New FTR Rifle build advise

[coolbox]

I am planning on a dedicated long range precision rifle, based mostly on F-Class and FTR shooting, and whatever comes along the way in our club matches (we have a 1000 yard range there) or occassional LR shooting events, vaguely based on F-Class moatly.
The caliber is 308 (FTR)

I plan to shoot factory match ammo in 175 grains, maybe tune it to my liking. Have plans for 185 berger juggernauts in future. 156s are not available in my neck of woods (Pakistan!!)

The gunsmith is Mik at Dolphin gun company, UK.
I have selected Bartlein SS 32" 1:11, 5R. Black duracoat.
Jewel HVR trigger
Dolphin modular FTR stock, black duracoat.

Action is where I am confused.
Available options are
-Barnard S (single shot) with nitride treatment (melonite)
-Nesika KT (repeating),
-Barnard SM ( repeating action) without melonite finish.

I am interested in repeating action, but Barnard is not available with Melonite treatment. I prefer SS or melonite due to the weather conditions we have here, humid, and often rains without notice !
BAT or other actions are not readily available, and will mean a real long lead time. In above three options, wait time is 3 months.

Your inputs needed, considering I prefer repeating action for such a match where I could use the mags (10 rounders). In F-class, magazine loading is not allowed.

 

[coolbox]

Well, I have selected the Nesika KT repeating action, with a single shot follower.
Throat set up for 175smk and 185 berger juggernaut mainly.
Lets see how this goes.

 

[Nature Boy]

I'm excited to see it when it's done and get a range report.

That Dolphin stock looks interesting

 

[The_Next_Generation]

Not sure if its allowable or not, or if they are even available out there, but you might want to give some 200gr+ projectiles a try. If for no other reason than to see how far a 308 can shoot. I shot the 208gr Amax @ ~2,550ft/s in my 308 before switching to 6.5CM. The new ELDx and Berger heavies have some ridiculously high BC's.

 

[Bart B.]

200 and 210 grain bullets will shoot most accurate in a 1:11 twist barrel for the 308 Win. cartridge that's 32 inches long. It may shoot 220 grain ones just as accurate in warm to hot weather when the air is thinner. Be sure the barrel's groove diameter is about .3075 inch and groove diameter about .2995 inch.

 

[The_Next_Generation]

200 and 210 grain bullets will shoot most accurate in a 1:11 twist barrel for the 308 Win. cartridge that's 32 inches long. It may shoot 220 grain ones just as accurate in warm to hot weather when the air is thinner. Be sure the barrel's groove diameter is about .3075 inch and groove diameter about .2995 inch.

Just where are you getting your information from? I know Berger recommends a minimum 1:11 for 200+ gr projectiles in the 30cal range, but I've seen them perform well in barrels much shorter than your 32" requirement. Shorter is stiffer, but obviously velocity results in more consistency in the wind and on unknown distance targets. Also, why do you recommend "about .3075/.2995" for groove/land diameters. Those are awfully specific numbers to end up qualifying them with "about".

The OP happens to have a 32" 1:11 bbl, and it will certainly chuck those heavy pills way out there. I'm just curious as to where you are coming from.

 

[Varminterror]

I don't know Bart from a hole in the ground, but I know what it means to earn those credentials in his signature line. While not as credentialed as Bart, I started laying down on F-class lines before F-class was cool. Wanna win matches? Bart's on track.

All of my most accurate rifles have always been single shots, and even when I used repeater actions, I used a single shot follower, so it was a waste of weight and receiver flex to use a repeater. I only use custom precision built repeaters for hunting rifles, or my few PRS competition rifles where the repeater is really an advantage, or nearly a necessity.

 

[coolbox]

@Bart B.
Thank you.
What throat length would you suggest for the 200/210 Bergers.

200 and 210 grain bullets will shoot most accurate in a 1:11 twist barrel for the 308 Win. cartridge that's 32 inches long. It may shoot 220 grain ones just as accurate in warm to hot weather when the air is thinner. Be sure the barrel's groove diameter is about .3075 inch and groove diameter about .2995 inch.

 

[coolbox]

Not sure if its allowable or not, or if they are even available out there, but you might want to give some 200gr+ projectiles a try. If for no other reason than to see how far a 308 can shoot. I shot the 208gr Amax @ ~2,550ft/s in my 308 before switching to 6.5CM. The new ELDx and Berger heavies have some ridiculously high BC's.

While they are allowed, I am restricted by availability being where I am. Even Berger185 juggernauts will be hard to come by, but am hoping they do. 175smk is what is generally available.

 

[Bart B.]

I get my info on what weight bullets shoot most accurate from .308 Win cases at different muzzle velocities from different twist barrels shooting the following combinations winning my share of the long range matches and/or testing them for bullet stability to shoot well at 1000 yards.:

24" barrel, 1:12 twist with 150, 168, 180, 190 and 200 grain bullets.
26" barrel, 1:10, 1:11 and 1:12 twist with 168, 172, 180, 190, 200 and 210 grain bullets.
28" barrel, 1:11 twist with 168, 180, 190, 200 and 210 grain bullets.
30" barrel, 1:13 twist with 155, 168 and 180 grain bullets.
32" barrel, 1:13 twist with 155 grain bullets.

In temperatures 20 to 100 degrees F and altitudes from 500 to 6600 feet.

Regarding throat length..........

