The advertised velocities of the 9X25 Dillon are established using 6 inch barrels the advertised velocities for the 357 Sig are set using 4 inch barrels. This means that if both were shot out of a G29 3.8 inch barrel the 357 Sig would very likely equal the 9X25 Dillion. When shot out of equal length barrels, to quote Paul Harrell "the difference would not be enough to make a difference".

 

More powder = higher vel. So yes, you get more out of the 9x25 over the 357sig but its a bigger gun Too. Kind of like 40 v 10mm argument. Powder capacity wins, any bbl length, but obviously longer bbls take more advantage of the powder gasses.
If you have a g20/G29 or 1911 & handload, the 9x25 is a good choice. If you are looking at factory ammo, the 357sig would be easier to feed.

 

The difference between the 357 Sig and the 9x25 Dillon is that the 357 Sig is ALMOST a 357 Magnum but only with 124 or 125 grain bullets, while the 9x25 is closer to the 357 magnum with bullets ups to 147-150 grains in weight.

The 9x25 Dillon would be good for a woods gun using 147 grain fmj-flatpoints but I still think I'd prefer a 10mm with 220 grain hardcast flatpoints.

9x25 Dillon

125 grain Speer Gold Dot JHP 1,700 ft/s 802 ft⋅lbs
147 gr FMJ-FP 1,495 ft/s 730 ft⋅lbs

357 Sig

125 grain Speer Gold Dot JHP 1350 ft/s 506 ft⋅lbs
147 gr Jhp Underwood 1250 ft/s 510 ft-lbs

While the velocity figures for the 9x25 Dillon above are from Wikipedia and are from a 6 inch barrel, Underwood also gives identical figures for the 125 grain and does not specify barrel length . But If I were going to carry a Glock 20 with a 357 sig conversion barrel, I migh jut go ahead and put a 6 inch barel in it that would stick out an inch and a half from the 4.6 slide and maybe even have the barrel cut back and re-crowned to 5 inches for faster presentation out of the holster and on target.

 

The difference between the 357 Sig and the 9x25 Dillon is that the 357 Sig is ALMOST a 357 Magnum but only with 124 or 125 grain bullets, whiclk the 9x25 is closer to the 357 magnum with bullets ups to 147-150 grains in weight.

The 9x25 Dillon would be good for a woods gun using 147 grain fmj-flatpoints but I still think I'd perfer a 10mm with 220 grain hardcast flatpoints.

9x25 Dillon

125 grain Speer Gold Dot JHP 1,700 ft/s 802 ft⋅lbs
147 gr FMJ-FP 1,495 ft/s 730 ft⋅lbs

357 Sig

125 grain Speer Gold Dot JHP 1350 ft/s 506 ft⋅lbs
147 gr Jhp Underwood 1250 ft/s 510 ft-lbs

The Dillon 125gr 1700 fps is the Underwood velocity out of a 6 inch barrel. The Underwood 357 Sig 125gr velocity is 1475 fps out of a 4 inch barrel. The G29 that the poster was referring to has basically a 4 inch barrel meaning the Sig would keep it's advertised velocity but the Dillon would lose 2 inches worth of velocity. The Dillon's 2 inch barrel loss would drop it's velocity down to the mid 1500s. Not enough difference to make a difference. This was what the OP was asking about.

 

I have both rounds in both large frame (5" 1911 357 and 6" g40 9x25) and small frame for the 357 (6" g24). The dillon is about 100fps faster give or take with all things being equal loading to their book OAL.

In a g24 with 6" kkm barrel I ran a 158g xtp (barrel throated for .357" diameter bullets) to 1525fps as a maxed out load at 1.155" OAL. The same bullet in 9x25 I ran up to 1650fps in a 6" bar-sto barrel loaded to 1.270" OAL. I can load the 357 to the same length as the 9x25 in big frame guns if i cut enough throat length and then the velocities get very close except with very light bullets that cant be seated out very far. With 125g and under bullets the 9x25 will always be a bit quicker but with 147g on up loaded to the same length they are very close.

