Since posting about my 6.5 Mystic in another post, there has been a number who have requested info and specs. Here it is:
The purpose of the design was to make a 1000yd BR cartridge that used a readily available, accurate, strong and cheap brass. Had to allow for near or 100% load density. Enough neck length for proper neck tension. Sufficient velocity to make it effective at 1000yd/m. Of course, be accurate, low in recoil, give relatively long barrel life, feed from mag in case of rapid fire requirements, use ballistically superior bullets, easy to get dies and components.
I studied the 6.5-284, an excellent cartridge in its own right, and found that max velocity was not often the most accurate, throat wear was considered high, recoil moderate but still a little on the high side, case rarely if ever full (this is a personal opinion. I like full cases of powder), components were a bit pricey. BUT it shoots very well. Most seem to launch 140/142gr match bullets around 3000fps.
What to do? For me, the answer was to make a slightly smaller case and basing that case on readily available brass. That lead to the use of the 308 Win case.
This is an improved wildcat where the shoulder is moved as far forward as possible and still leave a calibre long neck. Shoulder angle is 35 degs. Throat is extended to allow 140/142gr match bullets to seat well out to reduce case intrusion. If you look at the picture, you will see the comparision with the parent 308 case.
This case will not fit in a short action mag. A medium length action ie 7X57 mauser length is ideal. Of course, a standard length '06 action would also work just fine. Push feed actions are prefered as the sharp shoulder will not work in some controlled feed actions.
Of course, this is moot in most BR single shot actions.
Prep of this brass is very easy. First 308 win brass is sized at 30 cal and neck turned to 12 thou. The brass is then run through a 7mm neck sizing die to form the secondary shoulder. Location is such that when chambered, the bolt requires firm pressure to close. Cases are then fireformed using the cream of wheat method and out pops a case with a shoulder 90% formed. The first high pressure load finishes the job. I have yet to loose a case using this forming method.
I did my testing in a 25" aftermarket barrel, a bit short but was cheap. Velocites reached 2800fps but accurate vel for that barrel was around 2750fps. In a 28 to 30" match barrel, reaching 2850 to 2900fps should be no issue.
The slight difference in velocity isn't going to amount to that much more wind drift in the real world. Something I was willing to live with.
The rifle proved very easy to load for and accurate. A full, ever so slightly compressed load of H4831SC, gave the best results when lit with either Fed 210M or CCI BR2 primers. I used Fed Gold Medal brass which has a smaller capacity then Winchester. I was able to use 48gr of my lot of H4831SC and would expect up to 49gr using Win brass in this rifle.
The bullets are seated way out. In the picture, the bullet used is the then new 140gr SST which measures a very long 1.40". The boattail sits right at the shoulder/case juction leaving the whole case neck to hold on to the bullet. Perfect. The chamber throated so that the bullet was just off the lands. That could be adjusted to suit your style of land engagement.
At 200m, groups were 5rds in 1/2" or less. I am no BR shooter and this was no BR rifle, but was still very happy with the results. A match rifle/shooter would probably do much better. I did shoot several groups which were one hole. I believe the shooter was the weak link here. :lol:
So the design has met all my criteria for function and performance. Using approx 3/4 the powder of the 6.5-284 will help extend throat life and of course, reduce recoil. Case life is great and trimming not really needed when using the collet die.
Some testing the 6.5 WSSM improved case are using the same amount of powder to get the same velocity. For me, I trust that I can always get 308Win brass. Not so sure about the WSSM.
The best part is that custom dies do not need to be used for this wildcat. I use Lee Collet neck die in 260Rem with a shim (metal washer actually). Works perfectly. I seat bullets using the 260 bullet seater with no problems. One can easily adapt all available 260 bushing and sizing dies to work. This saves you a bunch of money. Can't be said for the WSSM wildcats.
I have really enjoyed this project from concept through to creation. The fact that it has met my expectations is a wonderful bonus. I am about to build a 16.5lbs BR type rifle in this cartridge to fully explore its potential.
If this is something you want to try, let me know and I will send you details on how to cut the chamber and a case to use as a headspace guage. Many gunsmiths already have the proper reamers on hand. Again a huge savings not needing another custom reamer.