I’m playing around in CAD and making a 375 Whelen reamer drawing. I’ve seen several other 375 Whelen reamer prints with neck diameters ranging from .398” to .407”. I want to just use 35 Whelen brass and neck it up. When you guys spec a neck diameter, do you just use the maximum possible brass thickness of the parent cartridge as your starting point or do you bases it on how the neck will get slightly thinner as it stretches? I know I am making this too complicated, but I’d like to know how you do it. If I base it on the thickness of the parent cartridge, the maximum neck diameter of the 375 Whelen will be at .405”. If I base it off a loose calculation for getting thinner as it stretches, the neck diameter will be .4038”. This is all at the case mouth. You can probably tell that I don’t want to turn necks. I’d appreciate some insight from you guys to hopefully avoid some headaches.

If my intent was only to use it as a bench gun, I'd likely go tighter. Otherwise, I like a little loosey goosey in a hunting rifle. I'd figure 8 to 10 thousandths should be fine.

Also, I'm assuming you are building one for yourself? What rifle and specifications? Also, dies? Thank you, the 375 Whelen and 400 Whelen are two that have always interested me

I no longer have a .375 Whelen, but did have a .375 Whelen Improved. May not be much help, but a loaded cartridge has an outside neck diameter of .4027".

Any data points are helpful. I just want to make sure I can use the thickest possible factory 35 Whelen brass for the 375 Whelen and have enough clearance. I’m thinking that I will be .406” at the front of the neck and .407” at the shoulder/neck junction.

When it doubt, it's easier to remove metal than it is to add it back.

Ray,

I had a 400 Whelen on a Winchester 70 for a bit, but sold it because I have an a Springfield action I want to build one on. It’s a fun cartridge. Had ZERO issues with headspace as my chamber had the proper .458” diameter shoulder.

I’m putting together the 375 Whelen just to have fun with and see how effective it is compared to my 9.3x62’s. I love my 9.3’s, but with the standard 375 Whelen I can fit 5 in the magazine vs 4 with the 9.3. Plus I already have tons of .375 bullets to play with. It’s going to be built on an FN commercial action with Lothar Walther barrel in a #2 contour(.600” at the muzzle). The dies are some old RCBS dies from the 1960’s. Should be a lot of fun.

As I mentioned in another thread, I just returned from Africa where I took my.338-06 with good success. My hunting partner and gunsmith took his .375 Whelen. He knocked the snot out of everything he shot at including a Roland and Ward “book” sable. All one shot kills. Some stem-to-stern. Those big boys on the ‘06 case are impressive!

I'd suggest .015" as an assumed max neck thickness for commercial (i.e. RP) brass in the .35 Whelen. The necking-up will reduce this thickness to 0.014". Therefore, your loaded .375 Whelen will measure 0.403" (0.375" + 2 x 0.014") with a loaded bullet. This is right in line with what lotech stated. I'm not sure what a good clearance is for the chamber neck. I personally wouldn't want it too "sloppy". Look at the SAAMI spec for neck clearance/diameter on the Whelen as a starting point.

A little slop never hurt anyone.

There is an article in HANDLOADER #119, January, 1986 on the .375 Whelen Improved. Haven't seen the article in a long time and don't remember whether dimensions are included. Neck diameter for the regular and improved versions should be the same.