I have done side by side comparisons to see the difference between a 5" and 6" velocities in 357. It is very powder dependent on how much variance you see actually.

Some Examples:
357sig: 14.0g AA9 with a 125xtp loaded to 1.155" OAL
5" velocity = 1612fps
6" velocity = 1632fps
20fps difference

357sig: 11.0g Blue Dot with a 125xtp loaded to 1.155" OAL
5" velocity = 1627fps
6" velocity = 1683fps
56fps difference

357sig: 11.0g 3n38 with a 125xtp loaded to 1.155" OAL
5" velocity = 1559fps
6" velocity = 1620fps
61fps difference

357sig 8.0g 3n38 with a 158xtp loaded to 1.155" OAL
5" velocity = 1235fps
6" velocity = 1276fps
41fps difference

Between the two rounds the 357 is much easier to get dies for, dillon carbide dies are seemingly forever backordered. I had a custom steel set built by Hornady for me and they turned out to be exceptional but they were $254 and a 2 month wait compared to a cheap $30 off the shelf lee die set for 357 sig which have been just fine.

Brass for either is not an issue. With the popularity surge in 10mm 9x25 brass is abundant. Just run 10mm brass through the 9x25 sizer and you're done. With the surge in 10mm popularity either round can get brass easily.

Other than the dies being an issue the 9x25 is worth getting into.

 

ok, I'll settle this. Go with 40 Super and stop messing around...

 

Want to bet they don't get that velocity out of a 3.9 inch barrel. LOL

 

Nope.

I prefer to buy caliber that have guns chambered for that round.

Several good 357 pistol platforms from Glock and Sig Sauer. Conversion barrels from 40SW to 357 sig too. Have a Colt Delta Elite with a 357 sig barrel board.

Not so much with Dillon.

 

I just dont want another caliber to reload for. I have a 357sig bbl for my Delta too, allows me to load a longer OAL, & many of my 40s have a 357sig bbl.

 

I would say it depends on the guns. If you want something to carry day to day, probably better off with 357 SIG as they're physically smaller and will lend themselves to better carry. If it's for a larger gun, say you already have a 10mm, then if you want to play around with the 9x25, go right ahead. In your case, you have a G29 so really it's up to you, but if it were me and I wanted to carry .357 SIG, I'd get a smaller gun, like a G33.

 

I have at least five AM 357 sig barrels from 4'' to 6''.

The four inch is a KKM barrel for a g23/27, yes it sticks out
a little in the g27, the rest are LW.

With the six inch in the g20/21 a 131gr cast PC, LBT blue lube
and a free check made from a beer can, went 1672 FPS, it was
a work up load, with 800x powder. 7/8'' at 34 yds.

The UW 125 GD in the six inch went over 1600 FPS, over
1500 FPS in the 4.5''.

Not as fast as my old 8'' 357 Automag, that was a real monster.

I do like the 357 sig and got a g31 for carry, yes, I have a 9 mm
and 40 barrel for it, they work great. Have the same set up for
some g22s and a g23.

I don't think there any reason for me to get the 9x25.

 

I have at least five AM 357 sig barrels from 4'' to 6''.

The four inch is a KKM barrel for a g23/27, yes it sticks out
a little in the g27, the rest are LW.

With the six inch in the g20/21 a 131gr cast PC, LBT blue lube
and a free check made from a beer can, went 1672 FPS, it was
a work up load, with 800x powder. 7/8'' at 34 yds.

The UW 125 GD in the six inch went over 1600 FPS, over
1500 FPS in the 4.5''.

Not as fast as my old 8'' 357 Automag, that was a real monster.

I do like the 357 sig and got a g31 for carry, yes, I have a 9 mm
and 40 barrel for it, they work great. Have the same set up for
some g22s and a g23.

