7mm TCU fireforming part 2

[jason280]

OK, my 7mm TCU carbine barrel arrived the other day.  I'd all ready formed around 50 or so cases, so all that is left is to fireform them.  Problem is, there is basically no way I can seat a 120-140gr bullet out far enough so it touches the rifling.  I can do it with a 165gr spitzer, but only barely (and with very little of the bullet actually seted in the neck).

So, here are my questions.  First, what is the minimum amount a bullet needs to be seated in the case?  Second, because of the long throat, should I simply only fireform with heavier/longer bullets?  Is it possible to fireform properly without the bullet touching the lands?  Thanks!

[Robert]

Fireforming with bullets seated into the lands is only needed with 'light loads' The TCU is a popular silloquette round...so it has a very generous throat to seat big long heavy bullets.  It is not neccesary to use light loads for fireforming the TCU. 'Starting Load' data works just fine.  In fact I have repeatedly heard people say that the fireforming loads are every bit as accurate as loads with previously fireformed brass.
  Beware when sizing brass and seating bullets...the TCU shoulder is very small and weak. If you do not lube well, it will flex up and down and get weak.  Make sure to also lube INSIDE the neck, or the expander ball will drag too heavily on the neck which will also damage the shoulder.  When I go to shoot my TCU I always bring a cleaning rod with an 'oversize' bore brush (45 cal). If pulled through from the muzzle end, this will usually remove a broken neck.  It is not fun to pack up and get ready to go to the range....take ONE shot and have to pack up and go home.
  If the brush does not remove the neck in the first  few attempts, wrap a patch around it to make it tighter.

[jason280]

So, is it not always necessary to seat the bullet in the lands to fireform brass?  My plan was to fireform with a starting load of 24gr of H335 behind a Speer 130gr BTSP, except the bullet isn't long enough to get anywhere near the lands.

[Robert]

That sounds perfect to me. That IS a suggested starting load for that powder.  Make sure you use a target and see how accurate they are, don't just pop them off to fireform.  You should have a lot of fun with those loads, and they should fireform nicely.  Use a strong light afterwards and look for any split necks and discard them.

[jason280]

Thanks for the info, Robert!

I'll go ahead and load a few, and see how it works out.

[haroldclark]

Hello Jason,

I shoot a bunch of 7mm TCU.  My eamil address is even seventcu@.  I have loaded and fired 8,648 rounds of 7 TCU in the past 6 years and more before I built my record keeping database.

Fireforming and touching the lands.  Robert is correct about fireforming loads being just as accurate as any other loads.  I have had one rule about seating depth and that is that no matter how far away from the lands the bullet is, always have at least one bullet diameter (.284") of the bearing surface in the case neck.  I never touch the lands with any bullet.

I have used several thousands of the Remington 140 grain PSP flat base bullet.  It is very accurate out to 421 yards at Turkey Silhouettes.  It won't be stable after that, though.

With the 140 grainer, I load 26 grains of H335.  After you get your cases fireformed, you can use 16.3 grains of IMR 4227 or H4227 behind the 140 grain bullet for a very accurate and pleasant load to shoot.

I have tried several powders in the same burn rate as H335 and I have found best results with H335.  

Heavier bullets work fine too.  I couldn't get the 168 grain Sierra to work well in my 14" barrels, but in the 26" rifle barrels, it is deadly.  I have a Remington 700 rebarred to 7mm TCU and a Custom Shop 26" SS.  They both like the Sierra.

However, my barrels and one of my buddy's barrels like both of the 162 grain Hornady bullets (BTSP and the AMAX) with 25.5 grains of H335.  BLC-2 will work well too.

I want to expand on the seating depth.  If the bullets can get close to the lands (I never let them touch the lands), still keep a bearing surface of .284" in the case neck.  The neck will guide the bullet into the throat.  If the bullet is not secured well by the neck, the bullet can and will tip.  Accuracy will not be a happy thing.

Harold Clark

[Robert]

I agree.  I never seat any bullets above the base of the neck.  I also 'try not to seat 'below' the neck, with the exception of boatails..I seat the tail below, with the widest part of the heel right at the base of the neck.

[jason280]

Harold,

Thank you very much for the information!  

I've been looking for a light recoiling gun for my girlfriend to hunt deer with, and I think the 7mm TCU will be perfect.  Plus, it will be a joy to shoot and very cheap to reload for.  

Any recommendations on a load for a 120gr Sierra spire point?

[haroldclark]

I've been looking for a light recoiling gun for my girlfriend to hunt deer with, and I think the 7mm TCU will be perfect. Plus, it will be a joy to shoot and very cheap to reload for.

