308>> 155 gr+Varget Befuddlement

rimfiremac

rimfiremac

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I've been trying to find a Varget/ SMK load for my rifle, and have run into a very confusing dilemma.

As stated in the Lee manual, the starting load for 155 gr weight with Varget is 44.0 gr, and the DNE load is 47.0 gr.

I'm running Federal brass, Federal Large Rifle Magnum primers, and 155 gr Sierra Matchkings with Varget, as stated. OAL is 2.81". Loadings are by Lee Classic Loader and brass is hand polished and prepped. Rifle is a 1975 Winchester Model 70.

Here's the dilemma... I took a batch out today with loadings: 44.4gr, 44.6gr, 44.8gr and 45.0 gr. Brass was on its 4th firing with limited to no signs of excess fatigue- all previous firings were in the 44-45gr range-
The oddity occurred right off the bat, when I noticed cratered primers on my 44.4gr load. Craters are uniform and smooth around and stand about the thickness of a piece of notebook paper high. Traces of blow by were obvious at the neck, but not to an extent more severe than that seen in factory loadings. Excessive bulging near the case head was not evident- about one in three cases have a ridge that is barely discernible by fingernail near the case head- barely. Primers are flattened and embossed, however maintain a radius minutely smaller than that on the interior wall of the primer pocket. Recoil and report were normal, or at least never unexpected in impulse.

Just for comparison, I ran a couple 155 A-max's at 44.3 gr with the same results. Shot great, but popped out with cratered primers.

One detail to note is that the bolt was not 'smooth' on closing for some rounds. It did not need to be 'forced' down, but it took enough pressure to get the mind going- will such a situation occur with brass that has been fired a few times from the same rifle and only neck resized? I only shoot one 308, so all brass is fire formed from the last firing.

Anybody care to offer their judgment on the situation?
 
Federal brass would be my very last resort. The reason the bolt is hard to close is because you neck sized. Even in my match chambers I find after about 4 loadings I need to full length resize just to bump the shoulder back a couple thou. You also do not need magnum primers for a .308 with Varget.

If you ask 50 Target Rifle shooter that use Varget and 155's likely most of them will tell you to go with 46.0 gr.
 
The first thing I would change is the primer..don't understand why you would use a magnum primer in the 308? And the mag primers can certainly increase pressure. I use CCR BR-2's because they have a good reputation for handling pressure because the cups are reputedly harder.
I use Fed GM brass and have compared it with Win and Lapua brass.. to find it is much thicker, so will have a bit less capacity. This can also elevate pressures.
 
+1 on the magnum primer possibly being the issue.

I use CCI BR-2's or CCI 200 Large Rifle under 45.0gn Varget with my 165gn Sierra GameKings and it's well below a max load with 2.710" COAL. A bit short, I know, but it's for hunting ammo and the extra jump doesn't affect my accuracy one (detectable) bit.

Hotter fire, higher peak pressures - switch 'em back to a standard LR primer and see what happens.

-M
 
Thanks all-

I'll switch to Win brass and LR primer's and see what happens.

A quick followup out of interest- if I load test with SMK's in 155 gr, and find a suitable node wrt powder charge, will that charge be a reasonable starting point to locate a common node charge for a 155 gr A-max, for example? I can see differences in contact area of the two bullets having *an* effect (the A-max has a distinct corner transitioning from the ogive to the body whereas the SMK does not), but can't wrap my head around a minuscule change in surface area causing a noticible change in performance, all other details constant.
 
Rimfire

Every bullet has different characteristics in its make up. Rarely can you do a straight bullet switch on a given load with out testing. FS
 
I wouldn't give up on the Fed brass so quickly...as I mentioned, I use Fed Gold Medal (yellow) brass .....after it has been (once) fired by the local Tactical Squad. It is good brass and shoots with reasonable consistency. After the initial resize, I neck size only...trim after about 6 firings..and discard it after I have fired it 12 times. Never had one with a split neck. With the Fed nickel plated stuff, I have seen neck splits after 12 firings so I never go more than 10. I am not a bench shooter, but none of my 308 sporter bolt guns average over 3/4 MOA using Fed brass.
 
rimfiremac said:
Thanks all-

I'll switch to Win brass and LR primer's and see what happens.

