Seating depth, True Flight barrels and the Kings

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tachyon
Posts: 157
Joined: Mon Jul 15, 2019 1:44 pm

Seating depth, True Flight barrels and the Kings

#1 Postby tachyon » Thu Mar 16, 2023 8:22 pm

So, here is what I found with the following parameters

Lapua Palma cases with
Federal GM primers with
42.9gn 2208 for 2620 with
Berger 200.20x with
1:10 30" True Flight barrel in the
Tas Kings

So here is the seating depth analysis:

69994263094__902AC7C2-8F55-4C32-AA85-E103A3091233 2.jpg


with 15 - 12 - 9 thou of jam working best. Just touching @ 3 thou produced an abysmal group.

Here's what that looked like on target...
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cheech
Posts: 384
Joined: Wed Jul 15, 2009 11:10 pm

Re: Seating depth, True Flight barrels and the Kings

#2 Postby cheech » Fri Mar 17, 2023 1:25 pm

Nice shooting , I’m running in a new truflite with 200-20x I get 2700fps no problem .

Daveh
Posts: 113
Joined: Tue Sep 08, 2020 9:40 pm

Re: Seating depth, True Flight barrels and the Kings

#3 Postby Daveh » Fri Mar 17, 2023 5:55 pm

Thanks for sharing.
Having them jammed doesn't concern you if you have to remove a live round?

Would you mind telling us the OAL.

Anyone else care to share...

Dave

Rogue22
Posts: 101
Joined: Sun Dec 20, 2020 8:53 pm

Re: Seating depth, True Flight barrels and the Kings

#4 Postby Rogue22 » Fri Mar 17, 2023 9:24 pm

cheech wrote:Nice shooting , I’m running in a new truflite with 200-20x I get 2700fps no problem .

What’s your charge weight to get around 2700? Ive got a rifle being put together atm to shoot the 200.20x and was wondering where to start. I’ve been shooting jugs for the past 2 years and this will be my first step into the 200’s

cheech
Posts: 384
Joined: Wed Jul 15, 2009 11:10 pm

Re: Seating depth, True Flight barrels and the Kings

#5 Postby cheech » Sat Mar 18, 2023 8:25 am

Daveh wrote:Thanks for sharing.
Having them jammed doesn't concern you if you have to remove a live round?

Would you mind telling us the OAL.

Anyone else care to share...

Dave


OAL = 3.175” - light 10thou jam nothing pulls out
32” barrel 9twist
SP Palma brass
CCI 450
44 gn 2208

tachyon
Posts: 157
Joined: Mon Jul 15, 2019 1:44 pm

Re: Seating depth, True Flight barrels and the Kings

#6 Postby tachyon » Sat Mar 18, 2023 1:38 pm

Daveh wrote:Thanks for sharing.
Having them jammed doesn't concern you if you have to remove a live round?

Would you mind telling us the OAL.

Anyone else care to share...

Dave


Hi Dave,

I had been avoiding jamming for that reason but it does seem more theoretical with what is (in effect) 50% jam - ie 1/2 way between touch and jam. I prepare my cases (neck turned to 0.135") with a Forster full length die, then a 21st century mandrel expander which gives around 2 thou of neck tension ie middle of the road.

If you think about pulling back (say 10 thou) from hard jam, and guesstimate a 10:1 slope where the ogive meets the leade pulling back 10 thou reduces the interference by 1 thou. That 1 thou of interference was entirely required to push the projectile back into the case, so, given the static coefficient of friction does not care about into the case, or out, all things being equal, it is more or less impossible for <100% jam to extract a bullet.

That said, I have seen people dump powder in their actions but that seems to be mostly MR shooters using 215 Bergers, in Winchester cases, over a lot of 2209 or RL17 and with the projectiles barely in the neck. How hard you jam, heating/cooling barrels and bullets, fouling, neck tension and how much of the projectile is in the neck all contribute to this possibility. My suspicion is that what happens is the combination of hard jam into a hot barrel. Between shots the barrel cools and shrinks, but this process is slow compared to the heat transfer to the bullet which I suspect expands and tightens the jam. At the same time the case neck warms and the neck expands.

Depending on the barrel (and the reamer used) the distance from touch to jam is 0.021-0.031". My testing suggests jammed about 1/2 way ie 10-15 thou seems to work best.

Bob Pederson, who has done a lot of winning over the past 50 years, distilled it down to "As a starting point, jam the Berger hybrids 10 thou, jump the Sierra's 10 thou".

My OAL is unlikely to be of use to you as freebore in 308 typically ranges from of 0.080-0.220". My reamer is a copy of one of Jerome's and has a 0.125" freebore and my OAL is around 3.075". I run a similar jam to cheech but his OAL of 3.175" suggests his freebore is more like 0.220".

cheech
Posts: 384
Joined: Wed Jul 15, 2009 11:10 pm

Re: Seating depth, True Flight barrels and the Kings

#7 Postby cheech » Sat Mar 18, 2023 10:23 pm

tachyon wrote:
Daveh wrote:Thanks for sharing.
Having them jammed doesn't concern you if you have to remove a live round?

Would you mind telling us the OAL.

Anyone else care to share...

