Savage 12 F-Class 6BR with Lapua Factory Ammo, Stiff Bolt Lift

[StephenSF8]

I am shooting a new Savage 12 F-Class with Lapua 90 gr Scenar factory ammunition. This combination is resulting in very stiff bolt lift after firing. Unfired rounds chamber and extract fine.

Before shooting the rounds I measured the cartridge neck outer diameters with a Mitutoyo electronic micrometer (.00005" resolution), and cartridge head space with a Mitutoyo electronic caliper (.0005" resolution) in conjunction with a Hornady Lock-N-Load head space gauge. I borrowed these two calibrated Mitutoyo tools from work.

After firing I measured these two dimensions with a Fowler dial caliper (.001" resolution, non-calibrated) at home.

Results: Head space grew from an average of 1.1598" to 1.166". Neck outer diameter grew from an average of .26921" to about 0.270". (Side note: I plan to borrow the Mitutoyo micrometer from work again and remeasure the fired neck outer diameters for better accuracy and resolution...)

It seems to me like there is not enough clearance between the chamber neck and the ammunition to allow the brass to expand, release the bullet, and spring-back. Has anybody else had this issue? Does excessive neck wall thickness / excessive neck OD cause stiff bolt lift?

 

[RWO]

"It seems to me like there is not enough clearance between the chamber neck and the ammunition to allow the brass to expand, release the bullet, and spring-back. Has anybody else had this issue? Does excessive neck wall thickness / excessive neck OD cause stiff bolt lift?"

If you haven't measured the chamber neck dia., your statement is meaningless. Regardless, tight neck chambers usually don't cause your problem. Hard extraction is usually caused by soft brass(unlikely with Lapua), high pressure( unlikely with factory ammo), or a rough chamber( most likely). Inspect the clean chamber with a good fiberlight and look for excessive tool marks. A little polishing might fix your problem.

RWO

 

[StephenSF8]

If you haven't measured the chamber neck dia., your statement is meaningless

I disagree, as does Glen Zediker: "...Fired case neck dimension tells usually within 0.0010" (there's some contraction)." -Handloading for Competition by Glen D. Zediker, pg. 95. By this logic, the rifle chamber is likely somewhere around .271". I am not stating fact, only using logic (instead of a chamber cast) to determine the most likely culprit.

Zediker also states a bit earlier in that paragraph that 0.0030" clearance is necessary for a High Power rifle to function flawlessly, and 0.0020" may work if cases are sorted for uniformity. By this logic, loaded round neck OD should be around .268" for flawless functioning.

I am not looking to make a chamber cast, only for the most likely reason for the stiff bolt. I agree that brass and pressure are likely not the issue with factory Lapua ammo, hence the question about excessive neck wall thickness / loaded neck OD. If the issue is neck thickness, I can easily turn the neck diameter down a thou when I reload these cases...i just do not want to if I do not have to.

I personally have no experience with excessive neck thickness and am asking for the experience of others that do.

 

[Ggmac]

I seriously doubt getting another more accurate tool is necessary !
I would consider your base diam at the .20 line . Lapua brass is usually a little large , that's why so many ring dies are sold . If it's all good , Lapua is usually .479 and most savage chambers have been about .468-.469 .
What is your fired brass measure at .20 and what do your primers look like .
Stop driving yourself crazy , you've gone above the usual . I'm impressed .
How bout some back round , how long have you been precision shooting ?, how long have you been reloading , what happens when you resize and shoot your fired brass , any problems ?
Is it a bone stock savage ? How old is the factory ammo , what temp ? How many rounds down the tube ?
The author you quoted , If my old brain remembers , is a shooter of semi autos . A completely diff regime for required ammo specs . A bolt gun is much easier to load for .
Savage rifles are noted for 'a little harder bolt lift ' compared to say remington .
Gary

 

[Ggmac]

Ok , walked the dog . What does you primary extraction look like , do you use a high pressure lube on it ? Are your fired case bases true 90 deg , in other words were trying to eliminate the possibility of uneven lugs either in the receiver or on the bolt head . What finish does your bolt face look like , smooth or rough enough to cause problems . Do you use lube on the cam surface of the bolt ? Have you changed the firing pin spring ? Or adjusted the spring tension ?
These are just a few of the issues iD be looking at before diving into chamber /cartridge issues .
More later , but please I need more info .

 

[StephenSF8]

Thank you Gary, excellent intel on the base dimensions! I am not familiar with "ring dies", is that another term for small base dies? Fired case are measuring just a hair above .470", and unfired cases are measuring about 0.469" using the Fowler dial caliper.

