12 Twist 22-250/69g SMK h/t Michael Courtney

[benchracer]

Thanks to information posted by Michael Courtney, I decided to try 69g SMK's in my 12 twist 22-250. Hodgdon load data showed 3499 fps mv from a 24" barrel using Superformance with a 70g bullet, so I used that data for my workup. I chose the 40.2g load, which produced a .445" group @ 100 yards and averaged 3579 fps from a 26" barrel. I can't wait to stretch the range with this load and see what it can do!

I have also prepared some test loads with RL-17, but didn't have time to shoot them.

Attached are images of my load workup and my rifle.

 

[dig]

Great info, looks like at that velocity you are having no problems stabilizing. This should be a fun load. I shoot the 69 in a 1/10 26 inch .223 with good results on a hot load. Keep us posted.

 

[benchracer]

Great info, looks like at that velocity you are having no problems stabilizing. This should be a fun load. I shoot the 69 in a 1/10 26 inch .223 with good results on a hot load. Keep us posted.

Will gladly continue to post results as I have them.

According to the information and spreadsheet/calculator posted by Mr. Courtney, a 12 twist is sufficient to stabilize the 69 SMK, even at lower velocities, but that same information also shows that a lower level of stability can reduce bc. When I shoot this load at longer range, I hope to determine whether or not it is stable enough to get the full bc value.

Michael Courtney's research was a real eye opener and an interesting read.

 

[Mikecr]

I missed it,,
How does that same information show that a lower level of stability can reduce bc?

 

[benchracer]

Here is the research Mr. Courtney posted. It specifically states that a stability factor below 1.2 results in lower observed bc's:

View attachment STABILITY.pdf


That research, along with the stability calculator Mr. Courtney provided, is what convinced me to try the 69g SMK's to begin with.

Here is the link where Mr. Courtney posted the information, post #27:

http://www.longrangehunting.com/forums/f30/22-250-600-yards-max-does-anyone-do-130140/index4.html

 

[Iron Worker]

What make of rifle is that ?

 

[benchracer]

It's a BRNO 98/22 mauser that has been sporterized with a Bell & Carlson Medalist stock and a Shilen pre-fit 26", #4 Contour, 12 twist chrome moly barrel.

 

[Salar600]

lucky you, at 3300fps my 1x12 shoots them accurately to 200yds, beyond that they fly in every direction.

I do much better with 55gr out to 600yds.

 

[benchracer]

lucky you, at 3300fps my 1x12 shoots them accurately to 200yds, beyond that they fly in every direction.

I do much better with 55gr out to 600yds.

That's good to know. I haven't had the chance to stretch the range at all yet, so it is very possible that I could run into the same issue that you did.

 

[Michael Courtney]

You really need to consider the pressure and temperature to assess stability. A load that won't shoot in winter at sea level may well be perfectly stable in summer on the great plains or in the mountains.

But stability alone is insufficient for a good long range load. Bullets won't tumble for stabilities between 1.0 and 1.4, but our work shows that you will consistently have lower BCs between Sg = 1.0 and Sg = 1.2. This is consistent with results from Bryan Litz and Sierra also.

 

[benchracer]

You really need to consider the pressure and temperature to assess stability. A load that won't shoot in winter at sea level may well be perfectly stable in summer on the great plains or in the mountains.

But stability alone is insufficient for a good long range load. Bullets won't tumble for stabilities between 1.0 and 1.4, but our work shows that you will consistently have lower BCs between Sg = 1.0 and Sg = 1.2. This is consistent with results from Bryan Litz and Sierra also.

My initial tests were done at approximately 1000 ft ASL in 70 degree weather with Hodgdon starting loads for Superformance to see if the bullets would stabilize from my rifle. The load workup that I posted was done at 1860 ft ASL in 75 degree weather. I don't have barometric pressure data for either day. According to your calculator, the 69g SMK would be very near borderline (Sg=1.2) at those temps and standard pressure (I don't know how to convert for altitude). I look forward to shooting at longer distances out to about 600 yards to see what kind of bc I am actually getting.

Of additional interest is Brian Litz's testing that indicates this bullet has a higher bc than listed by Sierra. If I end up losing bc with this bullet, I will also be interested in seeing how large the loss is.

At any rate, I won't be able to continue my testing until the fall. I will report back when I do.

Thank you for sharing your research. It has led me to try things I would not have otherwise considered.

 

[benchracer]

You really need to consider the pressure and temperature to assess stability. A load that won't shoot in winter at sea level may well be perfectly stable in summer on the great plains or in the mountains.

But stability alone is insufficient for a good long range load. Bullets won't tumble for stabilities between 1.0 and 1.4, but our work shows that you will consistently have lower BCs between Sg = 1.0 and Sg = 1.2. This is consistent with results from Bryan Litz and Sierra also.

I found a barometric pressure vs altitude table to help me do some rough calculations for the tested elevations:

Sable Systems

Plugging those numbers into the calculator you provided indicated that, with my chosen load, the 69 SMK's would stay above Sg= 1.2 down to about freezing @ 1860 ft ASL and down to about 45* @ 1000 ft ASL.

I am sure that having the ability to measure actual temp and barometric pressure would give me more accurate and useful information. Still, it's nice to have at least a ballpark idea of what to expect.

 

[benchracer]

I continued working with the 69 SMK's from my 22-250, this time doing a load workup with RL-17. I hope to stretch my loads with both Superformance and RL-17 out to 250 yards and obtain some chrono data on the RL-17 load next week. I expect 38.2 grains of RL-17 to produce around 3500 fps or so.

The Sierra TMK's (Tipped Matchkings) recently became available. I have some on order and hope to try those out, as well. I am interested to see if they will shoot as well as the SMK's.

 

[benchracer]

38.2 grains of RL-17 produced an average of 3615 fps for ten shots.

I gave the new Tipped Matchkings a try. They all hit the target sideways, so it looks like I will be staying with the standard 69 SMK's.