Is the Whisper Hot? or the 7TCU underloaded?

[Nate C]

Just curious... I am a big fan of both rounds, but since they have the same head diameter, and one is about 30% smaller how are people getting comparable velocities out of each?  

Are the operating pressures in the whisper higher?  :?

Basing this on some data I've seen for the 10" whisper which puts 130's at around 2000 fps, Compared to 120's at the same velocity from the 7tcu with a 10" tube.

I don't have the manual in front of me, perhaps I should recheck the numbers..

Nate C

[HHI 812]

a stainless SSK 9" 300 Whisper barrel I had, I chronoed the 125 BT @ 2100+fps, and the 150 BT @ 1900+fps. According to the SSK load sheet, I got from SSK, the SSK 10" was going faster than a factory T/C barrel in 14" length. Could be the 1:8 twist Shilen barrels?

[Bug]

If you use comparable bullet weights, neither is true. The Whisper will generate higher velocity, given equal pressure, because the bullet base is larger. This gives the pressure a larger surface area to push against, consequently, higher velocity. While the TCU and Whisper are based on the same case, and have equal backthrust, the smaller bullet will absorb a proportional, lesser amount of energy. The values of bullet pull, resistance to engraving, and frictiom in the bore, all are in favor of the smaller dia. bullet, but are overcome by the larger bullets base surface area. A simple way to illustrate this is with compressed air or water. A higher pressure can be held by your thumb with a smaller hole. As the hole gets larger, it is harder to hold................Bug.

[B_Koes]

Well here's my opinion to the fray.  The Whisper is obviously quite efficient in the context of a 10" barrel and the TCU rounds have just a bit more case capacity than is needed for a 10" barrel.  I still like the TCU family because eventhough you gain a bit of initial velocity with the Whisper (given equal bullet weights when comparing the 7TCU) the difference will soon be made up by virtue of the smaller diameter's greater BC and better penetrating ability because of higher sectional density.  Bottom line is that the comparison is nearly a wash because they are quite close ballistically speaking.  Pick whichever one tickles your fancy and have fun!

[Bob/FLA]

This is a great discussion!  Given the info above, can you shoot the 7tcu subsonic with any reliability?

[Nate C]

I agree the larger base (and larger bore dia -- ) can facilitate pushing gas/water/lead out of the bbl at a rate of less resistance.    :grin:  

I'm just not sure if the difference between 284 and 308 is sufficient to make up for the difference in case size..  The difference in volume <to me> seems quite high.  Also I'm talking 139's vs 150's...

All this is just my opinion and I don't have the equip to do a real pressure test, but my gut feeling is that these cartridges are not commonly loaded to the same pressures.  

I think the 300 is loaded hotter.  That is not to say that the 300 is too much, but maybe that we could be getting a little more out of our TCU's.

Regarding Subsonics... (I think all the TC bbl's whether they are 300's or 7tcu's have 1:10 twist rates, while JD's have 1:9 ).   I've played around with light charges of Unique in the 7TCU and did ok, but I am not sure if the bullets were fully stabilizing.  This type of load is not published anywhere that I can find, so take it with a grain of salt, and proceed with caution.

I agree that it is an interesting topic and would like to hear others perspectives / ideas.

Thanks.

[Jari]

Bug,
You write: "While the TCU and Whisper are based on the same case...", My english is not very good but I understand that Whisper is based in .221 Fireball case and TCU (6mm,7mm and .30) are based in .223 case...
Right...?

Jari

[B_Koes]

SSK builds their .300 Whisper with a 1-8" twist while TC puts a 1-10" on them so the max bullet weight that it will stabilize is around 200gr.  I think that the 7TCU's are built with a 1-9.5" twist.

I suppose that the 7TCU can be loaded subsonic, but it could use a quicker twist rate to handle heavier bullets which would make this setup more effective.

[Nate C]

Yup the 7tcu is based on the 223 rem, and the 300 whisper is based on the 221 fireball.

But - the 221 fireball is a 'sawed off' 223 rem.  :grin:

If you wanted to go thru the trouble you could make 300 whisper cases directly from 223 by trimming and running thru a form die...

[Bug]

I'm sorry for the brain fart. I meant to say same case head, not same case. However, as capacities are similar, and we speak of 10" barrels, I think the theory is still valid.............Bug.

[thomas]

The 6 and 7mm whispers? I think the article JD did on his 7MM whisper same bullet weights the 7MM was slightly faster the the 300
So what gives??
tom

[HHI 812]

He says, "Frankly, I don't know of any other cartridge capable of filling as many roles as teh 300 Whisper, when the cartridge is to be used for sporting purposes, my favorite setup is the 10-inch barrel Contender. The 300 is ballistically superior to the 6.5 mm and 7mm Whispers, although they are interesting cartridges"....."The 6.5 will push a 100 grain bullet, from a 10 inch SSK Contender barrel at 2150 fps, and it seems effective on Whitetails at over 100 yards. The velocity of the 100-grain 7mm, is about the same, but for hunting purposes the 300 is a far better choice than either of teh smaller cartridges."