7mm-08 Tikka: T3x Project

[Bill J H]

Tikka 7mm-08 project - (Moved from Firearms Section):

Goal is to use the faster twist Tikka 7mm-08 and see what I can do with "heavy for cartridge" bullets, etc. In essence, I enjoy tinkering with rifles and loads - especially accurate rifles like the Tikka.

The following came in last week - Rifle, Woox Wildman Stock, Mountain Tactical Long Action (LA) Bolt Stop, Tikka OEM LA magazine, Talley 1" Lightweight (low) scope mounts, and 100 count Alpha Munitions Brass. I also received Hornady 175gr SP Interlocks, 162gr BTSP Interlocks, 139gr BTSP Interlocks, and some Nosler 150gr Partitions.

Rifle is a Tikka T3x Lite, Blued, 22.4" threaded barrel. Total weight is 6lbs, 6oz of which the action and bolt weigh 4lbs 5oz.

Woox Wildman Stock - The stock is of great quality, fit and finish. Also the LOP is easily adjustable with spacers. The only drawback - it weighs 3lbs, 5oz; I wish it were lighter...by about a pound, as it makes the rifle weigh 7lb 10oz without my scope. I'm torn as to whether to use the much lighter OEM stock or go with the Woox - decisions...decisions...

I mounted a Swarovski Z3 3-10 on it for now as I develop loads.

Using my Hornady OAL gauge I noted the following measurements for when the lands were CONTACTED: 175gr IL 2.877, 162gr IL 2.866, 150gr NOS PT 2.855, 139gr IL 2.849.

Of note, my Tikka SA magazine measures a tight 2.846, this magazine would have not let me get to (actually very near) the lands. The Tikka LA magazine measures 3.381 which is a lot more than I need.

Replacing the Tikka SA Bolt stop with the Mountain Tactical LA Bolt stop took about 3 minutes.

For load development, I'm gonna jump right in the deep end with the 175gr ILs. I'll use my old standby Varget with CCI 200 LR primers. Varget has never let me down regarding accuracy, although, there are some other powders that might give a tad more velocity. I'll ladder test it and see what happens. Since I'm seating the bullet several thousandths further out than the Hornady ballisticians, I should have increased powder capacity before I begin to see pressure signs. I stress should as one never knows until you test

I'll give a report with pictures in a few days in the event anyone is interested.

 

[Bill J H]

Update 1

First range day: (80 degrees/partly sunny)

Components Used: Alpha Munitions Brass, CCI 200 LR Primers, Varget Powder, 175gr Hornady Interlock Bullets

COAL for all loads: 2.870 (about 7/1000 off the lands)

All grps were 3 shots.

Load 1: (Under book Max) 38.5 gr / Avg Vel 2371 / Grp size .4"
Load 2: (Book Max) 39gr / Avg Vel 2405 / Grp size .5"
Load 3: 39.5gr / Avg Vel 2435 / Grp size .8"

Observations:

As has been my experience with all the Tikkas and Sakos I have or currently own: These guns are shooters!

Book seating depth is 2.80 but due to the modifications I made, I can seat .070 further out increasing the space in the case by the same. With a 24" barrel, the book stated an estimated velocity of 2,500 and I am 95fps off that with a 22.4" barrel. They use different Brass and Primers, so based on my experience I'm right in the ballpark of where I should be.

Zero pressure signs were observed on the case/primer and the bolt was still buttery-smooth.

Loads 1 and 2 were under .5" while Load 3 came in at .8". All these are certainly within my margin of error, so the last group being a tad larger doesn't indicate anything to me; could be wind, different hold, heartbeat, etc. Once I reach my velocity limits, I'll shoot 5-10 shot groups to determine accuracy.

One thing that today's shooting proves - the gun will stabilize the 175gr Hor IL bullets. This is the longest bullet I'll shoot, so this is good news.

I'll load some additional bullets tonight and continue the ladder tomorrow with smaller increments.

Regarding the attached pics. Pic 1 is of the first grp. Pic 2 is the second group on the same target. *Note - I moved the scope .5" Right to better center the group. Had I not done this, I think grp 2 would've fallen directly into grp 1.

 

[sgt_zim]

There are only a handful of 7mm pills that might need a faster twist than 9, and most of those are made by Hammer bullets.

You'll probably have the best outcomes with your 9.5 twist using 175 gr Interlock, Partition, Grand Slam, SGK, and similar. Norma Oryx 170 gr will also stabilize

Required twist is a function of several variables, but principally it's about bearing surface relative to bullet mass. The greater the bearing surface, the greater the amount of friction between bullet and rifling, the easier it is to impart gyroscopic spin, so a slower twist works.

That's why slow twist rates like 14 often work for large diameter 400 and 500 gr bullets

 

[Bill J H]

My testing continues.

With Varget, I was able to attain velocities of 2450 before I noted pressure signs, notably flattened primers, though no caving. Additionally, my groups opened up to a sustained 1". Subsequently, I came to the end of that road.

I then switched to Ramshot Big Game; I have used this powder with great results in a 30-06. Unfortunately, there wasn't a great deal of data for BG and the 7mm-08. So I started at a reasonable load and worked up.

Here are the results of my last 3 loads with Hornady 175gr Hornady SP Interlocks:

1. BG /42.5gr/ 2,455/.75"

2. BG /42.8gr/ 2,482/.5"

3. BG /43.1gr/ 2,550/.5"

No pressure signs with these loads. I'm going to work a bit more with this powder, although I can stop here and be happy. My chrono went a bit wonky on me on my last string and I only caught the velocity of my last shot, so it does not reflect an average of 3 shots.

With Varget, I was able to work the 162 gr BTSP Hornady Interlocks to 2,700 with 1" groups. I've tried no other powders with these bullets.

More to follow.