We’ve received a lot of Private Messages and Emails about stability since we announced our 131 grain Blackjack bullet in 0.257″ and the length of 1.415″.
They scenarios range from 1:10″ twist 25 STW’s for mountain hunting to 1:10″ 257 Roberts out in desert flats. Unfortunately there haven’t been many rifles built with fast twist rate 25 Caliber blanks, so I wanted to put together a series of pictures showing how Muzzle Velocity and attempting to control Bullet Stability Factor by pushing your hand-loads faster and faster really does not help as much as people think. Having a gunsmith replace the 1:10″ twist barrel with a 1:7″ to 1:8″ twist does and you’ll have consistent BC and downrange results as you travel around the country for big hunts or shooting competitions. Below is a laundry-list of Stability Factor & BC effects from running different twist rates and velocities. By the end of this post it should be apparent a 1:8 twist will work quite well for Magnums over 3300 fps and 1:7.5 twist will work for nearly any other set of 257 cartridges.
1. Let’s start off with the Magnums and Super Magnums (257 Weatherby, 257 STW, 25 Nosler, 25-300 Norma, etc).
– Take a guy in the lowlands anywhere in the US around 1000′ altitude. He knows he can run these 131 grain bullets 3300 FPS in his 1:10″ twist magnum rifle. That ought to be fast enough, right? Nope. Using a standard 1:10″ at 3300 fps the combination doesn’t even enter into “Marginal Stability” at 1000′ altitude and 59°F – likely to see obvious accuracy issues like Keyholing at 100 yds. A lot of times this is where guys think speeding the load up may help.
– Now let’s say the guy has some way to push this bullet to 4000 FPS, somehow…
Will the bullet now be stabilized in the same conditions at 59°F and 1000′ altitude? Check out the graph below. Increasing MV by +700 FPS only brought the bullet into Marginal stability where the rifle may group accurately but it is suffering 14% BC loss. Add a Cold Front blowing through or heading downhill a little ways and your rifle is shooting like a shotgun again!
Here come’s the Cold Front and now your 4000 FPS rifle went from Marginal Stability back to UNSTABLE.
– Well, what if we take that 3300 FPS load up in the mountains to see how it will do in higher Elevations like 7000′? Again, we only enter Marginal Stability with a 10% decrease in BC. Like the 4000 fps setup with Marginal Stability we are only a Cold Front away or a hike downhill before we enter the UNSTABLE zone again and likely to miss whatever we’re aiming at.
– It’s about time we start thinking about putting a “fast twist” barrel on this rifle isn’t it?
– So, let’s head in the the gunsmith and chamber up a 1:8″ twist blank. Boom! Just like that you are Fully Stable and enjoying 100% of the bullet’s BC.
#2.) Match Rifles – Let’s cut straight to the chase. You want your Match Rifle to perform 100% and consistent no matter where you go or what conditions you find yourself in.
– You’ve crunched the numbers for all your Matches that ranging from Core Shooting Solutions near Crestview, Florida (236′ Elevation) to Telluride Colorado (8750′ Elevation) and that Alaskan Blacktail hunt you want to take on one of the islands full of giant bears (freezing temps and near sea level). You want across the board CONSISTENCY so you chamber up a 1:7.25″ twist 0.257″ blank and run it nice and easy at 2850 fps. Well, the good news is when you find yourself standing on the beach next to the water and the temperature outside is ZERO DEGREES your barrel and bullet combination is FULLY STABLE. You can travel anywhere down to 0°F without the slightest worry about stability issues or BC loss.
Now all of this was probably a bit overkill, but I wanted to lay some of these scenarios out since there is still some mystique about Bullet Stability and many guys still chase velocity thinking it will cure their accuracy problems. The 1:10 barrels guys may try to shoot heavy and long bullets from might work in some places on some days, but it should be apparent that if you want consistent ballistics and success on your hunts and competitions, use an appropriate twist barrel.
We will be stocking 1:7″ and 1:7.25″ twist blanks from Bartlein, Krieger, Lilja, and Rock Creek starting late June 2018!
For our initial BC testing we wanted to pick a cartridge that could cover the majority if not all of the practical velocity window competitors utilize in Long Range Competitions like the PRS, many state level clubs, & NALRSA which is basically 2900-3175 fps. We wanted great brass and a capacity that was not too-overbore that when loaded with lighter, slower charges near 2900 fps the reduced load density would still be in the zone for good accuracy . With those criteria one easy shooting cartridge came to mind: 25×284! Just run 6.5×284 brass through a bushing die and you’re ready to roll.
