Re-barreling one of my .308's - Twist rate?

[Mike6158]

I've got a Remington 700 Tactical and a 700 VTR, both chambered for .308 Win. I've never liked the VTR because of the way the barrel moves when it heats up.

The rifle will be used for night, suppressed, hog hunts (maybe coyote, from my back porch) but I would like to have some versatility to shoot sonic velocity and lighter bullets. I use a Night Optics thermal scope.

I've been working on a subsonic load for my .308. I use Lapua's 200gr FMJBT subsonic bullets with 11gr of Trailboss. I have not shot the 11gr test rounds yet. 10.7gr was 900 - 925 fps. I'd like to see 1,000 to 1050 fps with some consistency. They are decidedly more quiet than the usual sonic loads. I was seeing 80dB on an iPhone app with the phone in my pocket. My coughs register more than that

I used the TAC to test with. The TAC barrel has a twist rate of 1:12 and the VTR barrel has a 1:12 twist rate. The TAC barrel is longer. I don't think either will appropriately stabilize a 200gr bullet at subsonic velocities. But, since the VTR is not my favorite rifle and the TAC is a good shooter with the correct bullet / powder combination, I am considering letting Hart install one of their .30 cal barrels on the VTR. I can choose as fast as 1:8 twist all the way down to 1:18" twist. I have a preference for Hart barrels. I have a (DE) .338 Edge and .20 Beggs with Hart barrels and they are fine shooters

Since the initial goal is load them heavy and slow I'm leaning toward the 1:8 twist. Are there any downsides to choosing the higher twist rate? What if I choose to reduce the bullet weight and shoot "normal" velocities through it, suppressed or not (I know... a suppressor doesn't work as well with supersonic bullets. I does make a difference to the shooter though).

In the end, I supposed it doesn't hurt to have a rifle dedicated to one purpose (quiet).

 

[elkaholic]

From what I'm hearing, a 10 twist should be good. It should handle a 200 grain bullet just fine. An 8 twist would only be necessary for the longest, heaviest bullets made and would be impractical for a .308. The exception would be one of Steve's (Hammer) fine monos that we're in the 200 or so class. Might be a good choice.

 

[Mike6158]

I corrected the original post. I wrote 9.7g of TrailBoss and it was 10.7gr. I snuck up on it from 10g, 0.1g at a time.

Agree, heavier than 200 in a .308 is not practical. 200g is interesting enough. I wonder if there is a negative to shooting "normal" loads with a 1:8 twist? I only want to do this once... this time

 

[benchracer]

You can experiment with "what-ifs" here:

http://www.bergerbullets.com/twist-rate-calculator/

From what I can tell, if you want to go subsonic with 200 grain bullets, you are going to want an 8 twist. Whether or not the lighter bullets will still work will be heavily influenced by how light you want to go, how fast you want to push them, jacket thickness, and bore condition.

It looks to me like going slow and heavy will require a specialized rig. You WILL be sacrificing versatility. The open question is how much...

 

[Bravo 4]

I would go with the 8" twist (and a short barrel at that), especially if a can is involved. I have a subsonic suppressed hunting rig and use the Lehigh Defense fragmenting bullets. I highly recommend them, they aren't cheap however. On their website they recommend an 8" twist even for their 168 grain bullets.
But then again, if I were to go with a dedicated .30 cal sub/sup rifle I would just get a .300 Blackout. My experience is that the smaller the case the easier it is to get consistent velocity in subsonic loads. The larger case has too much space to try and fill, or when trailboss is used it hasn't been giving consistent velocities. I have been thinking of getting a single shot H&R in .300 BLK, if I'm not mistaken they have a 1-7" twist. Or maybe even better, the Ruger American Rifle.
Just my two cents, good luck with your project.

 

[Mike6158]

You can experiment with "what-ifs" here:

http://www.bergerbullets.com/twist-rate-calculator/

From what I can tell, if you want to go subsonic with 200 grain bullets, you are going to want an 8 twist. Whether or not the lighter bullets will still work will be heavily influenced by how light you want to go, how fast you want to push them, jacket thickness, and bore condition.

It looks to me like going slow and heavy will require a specialized rig. You WILL be sacrificing versatility. The open question is how much...

