Developing initial Wildcat charge weight

[miningshawn]

I am in the final stages of working in my new wildcat. I have 150 pieces of formed brass and I am itching to load 'em. The closest caliber I can find is 250AI, and Sierra has loading values for it in Edition 6. But.... The heaviest bullet is the 120gr - I am using Berger 135, 133, and BlackJack 131.

I have run multiple scenarios in GRT and settled in on some initial starting loads. They are very close to the starting loads for the 250AI. My thoughts now are to bring the rifles (two of 'em!) to the range and charge by 0.3gr until I start to see pressure signs, (ejector wipe, flat primers) but I am a little nervous because both of my actions very good at hiding primer pin flow (Defiance Ruckus with a flat-nose bolt, and a Falkor 7).

The 250AI examples I can find have 47.5-51 grains of H2O capacity, this is what is giving me pause. I don't know who to trust. My cartridge capacity is 49.75 grains of cartridge capacity. I have pulled out all of the stops to get the most efficiency from this cartridge - Ackley shoulders, straighter walls, small primer pocket, .308 parent case (slightly thicker walls for my length), and a longer neck.

I will be testing H4350, VV N550, RL15, and RL16 to start. FWIW I will be starting with H4350, VV N550, and RL16 at 39gr, RL15 will start at 37gr. The initial brass is once-fired Federal GMM, BR-2 LRP, and seated 0.005 from the lands. Once I get some good baselines I will be using Peterson Wildcat tubes and CCI 450 SRP's.

I'm not really looking for validation, I am putting this out there for folks to poke holes in my process and avoid any pitfalls. If you have some advice I would love to hear it!

 

[KMart]

Another cartridge to take a good look at for comparison is the 25 Creedmoor. I would think that the 250 AI and 25 Cmoor would be really close together. Check out the info available on the Blackjack website and you may find some usable info already with the 131 gr bullet.

I went through this exercise some times back. I shot a lot of 2 shot groups over a chrono, starting low, and looking for max.

 

[whatsupdoc]

GRT has Cartridge designer ability where you should be able to create a model
of your wildcat.

 

[Walt Krafft]

I would start with the slowest usable powder. Hopefully you will run out of case capacity before excessive pressure shows up. Record the velocities and go to the next faster powders and repeat.

 

[Clancy]

When I have worked with wildcats, I would pick a case with a smaller capacity, then pick a powder that was on the slow end for the smaller case. I’d start below max for the smaller case and work my way up.

Surely with data out there on 25 GT, 250 savage/ai, 25x47 and 25 creed you can find a starting place.

 

[Zero333]

I can run some #'s in Quickload and PM you with them. Just give me as much info as possible, like case length, bullet lengths, total Brass H2O Capacity.

The more data you can get the better.

PM me and I'll try to do my best.

 

[TZaun]

I might be wrong, but starting at 39.0 gr. of H4350 and RL-16 seems a bit high. Last winter I played around with the 131 BJ in a 25 SLR Imp. My formed cases (Lapua 260 Rem.) had an average of 53.7 gr. H2O. I hit pressure (ejector marks) with H4350 at 42.5 gr. and RL-16 at 42.0 gr. If I were in your shoes, I would drop down to at least 37.0 gr.

 

[miningshawn]

I would start with the slowest usable powder. Hopefully you will run out of case capacity before excessive pressure shows up. Record the velocities and go to the next faster powders and repeat.

I was planning to begin with N550 and work my way down, but I do have a couple pounds of H4831. I will probably start there. Thanks!

 

[miningshawn]

GRT has Cartridge designer ability where you should be able to create a model
of your wildcat.

I have put all of the parameters into the wildcat tool, and it matches my volumes precisely. I am having a little difficulty with starting pressure, so I doubled the "normal" of 3333psi as a starting point. This gives me very conservative starting numbers versus 25 Creedmoor, and I would have to perform the same round of guesses on a 250AI as there is no current data.
I have about 2-2.5gr less capacity than a Creedmoor, but I touch lands from the magazine OAL, (2.860" touch at freebore with all three bullets).
Thanks!

 

[357Mag]

Miningshawn -

Howdy !

Walt gave you a great idea... starting w/ a powder that is known to be comparatively " slow burning ".

IMHO - don't rely on fired primer appearance, as a valid indicator of load pressure.
Measure you casre' base diameters before fiting, and keep re-measuring after each firing..... to determine
when case expansion / pressure starts to indicate that undesireable levels are being neared. You can back off the powder charge from that point, and go looking for the most accurate load.

