.375 "surprise" wildcat

[Mclendon]

Background: Well it has been a year since I bought this rifle. It's is an Interarms Whitworth BARREL STAMPED 375 H&H Magnum. Upon shooting it for the first time, I looked at the spent case, and it's spitting out a different cartridge. Wonderful. A previous owner decided to bore out the chamber to an Ackley-esque cartridge and not restamp the barrel. Things could be worse, right? After consulting the internet (dangerous, I know) and several local reloading guys who's opinions I respect, I decided to keep shooting it as usual. I honestly have never shot a group from the bench, since it beats me around like a rag doll and I really do not want to put it in a lead sled. I have been very happy with the "field" accuracy thus far. I've been shooting exclusively Federal Power Shok 300gr 375 H&H ammo; I've put 120 rounds through it. I have taken a cow elk, 3 antelope, and any number of wild rocks/cans. Again, not vouching for MOA accuracy or anything, I just usually seem to hit what I'm aiming at, and where I perceive the cross hairs to be when the shot cracks off.









I sent some spent cases into a gentleman at RCBS to see if he could identify which of the various 375 wildcats the original tinkerer may have been going for. He responded that they matched none of their recognized cartridges. I have a set of digital calipers, and have tried matching my basic measurements to those listed in The Handloaders Manual of Cartridge Conversions (Donnelly & Donnelly, 2011) with no success. It is simply just off enough to be it's own entity.





----I am trying to reload it. I am a beginner reloader but have spent my time reading and learning and have only reloaded a few rounds for my 22 hornet at this point.----

----I do not wish to discuss re-barreling. I'm pretty determined to figure this out and am anxious to reload it as is; if only because it's unique----

If you're still here after that ramble, these are my questions I would really appreciate your help with:

-There are no factory dies for this, so I am looking at Lee's custom neck sizing dies…. This topic of neck sizing vs full length seems to really bring out differing opinions. For my situation, with this rogue cartridge that case almost no taper and sharp shoulder, will neck sizing only be ok?

-I have a block of Cerrosafe from Brownells to cast the chamber, would this help get chamber dimensions? Is there a better way?

-Since I have no designated case dimensions, how do I know how long to leave the neck without it running into the throat?

-There seem to be some simple tactics to figure out if your bullets are contacting the lands, should I seat them to contact when first starting out or back them off to keep the OAL down?

-Is it true that the brass may run less due to the sharp shoulder?

I intend on casting the chamber with the Cerrosafe to hopefully take some useful measurement, I just figured I could use some input to know what I'm looking for. Thanks in advance for your time and patience. I am ready to ge this project off the ground.

-Mack

 

[FROGO207]

Most of the die makers that make custom dies should be able to make a custom die set for you with a chamber casting and a couple spent casings. That said even when I neck size only with my bottle necked cartridges the brass usually needs to be bumped back slightly (minimal full length sized) after 5 or so reloads anyway. So I would just buy a standard die and only size as little as needed to allow the bolt to close with minimal resistance. That shoulder looks similar in shape to the 300 Savage round. I reload for that and the shoulder is not as "reloader friendly" as the similar .308 due to the way it is radiused. Keep us in the loop on what you do and what works. Inquiring minds and all that.

 

[Archie]

Sounds like fun!

In a bolt gun, I think neck-sizing only will be fine. If you're hunting, try the rounds you carry on the hunt through the action to make sure they all chamber without any problems. I have a similar 'wildcat' based on .30-06 and neck sizing works just fine and I've never had a problem with chambering.

For sight in and range trials, try a 'standing rest'. The easy way is to use a full size camera tripod with a cross piece screwed to the mounting plate. Perhaps a bit of old carpet or discarded sweat-shirt or bit of styrofoam to protect the fore-end.

Sounds like you've named the round: ".375 Surprise" is somewhat novel, but appeals to me.

-There are no factory dies for this, so I am looking at Lee's custom neck sizing dies…. This topic of neck sizing vs full length seems to really bring out differing opinions. For my situation, with this rogue cartridge that case almost no taper and sharp shoulder, will neck sizing only be ok?

I should think so.

-I have a block of Cerrosafe from Brownells to cast the chamber, would this help get chamber dimensions?

I should think so.

Is there a better way?

Used to be, 'custom' die makers would request three fired cases (from that chamber) and not ask for dimensions. I hope that still holds.

-Since I have no designated case dimensions, how do I know how long to leave the neck without it running into the throat?

Not sure what you mean here.

-There seem to be some simple tactics to figure out if your bullets are contacting the lands, should I seat them to contact when first starting out or back them off to keep the OAL down?

Seating bullets to contact lands is a technique used (mostly) by bench rest shooters to get maximum accuracy from a load/rifle. I suggest that's a bit pointless with this beast. Load ammunition to fit properly in the magazine (move freely, but not much back and forth movement in recoil) and not fiddle with the lands.

You'll hear some warnings about bullets touching the lands; that doing so will cause a spike in pressures. There is some truth to it, but if you begin at the low end and work up, it shouldn't be a problem. What you do NOT want to do is determine a 'maximum' load and then seat the bullet out longer to contact the lands.

-Is it true that the brass may run less due to the sharp shoulder?

That seems to be true in my experience. However, I think pulling the expander ball out through the case mouth stretches cases as much as shooting. I note the Lee Collet Neck Size dies I have don't seem to stretch cases.

 

[Grumulkin]

There are no factory dies for this, so I am looking at Lee's custom neck sizing dies…. This topic of neck sizing vs full length seems to really bring out differing opinions. For my situation, with this rogue cartridge that case almost no taper and sharp shoulder, will neck sizing only be ok?

Eventually you'll probably need to bump the shoulder back for easy cambering. I lost a lot of my enthusiasm for neck sizing when in one gun I found that cartridges assembled from neck sized cases were significantly less accurate than those assembled from full length sized cases. At this time, I pretty much always full length resize cases.

Of course, in your gun, it may be different.

I have a block of Cerrosafe from Brownells to cast the chamber, would this help get chamber dimensions? Is there a better way?

-Since I have no designated case dimensions, how do I know how long to leave the neck without it running into the throat?

A chamber cast will let you know how long to leave the neck. For custom dies, all you need is 3 fired cases to send to the die maker of your choice.

There seem to be some simple tactics to figure out if your bullets are contacting the lands, should I seat them to contact when first starting out or back them off to keep the OAL down?

If the rifle has a lot of free bore you'll never get the bullets close to the lands. How long your cartridges are will also be dictated by magazine dimension. In general, for copper jacketed lead bullets, close to the lands is best. For copper or gilding metal bullets, a bit of a jump is usually best.

 

[Walkalong]

As suggested, getting a custom full length sizer is, IMHO, the way to go.

You could get by neck sizing until the brass got hard to chamber, but minimal FL sizing would be best.

Innovative Technologies makes a "Belted Magnum Collet Resizing Die" that might help if you try the neck sizing only route, but isn't cheap. I don't know how much a custom sizer will run, but I bet it isn't any more, especially from Lee.

Nice looking rifle, and welcome to THR.