7MM twist

78stw · 08-17-2011, 08:33 PM

I have a factory 7mm stw 24" (I wish it was 26") barrel with 1-9.5 twist. My question is what is the heaviest bullet this will stabilize?

**wbm** · 08-17-2011, 08:43 PM

Have built two of these. In testing and load development, the Berger 180g Hunting/VLD was stable in that twist rate. Berger recommends a 1-9 twist rate for that bullet. At .659 BC and moving at 2800fps the Berger delivers very impressive ballistics at 1000. The first STW I had was from Devin Sinner and was a Savage 114 Ultra with a magnum contour 24" barrel. Shot extremely well with the Berger. The others used barrels from the Savage custom shop and were 26" varmint contour 1-9 twist. The STW excels over the 7MM Magnum with heavier bullet weights. IMHO it is easier to obtain great accuracy out of the STW than the 7MM Mag. Sure does burn a bunch of powder!

78stw · 08-18-2011, 09:52 PM

I thought I read somewhere that you sacrifice some velocity with a faster twist. Is this true? At present I am working a 175 BTSP load but am thinking of going heavier, which brings the questions; should I get a 26" barrel and what twist is optimal for hunting bullets 168-175gr 1-9 or 1-9.5 ?

**wbm** · 08-19-2011, 07:59 AM

You give up some velocity in a faster twist but I doubt between a 1-9 and 1-9.5 there is much difference.
The best way to find out if the faster twist will stabilize a given bullet is to shoot it at 300 yards or more...more is better. Also the brand of bullet will make a difference. As far as going from a 24 to 26 inch
it depends on whether you want or need the extra velocity. Personally I don't think the 7MM Magnum or STW should come in less than 26. Why pay for the extra boom if you don't get more zoom. (Damm that was bad)

Cycler · 08-19-2011, 10:52 AM

Originally Posted by wbm

You give up some velocity in a faster twist but I doubt between a 1-9 and 1-9.5 there is much difference.

I agree you won't see any difference. The downside with a too fast twist is with "over stabilizing" light bullets so, unless you expect to use varmint weight bullets in your STW, the 9 or 9.5" twist will be fine.

In fact, most .243 Win barrels have a 10" or 9.5" twist which will stabilize 100 to 105 grain bullets but seem to do fine with even 55 gr bullets so overstabilization isn't that much of an issue.

**Jamie** · 08-19-2011, 10:54 AM

Originally Posted by 78stw

I thought I read somewhere that you sacrifice some velocity with a faster twist. Is this true? At present I am working a 175 BTSP load but am thinking of going heavier, which brings the questions; should I get a 26" barrel and what twist is optimal for hunting bullets 168-175gr 1-9 or 1-9.5 ?

Yes and no on the velocity. If you are shooting 140 grn bullets through a 1:12 and a 1:9 then yep the faster twist will be a little slower. On the other hand a 1:12 won't stabilize the heavy bullets you want to use, so velocity loss is not an issue.

I (personal preference) do think it should be a 26" barrel. Why have a 7mm Mag recoil and noise and only get .280 Rem performance?

Berger bullets are usually very long and they advise 1:10 for the 162s and 1:9 for their 180 VLDs. Your 1:9.5 should stabilize most, if not all, 175s and possibly even the Berger 180s.

You can't overstabilize a bullet. It is either stable or not. If you use too thin of jackets on really light for caliber and spin them like crazy then they can come apart but that is not a every day thing. I had to build a 22-243 Middlestead and push some Blitzkings like crazy to see it happen. You are not going to see it in a 7MM caliber easily.