Scratching my head here....

[flyinbrian]

I'm shooting a Stevens 200 in .243 with a 26" factory varmint barrel. Last week I bought a pound of Retumbo to work up a load with the 105 A-Max.

Hodgon's online guide lists a max charge of 49gr. with Winchester cases with an estimated 2964 FPS muzzle velocity.

I started at 46gr and went up in .4 gr. increments. OAL 2.84", off the lands. Primer was F215M. The following are my chroneyed velocities followed by group size. All 3 shot groups:

46.4 = 3056 FPS .519" group
46.8 = 3101 FPS 1.009" group
47.2 = 3104 FPS .621"
47.6 = 3149 FPS 1.025"
48.0 = 3173 FPS .674"
48.4 = 3320 FPS .348"
48.8 = 3235 FPS .379"

I had slight primer flattening at 48.4 gr. that got no worse at 48.8.

What could cause these velocities to be so high, and what could cause such a huge jump at 48.4 with a drop off in velocity at a higher charge?

I don't think my chrony is off because I shot some 105 A max on top of 45 grs of H-1000 and they were right at 2995.

Any ideas?

Thanks in advance!

 

[wildcatter1450]

I'd say you've reached max in that rifle around 48.2. Is this a new lot of powder? If so, it may not display the same properties of a previous lot.

Mike

 

[jb1000br]

sure you didn't switch the last 2 around?

What Chronograph did you use?

JB

 

[Dean]

I have noticed that when you reach and or exeed max pressure that your velocities start to drop...time to back off of the charge

Dean

 

[flyinbrian]

Thanks for the responses guys.

I'm sure that I got the order correct in shooting the loads, and I'm going to test these on a friend's Pact chrony to see if the velocities are similar to my F-1 Chrony.

Dean, I've done some reading since my original post and on more than one occasion I've read the same thing, that velocites drop after max pressure is reached, so I'll take your advice and back it off a little.

I really like those two groups at the top end though....

 

[jb1000br]

I can almost guarentee it was chrony error...I have seen more error than that while comparing my Alpha chrony and Oehler 35p simultaneously.

How can velocity actually go DOWN while upping the charge? It can't...you can't defy laws of physics...the chrony error may make you think it has, but they can not be "accurate" numbers.

see my post at the bottom of the first page:

http://www.websitetoolbox.com/tool/post/6mmbr/vpost?id=1463640&highlight=oehler+shooting+chrony&trail=8

JB