Dave


Hi Dave,

I had been avoiding jamming for that reason but it does seem more theoretical with what is (in effect) 50% jam - ie 1/2 way between touch and jam. I prepare my cases (neck turned to 0.135") with a Forster full length die, then a 21st century mandrel expander which gives around 2 thou of neck tension ie middle of the road.

If you think about pulling back (say 10 thou) from hard jam, and guesstimate a 10:1 slope where the ogive meets the leade pulling back 10 thou reduces the interference by 1 thou. That 1 thou of interference was entirely required to push the projectile back into the case, so, given the static coefficient of friction does not care about into the case, or out, all things being equal, it is more or less impossible for <100% jam to extract a bullet.

That said, I have seen people dump powder in their actions but that seems to be mostly MR shooters using 215 Bergers, in Winchester cases, over a lot of 2209 or RL17 and with the projectiles barely in the neck. How hard you jam, heating/cooling barrels and bullets, fouling, neck tension and how much of the projectile is in the neck all contribute to this possibility. My suspicion is that what happens is the combination of hard jam into a hot barrel. Between shots the barrel cools and shrinks, but this process is slow compared to the heat transfer to the bullet which I suspect expands and tightens the jam. At the same time the case neck warms and the neck expands.

Depending on the barrel (and the reamer used) the distance from touch to jam is 0.021-0.031". My testing suggests jammed about 1/2 way ie 10-15 thou seems to work best.

Bob Pederson, who has done a lot of winning over the past 50 years, distilled it down to "As a starting point, jam the Berger hybrids 10 thou, jump the Sierra's 10 thou".

My OAL is unlikely to be of use to you as freebore in 308 typically ranges from of 0.080-0.220". My reamer is a copy of one of Jerome's and has a 0.125" freebore and my OAL is around 3.075". I run a similar jam to cheech but his OAL of 3.175" suggests his freebore is more like 0.220".


You’re spot on , we went with 0.215 freebore with allowance of throat wear , 200’s bearing surface in neck about 40% so plenty grip , these loads are fireforming at this stage but give good accuracy. I will do seating depth tests eventually

BATattack
Posts: 1275
Joined: Mon Dec 29, 2008 10:29 pm

Re: Seating depth, True Flight barrels and the Kings

#8 Postby BATattack » Sun Mar 19, 2023 4:17 pm

Risk involved in jamming all depends on neck tension. More tension = less risk of dumping powder in your action

Daveh
Posts: 113
Joined: Tue Sep 08, 2020 9:40 pm

Re: Seating depth, True Flight barrels and the Kings

#9 Postby Daveh » Mon Mar 20, 2023 8:57 pm

Tachyon, thank you taking time to reply in such detail. I have read your reply a few times.
I was interested in your overall length so I could compare with mine and Cheech letting his secret out leads me to believe mine is somewhere close.

I don't actually know what my freebore is and usually just find touch and set them back 0.015 for my starting point. From your explanation I could possibly have up to 0.030 I can move forward without worrying about pulling a projectile out.

I have a load up near Cheech and have been testing about 1/2 grain lower incase there was a more stable load. After seeing yours doing so well around 2620, I might go a bit lower still and see what it might reveal.

Thanks to both of you for the info.
If we catch up on a range one day we'll have a cold one.. My shout!

Dave

tachyon
Posts: 157
Joined: Mon Jul 15, 2019 1:44 pm

Re: Seating depth, True Flight barrels and the Kings

#10 Postby tachyon » Fri Mar 24, 2023 10:33 am

Daveh wrote:I don't actually know what my freebore is and usually just find touch and set them back 0.015 for my starting point. From your explanation I could possibly have up to 0.030 I can move forward without worrying about pulling a projectile out.


Hi Dave,

Your 30 thou guesstimate is probably on the money but why guess?

I find touch and jam like this

1) Remove the firing pin (and ejector) from the bolt
2) Prepare a case as usual and make sure you can chamber it with no resistance and the bolt handle dropping freely
3) Seat a projectile long, put a touch of case lube on the ogive and chamber it - now we have jam
4) Measure this, preferably using the ogive rather than the tip
5) Set up your seating die to suit this length
6) Add 15 thou extra depth to the seater to save time
7) Keep chambering this round, seated another 1 thou deeper until the bolt handle drops free (this is 1 thou-ish past touch)

Daveh wrote:I have a load up near Cheech and have been testing about 1/2 grain lower incase there was a more stable load. After seeing yours doing so well around 2620, I might go a bit lower still and see what it might reveal.

Thanks to both of you for the info.
If we catch up on a range one day we'll have a cold one.. My shout!
Dave


According to Dan Newbury, the theoretical Optimal Charge Weight for 200 grain projectiles and Varget (2208) is 43.1. This fits with my experience that 42.7 - 43.4 (depending on the lot) seems to provide a more stable ES/SD that other charge weights. That ~43grains gets me 2625 out of a 30 inch tube which is supersonic out past 1300 yards.

Note that I'm using Lapua cases. ADI cases have a smaller internal volume so need a touch less. Winchester had a larger internal volume so need a touch more to perform similarly.

http://www.ocwreloading.com/

Daveh
Posts: 113
Joined: Tue Sep 08, 2020 9:40 pm

Re: Seating depth, True Flight barrels and the Kings

#11 Postby Daveh » Sun Mar 26, 2023 10:22 pm

James, again thanks for the explanation.
Will do some checking and read up on the ocw from your link.
Time to do some testing/checking.
Dave


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