If you have reliable .250AI load dara and also for a notional " .25 Creedmoor " and believe your wildcat's case capacity to lie bewteen those two cases; you can use loads for the lower-capacity .25 cal case as a start point.

I recommend you go up .2gr at a time, and not .3gr . But hey, that's just me.

How long iare your rifle' barrels ?


With regards,
357Mag

 

[miningshawn]

Miningshawn -

Howdy !

Walt gave you a great idea... starting w/ a powder that is known to be comparatively " slow burning ".

IMHO - don't rely on fired primer appearance, as a valid indicator of load pressure.
Measure you casre' base diameters before fiting, and keep re-measuring after each firing..... to determine
when case expansion / pressure starts to indicate that undesireable levels are being neared. You can back off the powder charge from that point, and go looking for the most accurate load.

If you have reliable .250AI load dara and also for a notional " .25 Creedmoor " and believe your wildcat's case capacity to lie bewteen those two cases; you can use loads for the lower-capacity .25 cal case as a start point.

I recommend you go up .2gr at a time, and not .3gr . But hey, that's just me.

How long iare your rifle' barrels ?


With regards,
357Mag

The Defiance action (lower) is using a 32" SS McGowen Remage, 7 contour, 7 twist, with a Cortina tuner.
The Falkor action (upper) is using a 28" SS Proof, no contour, 7 twist, and a Patriot Valley Arms brake.

 

[SeabeeKen]

Case capacity for my 250ai lapua brass is 50.64 gr water. I tried 25 cm brass and found that near max loads expanded the thicker case head just enough to cause clickers. The .003 diff in head diameter and thicker web went into my chamaber enough that it didnt seem to spring back enough. Had to go back to 22-250 brass. This also happened when i tried reforming 243 brass. Not everyone has this issue, it depends on how tight the chamber was cut.

 

[357Mag]

I am in the final stages of working in my new wildcat. I have 150 pieces of formed brass and I am itching to load 'em. The closest caliber I can find is 250AI, and Sierra has loading values for it in Edition 6. But.... The heaviest bullet is the 120gr - I am using Berger 135, 133, and BlackJack 131.

I have run multiple scenarios in GRT and settled in on some initial starting loads. They are very close to the starting loads for the 250AI. My thoughts now are to bring the rifles (two of 'em!) to the range and charge by 0.3gr until I start to see pressure signs, (ejector wipe, flat primers) but I am a little nervous because both of my actions very good at hiding primer pin flow (Defiance Ruckus with a flat-nose bolt, and a Falkor 7).

The 250AI examples I can find have 47.5-51 grains of H2O capacity, this is what is giving me pause. I don't know who to trust. My cartridge capacity is 49.75 grains of cartridge capacity. I have pulled out all of the stops to get the most efficiency from this cartridge - Ackley shoulders, straighter walls, small primer pocket, .308 parent case (slightly thicker walls for my length), and a longer neck.

I will be testing H4350, VV N550, RL15, and RL16 to start. FWIW I will be starting with H4350, VV N550, and RL16 at 39gr, RL15 will start at 37gr. The initial brass is once-fired Federal GMM, BR-2 LRP, and seated 0.005 from the lands. Once I get some good baselines I will be using Peterson Wildcat tubes and CCI 450 SRP's.

I'm not really looking for validation, I am putting this out there for folks to poke holes in my process and avoid any pitfalls. If you have some advice I would love to hear it!

Miningshawn -

Howdy !

You might take a look @ reloading data for 6.5 Carcano, 6.5M-S; and even 6.5 Creedmoor.
Load data seen @ the Hodgdon reloading data center for the cartridges listed above, include some bullet weights closer to those you are going to use in .25" calibre.

The H2O case capacity listed for 6.5 Carcano and 6.5M-S are very close to the capacity you mentioned for your wildcat ( kwk.us/powley.html , " case capacity " button ). Powders can be found on the load data lists that are comparable in "burn rate " to some that you mentioned.

The N550 might make for an interesting powder choice ? When I wrote Kaltron-Pettibone years ago about potential applications for their " N5XX " series powders, they replied that their best use would be for propelling heavy-for-calibre bullets. Your .25" calibre bullet choices would qualify for that.

Please keep us posted on your progress.


With regards,
357Mag