A quick followup out of interest- if I load test with SMK's in 155 gr, and find a suitable node wrt powder charge, will that charge be a reasonable starting point to locate a common node charge for a 155 gr A-max, for example? I can see differences in contact area of the two bullets having *an* effect (the A-max has a distinct corner transitioning from the ogive to the body whereas the SMK does not), but can't wrap my head around a minuscule change in surface area causing a noticible change in performance, all other details constant.
Click to expand...

I switch out 155's all the time without a problem with the same load of 46 gr of Varget. Berger's, Nosler's, Laupa's, SMK and AMax. The only thing different is the seating depth.
 
While the mag. primers may be an issue, is it possible that the primer cratering is resulting from the fit of the firing pin and the hole?
 
I switched from SMK's (2155, not the newer 2156) to Amax 155's because I didn't like the ragged meplats on the SMK's, and the Amax's are slightly cheaper. I also use CCI BR2's and Varget (47gr), and I splurged on Lapua brass.
I seat the Amax 10 thou off the lands.
 
tiriaq said:
While the mag. primers may be an issue, is it possible that the primer cratering is resulting from the fit of the firing pin and the hole?
Click to expand...

This is a potential I considered... whether it is the case or not does not mitigate the concern, however :p I have read that if the firing pin clearance hole is loosely toleranced, then some flow back is possible into the hole.

I'll try switching primers to begin with... verify whether primer brand and material has anything effect, and then try to work my way to 46gr. From a trajectory analysis, I'm seeing a seven to eight inch drop from 100 to 200 yards, indicating velocity is on the low side, resulting from low pressures, but those pesky cratered primers have me spooked.
 
And a followup to the brass... I trim with a Lee trimmer and case length gauge every other firing- so if anything is stretching, it's the case itself. Note that with my current Lee Classic technology, I only neck size.
 
Just working up a load for my most recent project for which I used a 308 reamer with a .340 neck and .060 freebore...22" #5 contour barrel is a 1:12 twist. I have tried only 150SMKs pushed by Varget ...seems to like 45.5gr of Varget. Zeroed @ 200M, POI is 3.25" high @ 100M.
 
Alrighty... so I gave it a try again with Fed brass (3x fired) and CCI LR primers. As a datum, I fired the occasional Federal Crappy Tire 150gr round to see if I could discern any noticeable change in recoil.

Again the recipe is: 155gr Amax, Varget, CCI LR primer, Fed 3x fired brass.

Cratering was still present but not to the extent as loaded with a LRM primer.

For observation:

Federal factory load:
Jan20004.jpg


45 gr Varget:
Jan20005.jpg


45.5gr Varget:
Jan20006.jpg


45.7gr Varget:
Jan20007.jpg


And 46.0 gf Varget:
Jan20009.jpg


And for a final conundrum, the results of 46 gr Varget at 200 yards:
Jan20011.jpg


I think I'm going to quit reloading and take up sailing. My experience so far can be summarized::nest:
 
The low shot could be pilot error and the one out on the left might be wind but it is still a good group for 200 yards. It is less than .75 MOA. Your primer looks a little flat around the edge with the 46 gr load but not enough to worry about. Now start playin with your seating depth to see if the can get an even tighter group. In my rifle 155 A Max shoot best .020" off the lands.
 
Good call on both-

Both were pilot error... on both occasions I began to think about backing off and taking another breath before the shot when the trigger broke.

My sincere thanks to all for the input.
 
If you want to shoot bullets in the 150-150gr range, you might want to try the 150SMK's again. Both the 155 SMK's and A-Max's have a "long" point and may sit further out from the lands than the more rounded point on the 150SMK if you are loading an OAL length of 2.81"
 
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