MRX & TSX BC Values

[Festus]

Does anyone know if the grooves in the TSX and new MRX bullets from Barnes reduce the actual ballistic coefficient of these bullets with regards to drag. It would seem to me that a smooth shank would have less wind resistance.
Thanks, Festus

 

[wapiti13]

Festus, I'm not sure their overall effect, but even the rifling cuts in smooth bullets effect BC and airflow. The cuts were made to reduce bearing surface to eliminate copper fouling and pressure problems with some barrels. Only Barnes could probably answer the question.

 

[Fotis]

I can not speak on their BC as far as drag is concerned. One thing I can say is, all things being equal the MRX should have a slightly lower bc due to their shorter length. I say this due to the fact that they do have a tungsten insert --kinda like the Failsafe. Then again if you take the plastic aero tip into consideration that just might compensate for the shortness.

 

[zingdingo]

1st: Yes, the driving bands will increase drag, all other things being equal.

2nd: Modern aerodynamic theory could probably be used to determine the additional drag to a acceptable degree of accuracy, however that would only work for the bullets as they sit in the box, and would not apply once they have been fired. As wapiti13 mentioned, the deformation left by the lands and grooves affect the ballistics, and do so even more when driving bands are present. The exact manner of the change the barrel has on the bullet should vary from barrel to barrel, as both land and groove diameter are not set in stone, and virtually every different rifling option could have some effect (twist rate, #grooves, shape of grooves, etc.)

What I have been trying to imply with all this is that I feel in this case the only way to know EXACTLY how the driving bands affect the B.C. for you is to carefully experiment with them in your barrel. However, most of the effects of different barrels would be minor, so if someone did go through systematic testing of banded vs. smooth I would expect the results would be reasonably close to your own.

Just a theory, feel free to contradict.
Carl

 

[edge]

They certainly will add drag to the NEW bullet diameter, but how does this compare to the bore sized bullet?

You could probably assume the same loss for the driving bands as you get from a cannelure.

I do wonder if they are additive in the BC reduction or does the first one take the hardest hit and each subsequent one results in less reduction??

edge.

 

[Festus]

Thanks guys, good thoughts, all. Although MRX BC's aren't yet listed on the Barnes website (maybe they're still running tests), the BC's for the TSX are pretty respectable. The 225 gr. TSX has a BC of .482, compared to the Nosler AB 225 gr. of .550.
To gives Barnes the benefit of the doubt, I have to assume the grooves have been given consideration when the BC values were given.
I tend to agree with Carl that trajectory has to be demonstrated in the individual rifle rather than relying on any printed BC values. Nothing substitutes for range time. /ubbthreads/images/graemlins/grin.gif
Festus

 

[Jon A]

Yeah, they will cause drag. Here's an interesting pic:

Here you can see a secondary shock wave, which is adding drag, cause by the bullet's cannelure. That bullet's cannelure is much more shallow and "less square" than the grooves on the TSX's.

When the TSX's first came out, I didn't think it would be very significant but when actual tested BC's were surprisingly low (even to me /ubbthreads/images/graemlins/laugh.gif ) I started to think the grooves are at least partially to blame.

Anyway, the MRX's should still have nice BC's--a big improvement over the TSX's. The tip alone will improve them a bunch having a much smaller meplat and making the ogive longer (a length that does matter) even with the same profile.

And no, you don't need to worry about the shorter shank due to the tungsten core hurting their BC's at all. Here is a good discussion about that from the past. Those who have been here a while probably remember discussion of the 253 PRL which was shorter than a 210 Berger but had a BC of .880 or so....

 

[Festus]

I should think (and the photo supports this) that much of the air has been pushed out of the way by the meplat and ogive so the secondary and subsequent shock waves would have a diminishing effect on drag. I still think time at the range is the best way to determine flight path. I just used some of the biggest words of my life, I hope I didn't screw it up. /ubbthreads/images/graemlins/blush.gif
Festus

 

[big-foot]

Federal posted a drop chart for the .308 180 gr. I matched the chart and got a BC of .568 unadjusted.

http://www.federalpremium.com/ballistics...p;bulletwgt=180

 

[remingtonman_25_06]

Seems awfully high for a barnes bullet.

 

[jwp475]

The MRX is supossed to have a higher bc than the TXS I hav e shot the 180 TXS in 300win and RUM mag and a bc of .525worhs well for me. The 225 TXS in 338 from my experience the bc is lowwer than the .482 listed as it shoots with more drop at extended ranges than a .482 bullet should

 

[dog caller]

Here is a BC estimator

http://www.uslink.com/~tom1/calcbc/calcbc.htm

I just genericly punched in some numbers and the shorter the bearing surface, the lower the BC. Since the grooves cut in the bearing surface are actually an absence of bearing surface, that would make for a lower BC all by itself. Wouldn't it?

 

[kraky2]

Just a couple "seat of the pants" things I've seen and heard. There was a guy on one of the forums claiming to be an ex employee of barnes and he said that the rings do affect the bc cosiderably. From what I've seen in the gun magazines where they;ve compared actual bc to claimed I would reduce the barnes tsx by a minimum of 10%. Regarding cannelures it seems the hornady sst has one of the closest bc accurate claims and it DOES use a cannelure. They usually show up as good and usually better than a ballistic tip. It also seems that bc ratings seem fairly close out to 500 yds and then fall off on their way to 1000 yds. I guess the only way to test is to shoot and see. One thing I love about these forums is the experienced reports of the long range guys.

 

[jwp475]

[ QUOTE ]
Just a couple "seat of the pants" things I've seen and heard. There was a guy on one of the forums claiming to be an ex employee of barnes and he said that the rings do affect the bc cosiderably. From what I've seen in the gun magazines where they;ve compared actual bc to claimed I would reduce the barnes tsx by a minimum of 10%. Regarding cannelures it seems the hornady sst has one of the closest bc accurate claims and it DOES use a cannelure. They usually show up as good and usually better than a ballistic tip. It also seems that bc ratings seem fairly close out to 500 yds and then fall off on their way to 1000 yds. I guess the only way to test is to shoot and see. One thing I love about these forums is the experienced reports of the long range guys.

[/ QUOTE ]

I saw that guy and put no credence in his claim of being a ballistic tech for Barnes. The TXS do generally run 5 to 15 % lowwer than the listed bc from Barnes which is the bc for the original X-bullet.Barnes is corruntly establishing an bc for the TXS. The listed bc for 180 grain is .552 I am useing .525 and it works great for me out to 1000 yards.