Load Development for GP100 MC

[Ben_Snow]

Performing load development for a new 357M GP100 MC 4.2"

Using Berry's 158gr FP, new Star line Brass, and a light crimp from a Lee's FCD.

--Unique 6.8gr -7.0gr performed with fairly consistent accuracy (24 shots at each load). Same load that performs well in my 357M Blackhawk.

-- Titegroup 5.0gr was not consistent at all. Didn't expect much at all, just was an experiment.

--The surprise of the day was AA#5. It performed very well at 8.4 gr's a few days ago (and with no pressure signs), so tried it today @ 8.6gr and 8.8gr. Seems like the higher I am going the tighter the groupings, and while I don't see any overpressure signs the velocity might be getting a bit too high for plated.

Obviously I want to stick with AA#5 @ 8.8gr, or even venture a tad higher if possible. Problem is I cant find very little data for a Berrys 158gr FN using AA#5. The Powder manu only lists two loads @ 158gr:

158 HDY XTP Min 8.6 1,097 Max 9.7 1,256 CUP/COL 33,150 1.590
158 (L) LC SWC Min 8.6 1,100 Max 9.0 1,220 CUP/COL 34,500 1.590

Speer has a 158gr TMJ FN (closest thing to a Berry's FN ?)

Min 9.0 1,032 Max 10.00 1,152 CUP/COL 34,500 1.570


The Speer data sounds too high, and the Powder Manu doesn't have a good match. What to do? Continue testing at AA#5 @ 8.8, venture beyond to see if accuracy improves at the risk of plating failure? I don't have a chrono so looking for some input from those more experienced.

[T. O'Heir]

A 158gr TMJ is actually a jacketed bullet, not plated. According to Speer.
A lot depends on what you're doing with the revolver. Only use my GP for bullseye shooting with a cast or swaged 148 grain WC loaded to .38 Special target velocities.
Suggest you pick a bullet first. Do not just pick a load. You must work up the load from the start load.
5.0 grains of Titegroup is under minimum for a jacketed 158. Max. for a cast 158.
6.8 to 7.0 grains of Unique is for a 135 grain jacketed bullet. A jacketed 158 is 6.9 to 7.7 of Unique. A cast 158 is 5.4 to 6 of Unique.
Alliant's site gives max loads only. Reduce 'em by 10% for the start load.
"...data for a Berry's 158gr FN using AA#5..." You do not need bullet specific data. Just the weight and cast or jacketed. Use the cast 158 data on Accurate's site. 8.0 to 9.0. 1.590" OAL.

[Ben_Snow]

T. O'Heir Wrote

..." You do not need bullet specific data. Just the weight and cast or jacketed. Use the cast 158 data on Accurate's site. 8.0 to 9.0. 1.590" OAL.

Thanks for your response, but not sure if you answered my question or not.

The other loads are not relevant at this point, just interested in the AA#5 load. I'm confused by your post; first you say "pick the bullet, then the load", and then "You do not need bullet specific data". I did pick the bullet first, and now trying to determine the load? Your right TMJ are not plated, they use an copper electroplating process that covers the entire bullet including the base. The TMJ that Speer uses is supposedly thicker than a FMJ.

Some more info that may clarify from my end:

Purpose: Bullseye
Bullet: Berrys FP 158gr (I have some 148gr Plated DEWC on order)
Powder: AA#5

Again... I want to venture past 8.8 grs of AA#5 as my groups continue to shrink, but need some reliable data of how far the plated can be pushed past 8.8grs. I realize that the Speer TMJ are not plated, but its the closest comparable jacketed bullet at 158gr. I did consider the cast range of 8.0 - 9.0, but have been told over and over that plated needs to be pushed to low-mid jacket range and not to use lead data.

Again, thanks for your response... Hopefully someone else has loaded in that range before with AA#5/Plated and can provide input.

[Dufus]

The Speer Gold Dot is a plated bullet.

Speer #14 lists 158 grn GDHP @ 9.0 gr Start and 10.0 gr Max with AA#5.

[Ben_Snow]

Yes, in my Speer Manual the Gold Dot is lumped together with the TMJ FN. AA#5 9.0gr (1032fps) to 10gr (1152fps)

I am skeptical of those velocities, especially 1152fps when loaded all the way to 10grs.

Am hoping for verification from some of the forum regulars that have loaded AA#5 in that range.

