Twist rate and the TC venture

powdergun

powdergun

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I have a TC venture in 7mm rem mag. I have been having trouble getting 175gr bullets to group well. No problems with 140 gr bergers ( easily 1" or better) but 175 gr are a pain.

The twist rate on the venture is 1:10 and from what I've read it seems to be a little slow for the bigger bullets. Has anyone found a 175 gr combo that will do well in a barrel like this ?


I would like to shoot the larger bullet for hunting but if I have to stick to 140 gr then I guess I have to.

Thanks
 
powdergun said:
I would like to shoot the larger bullet for hunting but if I have to stick to 140 gr then I guess I have to.

Thanks
Click to expand...

1:11 is fine up to 140, so a 1:10 will stabalize better on heavier/longer bullets..Your going to have to experament to find out yourself..
 
I wonder if that 5R rifling is somehow to blame? The 175's may not be engaging into it as well as normal 1:10 rifling (pure speculation). 7mm rem mag standard spec is 1:9 - 1:10 so you are biased a little toward the lighter bullets there.
The venture in .270 has a even slower 1:12 twist and I did find a couple people online having issues with 150gr there but 0 issues with 130gr.

Obvious question but have you given the bore a clean?
 
Here are the real numbers: 1-10" barrel twst will stabilize anything up to a 160gr hunting bullet under normal conditions.
If you want to use heavier bullet you need a 1-9" unless you're shooting at high elevation and high temperature.
With a 1-10" 7mm barrel, you get the exact same stability issues as a 1-10" 27 caliber barrel and 270 Win hunters are limited to 150-160gr bullets under normal conditions (heavier bullets do work high in the mountains in summer).

Alex
 
No worries with gun hygiene . Regardless of whether I am testing 140 gr or 175 gr bullets the results are always the same. Lighter bullets group better.

I've tried all of my tricks with powder,seating depth, different brass, etc...
Just wondering if anyone had a good recipe for the Venture.

I can always just put some 3400 fps 140 gr Barnes bullets out of it. That should do the job on any Samsquanch I encounter in the woods:D
 
powdergun said:
No worries with gun hygiene . Regardless of whether I am testing 140 gr or 175 gr bullets the results are always the same. Lighter bullets group better.

I've tried all of my tricks with powder,seating depth, different brass, etc...
Just wondering if anyone had a good recipe for the Venture.

I can always just put some 3400 fps 140 gr Barnes bullets out of it. That should do the job on any Samsquanch I encounter in the woods:D
Click to expand...

Stability is mostly dependent on barrel twist, it is only lightly dependent on altitude, temperature and bullet velocity.
So take a caliper, measure your bullet's length and give it a spin in JBM Ballistics - Bullet Stability Calculator.

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

You'll probably learn more in 5 minutes on bullet stability with the calculator than spending days trying different load...
(I've spent days and hundreds of dollar fiddling on heavy 6mm 105gr and .270 165gr bullets stability ;) )

Alex
 
X2 thanks for the link. I am looking forward to doing some testing based on what the calculator is showing. Just need spring to come.
 
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