Fire forming 7mm TCU from .223/5.56 brass

[Snidely70431]

A TC Contender I got recently came with a 7mm TCU barrel. Checking online, I found that most videos showed using 7mm TCU dies to expand the .223/5.56 brass to 7mm, then fire forming the result in the barrel that will be using by firing a loaded cartridge. This process seemed unnecessarily complicated, not to mention expensive as it uses a 7mm projectile, of which there seem to be a shortage here anyway.

Being a congenital cheapskate, and lazy to boot, I decided there had to be an easier way.

I had read about fire forming without a projectile by loading Unique, topped by a small wad of toilet paper to hold the powder next to the primer, topped by cream of wheat, and the whole topped by a wad of wax. Being a southern guy, I substituted grits for the cream of wheat, and a small square of aluminum foil for the wax. I annealed the brass before loading it. I started with 4 grains of Unique, which did not expand the neck to 7mm, and quit at 8 grains, which sometimes expanded totally and sometimes did not.

Next I substituted Bullseye for Unique, and found that 5 grains always fire formed the brass perfectly to the chamber. I did this with 20 cases and did not have any neck cracking, even though I did not anneal 5 of the cases.

My next step will be to test accuracy, but that will have to wait until I can cast some projectiles. I will add to this post when I do so.

 

[BRatigan]

I have a load that was dead on accurate when I competed in IMHSA competitions if you would like it.

 

[Captcurt]

The problem with the TCU is headspace. It has to be perfect. When I tried expanding the neck to 7mm I sometimes had FTF because I had set the shoulder back a little. I found it easier to shoot a 223 and then expand the neck by partially resizing, setting the die just enough to size the neck and not touch the shoulder. Worked well. Another thing that I learned was to use the softest primers that I could get. My Contender had a soft firing pin spring and wouldn't always fire a CCI primer. I had better luck with Winchester or Federal.

 

[Krogen]

Back in the day, I used a 7mm TCU. You'll need to anneal the cases after expanding. I quickly learned that it's a big stretch from 5.56mm to 7mm and the brass work hardened. This resulted in cracks after one firing. Annealing has to be done properly and consistently. It's easy to overdo it.

 

[243winxb]

The fl die i had, could not be set to contact the shell holder. If it did, shoulder set back was excessive.

Many split necks. Sold barrel & dies after one outing.

The 7-30 Waters is a better cartridge, in a Contender.

 

[Snidely70431]

The fl die i had, could not be set to contact the shell holder. If it did, shoulder set back was excessive.

Many split necks. Sold barrel & dies after one outing.

The 7-30 Waters is a better cartridge, in a Contender.

Your opinion. Opinions are like.... I will wait to form an opinion.

I have a load that was dead on accurate when I competed in IMHSA competitions if you would like it.

Appreciate the offer, but since I will be playing with paper patched projectiles I will cast myself, I have to doubt the relevance.

 

[dh1633pm]

I do want to know how it turns out. Don't have this caliber, but brass conversions are always of interest. Especially lessons learned. Thanks for sharing your experiences thus far. I have used a method similar to yours using No 5 (have a lot of it) forming brass for a Roller that I have. Also working with my dad doing fire forming on his .257 Roberts Improved. Then there is converting 284 brass to 7.5 Swiss.

 

[Armorer 101]

The simplest way to load the 7mm TCU using a cast bullet is with the RCBS 145g Silhouette bullet over 15 gr of 4227. I size the bullets to groove diameter after powder coating. I fill the case half way up the neck with spherical buffer. Compress by seating the bullet. This is a published cast bullet load in the Hand Loading Annual.

 

[P Flados]

I use a light (70 gr) PC coated cast bullet with 8 gr of Titegroup for fireforming. This is just enough pressure to get a good fireform and it makes a decent mid range target practice load.

I also use the 70 gr bullet with tumble lube and an even lower charge for a target practice load.

So my extra cost for a fireform is only a few grains of powder plus the cost of PC coating but I am getting a target practice shot out of the deal.

The non-bullet fireform costs include primer, powder and your granular material. It is all cost with no "benefit" from a shot at the range.

 

[Snidely70431]

The problem with the TCU is headspace. It has to be perfect. When I tried expanding the neck to 7mm I sometimes had FTF because I had set the shoulder back a little. I found it easier to shoot a 223 and then expand the neck by partially resizing, setting the die just enough to size the neck and not touch the shoulder. Worked well. Another thing that I learned was to use the softest primers that I could get. My Contender had a soft firing pin spring and wouldn't always fire a CCI primer. I had better luck with Winchester or Federal.

According to Bellm, a TC parts supplier, Contender hammer springs fatigue over time and need to be replaced periodically. I had a FTF problem and have ordered new springs. I guess I will see if this helps.
https://www.bellmtcs.com/tc-contender-hammer-spring-2

 

[243winxb]

The fl die i had, could not be set to contact the shell holder. If it did, shoulder set back was excessive.

Causing misfires.

 

[Snidely70431]

I use a light (70 gr) PC coated cast bullet with 8 gr of Titegroup for fireforming. This is just enough pressure to get a good fireform and it makes a decent mid range target practice load.

I also use the 70 gr bullet with tumble lube and an even lower charge for a target practice load.

So my extra cost for a fireform is only a few grains of powder plus the cost of PC coating but I am getting a target practice shot out of the deal.

The non-bullet fireform costs include primer, powder and your granular material. It is all cost with no "benefit" from a shot at the range.

You have to size the .223 case up to 7mm before you can load the cast bullet, which is unnecessary using the granular material (grits). A 24 oz box of grits is $1.34 at Walmart, and I weighed the grits I used at 13 grains. The calculated cost of the grits is about 1/625 of a penny.

I pick up my .223 brass at the range, so that cost is borne by the guys who like to shoot their AR15 clones a 30 round magazine at a time.

The last Bullseye I bought cost me $40 for a pound, so the 5 grains I use costs me a bit less than 3 cents.

A thousand small rifle primers cost me $55.65 including tax at Sportsmans Warehouse, which is about 6 cents each. My total out-of-pocket cost for each fireformed case is maybe a dime, allowing for a 20% failure rate, which is pretty generous.