7mm TCU case head almost separates

[MrK.]

I have been shooting a 7mm TCU 14in contender for about 25 years. The original 250 pieces of brass I had were getting old and I was losing track of how many times they had been reloaded so I decided to start throwing them away as I shot instead of reusing. I originally had good luck with a Speer 145gr spitzer over 29gr of H335. While admittedly warm this load was a 1 1/2 grains under the Max in my Speer #11 manual. I finally got down to about to about 20 loaded rounds so I bought some once fired Remington .223 brass and started over. I decided I was getting older/ wiser and there was no sense in pushing it with hot loads anymore. I resized the cases and loaded up with 27.5 grains of H335 and the same bullet. This is 3 grains under the max load in the Speer #11 but still 1 1/2 grains above what Hodgdon has as a max on their site. I happily went to the range with a fresh box of 100 reloads. I knew I would have to adjust my scope for the milder loads. The first shot seemed just as hot as the others but I did not think much of it. The second shot seemed the same. When I layed the two fired cases side by side I noticed they both had a bright ring in the same spot. I stopped shooting and put it all away until today when I decided to investigate further. I cut one of the cases open and sure enough there was a very thin spot where the case had stretched,see pic). My questions are this.

1. Obviously I misadjusted my resizing die somehow. What did I do and what can I do to make sure it does not happen again?

2. Is this lot of formed cases salvagable or should I just get some new brass and start over.


Thanks

 

[Bobs243Ackley]

I think that you pretty well hit the nail on the head as to what the problem is for your T/C. I have been shooting the 7T/CU ever since it was introduced and have found that the FL die adjustment is critical to case life with rimless rounds in the Contender. Because of this very issue, I like to make my brass from .222 Rem. Mag. brass so that I can fit it to the chamber. I like to leave it a little long so that I cannot close the gun. I will then size it back a little at a time so that it takes a light snap to close the gun. Once you have the FL die set for this type of adjustment, lock the lock ring down so that it cannot be moved easily! If I am using .223 brass, I will seat the bullet about .020" into the lands, or further, so that I will still need a light snap to close the action. This will keep the base of the case in contact with the breach face during fireforming, if you prefer to use .223 brass.

On the brass that you have, I would discard it and start with a fresh batch. By the way, you can also use the .204 Ruger brass to form the T/CU cartridges and this would give you the availability of other brass to use other than Remington.

Cordially,
Bob Blaine

 

[MrK.]

you can also use the .204 Ruger brass to form the T/CU cartridges and this would give you the availability of other brass to use other than Remington.

Thanks Bob,

The local reloading supply store was out of .223 but they did have one bag of .204 Ruger winchester brass. I did as you suggested and made it a slight crush fit. I ended up splitting the neck of about five of them while sizing. I went ahead and bumped the load down to 26 grains seeing as I was changing brass mfg. I loaded 20 and went shooting. I did not have the accuracy I had in the past with my previous load but had no problem keeping 5 shots inside 1 1/4in at 100. Now that I have my method down I am sure I can get back to where I was before.

 

[RickB]

What dies are you using? Both RCBS and Redding have a tapered expander which smooths the expansion of the case neck. If brass is at all hard, such as previously fired cases, it is better to lightly anneal the case mouth before expanding. I have not tried using .20 Cal brass as my shooting of a 7 TCU was well before the .204 Ruger, but it may be that it is too great a step up without annealing.

The "usual advice" on fire forming 7 TCU cases was to jam the bullet into the lands so that the head space would be set properly on the first firing. This usually took a long/heavy bullet such as a 160 gr Speer to reach the lands.

Hot loads will lead to case head separation with the TCU. Some people used to shoot "ram loads" that were good for one shot only,and then throw the brass away) at some ranges. Needless to say, those loads were not openly discussed.

I had good luck with,new) commercial .223 cases. As I was not fond of trimming cases I never used the .222 Mag cases,which were also quite hard to find). As the .204 Ruger cases are basically the same length you will need to check their length and trim as necessary.

One other reminder. Most people "indexed" their cases, that is placing them in the chamber with the case head markings in the same way so that it could be inserted in the chamber the same way after neck sizing it. Some of the chambers were not exactly round and/or symetrical and this could cause some issues if not "indexed".

Old cases frequently have hardened from just sitting there a number of years and do not do at all well if you try to use them again. It sounds as though this may have been what happened to yours.

Good Luck.

 

[MrK.]

Old cases frequently have hardened from just sitting there a number of years and do not do at all well if you try to use them again. It sounds as though this may have been what happened to yours.

I threw out all of my old cases I am working with brand new now.

What dies are you using? Both RCBS and Redding have a tapered expander which smooths the expansion of the case neck.

I have RCBS dies. I did the case neck expansion in steps. from .204 to .223 to 6mm to 7mm. The 6mm was bulging the neck slightly. I quit using it and went straight fron .223 to 7mm. That is when I split a few. No big deal. I can live with splitting 5 out of 100.

As the .204 Ruger cases are basically the same length you will need to check their length and trim as necessary.

I use a Lee trimmer. The cases were grossly over length. The Lee trimmer is quick and easy with the use of a cordless drill and a pair of pliers to hold the cutter. I expanded to 7mm without moving the shoulder then trimmed. Then I sized for the crush fit as noted above and checked case length again.

I have never noticed that my chamber was out of round or not. I have heard that some were off center slightly. I have not noticed this either but have not really checked. I will do so.

Thanks