.20TAC with 55gr Bergers

[Big Al]

Guys,

I have a 9 twist 20TAC with a 20" Pacnor barrel and since I use 55r Bergers in my 9 twist 20BR I thought I would give them a try in the 20TAC, I wasn't expecting much to be honest as Berger suggests an 8 twist and the TAC won't drive them as hard as the BR, so far though my initial findings are encouraging.

Firstly I started with Vit 133 as I used this powder with great success in a .223 shooting 55gr bullets so figured that the same case with the same weight bullet might work. I set the Bergers back 0.020" and loaded some single rounds just to check for pressure and to see if they would stabilise, I started at 20.0gr and went up in 0.5's to 22.5gr. No signs of pressure and the holes in the target were clean cuts at 100yds.

Back to the reloading bench I chose a load to begin with of 21.5gr. I then seated 3 rounds at the following different lengths starting with just touching the lands and then working away in 0.040" jumps as per what Berger recommends with these very long bullets, the results were promising and as follows;

Touching = 1.25"

-0.040" = 1.00"

-0.080" = 0.75"

-0.120" = 0.45"

With 21.5gr of N133 I was getting 3175fps and no signs of pressure. What I find really interesting is that again (as with my 20BR) these bullets group best when jumping a fair bit. Its got me wondering if I would have also gone back to -0.160 to see if the group got any better?

Anyway, Ive loaded up again with the bullets jumping 0.120" and then tweaked the powder charge starting 0.3gr lower at 21.2gr rising in 0.3's to 22.7gr and see what we get. Hopefully I can get out again in the morning before the wind comes for what looks like the rest of the week

Ive never delved into the realms of bullet stability in the past as Ive always had twist rates that were recognised as suitable for the bullet weights I wanted to shoot. If the holes are clean at 100yds does that mean Im good or can they become unstable at longer range? My plan was to hopefully find a good load from the next OCW test and then start shooting some paper at 200-300yds to see if the holes are clean cuts?

All good fun and I would be a very happy man if I could get my rifle to shoot these bullets, the good BC of nearly 0.400 really would make the .20TAC a very interesting long range round.

[Si-Snipe]

Al how do you find the expansion on vermin with the 50/55 Bergers?

[Big Al]

Al how do you find the expansion on vermin with the 50/55 Bergers?

 

Ive not shot anything live yet Simon, I just got the BR load sorted a few weeks ago now and the chance hasn't presented itself yet. I spoke to Dave about his experiences of drilling in rabbits which isn't good, my main quarry is crows and we both felt that they would be fine for that purpose but as yet its unproven. Then next few weeks should see the action begin.

 

Ive read lots from guys over in America who say they expand well on their quarry so the jury is still out Im afraid.

 

What are your thoughts based on what you saw with Dave?

[rsc1960]

Hi Al.

 

What's the recommended twist for the 55's, I'm running a 1/12 and soon I hope to have a second 20 tac with a 1/11' I love the 40's and they work very well out to 300' plus on bunnies etc,

 

Max distance on a fox was 367 yards so I'm not sure if changing the twist rate for is needed,

 

RSC,

[Big Al]

Berger suggest an 8 twist but many have found a 9 twist will work, its unlikely your rifles in the twists you have will like them Im afraid.

[Si-Snipe]

Hi Al.

 

What's the recommended twist for the 55's, I'm running a 1/12 and soon I hope to have a second 20 tac with a 1/11' I love the 40's and they work very well out to 300' plus on bunnies etc,

 

Max distance on a fox was 367 yards so I'm not sure if changing the twist rate for is needed,

 

RSC,

If you really want to prioritise a build around a particular bullet don't get a marginal twist for that bullet. A tighter than required twist will not cause you a problem but too slow a twist will. I have a 1:7 223 which I built for shooting 75/80g bullets. It shoots 55g SBK into well sub 0.3 MOA. Most of the time it's around the 0.2's. My friend has a 1:7 too and shoots 80's and 55's both with good accuracy.

I did notice that the 55's were a little more critical to tune via seating but once done is prob more accurate than the 1:12 I had.

What I'm saying is if you want to shoot 55's go 1:8. You can still shoot 40's with good accuracy.

[Laurie]

If you want to play around with stability exrercises, Google Millers Twist Rule and download a simple spreadsheet. You do need to know the bullet length though to use it. (Despite what people think, bullet OAL in relation to diameter - bullet length expressed in calibres - is the ratio which determines the required twist rate and within any such value a heavy bullet actually needs a slower twist rate than a light one.) So, you may need to ask around from people who own examples or who have a copy of Bryan Litz's latest book which lists the dimensions of getting on for 300 bullets.

 

However, doing the twist rate calculation for Bergers is easy-peasy, just click onto

 

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

 

and select your bullet from the drop-down menu and fill in MV etc in the boxes.

