25GT revisited 11/2023

High Desert duck

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Minuteman
Sep 1, 2014
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The 25 CM is awesome. The Blackjack 131 ACE is incredible. I have been shooting them over the past year and it has been a hammer. It only had one flaw that I could find. The recoil is on par with a 6.5 CM. Spotting shots off a barricade inside of 500 could be difficult. As I got to the end of the barrel I decided to attempt to address this by moving to a smaller powder load and a smaller case. I thought it through and looked at the 6GT. After crunching some numbers I thought about necking it up to take the Ace. I figured if I ran H4350 in a longer barrel the GT case would get the heavier projectile running around 2800 FPS.

Looking at what the 6GT guys were doing it looked like the Ace would run the same or better wind drift than the 6’s but with more drop. The additional benefit would be a cartiridge that was less overbore than the parent and in theory might extend barrel life.

My goals in making this cartridge are:
1. Less recoil
2. Good wind drift
3. Longer barrel life

I mocked up a case and ordered a reamer from Dave Manson Precision Reamers. They were very helpful and took great care of me in making the reamer and then working with me when I needed to regrind it to shorten the free bore.

To start the rifle specs are:
Impact Precision 737r
28” Bartlien heavy varmint 5R 1:7
Silencer Tech 30 cal suppressor
Trigger tech special
Skim bedded Bell & Carlson M5 stock
792B37E4-6DB0-49CC-9948-8D8078891158.jpeg


edited to add barrel twist
 

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I am running the RCBS Matchmaster die set. I am normally a Redding guy but this was all that was available when I started my project.
the dies are well made and good quality. I have had to make some modifications on the seating die. The floating portion of the die was reamed out to match the new dimensions. The neck was opened to .287 and the bullet portion was opened to .261. The seating stem seems to be working although I may end up relieving the interior a little to ensure it is not making contact with the bullet tip. So far it’s seating plus or minus .001.

For brass I am using the Hornady GAP 6GT. I have two separate lots and the 2nd lot seems to be more consistent weight wise but both are within 1 grain of each other. I necked up the cases using a carbide Sinclair turning mandrel (.255) and Hornady Unique lube. The necks opened up with no problems and much like every case I have changed to neck dimensions up or down runout ran from .002 to .007, average of .005. After going through the gun once the once fired brass is .001 after sizing. I also tried necking it up from .241 to .255 to .262 then neck sizing down but the difference in the run out didn’t seem to be worth the extra working of the brass. All cases have been chamfered by hand until I open up my new 6GT shell holder.
I trim with a Giraud trimmer and Mr. Giraud was kind enough to talk me through how to open up the neck to accept the new brass. That is currently on the to do list as I have another 350 cases to neck up and fire first.
I do my brass prep on a Dillon 550 and am using the #1 plate and buttons. Station 1 is a universal decapper, station 3 is the body die using a .278 bushing, and station 4 is the turning mandrel.

I am using H4350 but will run a ladder on N555, and IMR4166. Maybe varget But I don’t have much of that.
5901A6C7-4616-48C4-B7DB-04325AF5B51F.jpeg
 
The cartridge specs:
COAL 2.680
Jump .005
CBTO 1.933

H4350
CCI 450
Blackjack ACE 131 (lot 0137664195856)
These are the first 20 shots out of the barrel.
At 36.3 to 36.6 the powder was at the body shoulder junction.
The last 4 loads were compressed.
the last two loads seemed to loosen the primer pockets up a little. And showed a really faint ejector swipe.
the 2nd to last load the bolt was very slightly stiffer.
The recoil was sharper after 37.5
I know it’s a very long ladder but I had no data to go on.