I don't think there any reason for me to get the 9x25.

You are correct, there is no practical reason to use a 9X25 for SD over a 357 Sig. This young man did a test with recently purchased Underwood 124gr 357 Sig JHP ammo. The 4.5 inch G31 he used got a velocity of 1560 fps with 665 ft. lbs. of energy. That is more velocity than both Underwood and the large ammo companies have for their 357 Mag ammo. Add another 1.5 inches to this Sig barrel to equal the test barrel length for the 9X25 and the 357 Sig will for all practical purposes match the 9X25 in velocity.

I would really really not want to be hit with the 115gr 1650 fps smoker as well!

 

I personally consider the .357 SIG, 9x25 Dillon, and .357 Magnum to be pretty much equals in the real world. All will get the same job done with 125 grain bullets. The Dillon has a slight edge over the SIG, but nothing worth worrying about really, and the old .357 Magnum has a slight edge if you want heavier bullets.

I have personally worked with the 9x25, but I am a serious handloader. Downside so far is that about 5 - 10% of brass is lost in the forming process, usually at the expander stage. I attempted to prevent that by annealing 20 pieces of 10mm brass prior to forming, and it was a disaster. 100 percent loss as the cases collapsed rather than form a neck.

Still, it is a fun round to play around with. I have launched 115 grain Sierras at 1709 fps from a ported 5.5 inch barrel with no muzzle flip, 90 grain Lehigh XDs at a bit over 1800. Next up are some 125 grain Sierras and 68 grain Lehighs.

 

I personally consider the .357 SIG, 9x25 Dillon, and .357 Magnum to be pretty much equals in the real world. All will get the same job done with 125 grain bullets. The Dillon has a slight edge over the SIG, but nothing worth worrying about really, and the old .357 Magnum has a slight edge if you want heavier bullets.

I have personally worked with the 9x25, but I am a serious handloader. Downside so far is that about 5 - 10% of brass is lost in the forming process, usually at the expander stage. I attempted to prevent that by annealing 20 pieces of 10mm brass prior to forming, and it was a disaster. 100 percent loss as the cases collapsed rather than form a neck.

Still, it is a fun round to play around with. I have launched 115 grain Sierras at 1709 fps from a ported 5.5 inch barrel with no muzzle flip, 90 grain Lehigh XDs at a bit over 1800. Next up are some 125 grain Sierras and 68 grain Lehighs.

I failed to note that my velocities are not maximum charges, but where I decided that chasing ejected brass down was becoming inconvenient. In both weights, I hit around 100 fps more as I worked up the ladder, but when the brass was getting flung 20 feet I figured that slide velocities were getting too high, so dropped down to the slightly lighter charges. And when a Glock 20 is flinging brass 20 feet with a 20 pound spring... the load is zippy!

Even the far-flung cases showed no pressure signs. Primers were slightly flat, no noticeable feed ramp bulges, no, well, anything really.

Still kind of new to this round, but my current go-to is 11.2 grains of Power Pistol with either of those bullets.

Oh, and I have decided to standardize my 9x25 with small pistol primed brass, as the case is slightly stronger in the head. And it avoids accidentally confusing it with 10mm rounds with large primers as a quick visual check.

 

@JDSTG58 for dillon you will want barrel that can accept compensator. And you will want bullets that can work at 1800 fps or higher.

You will also want to wear double ear protection, and avoid shooting it in indoor range.

it will not be a carry option, after you realize how it handles.

It is flatter shooting, probably more like a rifle with a 90 grain bullets. So also a reason to have this on a longer platform (eg G40 with optics).

9x25 Dillon

Who here shoots it? I do and it seems to be riding a bit of the 10mm wavelet. Unfortunately neither Barsto nor KKM will make a 9x25 barrel for the 10mm P220, claiming they cannot get it to feed reliably. I'm stuck with my G40, which I really don't care for. But I like the round too much.

www.sigtalk.com