 

Doing this for the 55gn .20 and inputting 3,050 fps gives Sg values of:

 

12" twist .................... 0.610 (unstable under all conditions)

 

11" twist .................... 0.726 (unstable under all conditions)

 

10" twist .................... 0.879 (unstable under all conditions)

 

9" twist ..................... 1.08 (barely stable. May be unstable under some air conditions, very cold etc. Berger says BC is reduced by 13%.)

 

8" twist ..................... 1.37 (stable, but below the optimum level for obtaining full BC. Berger says BC is compromised by 4%)

 

7.6" twist .................. 1.52 (stable and full BC obtained)

 

These all apply at 'standard ballistic conditions' - 59-deg F; 29.92 inches mercury air pressure. So shooting in a heatwave on top of Ben Nevis improves things a bit; shooting in anticyclonic conditions on some foreshore in minus whatever makes them a bit worse.

 

In practice, 1 in 8 is there, but it needs a true 1 in 9 to work at all and it becomes iffy depending on the ambient conditions, but as the aim of using 55s is normally to improve BCs, an over 10% performance degradation may make the choice of this bullet weight self-defeating.

[gbal]

+1 on Laurie's recommendation of the Litz/Berger analysis.

 

Much degradation of BC will compromise anticipated ballistic improvement; (it's unlikely the anticipated gain will exceed 15%,but the loss might get close); and marginally stable bullets are unlikely to do much good to accuracy either.(cf the 168g 308 story).

It is probably realistic to assume similar effects in other makes of bullet,though the exact data are not available.

And measure your barrel twist accurately...1/4 inch out might matter.

 

Thankfully,twist rate has but a minor effect on velocity per se (and hence BC).....Litz again:

 

Testing 308,"MV correlated with twist rate around 1.33 fps per inch of twist",or put more clearly perhaps-there is 5fps less mv from a 1 in 8,compared to a 1 in12. It's unlikely calibre will change the figure much.

 

Negligible-be grateful-it could have gotten quite complicated!

 

gbal

[247sniper]

Will be interesting to find out how the 50/55 Bergers work out on small vermin, like rabbits etc

 

I have spoken to several people who run .20BR's 204's etc zipping the 50/55 Bergers out at lighting speeds on rabbits and they just drill straight though them and dont expand, the rabbits just crawl off with a pencil size hole in them and die later!

 

I would suspect yours Al will be the same?

 

Keep us informed.

 

Steve

[6.5shooter]

I would think the hydraulic shock on such a small critter such as a rabbit due to the high velocity will kill the rabbit effectively enough.

Could be wrong but Im guessing the effect will be pretty devastating.

[gbal]

"Back in the day'- 70s on,I found that the 17 Rem (25G@4000) was the most effective rabbit cartridge.

 

It simply did not fail-hydrostatic shock was considerable too-spare details. Carcass damage on shoulder shots was not an issue,and few bullets passed through.But it was terminal,on the spot.The soft point 222 was fine too,with much less hydrostatic,but not so authoritative always as the 17rem.I don't recall a hit rabbit that moved from the spot-accuracy was sufficient for secure shoulder shots to 225y with both-the 17 was never as consistently sub 1/2 moa,but pretty close. Add 75 yards and some wind,hits were still very effective,but less secure,so were not routinely taken-shooter limit perhaps,but cartridge is getting out of it's comfort zone too.Most rabbit rounds are,some far earlier.

 

Each cartridge/loading has to be field tested,and few approach 100%-the 17 rem was and did.

I do not know about the generality-but it should be emphasised that an MV of 4000 fps is pretty quick,and the bullets were by design near fragmentary-I don't recall ever retrieving one,or decent piece of one.(55g may/not be as devastating,by design-heavier tend to have a little more integrity,and less velocitybut it's variable.)

 

I'd expect the hot 20s/bullets to be similar,and rifles perhaps a tad more accurate-but it was really a one shot game,and still should be.

gbal

[Big Al]

Will be interesting to find out how the 50/55 Bergers work out on small vermin, like rabbits etc

 

I have spoken to several people who run .20BR's 204's etc zipping the 50/55 Bergers out at lighting speeds on rabbits and they just drill straight though them and dont expand, the rabbits just crawl off with a pencil size hole in them and die later!

 

I would suspect yours Al will be the same?

 

Keep us informed.

 

Steve

 

I would suspect that shooting it in the kill zone will have the desired effect Steve, just as .22lr round nosed target bullet works instead of a HP when you hit in the right areas. I think the problem most likely comes from people taking unrealistic punts at too long a range and putting a bullet into a non vital area.

 

As far as Im concerned a rabbit isn't a 10" long target on a windy day, its still a 3" one and as such the rifle will be used at distances and in conditions where this level of accuracy is pretty much guaranteed. That doesn't mean that I won't dial for the wind but Im not looking to rip it apart with an 80r amax impact anywhere. Im not directing this at you but you do see it.

