Hi all,
I recently encountered a minor problem trying to load some 8.15x46R brass into my recently acquired Wehrmannsgewehr where the rim diameter of the brass was too large. I came up with a solution to trim the rims with my lathe, but wanted to know if anyone else has a better method? 

Little more background - I bought some Qual-Cart 8.15x46R brass. The rim diameter measures 0.506" which is larger than the CIP max of 0.488" (12.40 mm). The larger rim doesn't cause any issue in my Schützen rifle (Aydt) because the rim rests on the breech face of the barrel; however, for the Gewehr 98 Wehrmannsgewehr this is an issue as the brass rim needs to fit into the bolt face and the 0.506" diameter is too large. The larger rims also cause issue when feeding from magazine well into the chamber. See first picture below. 

What I ended up doing was making some tooling that holds the brass via the primer pocket & tail-stock along with a mandrel that allows me to hold the neck of the cartridge using a chuck without crushing the neck. See second & third picture below. The trouble is getting the run-out to be small - usually it runs around 2 to 5 thou. I'd like to find a way to minimize that so my rims are concentric with the case body. With the case in the lathe I trim a small amount of the rim each pass and check until I got the diameters below the 0.488" CIP spec. After performing this tedious task for my 20 cases the brass worked fine in the rifle. 

As a curiosity digging through some cartridge specs I note that the 8x57mm Mauser (rimless) base diameter max is 0.473". The 32-40 and 30-30 rim diameters are 0.506". So when the Gewehr 98s were converted in Germany over to Wehrmannsgewehr with the 8.15x46R cartridge it was fortuitous that the rim diameter wasn't much greater. However here in the U.S. since 8.15x46R brass is hard to find many convert 32-40 or 30-30 brass (with a 0.506" rim diameter) to 8.15x46R. So as a caution please note that this brass will not fit in a Wehrmannsgewehr unless the rims are trimmed! I find it curious the Qual-Cart brass (stamped 8.15x46R) has such a large diameter so also take note. My RWS 8.15x46R measures 0.486" for the rim diameter and works fine. 

But if anyone else has a faster/easier way to trim brass rims I'd like to hear. Also for interest the final picture I have is my Wehrmannsgewehr out at the range while I was zero'ing it in. I'm using 10 gr of 4227 with a 182 gr stop-ring bullet, same as for my Aydt. 

Thanks!
-Dave

Dave,

I use the same basic tool you made to hold on brass for turning down rims, but to minimise runout, I actually turn it the other way round: i.e.: the part that goes into the primer hole goes into a collet chuck, then put the brass in, then your inside pin and press firmly with the tailstock live center (you have to modify the inside pin to suit)

As you're taking very litle material, the press contact is enough to get the brass turning, and the proximity with the chuck allows for a minimum runout.

However, the rim will be concentric with the primer pocket, not necessarily the case itself...


(I hope the technical terms are undestandable, not my native tongue  )

Soft collet, bored to the taper of the case. Getting the compound set to the proper angle is tedious. Hold a case by the neck, center in the primer pocket. Find the high and low spot and average them out. Or just measure the case diameter here and there and set the compound off a straight rod. Depth in the collet is eyeballed.

Lacking a soft collet, a slug of aluminum split with a hacksaw will work fine. Turn it with a flange to avoid it vanishing into the spindle.

I find that the primer pocket is usually close to concentric to the rim. But the body can have run out. I think this is from the brass drawing process.   

I use a live center in the primer pocket. No need for a special mandrel. At the other end I use a collet with a close fitting mandrel inside to prevent the mouth from being crushed. This is fast and easy for me.
Steve

Thanks all for the advice. A good point was made about the concentrically of the primer pocket with the case and the rim. On measuring some samples I noticed they are not perfect so that does account for some of the run-out issues I've been seeing. I like the idea of using the 4-jaw chuck with the brass reverse because then I could adjust the 4-jaw to compensate for the run-out. I'll give it a try and report back on results. 
Cheers,
-Dave

My experience most 3 jaw chucks have about .003 run out. Some may be better.   Have a # 1 Jacobs drill chuck 1/4 inch capacity mounted on a Jacobs straight shank. Chucked in the 4 jaw on a 1955 Logan 11 inch can be dialed in to .001 run out. This measured with a 1/4 inch dowel pin & .001 dial indicator. 

Have a .0005 indicator & reduced run out further.  No real need to be that true just seeing if it can be done. Reducing rims all it needs to do is fit, precise fit back end of the case not necessary & may be a negative. Too tight may not chamber when the gun gets dirty.

Opinion, worth what it cost .

Boats

This thread makes me feel bad.  I inserted a wood dowel segment into my reformed 30-30 cases, chucked them into my Pakistani lathe (cheap drill press) and ran a file against the rotating rims.  Works for me.

Frnkeore,
With my 3-jaw in the picture I can hold about .003" run out when I stick in a straight bar. I can dial in usually with .0005" with the 4-jaw. I actually found I could put in my drill chuck (held on the headstock with a MT 2) to about 0.001" so ended up using that as it was good compromise between speed and run-out. I'd use my collet die but don't have one sized that  works well with the OD of the brass neck. By keeping the rim spinning on the stationary center on the tail-stock side does reduce run out from the headstock but as discussed earlier doesn't help if there's not concentricity between the primer pocket and the case/rim.

I didn't mention this earlier but I like to have the set up with the front of the rim facing out so I could also trim the thickness as an option. I noticed the Qual Cart brass rims run about .058" thick and my Aydt needs them under 0.055" to fit. I don't want to reduce the rim from the base end as that would simultaneously reduce the primer pocket depth.

Also agree this might be overkill for most applications but as noted earlier this particular application requires a bit more precision as the Mauser bolt face holds the rim and the chamber holds the case body so if there is gross off-concentricity between the two then the brass won't chamber. I could just reduce the rims way down but then the extractor has trouble. 

Appreciate again the comments so far. Thanks all.
-Dave