Thanks for the link. That's very handy. The Lapua FMJBT has a G7 BC of .211 and it's 1.333" long. The calculator says, for 800 - 1050 fps it's marginally stable at 12, stable at 10 and faster. Lapua must've ate their Wheaties when they designed the bullet.

I've been playing around in the calculator with lots of bullet combos (Barnes TTSX, Berger Hunting, etc) the 1:8 will definitely put the bullet I'd want to use on the high end of stable between 800 and 1050 fps. So will a 1:9. The reality is, for subsonic ammo, you don't want to use a bullet lighter than 185gr. There's not a lot of energy in a 200 gr bullet and going lighter isn't going to help. Especially with a big ole hog.

Here's a point blank range curve for the 200 gr FMJBT at 100 yards. It looks like someone threw a hand grenade

Yes, specialized. The rig will be for hogs at night. I'll put my Night Optics thermal imaging scope on it (specialization #1) and I plan to suppress it (specialization #2). Max yardage will be up to but less than 200 (for coyotes) and that may be a stretch for the optics and safety.

I have a 700 Tactical in .308 and I never shoot the VTR so modifying the VTR won't hurt my feelings any.

Neither rifle is my go to rifle for long range. I have my .338 Edge for long range and my .20 Beggs for intermediate range smaller game. I also have a .223 Tactical but I moved the Nightforce from it to the .20 and I haven't replaced the scope yet.

On a side note- at 900fps... the sound without a suppressor is pretty impressive...

 

[Mike6158]

I would go with the 8" twist (and a short barrel at that), especially if a can is involved. I have a subsonic suppressed hunting rig and use the Lehigh Defense fragmenting bullets. I highly recommend them, they aren't cheap however. On their website they recommend an 8" twist even for their 168 grain bullets.
But then again, if I were to go with a dedicated .30 cal sub/sup rifle I would just get a .300 Blackout. My experience is that the smaller the case the easier it is to get consistent velocity in subsonic loads. The larger case has too much space to try and fill, or when trailboss is used it hasn't been giving consistent velocities. I have been thinking of getting a single shot H&R in .300 BLK, if I'm not mistaken they have a 1-7" twist. Or maybe even better, the Ruger American Rifle.
Just my two cents, good luck with your project.

At 10gr I had about 50 fps variation in velocity. Bumped it up to 10.8 gr (in .1 steps) and the variation dropped to 20 fps. I haven't shot the 11gr loads yet. They are obviously quieter even without a suppressor

I've pretty much set my mind on 1:8 at this point. The calculator link ^^ was a big help. My son-in-law has a suppressed .308 (and a few other calibers) that he uses in his hog hunting side business (Bad *** Hog Dogs). Originally, I was just going to work up some loads for his .308. He shoots commercial ammo now and they are pricey. I had no intention of going down the path of OWNING a suppressed rifle but now that I'm all in ) My goal is to convert the VTR to something useful.

 

[86alaskan]

IF it were me, I'd go with the 1-8" for the heavies. It won't hurt you with the lighter supersonic rounds, but will really help out with subs. There are some really great heavy sub rounds out there, and by going with a slower twist you'd be limiting yourself out of those rounds.

As far as consistency, you should definitely try a Lee Factory crimp die and give those subs a good firm crimp. I found with my 300BO that the crimp made the ES way lower. I think it's due to the fact that the powder has something to act against in a fairly uniform fashion. When you just use neck tension, the bullet may start to move unpredictably at those lower pressures in a sub. I've found that factory crimp die to improve consistency in a bunch of my rifle and handgun loads.

 

[Mike6158]

IF it were me, I'd go with the 1-8" for the heavies. It won't hurt you with the lighter supersonic rounds, but will really help out with subs. There are some really great heavy sub rounds out there, and by going with a slower twist you'd be limiting yourself out of those rounds.

As far as consistency, you should definitely try a Lee Factory crimp die and give those subs a good firm crimp. I found with my 300BO that the crimp made the ES way lower. I think it's due to the fact that the powder has something to act against in a fairly uniform fashion. When you just use neck tension, the bullet may start to move unpredictably at those lower pressures in a sub. I've found that factory crimp die to improve consistency in a bunch of my rifle and handgun loads.

Thanks for the heads up on the Lee factory crimp die. I'll be giving that a try