 

I havent pursued the 55r/Tac thing so vigorously after Laurie pointed out the potential compromised BC, I will get around to it later maybe but in the meantime will leave these bullets for the 20BR I think. On a recent crow at 310yds from the 20BR it killed it stone dead but the damage was not as comprehensive as a 40gr vmax is, the exit wound was around half the size so clearly they are not so explosive, then again dead is dead.

[247sniper]

 

I would suspect that shooting it in the kill zone will have the desired effect Steve, just as .22lr round nosed target bullet works instead of a HP when you hit in the right areas. I think the problem most likely comes from people taking unrealistic punts at too long a range and putting a bullet into a non vital area.

 

As far as Im concerned a rabbit isn't a 10" long target on a windy day, its still a 3" one and as such the rifle will be used at distances and in conditions where this level of accuracy is pretty much guaranteed. That doesn't mean that I won't dial for the wind but Im not looking to rip it apart with an 80r amax impact anywhere. Im not directing this at you but you do see it.

 

I havent pursued the 55r/Tac thing so vigorously after Laurie pointed out the potential compromised BC, I will get around to it later maybe but in the meantime will leave these bullets for the 20BR I think. On a recent crow at 310yds from the 20BR it killed it stone dead but the damage was not as comprehensive as a 40gr vmax is, the exit wound was around half the size so clearly they are not so explosive, then again dead is dead.

 

 

As long as you can put every bullet in your 3" kill zone every time then im sure you will be fine. You must have learnt to manage and cope with the "basics" on your recoil management if you can guarantee that level off accuracy everytime then?

[Big Al]

 

 

As long as you can put every bullet in your 3" kill zone every time then im sure you will be fine.

 

Yes, I expect I will.

 

My 20BR is mainly for crows in the 200-300yd range so providing the conditions are not stupid keeping things inside 3" isn't really that difficult.

 

You must have learnt to manage and cope with the "basics" on your recoil management if you can guarantee that level off accuracy every time then?

 

 

Yes thanks, it didn't take long to work it out with a bit of friendly advice, its not really rocket science is it?

 

This time last year even after years of rifle shooting I hadn't really considered shooting at such small targets 300yds away, 12 months paper punching and testing has shown me whats what. I guess it couldn't have been that difficult or we wouldn't have Youtube full of as many 500yd+ vermin snipers and as you keep telling us, practise does make perfect.

[247sniper]

 

Yes, I expect I will.

 

My 20BR is mainly for crows in the 200-300yd range so providing the conditions are not stupid keeping things inside 3" isn't really that difficult.

 

 

This time last year even after years of rifle shooting I hadn't really considered shooting at such small targets 300yds away, 12 months paper punching and testing has shown me whats what. I guess it couldn't have been that difficult or we wouldn't have Youtube full of as many 500yd+ vermin snipers and as you keep telling us, practise does make perfect.

 

 

Taking advise from the right knowledgeable people, learning your equipment and the correct practice methods, imagine what another couple of years experience in the field will bring you, you should be dropping rabbits at 500 yards no probs

 

But keep at it andkeep trying fella

[gbal]

Well yes,but some you tube are the truth perhaps,but not the whole truth-ie some probably omit/blur over the 'sighters' etc-all the shots are do -able,perhaps but not just turn up lie down and first shot 874 yard rabbit. No.

AS Steve says,the advanced careful shooter with good gear and practise is way ahead ,but still makes a few misses-in wind etc. The really honest report these-but i can make a video of "first shot hit on 1000yard clay pigeon"-its an editing not shooting skill. We might be shooting all day if it's a 223 cheapo of course.

I have little problem if all the practise is on non sentient targets. 100% success on live targets is fine too,if you eat them!

g

[rsc1960]

I would think the hydraulic shock on such a small critter such as a rabbit due to the high velocity will kill the rabbit effectively enough.

Could be wrong but Im guessing the effect will be pretty devastating.

I have to agree,

 

Often I don't have much to pick up, mostly they are just headless glove puppets,

 

I use and chose my 1/12 the 1/11 will still run the load I use now with my truck gun,

 

Laurier,

 

A cracking link thank you, but since some experts think they know better, I'll await the results and wish him well, and I hope his choice works for him,

 

RSC

[rsc1960]

7431

Bullet Berger Match Varmint BT

Bullet Weight 55 grs

Powder AR2208 (ADI)

Powder Weight 26.7 grs

Primer CCI BR-4

Brass Make Dakota/Lapua

Barrel Length 26.42" (670mm) (inches)

C.O.L 2.34 (inches)

Velocity 3485 fps

Group 100 yds 0.4 (inches)

Submitted By iTzSissyGirl

Gun Info 8.5 twist barrel, Tikka Tactical action.

Comment Projectile de-stabilises past 1050 yards with this twist/velocity combination.

 

 

JUST FOUND THIS, AND IT'S A 8.5 twist