.20ppc twist rate

[X Count]

Hi all,

Looking to put together a 20ppc fox rifle with heavy barrel around 24" long and would like to be able to use 50gr customs when I can get them and fall back to 39gr SBK if I can't get reliable supply.

I can get a 1-8 twist and think that will be about rite for the 50s BUT I'm concerned that it's going to be blowing up the 39s. This will be about 20 shots per night and cleaning after each night so not getting hot with long strings like when shooting dogs.

Has anyone here played with 39s in a 1-8, did you have blowups and was your accuracy good?

 

[Gabe22BR]

1-9 works fine

 

[Tommie]

Agree with Gabe. Bullet length is the issue and knowing how long these 50 grain customs are would be helpful but I doubt they’re longer than 55 grain Bergers which stabilize fine with 1-9” twist. It’s possible a 1-10” twist rate would work with the 50’s.

 

[X Count]

Yeah it's funny. Berger calls for a 7.75 twist for the 55gr to be at 1.5 at sea level!

The barrel maker has a 1-8 in stock. I'm just weighing up if that is going to actually cause me problems

 

[L.Sherm]

Take Gabes advice 1-9

 

[SHall]

If this helps. I have shot 3- 8 tw barrels and one cut rifling 7twist 20 PPC with 40g V-Max and 40g Nos BT at 3900fps out to 500 yards at my range with no blow ups. Real world results is what I look at. The only paper calulations I look at are my targets. Lol

 

[L.Sherm]

That is why don't believe you have to have a 1-8 to stabilize a 55 Berger 20 cal

 

[X Count]

Unless I wait 12 months my options are an 8 or a 10 twist :-(. Ideally I'd like a 9 like you guys are suggesting

If this helps. I have shot 3- 8 tw barrels and one cut rifling 7twist 20 PPC with 40g V-Max and 40g Nos BT at 3900fps out to 500 yards at my range with no blow ups. Real world results is what I look at. The only paper calulations I look at are my targets. Lol

I've read that those bullets have a thicker jacket than the 39sbk so that may be helping you. How many rounds have you had on those barrels?

 

[L.Sherm]

sounds like you dead set on one barrel maker

 

[Evan]

My Hart 9 twist in 20 Vartarg stabilizes the 55gn Berger at 3000fps very well. Best shooting barrel I've ever owned.

 

[X Count]

sounds like you dead set on one barrel maker

Not at all but I'm located in Australia so any quality barrel custom ordered form the US is going to be 12 months at the moment. So dealing with what can be obtained in the county at the moment.

 

[L.Sherm]

Ah I see

 

[L.Sherm]

What elevation are you at in Australia?

 

[X Count]

I'd do majority of shooting at 0-1000ft

 

[L.Sherm]

Personally I would order a 1-9 and get exactly what you want, if you can't wait I would get the 1-10 and shoot 39- 45 ish grain bullets and I wouldnt be surprised if the 10 didn't stabilize a 50 gr

 

[L.Sherm]

If you play with Bergers twist calculator and put a 55 at .800 length at 3500fps at sea level you end up with a 1.3 SG with a 10 twist
Thats exactly what my 20BRAI is with a 9 at 3,000 elevation and a 55 at .908 length

 

[X Count]

Yeah your on the money. I did a bit of the same in a crude way trying to estimate the length of these 50s and came up with .908/55 X 50= .825.

Did a bit more research and found info on the midway site about the discontinued Berger 50gr and they are listing the length at .845 and reccomend a 9 twist.

 

[X Count]

Putting the 50gr Berger dimensions into their calculator at 3750 gives 1.07 SG. Depending on how conservative that calculator is isn't not looking good!

 

[L.Sherm]

This is what Berger twist calculator comes up with at .845 length

 

[L.Sherm]

Can you even get your hands on some 50 grain bullets? If you can I would find out the length