The purpose of this project was to:
1) Use a 7mm 9twist, fluted Shilen SS Select match heavy barrel with muzzle brake
on a switch barrel Savage action. Show that this system and a properly machined barrel can provide match accuracy.
2) Use up my stash of '06 brass.
3) Create a wildcat that does not need custom dies, nor reamer (the 280AI reamer that many gunsmiths have will work. Either 35 or 40deg shoulder is fine).
4) Reach standard 7RM/WSM/RSAUM performance in a 24" barrel and use less powder to do that. Bullet of choice would be the 162gr Amax as I want this to be my 1000m 10lbs class rifle. So target velocity would be 2950fps or faster without excessive pressure.
5) Prove that matching a powder to case volume/bore/bullet is what determines so call 'effeciencies', not case shape. Pressures would be held to conventional pressure signs NOT '06 SAAMI limits.
6) Long skinny rds can be every bit as accurate LR as short fat ones. This means bug holes at 100yds and sub MOA out to 1000m. I like the new tech but get frustrated by all the misguided hype.
7) Freebore isn't as bad as I had originally thought.
In short, the 7 Mystic is my version of the 280AI and its many variations. The whole project started because of my two 7RM's. Shooting them has been an absolute joy using 162gr Amax. I wanted to build a smaller case for less recoil in the light class usually shot at the Osoyoos 1000m fun shoots.
The '06 case was the parent case as I have a bunch of brass and this would mean all I needed was to neck down to form the secondary shoulder needed for fireforming. From the many number of 280AI type wildcats, I knew the case capacity and performance would be an ideal match.
Reg. '06 brass is run through a 7RM FL sizer and it forms a perfect second shoulder. One step and ready to fireform. Cases were fireformed using the Cream of Wheat method. All further sizing is done in a Lee Collet 7RM neck die. Seating done in a 7RM seating die (really does work well). So all you need is a Lee Delux die set ($45) and you are ready to load ammo.
I did trim slightly and neck turn enough to take a hair off at least 50% of the neck circumferance. Just cleans things up.
The barrel was sent to Dennis Sorenson with some necked down brass to use as headspace guages. The barrel returned in a very short time with BR quality machining and fit. Believe me, the thread fit on action and barrel nut is interference tight (you need light pressure using the nut wrench to screw on, hand assembly isn't easy - perfect). Set up for zero headspace for a rock solid lock up. These Savage actions are the only commercial actions I have played with that don't really need the lugs lapped to lock up very well. Maybe it's that floating bolt head.
From shooting lots of similar cartridges in different calibres, I knew that H4350 or H4831SC would be the ideal powders. I put in Fed 210M primers to handle the ignition chores and H4350 for the first powder. I have found the Feds to work very well but show pressure signs 'faster' then the CCI BR2 primers. This would keep me from going to hot too fast.
With my chrony, I shot two rds starting at 54gr. Way too low (2750fps). Jumped up to 56gr for a bit more velocity (2830fps) and a 1/2" group. Up to 57.5grs and 2934/2942 fps and a bit under 1". Cases still extracted easily and showed no pressure signs. I knew I was getting close.
The next load at 58gr cut one hole and 2949/2960fps. Voila!! Still no excessive pressure signs but primers are starting to flatten meaning I am in magnum pressure territory.
At 58.5gr, obvious pressures signs showed. Velocity was 2949/2971fps and groups opened up a bit to 1/4". For the 7C ambient temp, this was as high as I will go. Will back down a bit more during the spring/summer or as tuning requires.
All design goals met so far. Now to come back another day and confirm.
The next time the weather was much colder (a few degs below zero). 58gr showed 2951/2925/2932/2917fps. A bit off and groups around 1/2". Going up to 58.5gr was 2951/2960/2947fps and back to big bughole group. Going to 59gr reached 3000fps but groups opened right up to 2" and we be toasty.
Seems 2950fps avg and magnum pressures is where this combo likes to be.
This barrel shoots its best just below 'excessive' pressure signs which is ideal in my books.
I switched to H4831SC but velocity never exceeded 2850fps before groups opened up (60grs of powder). Accuracy was also very good around the 2800fps mark. Again, showing how critical powder choice can be in obtaining max performance.
In this rifles case, the perfect powder would be H4350 and a half. H4350 is just a hair fast (quite peaky too) and H4831SC too slow. Maybe Re19/22 would be ideal???? Maybe a different primer??? I can go to 60grs of some powder so maybe there is a bit more velocity and/or give me a wider sweet spot. Either way, the 7 Mystic is working to design goals.
More shooting will follow to again verify my results and shooting at longer distances will start once the snow melts and temps go up. Pretty hard to get great groups when your fingers are a bit numb. Barrels don't get hot though.
If you are wondering why I shoot two rd groups when testing, it is because I am very confident in how I shoot and the consistency of my ammo. So unless I screw up, a load that shoots 1" is never going to improve. Conversely, cutting two or more rds in one hole is rarely a fluke, especially if you repeat a few times. I don't feel the need to drive many bullets into tiny groups to prove a load or cartridge. I prefer that barrel wear be spent shooting LR targets.
At 58gr, I am using less powder then either the 7WSM and RSAUM to get the same performance. The 7Mystic shatters performance limits and is the shape of all hot rod cartridges to come. Three colour glossy ad with dead really big animal. Zip, Zam, Blam, POW, and other marketing splashes...
Have I just discovered the 'magic' bullet...??????? The next great cartridge evolution????? :eek:
All I have done is my homework and matched components for best effect. In fact, the case volume of my Mystic is within spitting distance of the RSAUM (so is the load data which I graciously used to work up from). At magnum pressures, performance is within the difference found in rifles of the same cartridge.
This performance is nothing new for 280AI and wildcats in a smooth barrel.
So long skinny or short fat makes precious little difference, especially in a hunting rig. Choose whatever makes you warm and fuzzy.
Of course, there are ideal case designs for very specific short range competive shooting. For 1000yd/m shooting, I am guessing that 10fps spreads and groups in the 1's at 100yds bode well for this cartridge and barrel performance.
The reason for point 7) was that in the chamber cutting stage, Dennis highlighted that the 280AI reamer he was using would move the throat about .150" ahead of 'ideal' (actually 0.115" in the rifle). Quite a bit of freebore but the bullet would still be fully supported by the neck as it engraved.
I have always loaded my match bullets as close to the lands as possible and was quite nervous that this wouldn't work. But hey, in the quest of knowledge - full speed ahead.
If it failed, I would seat the bullets out further. Right now they are seated to fit in the mag (I use the same seating die setting for three rifles with equal success - go figure). If that failed, I would just set back the barrel again and use a standard 280AI case.
The freebore has provided me with the big benefit of running faster velocities without excessive pressures. The same thing Mr. WBY pioneered all those years ago.
The key then for accuracy isn't the closeness of the bullet to the lands (at least with this very long bullet) but that the bullet engraves TRUE with the bore before it leaves the case neck. Using fireformed brass sized in the Lee die produces ammo with very little runout.
A short throat or jamming into the lands would be very helpful if high runout ammo or certain VLD bullets were used (bullets will have their own preference so test accordingly).
Having a chamber cut true with the bore doesn't hurt either. Great work Dennis.
The 7 Mystic project has been a success and met all my 7 goals. I hope this will inspire you to start reloading with a different view and maybe even help you into the wonderful world of wildcats.
There are no free lunches but it is nice to know where they give you an extra big serving of the good stuff.
From Left to Right: Orig '06 case, necked down ready for fireforming, fireformed, Amax seated, Amax for bullet length reference.