ExactShooting.com Custom Sizing Die – Experiment #1 Results

So we have initial results. I’d like to thank you all for the views on my video.

We will be testing this die set more over the next year. This is out of my pocket and out of my own curiosity. I have the credit card bills and had the arguments with my wife to show for it. I must caution, because of some things people seem to have in their heads, that this isn’t ever going to make a 1″ gun into a .5″ gun. Anyone suggesting such a thing is either a fool or a liar. What you should be expecting is to reduce variability in your ammo which reduces things like flyers & SD’s. Effects on group size, maybe small ones should be expected as a normal effect of better consistency but because barrel harmonics are involved there so heavily it’s best to keep your hopes in check and out of the land of silliness.

I set up a partially blinded experiment with unfired, 2x fired and >5x fired cases. We (Coach and I) sized up 50rds of each from my Exact die and 50 of each from Coach’s Redding die and tested that in Coach’s rifle. Coach’s rifle has somewhere over 1900rds down the pipe now which is a concern as you’ll see soon. We set the ammo up identically in everything from components to neck tension. We ran 10 shot groups which were composed of 2 non-consecutive 5-shot groups fired at the same aim point. Coach loaded, packed and labelled the ammo boxes (labels are “1” and “2”) and didn’t tell me till after the shooting was done which was which. I pulled the rounds from the boxes, logged data and called the target to engage while coach did the shooting. That way neither of us knew during shooting which ammo was being fired at any given time. That was the best way I could think of for me to pull out experimenter induced bias with a research team of 2.

The result of the first accuracy test was null. That is to say that the numbers difference in average group size was not outside the level of statistical noise. The exception was with brand new brass. It always shot more consistently than reloaded brass and so I removed those results from the full data set due to the noise they introduced. We also weren’t meant to be testing new brass as that would not apply anyway but I wanted that data for another experiment I’ve been running. This is all precisely what was expected. I expected no big result (but certainly hoped for one) in accuracy simply by going to full length resizing and having extremely consistent neck tension and headspace.

Because the result is null though, we’ll re-run the experiment on that rifle just before we replace the barrel, just to verify the results reproduce reliably. We also did some velocity testing as part of that and there was no statistical change in average velocities or SD’s except that in the new brass loads but it was more consistent set to set. Why pull the barrel? The rifle used for that run of the experiment now has ~1900 rounds through it in 6XC with a single load spec (38.5gr H4350, F210M, Norma brass, 115gr HBN coated DTAC). The load is mild; generating only 2800fps, but we know that that barrel is within a few hundred of being pulled on principle; if not actual need, as far as match work goes and it may not be capable of the repeatable accuracy that might show up with the Exact die. So, we’ll try another barrel. A new one. Actually, a new two! So stay tuned, there’s more to come.

In September I purchased 2x new barrels which I got as blanks from the same production run (from Black Hole Weapons). I purchased a new custom reamer in 6XC that produces a chamber that is very tight to the dimensions of the Exact die. Thankfully you can order a reamer with any number of customizations and it’s still the same price as a custom reamer with just 1 custom dimension. Unfortunately it takes weeks for such a reamer to be made. Over the winter I handed the whole works over to a gunsmith friend of mine that also makes ultra-precise gauges as a business. So, he has the equipment and skills to set up barrels that are truly as identical as we could make them and identical enough for a useful experiment to come out of it despite a sample size that’s extremely small.

Anyway, I got both barrels cut, profiled and chambered identically. It was at great cost too. The cost to set each one up was double what I normally pay him to set up a barrel for me for each barrel with over 15 hours of work on each one. These are our new match barrels for the next 2 seasons too. Coach and I will be shooting from the same ammo box so we can share data. Maybe we’ll pick up a few points on same-day wind calls.

We did have a non-null result and from a different direction, which I also predicted. That was that with loads that were sized with my ExactShooting.com die we never had trouble closing the bolt. It was, in fact, always exactly the same effort. On the cases that we sized on the Redding neck die that Coach uses bolt close effort was either not much or a TON. Some post-facto testing later on with coach’s FL die showed the same random bolt close effort. This is obviously due to random headspacing which means that Coach’s FL die probably needs a thou or two buzzed off the bottom. Irrelevant though because we’re testing what’s available out of the box and his FL die out of the box didn’t cut it so I suspect that a lot of FL dies out there may be a little long or short and aren’t sizing things like people think they are.

That is only the results from a well used barrel. We will be running this exact same test using the 2 newly set up barrels. One will be on the same gun (Coach’s match rifle) while its twin which now has just under 400 rounds on it is on a different my “Hot Dog Gun” match rifle. I don’t expect any difference but I could wind up being surprised. The new barrel on Hot Dog Gun is extremely accurate so far, better than Coach’s rifle on its first day. We’ve already developed a load for the new barrel that runs things a bit faster (2980fps) so hopefully with more pressure more differences might start to manifest.

One of the cool things about the ES die is you can pull the body/shoulder portion out and still use the neck sizing portion which itself is easily adjustable for neck tension and neck sizing depth. When you start getting hard bolt close you can dial in .0005″ or .001″ or .0015″ or whatever amount of push-back on the shoulder with an easy click adjustment and know it’ll give that to you exactly. We’ll be running a neck tension accuracy test here real soon. We’ll see if .0005″ increments makes real differences on paper. First though, I’m ordering some brand new brass for that test.

Cost is fairly high for these dies but not unprecedented. That’s true but, beside the point. If you have the money then that’s not an issue anyway. Functionality is THE issue. It’s perfectly functional and makes it super easy to dial in neck tension at .0005″ increments for those really finicky loads, to dial neck sizing depth at .020″ increments and to dial how far back you actually push your shoulders in .0005″ increments. They’ll make one to a reamer print too. How precise are the dies? Well I had my machinist do some gauging to see if they were that precise and he was pretty darned impressed.

For benchrest guys and F-class guys, I think this is really packing the potential to up their game a bit but only because those guys tend toward having done everything else already. BR and F-class are the only places I can think of of offhand where neck tension and headspacing are tightly controlled by the shooters both routinely and with an obsession rarely seen.

Is it going to help joe sixpack? Well no, to be honest. Joe doesn’t know enough to get the potential benefit to begin with. Owners of this die will 100% want to keep their brass sorted by number of firings. They’ll know about what spring back is and why it’s important to them and a lot more. They will be the type that can’t deal with unexpected 5’s instead of 0’s or 1’s in the 4th decimal place of a measurement. The right owner for this die is someone very much like me in the respect that they are prone to setting up narrowly defined experiments and to analyze the statistical data that results before forming opinions. They’re nerds.

For Coach and I the benefit is being able to share ammo and ballistics data in a match, not running out of time anymore on match stages due to bolt cycling problems, not overworking or insufficiently sizing the brass and being able to make subtle adjustments with truly minimal effort as precisely as adjusting a tactical rifle scope.

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