Any recommendations on a load for a 120gr Sierra spire point?

Harold’s response::
120 Sierra SP #1900
Cartridge Overall Length = 2.305”  (Pressure increases if the bullet is seated deeper)
Powder = 28 grains of H335
The bullet will be seated to a depth of .340 inches.
In a 21” barrel the velocity will be about 2453 fps.
You said a carbine, but I don’t know the barrel length.  If it is a 16.25” barrel, the velocity will drop to about 2320 fps.

In the 21-inch barrel, you will have about 93% of the powder burned and the efficiency rating is 30.1%.  That is a very good scenario.

I use mostly Winchester Primers with great success.  I can get them at my Range store and that’s another reason.

Another note:  I use Military Surplus Powder WW844 that I buy for less than $10 a pound delivered.  You have to buy it in 8 pound jugs and we usually buy it in a 32-pound case to get a cut on the Hazmat fee.  I also, use WW846 (BLC-2) in my 7mm BRs, 7mm Mauser and a couple of others.  I use the WW844 in my 308 Winchester Full power loads.

I run a match for Long Range Handgun Shooting at our 500 meter Rifle Range.  Last week, my buddy shot a 40 out of 40 using Military Surplus WW846 powder.  The load is one that I developed a couple of years ago for the 7mm BR cartridge.  He used a 20” Van Horn barrel on a Contender frame and his accuracy was absolutely excellent.  I spotted for him and called aiming points for him.  It was great fun.

Have a great time with you TCU.

I have been working with mine this afternoon.  I have 2 –14 “ barrels.  The throats of both of them are worn badly, but one is really gone.  I’m going to send it back to Thompson for replacement.   My buddy is on his 3rd 7TCU barrel and Thompson keeps replacing the worn out barrels.

Great company to do business with.

Harold Clark

[jason280]

Harold,

Quick question on the velocity of a 120gr bullet out of the 7mm TCU.  Nosler lists a 120gr at 2400+ fps with RL7 out of a 14" barrel.  I actually called Nosler to ask them about this, and they said the info is correct.  I can't remeber the powder charge, but they stated it was safe.  Is 2400fps possible out of a 14" barrel, or are they being a bit optimistic?

[haroldclark]

2400 fps from a 14" barrel??  I suppose it is possible.  According to my data the maximum allowable pressure in the 7mm TCU cartridge is 55,114 psi.

If you load up 25 grains of Rel 7 and seat the bullet to a depth of .294" into the case, your pressure will run 61,900 psi.  Thompson Center suggests that you keep pressure in any contender down to 44,000 PSI.  They will support a bit more, but 61,900 PSI is not going to work.

If you want more velocity, get a bigger gun.  Don't try to make a magnum out of a tiny little cartridge.  The cartridge will do most any game on this continent.

I have a rifle in 7 TCU that an old smoke jumper had rebarreled from a 222 Remington.  An Eskimo Guide in Alaska killed everthing in Alaska with the 222 Remington.  The smoke Jimper wanted a bit more bullet and made the shot out rifle into a 7mm TCU and took everything he shot in Alaska.

I have had an experience with the Nosler 120 gr. Ballistic tip and a load from the Nosler book.  The presure was outrageous and the primers barely stayed in the case.  I just pulled all the bullets last week since I wasn't going to shoot them.  The suggested IMR 4227 for the load.

I have used Rel 7 in several small capacity cases and the pressure will peak quickly.  I use a lot of Reloader 7, but with cast bullets only.  It will work well for reduced loads to, but I don't find it acceptable for max loads.

The line between acceptable pressure and an explosion is very fine.  

Harold Clark

[jason280]

That was pretty much my question.  The Nosler book lists a maximum of 26.5gr of Re7, and also shows a 2400+ load with H322.  I'm not trying to make the gun into 7-30 Waters, but I do want to milk as much velocity from the case as possible.  However, I do want to keep the pressures respectable.  

Also, it was my understanding the Contender could handle 50k+ pressures with a .223 size case.  After all, the .223 operates at a pressure of around 55,000 CUP, and is considered completely safe in the Contender frame.  I'm not advocating pressures greater than 55k, but it would seem reasonable to conlude that pressures in the 50-55k range would be OK.

Please don't misunderstand me, I'm not trying to push the envelope with this cartridge.  I know its limitations, and I'm not trying to load it to something its not.  I was simply confused by the load data in the Nosler book.

[Steve P]

8.0 grains of Unique with a cast bullet will fireform your brass nicely.  It will also be a mild load and good for your girlfried to learn to shoot the gun with.  

try it, you'll like it.

Steve