thinking about 16-20 weeks after I had fire formed brass to get a resizer die, working through chamber design, etc so I just did the easy button and went with the AW2 reamer with an additional .025 freebore added for 245 EOL and 250 ATips. Reamer prints available and dies in stock at Bullet Central. Also I wanted the ability to either run an internal center feed box or a DBM and felt on that large of a case that the slightly softer shoulder angle may feed better.

 

[tim_w]

I had a 40° shoulder 300 NMI drawn up in Quickdesign and was about to send to Manson. The I got to thinking about 16-20 weeks after I had fire formed brass to get a resizer die, working through chamber design, etc so I just did the easy button and went with the AW2 reamer with an additional .025 freebore added for 245 EOL and 250 ATips. Reamer prints available and dies in stock at Bullet Central. Also I wanted the ability to either run an internal center feed box or a DBM and felt on that large of a case that the slightly softer shoulder angle may feed better.

This is what my reasoning was.

I like @7.2 gunner had everything designed with a 40° shoulder. Then I started seeing reports from basically all the NM about clickers after a few reloading. These were from the very best die manf sent 3x fired unsized cases. The issue was these cases needed a bit more base sizing I believe. It was Alex that had worked it out and tweaked numbers to make it all work and minimal sizing but no more clickers. On top of all that he worked with BC and had dies made and kept in stock. For me that is a huge benefit. Hard to beat turn key that is 99% of what I had in mind. I understand others may not feel the same way. It's nice to havr complete control and make it yours.

 

[jrock]

I'm a fan of the NM case and have one in 338. I trim my brass ever 3 or 4 firings and it's minimal. I have Norma brass. I stuck with the standard case to avoid the higher prices of custom dies. Although, if you can afford the car, you can afford the gas.

Fire forming is fun! I wouldn't shy away from that if you want an improved case design. +1 vote for AW chamber config.

 

[KH_Outdoors]

I'm gathering parts for a short barreled build in 300 NM, and I'd like to avoid fireforming but am concerned about excessive neck growth with the 20 degree shoulder.
Those of you with experience how often are you having to trim the necks, and hows case life with Lapua brass?

Following

I'm working on a 20" suppressed 300 Norma (standard) soon. Pretty intriguing case to start with and in a 20" version. I was thinking running 200-215 class bullets to keep speed up. Maybe mono's. I think I would go longer on the barrel for a 300 Norma Improved though. 24-26" maybe?

Look forward to seeing how this build shakes out for you.