We broke in the Rock Creek 5R 1:7.75″ Twist 28″ barrel with Sierra 117 soft points – you could immediately tell the Rock Creek barrel was going to be a hammer with 2-2.5″ 5-shot groups at 500 yds in field conditions (and that was shooting a bullet with a 0.349 G1 / 0.180 G7).
When we got back to shop we loaded up Norma 6.5×284 brass with H4831SC and Sellier & Bellot primers. Then we seated 131 Blackjack ACE’s 0.010″ off the lands for the velocity data seen in the graph below as well as the rounds we loaded for BC testing over the Oehler System 88 to compare with our field estimates from earlier shooting. After two days of shooting in afternoon-to-evening and morning-to-afternoon conditions we averaged the 1000 yard results to 0.330 G7 BC for 2930 fps & a slightly higher 0.333 G7 BC for 3140 fps! For any bullet going into a short action magazine and fired from a 308 bolt-face parent case 0.330 G7 BC is impressive – on top of that, this is a 0.257″!
The results were slightly better than our estimate of 0.325 G7 but we will continue to publish our results as we test different twist rates like the 1:7″ Twist 3-Groove Lilja’s, the 1:7″ Twist 6-Groove X-Calibers, 1:7.25″ Twist 5R Rock Creeks, 7.25″ Twist 4-Groove Kriegers, & 1:7.25″ Twist 5R Bartlein barrel blanks.
If you plan to shoot Long Range Match type cartridges like 25×47 Lapua or 25 Creedmoor 1:7 – 1:7.5″ twist barrels are the preferred setup if you’ll be traveling to different elevations and climates. If you plan on building a magnum like 257 WBY, 25 SAUM, or any of the 25-06, AI’s, or Gibbs variants consider ordering a 1:7.75″ to 1:8″ twist barrel to reduce the likelihood of bullet deformation due to excessive RPMs from the combined twist rate and blistering velocities above 3200 fps.
That being said, we saw no issues from the 131 ACE bullets going 3140 fps over extended strings of fire in our 1:7.75″ twist Rock Creek Barrel. Even in switching winds and moderate mirage, the combination proved consistent 1/2 MOA groups on 5 shots and less than 1 MOA at 1000 yds on 10-12 shot strings – all that performance with your average skill level long range shooter (although we had some of the best wind coaches you could ask for!).
Soon we will do some extended range testing out to 1320, 1500, & 1760 yds running the Blackjack 131 ACE in the 25×47 Lapua at 2840 fps & the 25 Creedmoor near 2950 fps from 1:7″ Twist X-Caliber Blanks. Stay tuned for more testing and product release dates!
We will be keeping records of velocity-windows, load development, & approximate barrel life from all of the barrel blank manufacturers we will carry including Bartlein 5R, Krieger 4 Groove, Rock Creek 5R, Lilja 3 Groove, & X-Caliber 6 groove barrels.
We understand these results may not represent the performance of every blank, even coming in the same twist rate from the same manufacturer, but we will compile the best data we can so we can provide the best starting points for our Shooters.
This graph represents two sister barrels manufactured to the same specs, at the same time, from the same MFG. We will produce additional graphs when more comparison sets of barrels get tested after break-in.
We were very glad to see the 25×47 Lapua run so well!
2950 fps with no signs of pressure! That velocity combined with our 0.330 G7 Ballistic Coefficient really makes for one hell of a match rifle setup in standard length Accuracy International magazines.
The 25 Creedmoor ran well and reached 3000 fps with faint ejector marks – at 3050 fps the brass began to have shiny ejector marks and we do not recommend shooting tactical matches or hunting with loads that hot.
Again, every barrel and rifle is different so always do your own conservative load development – if you are inexperienced as a reloader, get in contact with a reputable gunsmith or seasoned competitive shooter.
I’ve shot Prime 6.5 Creedmoor brass for a few years now and it is definitely high quality stuff. Now that the Lapua produces great Creedmoor SRP brass we wanted to test velocity window differences between the two. We were quite surprised how close these two samples of brass ran with eachother. These tests were done with 117 grain Soft Point spitzer-style bullets that we have shot in each new barrel until we are comfortable the blank is “broken-in” and speed has mostly stabilized. Please take note the charge weights and resultant velocities are for 117 grain bullets, not our Blackjack 131 gr ACE. We will update this data with Hornady Brass comparison soon!
Folks, we will be updating the website over the next few days with Technical Info on the Bullets, Barrels, & Reamers as well as setting up the products in the Web Shop.
Although we’ve had many requests none of our in-stock items will be up for sale for another 2-3 weeks when we take reservations for the Krieger, Bartlein, Lilja, & Rock Creek Barrel Blanks that are coming in soon.
So, stay tuned to Facebook.com/Blackjackbulletco and this website for the announcement when the Web Shop goes live!