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Lapua Palma .308 and 8208 XBR primer test

This was posted in another thread in response to a member's question but I thought that other folks might be interested, so posted it here.

I went to the range Friday and, among other things, shot a 100-round series in my Borden/Eliseo RTM. The series comprised 100 Lapua Palma cases loaded with 44.0 8208 XBR, Berger 155.5 BT-FB seated 2.867, just touching. The barrel is a 31" Bartlein 10" twist MTU with a PT&G Palma chamber. I used a Nightforce 12-42 BR for this test with the forend and rear bag riders attached, running in a Farley Co-Ax and Edgewood Minigater. Brass prep consisted of running all cases through the Sinclair expander die with a neck-turning expander. That provided ~.0025 tension. Case mouths were lightly deburred. 20 each cases were primed with Rem 7½, Wolf KVB-5.56M, Fed 205M, CCI 450 and CCI BR4. QuickLOAD predicted 2884 fps.

This rifle is a pain for me on bags. It handles really well prone with irons but I just cannot get a groove with it on the bench. It is very muzzle-heavy and does not ride bags well. My best results come from grabbing it very hard and pushing the butt down into the rear bag and back into my shoulder. It would not have been a pleasant day if I did this for all 100 rounds. So, I made a full effort on at least one group per primer and the rest somewhat less so. The best groups for each set were:

Rem 7½ .334
Wolf KVB-5.56M .246
Fed 205M .290
CCI 450 .297
CCI BR4 .345

I would not take any of these as definitive, it was a long day and I did not clean the barrel until afterward. It was, by the way, remarkably easy to clean and had almost no copper. Gotta love those Bartleins. Also possibly affecting my result was a group of 25 Russian exchange students shooting next to me. No, I am not kidding. They were all college kids and very enthusiastic. They fired a number of rifles, among which was a semi-auto AKM. Call me old-fashioned but I was always taught that giving a loaded AK to a Russian is a bad idea. ;) The kids really behaved well, seemed to have a great time and some actually hit the targets regularly. Their presence did not help my concentration, however.

The attached text file lists each 5-shot group for velocity statistics. A summary is at the bottom. Several interesting results emerged. The missing chrono items were caused by me. I unplug the unit to conserve battery power when idle and stupidly did not plug in before restarting. Maybe I can blame that on the Russians. ;)

1. The velocities were remarkably consistent and ES/SD better than LR primers and the same load.
2. Even though it was only a few fps difference, the CCI 450 gave the lowest mean velocity. That could easily change with more rounds fired. This is a small sample.
3. CCI BR4 primers gave an extreme spread of 13.8 fps for 20 rounds with SD of 3.8! I have never seen a result that low on this size sample.
4, Accuracy was very good with all primers, better overall than any LR I have tried with this combo.
5. I will be using Lapua Palma brass in this rifle, henceforth.
 

Attachments

Thanks for the detailed info!

My current Palma rifle is a 30" Broughton 5C 1:11 fitted to my Gilkes-Ross action (bought mid- 2005) by Mike Ross.

The 2156C Sierra's I'm shooting this year just touch the lands in the "chamber proxy gauge" (made from the barrel blank cut-off when the barrel was fitted) @ 2.9180" while the Berger 155.5 BT-FB I have touch @ 2.9710".

Only used 205M primers in my first batch of Lapua Palma brass, never shot 'em over a chrony, but the same bullet + load + Lapua 308 brass with KVB-7 primers gave 2960-2975 fps last year @ 50°.

Your 44.0 grain 8028XBR load will serve me well as a benchmark when I get around to doing further testing / shooting later this season.
 
The same load with LR primers produced the following, same rifle.

CCI BR2 2949 avg
Fed 210M 2928 avg

The SR primers produced from 40-60 fps less velocity but much better ES/SD and better accuracy.
 
I've never shot off a rest at anything farther than 100 yards. My 'informal' testing with the SR vs LR Lapua Palma/308 brass was done with a sling & match sights in competition at 800 - 1,000 yards.

On paper, I couldn't tell the difference between the two cartridges: both held waterline 10-ring elevation.

In view of your velocity delta, I'm motivated to try and get a chrono in front of my muzzle soon for a day of more closely monitored testing. I doubt there'd be a difference in how Varget vs 8028 XBR reacts to LR vs SR primers but I won't know for certain until I get back onto a shooting range.

I do strive for a bit less neck tension - .001" - .0015" - these days.

I'll probably try both propellants, just to add another set of data points under the same conditions to the mix.
 
A point worth noting is that the unturned necks were expanded and not sized. The seating force felt very uniform. I may try sizing with a bushing that will allow ~.001 neck expansion when using the mandrel. I do not use expander balls because of the non-uniform way they expand the neck but the Sinclair mandrel is a straight cylinder and probably produces better results. I may also try the carbide turning mandrel which is slightly larger than the expander.

If the necks are turned well, this approach is moot. When neck walls have some variation, expansion might produce better uniformity.
 
I agree with regard to expander balls vs. Sinclair's tools. I make it a practice to run all new cases over an appropriate Sinclair E-size mandrel before any further operations. If nothing else it irons out the little kinks necks seem to incur between being packed at the factory and being unpacked at my reloading bench.

Your carbide turning mandrel (Sinclair?) is larger than the expander? I'd have thought just the reverse to be true; an expander is the larger to account for brass spring-back, while a turning mandrel is smaller so that friction is reduced.
 
Have either of you tried Redding's floating carbide expander ball? As far as I can tell, it seems to cure/eliminate about 99% of the perceived ills associated with traditional expander plugs...
 
spclark said:
Your carbide turning mandrel (Sinclair?) is larger than the expander? I'd have thought just the reverse to be true; an expander is the larger to account for brass spring-back, while a turning mandrel is smaller so that friction is reduced.

The expander I used is not stock. I polished this one to .3055. The stock expander is .3068 and the carbide is .3060.

memilanuk said:
Have either of you tried Redding's floating carbide expander ball? As far as I can tell, it seems to cure/eliminate about 99% of the perceived ills associated with traditional expander plugs...

Monte, I have not tried Redding's offering. I had the Sinclair stuff for neck turning and never bothered to look elsewhere. The cylindrical expander still appeals to me in forcing the neck ID to one concentric diameter. I have a Neco gauge unit, sounds like some experiments are in order.
 

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