PPV And 308 Winchester Revisited

[kilotanker22]

CAUTION: The following post (or a page linked to) includes or discusses loading data not covered by currently published sources of tested data for this cartridge (QuickLOAD or Gordon's Reloading Tool data is not professionally tested). USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.




Awhile back I tested Power Pro Varmint in my 308 with 168 grain ELD Match bullets. I was using Lapua Palma brass and the small primers were just not igniting the powder fully. Plus I had a bad pound of powder. Fast forward a few months with warmer weather and I decided to revisit this powder bullet combo. I got some Lapua large primer brass and some CCI #34 primers. Using the same load as last time, 44 grains PPV, 168 grain ELD MAtch.

My results were much better this time. This is from a 20" Savage 10 GRS, using a Leupold VX5 HD 3-15x scope. The velocity data was from a seven shot string as I didn't want to load too many of these. This is also with Virgin brass. After setting the powder measure for the weight, none of these were weighed. They were dropped with the RCBS Uniflow. Of the seven shots, two were used to zero the scope as this load shot to a significantly different point of impact from the ball ammo I have been shooting. The last five were the group I shot after getting my zero close to point of aim. The photo attached contains those five shots fired from 100 yards with a bipod and rear bag.

168 ELD, 44 grains PPV

Avg 2598
SD 5.2
ES 14

Needless to say, but I was impressed with those results. I decided to try some hunting ammo I have loaded for another 308 rifle. I was stunned to see the velocity I got from this barrel with the following load. Lapua Palma brass, CCI #450 primer, 45.7 grains Varget, 168 ELD

Avg 2704
SD 7.4
ES 26.

Group wasnt the best, but my muzzle brake loosened up and I did not have the tools to tighten it, and I was out of ammo. I will revisit this load again in this rifle for sure. 2700 fps in a 20" 308 with a 168 is cooking along pretty fast. SO far I am very impressed with this gun.

 

[Unclenick]

Congratulations on finding a promising combination. You might want to send that to Alliant with the suggestion they consider listing PPV data.

From your Varget data, assuming your chronograph is behaving itself, it looks like your barrel and chamber and brass combination are fast, but it could also be explained by powder lot burn rate and the following differences: As compared to Hodgdon data, your bullet is a little longer, so if you use the same COL, you will be taking up more space in the case. Your Lapua cases already have a couple of grains less water capacity than the Winchester brass they used. Taken together, you are starting with less combustion volume, which raises pressure and velocity. Plus, I don't know how your small rifle magnum primer's performance compares with their large rifle standard primer, but all the differences could contribute to running at a higher pressure than book values.

What would be useful for you to do is buy one box of Federal GM308M with the 168-grain Sierra, and see how your velocity compares to what is on the box. The conditions under which the velocity on the box was determined were to condition the ammunition at between 60-80°F. The gun will start out at this temperature, too, so if you keep the ammo at home for a day and drive to the range when it is close to 70°F, you probably won't have to do anything else about conditioning. The chronograph will be optical and will have its center between screens at 15 feet from the muzzle. The bullets are handled to keep powder over the primer. The GM308M I've had in the past had slightly compressed powder so handling the case to keep powder over the primer was not necessary. But suppliers change over time, so shake one round or pull the bullet on one to see if that is still so. If not, use the SAAMI handling method. This involves keeping the rounds upright in their tray or ammo box on the bench. When you pick one up to fire, you rotate it slowly in the vertical plane, pausing when the bullet is nose down, then finish the rotation up and pause again with the bullet up. You then insert the round in the gun slowly and keep the nose up as much as possible until it is horizontal in the chamber to minimize disturbing the powder position. You slowly place it in the chamber all the way with your fingers. You then close the action gently so as not to disturb the powder. I have found turning the gun sideways or even almost upside down lets me keep the bullet tip up as much as possible during inserting the round. My range does not allow loaded muzzles to elevate above the target berm. If yours does, it is easier just to load slowly with the muzzle angled up and then bring the gun slowly to horizontal to shoot. The universal receivers used in the SAAMI procedure commercially are heavy and fixed horizontally, so that isn't possible for their procedure.

Conventional wisdom (and QuickLOAD) say you should be 100 fps slower (QL says 102 fps) with a 20" tube if your chamber and bore dimensions match the Federal P&V barrel. They rate the ammunition at 2650 fps, so your expectation is 2548 fps, and if you come in faster than that, it confirms your gun runs higher pressures than typical. QL can be used to estimate how much higher and what percent of commercial loads will give you a pressure match.

You can check a chronograph with about any bolt action rifle chambered in 22 LR using a box of Match ammunition to see how the readings compare to what is on the box with the ammo similarly conditioned and the powder at the back of the case. This generally works pretty well because the 22 Rimfire burns its powder completely in any barrel of 20 inches or more, and even an 18" barrel is enough with many brands of ammo. The result is very little velocity change during coasting past the burn-up point. However, 24" is the standard test barrel length if you want to stick with that.

 

[kilotanker22]

Unclenick, I am loading them to 2.850", so .050" longer than Hodgdon. The 45.7 grain charge and eld seated to this length is a slightly compressed load. I chose this length for no other reason than fitting the magazine. These cartridges are about .040" from contact with the lands. The load might not even be compressed, but there is so little room in the case that I cannot hear powder moving when shaking one.

I intend to try this same load again. I shot all of it I had made yesterday, but after seeing the chronograph results, I definitely want to work on this more. The choice to use PPV originally stemmed from not being able to get Varget and I have plenty of PPV on hand. I am not showing flattened primers, no cratering, no ejector marks on the Varget load or the PPV load. I am going to try the Varget load with the CCI#34 primer and virgin cases. Then see if the pockets loosen up after the first shot or two. I do realize that higher pressure is harder to spot on small primer cases.

I will share my results with Alliant, this seems like an excellent powder for 308 WIn.

 

[kilotanker22]

Also, with my Hornady comparator headspace on new cases measures 1.620". Fire formed cases measure 1.621". Partially sized cases with the shoulder moved forward to 1.622" offers some resistance on closing the bolt. 1.623" gives significant resistance. I am bumping the shoulder back to 1.620".