How do you decide on an improved cartridge?

[jb1023]

I am researching a 300 or 338 Norma Improved as my next build but this applies to any Imp really. There are so many choices in the 300/338 NM Improved category, without talking to each designer, if you can even find them, or designing my own, how do I know if one can use factory ammo, in a pinch, or needs COW or jammed or some other forming steps? For this build I want to fireform, trim and be done (factory, COW or jammed are all fine and does not matter). With Peterson, Lapua and ADG all making or soon to be making brass I'm pretty settled on a 300/338 NMI, I just don't know which one. Can I only look at the versions who's designer is active online or is there a way to tell by looking at a drawing?

 

[TG-5150]

Tagging in and watching what gets posted. I'm in a similar boat, being a kitten "Wildcatter" . Hahaha

 

[snox801]

All the designs are so very close. Don't put to much thought into it. They will gain capacity over the factory spec but once it's improved they will all be close. I can't tell you on which could shoot factory ammo in a pinch. I think that depends on the parent case. Most lapua improved cases will in my experience. That's just something you will have to see when complete. I will be watching closely as my next build may follow your lead.

 

[cjuve]

I am currently in the process of putting together an improved version of the 300 Norma for myself, by no means am I an expert and I am sure that others will have more to add.
In order to tell if the reamer has the ability to be chambered to shoot factory rounds you need to compare the sammi print and the improved print and compare the outside dimensions at the shoulder, length at the shoulder,lengths at the neck shoulder junction, neck diameter and free bore lengths. Things that could keep you from shooting factory ammo are if the shoulder has been moved forward and the neck length shortened. The free bore has been shortened where you can't chamber the factory rounds, the neck diameter is tight. There are definitely versions out there that it would be best to neck up and create a false shoulder to fire form.


Also, when the rifle is chambered it is a good idea to have the factory brass that you plan to shoot with the smith so that he can make sure that the fit is correct.

One of the best things you can do is talk to a good gunsmith and to the guy that is building the reamer. Dave Manson has been great for me to talk to.

 

[jb1023]

All the designs are so very close. Don't put to much thought into it. They will gain capacity over the factory spec but once it's improved they will all be close. I can't tell you on which could shoot factory ammo in a pinch. I think that depends on the parent case. Most lapua improved cases will in my experience. That's just something you will have to see when complete. I will be watching closely as my next build may follow your lead.

Yeah I agree, I'm not concerned about which one in terms of performance as I figure they will all be superior to my abilities, it is just the forming of the parent case, Norma Mag in my case, into Imp I am concerned about.

 

[WeiserBucks]

I'm no expert on the subject , but folks I shoot with claim that 35 degree shoulders feed much better than 40 degree .

 

[L.Sherm]

As stated above I would go with no more than 35 degree for feeding reasons if you wanna repeater. Next would be do you wanna turn necks or not and have your reamer based on that and brass neck thickness.

 

[L.Sherm]

The Peterson brass for the 300 Norma is good and I have no doubt the Lapua will be when it hits the market. If your in a hurry I would get a reamer made off the Peterson brass if not then wait on the Lapua and see how the 2 compare.

 

[RockyMtnMT]

We did our reamer with a 37* shoulder and a min body taper. When the chamber is cut it is to have a slight crush fit on virgin brass so it can be formed with bullets or the cow method.

Steve

 

[J E Custom]

There are many opinions on which shoulder angle is best, so you will get many opinions.

The things I consider when improving a cartridge are =
1= does it realy add much/any improvement to the potential velocity.
2= Is it easy to fire form and can you shoot parent case ammo in it with good accuracy. (PO Ackley did lots of test for this and settled on 40o shoulder as the optimum angle and .004 thousandths shorter chambers for the parent case.
3= Is it a staggered feed or center feed. (Staggered feed mag boxes don't particularly like shoulder angles over 25o and tend to damage the bullet point because it has to make a double S to chamber).

There are several reasons for "Improving" a cartridge and these have been my findings.

1=Improved efficiency (More velocity , with less powder).
2=Slightly more case capacity allowing the use of slower powder.
3=Longer/better case life because the improved versions tend to lengthen less when fired and don,t need trimming as often if ever.
4= Often a better more consistent powder burn. (Better SDs and ESs)

Deciding on the shoulder angle depends a lot on the firearm type, use,
type and size of parent case and the needs of the owner.

Improving a cartridge is not always a measurable benefit and can be a detriment if all the considerations are though out. Case capacity differences between 30o and 40o is almost immeasurable and best angle must be selected for other reasons. I have tried up to 50o shouldered cartridges and found no advantage. so my recommendation for best improved shoulder angle would be 40o if using a center feed mag, 30o max on a stagger feed, and 25o max for a semi auto.

When all the considerations are met in the correct format, The improved cartridges can be amazing and perform better than expected. when they are not. Welllll you know the answer to that.

J E CUSTOM

 

[Alex Wheeler]

The 300 Norma is already big. The reason I improved it was because I hate trimming brass. I chose 35 degrees same as the wsm for feeding purposes. 30-40 degrees will suite you and you will not see an accuracy difference.

 

[jb1023]

So I think I want to go with a chambering that will allow me to shoot parent case ammo and I want the shoulder between 35-40*. I have looked up where to buy a reamer and came up with 4 makers. PTG seems to be the biggest or at least the one I see mentioned around here the most. There is also Manson, Clymer and JGS. Is PTG the place to go or perhaps I should ask if there is one I should avoid? I recall reading about one whose service went to hell a few years back and several posters had to send their reamers back as they were not correct and they were getting grief and such but I don't recall which it was. I'm guessing all of their prices are fairly close. I will be doing my own research but thought I would ask here as well.

 

[WildRose]

You may want to consider talking to Whiddon Gunworks.

https://www.whiddengunworks.com/hydraulic-form-die/

 

[Swamplord]

Ryan Pierce at Piercision Rifles builds a 30 degree 300 Norma Mag Improved that fires factory 300 Norma ammo to fireform, can load up straight factory fresh 300 Norma Mag brass and fire in chamber safely, he's been using the new Lapua brass

My 300 & 338 Imp are a bit different with 35 degree shoulders moved up for max capacity so they require a false shoulder for cow forming or bullet into rifling .... they feed smooth out of the DSSF 3.850" Accurate Mags and I have been using my 338 Precision Rifled Ordnance for hunting the last two years, I retired my 338 Edge because of the 338 NM Imp

as I mentioned before on a thread here on this site, all of the improved versions off the 300 & 338 Norma Mag parent cases will perform very close to each other, they will vary by a grain or two in h20 capacity but it's not much to make any difference, most of the difference in velocity will be due to barrel length and freebore length in the chamber

I've been messing with 250 pcs of the new Peterson 300 NM brass and have mangled it into my improved wildcats in 257, 6.5mm, 7mm, 30 cal, 8mm, 338, 375 and 408 cal, excellent stuff to wildcat from

also did same with 200 pcs of the Lapua 300 Norma Mag brass I was fortunate enough to get from Ryan Pierce some time back, excellent stuff as well and can't wait to see the 338 NM brass out from Lapua