The rifle is new and bone stock, no changes or fiddling to anything other than mounting a Vortex Viper PST 6-24x scope and cleaning the bore and chamber. This is the first time I have shot it. I use a little Hoppes gun grease on the back of the locking lug and bolt cam surfaces. Primers look fine, and the once-fired cases are now flat-liners on the concentricity gauge, measured at the neck and body. I don't think I have a way to determine whether the case heads are square or not (presuming this is what you meant by "true 90 deg bases").

All that said, I think you have led me to the issue...I can see straight machining marks on the back of the locking lugs (looks like it was ground), but I also see some circular witness marks on the right lug...this makes me think the lugs are grinding into an imperfection on the lug recesses when I open the bolt after shooting.

Background about me: Handloading since 2002, primarily 223, 308, and 9mm. I started "precision shooting" in the late 90's with a factory Remington 700VS. This Savage is my first 6BR, and my first Savage for that matter. My normal sizing procedure is to bump the shoulder with a Redding body die, and then neck size with a Lee collet die. With the 6BR I plan to use a Redding S die to bump the shoulder and size the neck in one operation. I have never had function issues with handloaded ammo. Overall I would say I am an "intermediate" skill handloader, and trying to get better!

 

[Ggmac]

Try some lube on the primary extraction cam , it's located on the rear bolt gas shield , sometimes tolerance stacking can make it non existent or very late . Slowly open your bolt while viewing the bolt handle , watch for when and where it contacts , make sure it's smoothand lube it well .
The bolt lugs look OK , normal for a production savage . Make sure the action screw isn't binding on the bolt lug , that would be on the outer part of the right lug .
Yes I was referring to the base being square , which if even a little < .001 could make you resize the case by opening on a fired cartridge .
Gary

 

[Ggmac]

Ah , I reread you post concerning bolt lus . If you have a Borescope , I would investigate it . Clean well , dykem the lugs and check contact , keep an eye on that , it could be some grit scratches or a receiver imperfection .
Nothing to worry about yet , only if it continues to grow after cleaning .
I would cycle the action a couple hundred times , empty of course !
Ring die just resizes the base , you can take a Lee carbide 45 ACP die (resize, decaping )
And use . It doesn't touch any other part of the case

 

[Ggmac]

Before you get any further into this , I would ask a friend with a savage to let you shoot his , then compare . Nat Lambeth designed a bolt lift kit .
Sorry nat if I mis spelled your last name , old age just doesn't give me a break .
Gary

 

[StephenSF8]

Thank you for all the information Gary! You have given me plenty of leads to follow up on. I do not have a borescope at home, not sure if work does but I'll ask around. If it comes to it, I may remove the barrel and see if I can get a view of the lug recesses from the business end of the receiver. All that means is I'll be buying an action wrench, barrel wrench, and 6BR headspace gages a little sooner than expected

 

[Ggmac]

Good luck , keep me informed . If you need a ring die , I do the lathe work free . Just buy the die and send $7 for return shipping .
Gary

 

[StephenSF8]

The problem seems to have worked itself out. I removed the stock to lighten the trigger pull and check if the action screws were binding. I liberally greased the bolt lugs and cam surfaces, quite a bit more than I do for my Remington 700's. No more stiff bolt on firing, but I'll be keeping an eye on it.

In case anyone is thinking about getting this rifle, it shoots pretty well with Lapua factory ammo. Today I shot a fifteen shot 150-8X on a F-Class target reduced for 200 yards in a 5 mph wind with 10 mph gusts (a scan of the target is attached). The group was 2.025" wide (0.967 MOA), and 1.137" tall (0.543 MOA); the computer is telling me I can expect 1.1" drift in a 5 mph crosswind at 200 yards. So I would conclude this rifle/ammo combo is probably capable of 0.5 MOA at 200 yards, similar to the results here: http://bulletin.accurateshooter.com/2008/07/savage-6br-factory-rifle-delivers-superb-accuracy/

 

['Freak]

I disagree, as does Glen Zediker: "...Fired case neck dimension tells usually within 0.0010" (there's some contraction)." -Handloading for Competition by Glen D. Zediker, pg. 95. By this logic, the rifle chamber is likely somewhere around .271". I am not stating fact, only using logic (instead of a chamber cast) to determine the most likely culprit.

