Forums - View Single Post - 6 Dasher: Case Forming & Load Development
Old 06-29-2021, 09:27 PM
Nontypical Buck
Nomercy448's Avatar
Join Date: Oct 2009
Location: Kansas
Posts: 3,821

I'll back track some photos of the hydroforming steps in another post in here soon - need to break out a little better camera than my cell phone to be able to discern the difference between shoulders, and some of the gear - BUT...

First, after complaining my way through 200pc of hydroforming and cursing myself for not having more than 11 spent small rifle primers in my entire inventory of fired brass, another local precision rifle competitor dropped me a gift of 250 spent primers on Sunday night, so I wouldn't have to cycle through the same 11 primers over and over, losing time in process. That picked up some processing speed for me - still tedious and a massive mess, but less obnoxious than batching through with only 11 primers at a time, decapping and recapping as a small batch. I primed all of my remaining 200pc and hammered through the hydroforming (literally) within a couple of hours.

*Reminding here that I had set my hydroform die long enough to produce brass too long to allow my bolt to close, such that sizing in the sizing die would push the shoulder back slightly and create a consistent shoulder across all of the brass, with more consistent shoulder angle and internal capacity after hydroforming.

Sizing Die Set Up: I use the "bolt close" method for determining headspace for shoulder bump to set my sizing die - I strip the firing pin assembly, extractor, and ejector, then progressively size the case shorter and shorter until the bolt will JUST close, then shorten the die another 1-2thou. I use Redding Type S Bushing Full Length Sizing dies, with 0.269" bushing and the expander removed - I chase my sizing die with a Sinclair mandrel expanding die with a 0.241" carbide expander, and with the dead soft Lapua brass, that leaves me 2thou neck tension.

Seating Die Set Up: To determine my seating depth, I use the "bolt open" method. For my precision competition ammunition, I use the L.E. Wilson Chamber Type Seating dies - I prefer the standard seating die body with the micrometer top - it ends up a few dollars cheaper than the micrometer body version of the Wilson die, and fits my hand better while cranking through the seating process. I replace the extractor into the bolt, but not ejector into the bolt, and seat the bullet long enough to assuredly jam into the lands. I progressively seat the bullet deeper and deeper until the bolt will close - once it closes, the "test" becomes feeling the primary extraction when OPENING the bolt. The jammed bullet will hang in the lands, so the extractor has to do a little work to unseat it. When at "kiss length," the slight "click" of the unseating will go away, but there will remain a slight dragging sensation. Another thousandth seated deeper, that entire sensation will go away... With the Berger 105 Hybrids, I start 5 thousandths off of the lands and leave my COAL alone as the throat erodes, so I shortened the COAL 5 thou from "kiss length," and the die was set.

For reference - in this case, as I do any time when processing larger volumes of brass, I set the dies up in my Lee Classic Turret to reduce my time wasted moving cases in and out of the press. Cranking through, I had a Lee Universal Decapping die in the #1 position to push out the spent primers used for hydroforming, the sizing die in the #2 position, and the mandrel expander in the #3 position - with the #4 position empty. Not as fast as processing on a Dillon, but far less expensive and still much faster than batching through on my Co-Ax.

With the Sizing and Seating dies set, the only thing left to work out is the powder. The 6 Dasher and Varget go together so well that they make peanut butter and jelly jealous, so it's just a matter of finding the node. UNFORTUNATELY, I also know my barrel needs to stretch its legs a bit before settling into a muzzle velocity - barrels tend to speed up as they foul in, and I needed to reach the end point sooner than later. So I loaded up 120 rounds of 29.5 grains, and set about breaking in the barrel. A relatively arbitrary choice, just a nice number which I knew wouldn't blow up my rifle. I hauled the rifle out to a local indoor 100yrd range near home, pulled my cheek piece, boresighted at 50yrds, fired one shot, dialed to place the bullet 0.2mils low, then cast the target back to 100yrds, dialed to point of aim, and burned out the hundred and twenty rounds.

For kicks, I plastered several target stickers on the page and hung my Magnetospeed V3 on the muzzle to be able to watch the velocity as it raised and stabilized through the burn in process... Here are a couple of the target spots, 5 shots each producing a 0.2X" and a 0.4X" group, and a 16 round velocity sample set offered a 6.2fps Standard deviation... Frankly, this arbitrary load I pulled out of a hat would be able to win any PRS or NRL match in the country...

Following this burn in process, I fired a triplicate test of 10 rounds each of 0.2grn increments from 29.5grn to 31.3grn. I cycle through these in sets of 10, firing one shot of each charge at its respective target spot, then let the barrel cool, and repeat 2 more times. In general, I tend to expect my groups will be sufficiently small for PRS competition if I follow the above procedure, so the main focus of this load development is to identify powder weight nodes where the the muzzle velocity remains stable despite purposeful changes in the powder weight. Reloading processes aren't perfect, so finding the powder weight node tells me where I can load without perfection and still deliver stable velocities - I call this "forgiveness" in the load. When a load is in a node, it'll "forgive" a little variability in charge weight, bearing surface length, neck tension, etc... and still deliver a reliable muzzle velocity, meaning one bullet will fly through gravity just as long as another, and offer the same drop at range as the other...

Since I have to shoot at "something," I use an array of target spots as my points of aim while firing over the Magnetospeed, pictured here. From top left to bottom right, these are 29.5 through 31.3grn in 0.2grn increments. The largest of these groups is 0.6X", so again, any of these are shooting small enough to win any PRS match in the country. What I can't say is relevant among these is any variation in group size, shape, or location. Shooting this test 5 times over, each individual test might look completely different. It's nice when the smallest groups align with the most stable velocity node, but only shooting 3 shot groups, the group size isn't a great indicator of load performance. The velocity stability, however, IS a great indicator of what my groups will look like down range, and what size of targets will be within my grasp on the clock at matches.

This is the real meat-and-potatoes of this test - the velocity curve. I'm looking for "flat spots" where shifts in powder charge have little to no influence on muzzle velocity. For this test in this barrel, a sweet little node revealed itself between 29.9 and 30.1grn. Convenient, as remembering 30.0grn as the center of my node is pretty easy...

Seeing this, I loaded 230 rounds at 30.0grn, 5 thou off of the lands, tested 10 for velocity (6fps standard deviation), and shot two 5 shot groups into .3x" and .4x" to confirm my zero, and took the remaining 210 rounds out to the Punisher Positional match at Severance Training Center in Conway Springs Kansas, a 2 day national level PRS match. I fired 20 stages over Saturday and Sunday, 308 to 940yrds on targets from ~3/4 to 3MOA, and didn't drop any of the points on the longest or smallest targets. Positional stability, recoil management, and slapping triggers are my enemies, and remained to be so - but the load precision and stability wasn't to be blamed for any of my dropped points. Bad trigger management and some rushed and unstable positions marked my first day - I shanked two stages on the first day and dropped 7 points each, and wobbled on two other stages where I dropped 4 points each, only shooting 69% on the first day. NOT the picture of consistency I wanted to be - needed to be. On the second day, I staved off my silliness much better and shot much more consistently - 84.7% on the day, only dropping 1-2 points on each stage and cleaning a few stages (no misses). Competition was extremely stiff, as this match was also an AG Cup Qualifying event, so my overall placing wasn't great. I did raise 11 places from the end of Day 1 to Day 2, and the ~10 extra points I dropped on the first day cost me 15 places!!! But the match was awesome, with a lot of unique opportunities to challenge our marksmanship skills, so it was a great weekend of shooting with great guys and gals either way!

Nomercy448 is offline