Throat (or leade as it's often called) is the tapered rifling from freebore diameter (unrifled part of the bore from case mouth to start of the rifling that's a few thousandths inch larger than bullet diameter) to where the rifling tapers down to bore diameter. Where the bullet contact point on the rifling is relative to the chamber mouth is determined by how llong the ammo will be from head to bullet tip with that contact point some distance back from the rifling. A competent gunsmith can figure that out with one of your dummy rounds along with the distance you want the bullet to move before it touches the rifling and the throat angle his chamber reamer produces.

I've shot Sierra bullets with zero to over 1/10th inch jump to the rifling. On rounds with very straight case necks and therefore bullets relative to the cartridge long axis, it doesn't make much difference in their accuracy. With bullet runout more than 1% of bullet diameter, it helps if the bullets' are gently pushed into the rifling when chambered. That helps them start straighter into the rifling.

Keep in mind that .308 Win throats/leades advance from bore erosion about .001 inch for every 30 to 40 shots; depending on bullet jacket hardness and peak pressures. If you want to keep the bullet's jump to rifling distance in a .001 inch sprerad, you'll have to seat them .001inch shallower every 30 to 40 rounds fired. I've not seen any significant accuracy falloff with the throat advancing .030 inch for a given cartridge overall length.

 

[coolbox]

Bart B
Thank you.
I think I should have asked for what COAL to provide to gunsmith considering that I will be using
-175smk based factory ammo (~2.81", similar to m118 LR) (2750fps on avg from similar setups as mine)
-reload factory ammo to 2850 fps plus, subject to accuracy node
-and reload with Berger 185 juggernaut, aiming 2800 fps, subject to accuracy node.

Reloading for higher fps might require higher COAL

He is located in UK, and I cant send him a dummy round. I dont know for sure myself what COAL will I end up with when I reload, equipment will be with me around the same time as the rifle.

Additionally, how much higher a COAL would be required for the Berger 210 gr compared to the 185 berger juggernaut? Or does it not matter?

 

[Bart B.]

You control the loaded round's OAL by how deep you seat bullets in the case.

I don't know what COAL difference there is between the Berger 210 and 185 grain bullets. It may be the difference in bullet length and that can be found on Berger's web site. I've only shot Berger 30 caliber 155's in my 308 Win rifles.

Found an interesting site that explains the difference between Berger's secant ogive shaped bullets and the tangent ogive Sierra and others use:

http://www.accurateshooter.com/ballistics/tangent-vs-secant-vs-hybrid-ogive-bullets/

Most interesting is the comment from a multiple record holder shooting Berger secant ogive bullets in benchrest matches:

... a change of .005″ in seating depth “can cause the group size to increase substantially”.

I don't know what "substantially" means in group size, but I'd guess it's at least 20% to 30% bigger.

The bullet's jump distance to the rifling is not controlled by the COAL number; length from case head to bullet tip. Bullets have a couple thousandths inch spread in the distance from tip back to where their ogive touches the rifling. And the case head is a few thousandths inch away from the bolt face. The bullet's position in the chamber is determined by the distance from the case shoulder to bullet tip. Doesn't the case shoulder bear hard against the chamber shoulder when fired? Do all of your resized cases have the same distance from case head to shoulder; case headspace, so to speak? A couple thousandths spread in case headspace is normal. I've seen as much as .005" depending on the amount of and type of case lube used on the cases and how much spring the reloading press has.

When one considers all the dimensional tolerances in a round of ammo, keeping a given lot of ammo's bullet jump distance to the lands the same for every shot is often an exercise in futility. Whether the reloader knows it or not.

While Berger's new hybrid ogive is a compromise, I think the accuracy difference across all ogive shapes is very small. And the emotions someone has that makes one ogive shape seem better will probably have the biggest deciding factor in which one they want to use. Given the way most people test their ammo, either one may well be their favorite.

 

[coolbox]

Bart B
Thank you.
I should have been more specific with my reloading term. I will only 'top up' factory ammo. Tune them to my rifle and my fps requirements. I will not be using fired cases, as of now at least.

I will see of I can find base to ogive of different bullets as well as bearing area to see if the longer Berger 210 grain bullet in particular is still shootable.

 

[Bart B.]

What does "top up" mean? Never heard of that.

You may need a chamber with an extra .100 inch freebore to get enough powder in the case to shoot 210 grain bullets with maximum safe pressures. Powders in the IMR4350 range have proved best for that bullet weight and heavier ones up to 250 grains in 308 Win cases.

 

[coolbox]

The factory ammo gives about 2750 fps on most other similar custom rifles. I will add powder to get to 2850 fps or so, subject to accuracy node, and use the same cartridge otherwise.
I meant that I will add powder or fps, by top up!

Thank you !

 

[Bart B.]

Are you referring to factory ammo with 175 SMK bullets shooting from a 32" barrel at 2750 fps?

I think that's about normal for factory ammo at maximum safe pressure. If you add more powder to get another 100 fps, it's been my experience that velocity spread gets higher and accuracy gets worse doing that.

I think a 32 inch barrel in 308 Win will shoot 210 grain bullets about 2550 to 2600 fps at safe max pressure.

 

[coolbox]

Are you referring to factory ammo with 175 SMK bullets shooting from a 32" barrel at 2750 fps?

I think that's about normal for factory ammo at maximum safe pressure. If you add more powder to get another 100 fps, it's been my experience that velocity spread gets higher and accuracy gets worse doing that.

I think a 32 inch barrel in 308 Win will shoot 210 grain bullets about 2550 to 2600 fps at safe max pressure.

Yes, I was referring to factory ammo 175smk, shooting 2750 fps. Thank you for the velocity and accuracy spread headsup. Might very well end up using just about the same fps!