Zediker also states a bit earlier in that paragraph that 0.0030" clearance is necessary for a High Power rifle to function flawlessly, and 0.0020" may work if cases are sorted for uniformity. By this logic, loaded round neck OD should be around .268" for flawless functioning.

I am not looking to make a chamber cast, only for the most likely reason for the stiff bolt. I agree that brass and pressure are likely not the issue with factory Lapua ammo, hence the question about excessive neck wall thickness / loaded neck OD. If the issue is neck thickness, I can easily turn the neck diameter down a thou when I reload these cases...i just do not want to if I do not have to.

I personally have no experience with excessive neck thickness and am asking for the experience of others that do.

Thinkin' Mr. Zediker is talking about when shooting “High Power” competitions, not about ~ a [any] high power [powered] rifle. Good book...

 

[StephenSF8]

Thinkin' Mr. Zediker is talking about when shooting “High Power” competitions, not about ~ a [any] high power [powered] rifle. Good book...

You are correct, the entire book is about handloading for High Power competition, as opposed to Benchrest. Zediker makes the point many times throughout the book that High Power rifles must function with minimal fuss (my paraphrasing), whereas Benchrest shooters control every variable associated (chamber dimensions/high-dollar custom actions, case dimensions, everything) and can therefore use much tighter clearances.

 

[RonAKA]

This Savage is my first 6BR, and my first Savage for that matter. My normal sizing procedure is to bump the shoulder with a Redding body die, and then neck size with a Lee collet die. With the 6BR I plan to use a Redding S die to bump the shoulder and size the neck in one operation. I have never had function issues with handloaded ammo.

I have the Savage LRPV in 6BR. While not perfect it has shot quite well for me. I forget the numbers exactly but the neck diameter on mine does seem to be quite tight based on the old rule of thumb of subtracting 0.001" from the fired case values. I use Lapua brass but have never fired a factory loaded round of any kind in it. I would not suspect the Lapua ammo as the problem. Over pressure should not be a problem either with factory ammo. In any case I have never experienced a heavy lift, and I have handloaded to the full limits. I'm thinking it might be a factory chamber finish issue and perhaps it will work out. Polishing the chamber and neck without removing any significant material might help. I note your post that it appears to be getting better. It may improve when you reload your first firings.

On reloading procedures I will share my experience. I use the Forster Bushing Bump Die for resizing. I use the bushing that just sizes the neck down to the point where the expander ball just kisses the ID to round it out, and no more. Can't remember the bushing size, but if you are interested I will pull it out of my die to see what it is. I use the Forster die as a cartridge length gauge and target my resizing stroke just bump the shoulder 0.001" back. The neck bushing is positioned within the die to only resize about 2/3rds of the neck. I leave the back 1/3rd to keep the cartridge concentric in the chamber. The other feature of the Forster die is that you can adjust the position of the expander ball so that it is very high in the cartridge, and starts to expand the neck while the top of the neck is still in the sizing bushing. This helps to keep the neck concentric. With 5 firings on the cases there is no hint of needing any more than the shoulder bump and neck resize.

The Savage has not been without some issues though. I have a 12 twist barrel in mine, but it seems Savage chambered the throat to SAAMI specs for throat length to accommodate the longest bullets with a fast twist. So I am stuck with a 12 twist barrel that is maxed out with a 80 grain FB, and when I try to go much shorter in bullets for 100 yard groups, I run out of neck to seat the bullets. I still have been able to get some good groups with 68 grain Bergers. Three consecutive 3 shot groups below from my ladder testing. I still fight random flyers, and suspect the long throat with shorter bullets is part of it...

 

[StephenSF8]

Thank you for the tips Ron. If you get a chance, let me know what bushing sizes you are using. Since the loaded Lapua ammo neck outer diameters were measuring between 0.269" to 0.270", I was planning on getting 0.268", 0.267", and 0.266" bushings and seeing what works best.

I too seem to be fighting random fliers (is it flier, or flyer???)...attached is a 9-shot group at 100 yards with one high flyer that opened the group from 0.44" to 0.68". Frustrating, but I'll take it with a factory rifle shooting factory ammo.

 

[Shynloco]

... Frustrating, but I'll take it with a factory rifle shooting factory ammo.

That's fantastic considering it's "factory ammo." IMHO, the "flier" is the result of something inconsistent in the load that shot it. Not at all surprising when it comes to "factory ammo." Handloads won't do that unless the shooter makes a mistake, even in that "factory rifle" in the form of a Savage Model 12 Benchrest Rifle.

Alex