C. Sharps Big Fifty?

[Eric Johanen]

Kurt, if she keeps behaving herself and putting shots into nice small groups, She will be a pleasure to keep fed!

[Eric Johanen]

Got the heads up from Tom at Accurate Molds and the 51-550S is on the way! I've got a pot full of 20/1 ready to run some bullets. If it get here this week I'll cast over the weekend and test them early next week.

[Martini2]

Obviously the proof is in the shooting. However if your into a little math try this
http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

JBM calculators on computer take the work out of confirming "Stability Factor" A result near 2.0 and up pretty much is in right rifle range.

[Eric Johanen]

Martini2, I ran calculations for the BACO 512-625 and got 2.213. The Accurate 512-550S went 3.237. Am I correct that the lower the number the higher stability factor?

[Eric Johanen]

Accurate Mold 51 550S came in today's post and Tom did a great job! Dimensions are spot on: Cast of my mix they are 1.178 inches long, .511 diameter body, first band is .500 and the nose just above is .4975. Weight is 555 + or- a smidge. I'll be casting and loading tomorrow and hope to get back on the range on Sunday. I'll let everyone know how they fly. Some with GOEX 1 fg and some with OE 1.5 fg.

[J.B.]

Given that this bullet is a slightly 'bigger brother' to the 465S, I'd be surprised if it didn't perform well in the 1/26" twist. Designed to be set into the lands also... Did you go with aluminium or brass for your mould ? Tom certainly does great work . He does it promptly and to a fair price. Almost makes me want another mould.... Lets see ??

[Eric Johanen]

I had Tom cut these blocks in iron and they really cast nicely. Most fall from the mold and a few need a little tap. Great workmanship and a really fine mold! Both of the Accurate Molds I have show really nice bases, Flat and sharp! I think it has to do with the heavy sprue plate and the way its mounted/adjusted. I'll be looking to Tom in the future.

[Martini2]

The Government folks that calculate such things indicate 1.5 as one of their recommendations. The 2.0 factor was proposed here as more practical due to fact we talking Cast PB projectiles (and not the J word ) Some find slightly lower 1.2-1.3 in smaller calibers to their likening. For your example of SF= 3.0+ lets consider the following. Some bullets may be over stabilized and still work. We have to be careful how this is applied. In one case, primarily in smaller calibers and very tough construction (solid base copper jackets) that can be tolerated. In BPCR it may be important to consider bullet material limitations. Simply put if a bullet is out of round, has surface imperfections or form variations (nose slump) excessive bullet spin will not make them stable. If your example calculates out to SF=3.0+ the bullet spin rate for that bullet may be detrimental. Another example, pick a nominal velocity for BPCR of 1200 fps and factor in (Big .50)weight and length. I read some where that bullets of at least 2 diameters in length min. settle down better in flight (given the right velocity and twist). Now as bullets get that long it's left it to you to fit a Fifty cal. with 2 inch or more projectile and fire it. To visualize, If we might over simplify, equate BPCR long range trajectory with a well thrown football one might visualize the smooth spin and path. The bullet or object just "goes to sleep" no wobble no lost motion. AND in that vision one can see the front point of the ball tip over and follow the curved path to target. Over/under stabilization in bullets or footballs will cause the nose to yaw or not follow the curve as it crosses over mid point, then things go wild. Like to suggest an easy way to check your combos "stability" and that is to make up some target backers of 3-4 thicknesses of corrugated card board and shoot them at distance. Remember tilt the top of target back slightly (or more to match incoming path) Then use calibers to carefully measure roundness of bullet impacts. If your bullet is completing it's journey sidewise you'll have certain proof. If you can bump up velocity and stand the recoil a bit, impacting bullets on close edge may be stabilized. I apologize that this topic is so involved, interesting and important to our hobby there are no short nor complete answers.

[Eric Johanen]

That is why I was considering trying the OE 1.5 fg. Maybe a slight increase in velocity would help the 555 grain bullets go to sleep. Worth a try. If it look's promising, I can go to the OE 2 fg. Will see what happens on the target.

[Eric Johanen]

Shot the 50 90 with new Starline brass, CCI LR primer, 110 grains of GOEX 1 fg and a .030 vegi card and milk carton poly wad. Seated the Accurate Molds 51-550S seated to the first band. Wiped between shots and used the 25 yard Timed and Rapid target at 100 yards. 6 O'clock hold and full blade in the notch and it printed 5 inches high, top of the black a little left. Moved rear to the right and held half a blade and the group was 1 & 3/8th's vertical X 1 inch horizontal centered between the 9 and 10 ring at 9 O'clock. Needs just a bit more right to center up. Surprised at just how well these shot! No evidence of tipping or anything weird going on so it looks like that 555 grain bullet will stabilize at least to 100 yards. I'll have to try it out at 200. Now I can get to work as I have 40 fire formed cases to work with. I think this bullet will work with the 1 X 26 twist and that is a good thing! Next time out I'll center up the sights and give it a try at 200 yards. If I can get it working I just might give it a run at the next steel match. That would be good fun!!!