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MRX & TSX BC Values

 
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  #1  
Old 01-17-2006, 02:46 AM
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MRX & TSX BC Values

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
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Old 01-17-2006, 03:40 AM
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Re: MRX & TSX BC Values

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.
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Old 01-17-2006, 09:33 AM
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Re: MRX & TSX BC Values

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.
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Old 01-17-2006, 10:34 AM
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Re: MRX & TSX BC Values

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
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Old 01-17-2006, 10:58 AM
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Re: MRX & TSX BC Values

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.
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Old 01-17-2006, 03:37 PM
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Re: MRX & TSX BC Values

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. [img]/ubbthreads/images/graemlins/grin.gif[/img]
Festus
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Old 01-17-2006, 06:17 PM
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Re: MRX & TSX BC Values

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 [img]/ubbthreads/images/graemlins/laugh.gif[/img] ) 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....
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