Kimber 84M Montana .308 Win hunting load development

[larueminati]

Very nice groups, some of the best i've seen from a Kimber. Nice work.

 

[MCMXI]

You give up some BC with the tangent ogive but you get seating depth flexibility for loading for short throat chambers and magazines.

But it should be noted that the Berger VLD bullets have a secant ogive and Berger suggests trying as much as .130" of bullet jump. These days I don't buy into the notion that any bullet has to be up close to the lands to shoot well.

 

[flyguyskt]

I shot the rifle first time today to break in the barrel with some 150 grn federal ammo. cheapest I could buy! Once I got scope somewhat dialed in, I shot 4 groups of 3. Scrubbed barrel after each group and All were sub MOA with best being around .5". Can't wait to dial in hand loads to what I think will be a sub 1/2 MOA 6# 3oz hunter!!

starting with nosler ballistic tip 150 grn, 46 grns Varget . 2.840, 2.830, 2.820, 2.810, 2.800

 

[MCMXI]

@flyguyskt ... looking forward to seeing your results. Do you have a chronograph?

 

[flyguyskt]

Yes. I will be checking loads with a chrono in order to build accurate ballistic Tables.

 

[Peakbagger46]

According to Barnes these are the optimal velocity "windows" for the .30 cal bullets. Going with a MV of 2,750 fps and the 1,800 fps minimum, the 165gr should be effective in terms of expansion from 0 to at least 550 yards which is about as far as I'd want to shoot an elk or deer with a .308 Win.

.30 cal 150gr TTSX 2,000 fps > 3,000 fps
.30 cal 165gr TTSX 1,800 fps > 3,000 fps
.30 cal 180gr TTSX 1,500 fps > not tested

About five years ago I loaded some 130g TTSX in reduced velocity (H4895 youth loads) for my wife’s .308. A call to Barnes assured me the velocity I was pushing the bullet at was more than enough for expansion.

I ended up using that load on a mulie doe at 80y, broadside shot (behind the shoulder) off shooting sticks. I recovered a small chunk of lung and virtually no blood trail. Spent hours attempting to track and perform grid searches in pinion/juniper and never recovered the deer.

I’m convinced that bullet completely failed to expand. Out of many kills, this was the only big game animal I’ve failed to recover.

The only other animal I’ve taken with Barnes was a doe at 80y with the standard 165g X with a full power .308 load at around 80y. This bullet (also behind the shoulder) failed to expand and the deer was put down with a second shot on the run.

Two bad experiences aren’t exactly scientific evidence, but they do offer some data. Perhaps the monolith bullets need to impact heavy bone to expand?

Outstanding load development with that lightweight though!

 

[flyguyskt]

With 46 grns varget and 150 grn nosler ballistic tip i'm getting an average of 2775fps. Best accuracy so far is at OAL. 2.793" , apprx .75MOA

 

[.3MOA]

@MCMXI 2 questions:

1. Barnes' recommendation from https://www.barnesbullets.com/wp-content/uploads/2017/07/308WinchesterForWeb.pdf
is that max for Varget is 44.5 gr (compressed) but you went a fair bit beyond that. Did you compensate for the shorter barrel ?
Is there info from Barnes I'm not aware of for shorter barrels ?

2. I just got some Lapua 308 brass and it comes consistently at 2.007". I think (and I may be wrong) that the SAAMI spec
is at 2.015" but I think you mentioned sizing Lapua brass down .002" to meet SAAMI. What am I missing ?

I'm new at reloading so I may be asking questions I should know the answer to ...

 

[MCMXI]

1. Barnes' recommendation ... is that max for Varget is 44.5 gr (compressed) but you went a fair bit beyond that. Did you compensate for the shorter barrel ?
Is there info from Barnes I'm not aware of for shorter barrels ?

The C.O.A.L listed by Barnes for the 165gr TTSX is 2.735" but I used 2.810" which is .075" longer so the pressure is reduced. Also, for the 84M, the bullet is way off the lands so lower pressure too. Barnes recommends at least .050" off the lands for their solid copper bullets to prevent a pressure spike as the bullet is engraved. The theory is that the bullet moves out of the case far enough to allow pressure to drop before it makes contact with the lands in the leade where the pressure can start to increase due to higher resistance.

2. I just got some Lapua 308 brass and it comes consistently at 2.007". I think (and I may be wrong) that the SAAMI spec
is at 2.015" but I think you mentioned sizing Lapua brass down .002" to meet SAAMI. What am I missing ?

I was referring to the location of the .400" datum (diameter) on the shoulder and not the overall case length. Trim length for .308 Win brass is 2.005". SAAMI lists the case length as 2.015"-.020" but most reloading manuals suggest a nominal dimension of 2.005" which makes a lot of sense.

 

[.3MOA]

The C.O.A.L listed by Barnes for the 165gr TTSX is 2.735" but I used 2.810" which is .075" longer so the pressure is reduced. Also, for the 84M, the bullet is way off the lands so lower pressure too. Barnes recommends at least .050" off the lands for their solid copper bullets to prevent a pressure spike as the bullet is engraved. The theory is that the bullet moves out of the case far enough to allow pressure to drop before it makes contact with the lands in the leade where the pressure can start to increase due to higher resistance.



I was referring to the location of the .400" datum (diameter) on the shoulder and not the overall case length. Trim length for .308 Win brass is 2.005". SAAMI lists the case length as 2.015"-.020" but most reloading manuals suggest a nominal dimension of 2.005" which makes a lot of sense.

Got it thanks !

Follow-up question:

1. My rifle's maximum COAL for Barnes bullet + Lapua brass (bullet on lands) is 2.946" +-.0005".

At 2.810" COAL I'd be 0.136" off the lands which is a little over maximum distance (minimum COAL) recommended
by the specialist at Berger, Eric Stecker you quoted somewhere regarding the 24-round optimum COAL determination
experiment.

For this particular rifle / bullet combination I'm guessing the suggested range should be shifted by Barnes' minimum
off-the lands recommendation of 0.05 + 0.01 for safety margin.

What do you think about (for hunting):

1. .060 off the lands (jump) 6 rounds
2. .100 off the lands (jump) 6 rounds
3. .140 off the lands (jump) 6 rounds
4. .180 off the lands (jump) 6 rounds


2. For the 0.002" case resizing, do you use a full length sizing die or a bushing die ?

Thanks !

 

[MCMXI]

@.3MOA, the 84M box length is around 2.835" so I don't see how you'd be able to get to .060" or .100" off the lands unless you single load without using the magazine. Based on your 2.946" measurement, with a C.O.A.L. of 2.830" you'd be .116" off the lands. Using Barnes' C.O.A.L. of 2.735" you'd be .211" off the lands. So you could shoot three loads with the following C.O.A.Ls. I didn't play with the C.O.A.L at all and chose 2.810" based on the location of the annular grooves in the bullet. You don't have to line up the case mouth with a groove though.

2.826" > .120" off
2.786" > .160" off
2.746" > .200" off

For the 0.002" case resizing, do you use a full length sizing die or a bushing die ?

I use a Redding neck sizing die followed by a Redding shoulder bump die. I'm not claiming that my method is any better than anyone else's. I just stick with what has proven to work for me. I'm trying to control shoulder location and neck tension while keeping the runout of the cartridge to a minimum.