[Real Gun]

The numbers tell me that if you are doing okay at 8.8, stop there. Use up the bullets and then buy a real revolver bullet especially suited to magnum loads. Let existing load data be your guide for what bullet to buy.

If you like Accurate, #9 or 4100 are better choices for real 357 Magnum. I use #5 in 32 H&R and dabbled unsuccessfully with #7 in 41 Magnum. #7 ran better in 45 ACP, but at a more robust load than typically used for IDPA and such, barely making power factor.

[Nick_C_S]

What to do? Continue testing at AA#5 @ 8.8, venture beyond to see if accuracy improves at the risk of plating failure?

You can. But at 8.8, I share your concern of overdriving the plated bullet if you go much further.

Problem is I cant find very little data for a Berrys 158gr FN using AA#5.

I think you're over-fixating on published load data at this point. You have real world, first-hand data now. You should decide to continue working up (or not) based on the first-hand data you now have. The beauty of 357 Magnum - especially with a robust Ruger GP100 - is you can see clear signs of pressure, and back off.

I've loaded 158 XTP's up to 9.2 grains. 1097 f/s 3" bbl; 1159 f/s 4" bbl. This loading experiences slightly flattened primers; and that's why I ceased the work up. (This isn't a loading I shoot frequently. Its purpose is defense protection though a short barreled gun.)

And my 9.2 is just for a loose reference and to show what my opinion is based off of. My loading and your loading are somewhat different. I don't know what our seating depths are relative to each-other, etc. But what it does tell me is that you must be getting up there in pressure at 8.8 grains; and those plated slugs are being driven pretty darn hard now. Keep in mind that plating breakdown is as much a function of pressure as it is velocity; maybe more so.

[Unclenick]

With a Ranier plated bullet, QuickLOAD shows 10 grains of #5 within about 10% of the CIP's top pressure for the cartridge. The CIP uses a higher number than we use, due to measuring system differences, but it is what ammo imported from Europe and the former Soviet Block countries is loaded to and that ammo works fine. But that pressure is probably a bit high for a plated bullet.

If you are worried about copper stripping, you can dip the bullets in a little bit of Lee Liquid Alox thinned 2:1 in mineral spirits.

Mr. O'Heir is old school. He and I have discussed how physical standards have changed since we were in school. For bullets, there was a time, not many decades ago, when all bullets with jackets of the same weight were loaded with the range of powder charges. That's what he means by not needing bullet specific data; just bullet weight data. However, alas, things have changed and bullet construction is no longer as similar from one to the next as it once was. The current Norma manual reports that, using the 270 Winchester, M.L. McPherson and another fellow loaded every kind of 150 grain bullet for it that they could get (except lead), and loaded them in the same cases with the same primers and the same powder charges in the same pressure measuring gun and got something over 30% variation in pressure depending on the bullet. So in modern times, what with plated bullets, solid bullets, updated bullet designs and whatnot, it is no longer true that bullet weight alone will give you a good load recommendation. This Alan Jones article sums it up.

[Ben_Snow]

Ok, no more waffling

Going to venture to 9.0gr, but only 6-8 rounds and look for pressure signs. If the target groupings don't improve, or start to decay, I'll drop back to 8.8grs and call it a wrap.

Nick Wrote

Keep in mind that plating breakdown is as much a function of pressure as it is velocity; maybe more so.

^^^ That I did find interesting

Real Gun Wrote

Use up the bullets and then buy a real revolver bullet especially suited to magnum loads

[Nick_C_S]

Gotta love Dirty Harry.

Liked him so much, I bought his gun

[Ben_Snow]

Plated for 44Mag? Have any loads?


never mind, another topic for another day... Marvelous

[Unclenick]

Keep in mind that Elmer Keith developed the .44 Mag with bullets that, in his final blend, were 16:1 lead:tin cast bullets. About BHN 11 or 12. With a smooth and even diameter bore, it can be done.

Originally Posted by Nick_C_S

Keep in mind that plating breakdown is as much a function of pressure as it is velocity; maybe more so.

I think it's all pressure. If velocity were the actual culprit, loads that worked fine in a short barrel gun would get into trouble firing from a longer barrel of the same condition, because it would give that same load more velocity. I've never seen that happen. I think the use of velocity to determine the load limit is pretty much analogous to using bullet weight to determine barrel twist requirement. The latter assumes all same-shape, same construction bullets, while the former assumes all same-length barrels.