4A6CB421-B496-432D-94B5-2DEE62E951E0.jpeg
 
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Lets see the cartridge! (preferably next to it's family for comparison)

What kind of OAL and freebore did you decide on?
I ended up at a free bore of .155. This puts the top of the boat tail about .020 above the neck shoulder junction and the bottom of boat tail about .075 into the body. I wanted to mimic the neck to bearing surface of the BR cases to the extent I could.
86FF6293-1210-4106-8EB7-F6A31B128797.jpeg
 
Ran 75 rounds through the barrel at 36.9 to finish speeding it up. It went from 2788 to 2795. We shot it side by side with my buddy’s 6BR, the recoil felt very comparable to both of us. I think that I am helped out that my rifle weighs about 2.5 pounds more than his. But off a barricade both were easy to shoot and spot shots at 200-300. First groups were outstanding. I will be upfront. I am not a great group shooter and don’t just like lying in the dirt shooting at 100 yards. I have a tendency to yank one in five. Sometimes I’m on.
my first 5 round group(shots 25-30)
AEA27D06-8F73-406B-BF7A-143CDC355234.png

My buddy’s group (shots 31-35)
CCC02440-DB13-45B8-A777-3F03A9432C7E.jpg


And a group at 1000 winds were gusty 10-12 but drop was pretty consistent. (Shots 38-43) 1 MOA group.
C8E9C9A4-9E46-4937-97AD-30E877F841D2.jpeg
 
VihtaVuori N555
Very consistent. Put all 15 shots in a 2” circle at 200. Very mild recoil. Never showed any pressure signs. 3 shots at 38.0 about 1 inch at 200 yards.
Ran out of case capacity at 38.0 grains.
Body to shoulder junction reached at 36.2.
36.8 and up were compressed.
35446C0D-EE85-48B2-AA93-136A83E7FD6C.jpeg
 
IMR 4166
At 33.9 powder was still below neck shoulder junction.
never saw any pressure signs. The recoil pulse seemed sharper than the H4350 or the N555 in every charge weight after 30. I may be worth exploring but I only have 1 pound so maybe in the future.
4714373F-CBF9-4047-A0F5-5E0D33EB58D8.jpeg
 
The round seems super easy to load for kinda like the BR. Pick a speed, find the seating depth, and go. I will shoot it this weekend at my club match.
With the load development complete I have settled on:
Hornady GAP 6GT brass
Blackjack 131ACE
36.7 H4350
CCI 450
.005 jump
COAL 2.680
Neck tension .002 (.003 on virgin brass)
Trim length 1.712
Neck diameter loaded .2815

I ran seating depth tests and oddly if you’re familiar with the Ace it has certain jumps it likes in all cartridges. In the GT the .018-.020 range did not work as well as the .005. It was consistently .15-.20 larger than the .005.

The cartridge seems very easy to load for as I ran multiple groups at multiple loads over the magneto speed in every one is was almost exact an SD 7.5 and ES of 21.

Here is the magnetospeed data for the final load and final group. Please remember I don’t like shooting groups. I am normally a .5 +\- .1 shooter. The flyer was my cold bore. Without the flyer it is a .42 group.
MIN 2800
MAX 2805
AVG 2802
SD 2 ES 5
Shot 1-2805
Shot 2-2800
Shot 3-2802
Shot 4-2802
Shot 5-2804
6C8FCA6C-9060-4318-8707-81BBD515F7B6.png
 
Sorry I have neglected this thread. I have been updating a thread in the bolt gun section. People didn’t seem to be interested in the reloading mechanics. 25 GT thread
On the reloading side the only problem I’m having is with the match master seating die. The 6mm stem is giving me a little variation in CBTO but it’s not really hurting groups or SD’s so I’m slowly working on it.

I have a little over 550 rounds on it so far. Throat erosion looks good so far at .001-.002. The brass is on its second firing and has straitened out. Run out is down to less than .002 total run out. The gun consistently puts down .5 MOA groups. Smallest .3 largest .6. Last time I ran it over the magneto speed es of 5 SD 2.2. First 4 shots were the exact same speed.
The final load I settled on was 36.7 of H4350 cci 450 .005 off the lands. 2800 FPS.
We ended up running it to 1500 yards and it was pretty easy to hit our 3x4 foot steel, in a shifty 11-1 o’clock 5 mph wind. At 1940 yards I went 1/9 and the group looked pretty big. That was about 100-150 yards past transonic. So I’m pretty sure the bullets didn’t like the transition but that’s along way and like I said that shifty off the nose wind makes some big movements in a 3.4 second bullet flight.
I’m really happy with it. Recoil has been great I’m seeing trace for the first time through the scope. (Prone) and seeing splash and hits off barricades past 250 or so.
 
Sorry I have neglected this thread. I have been updating a thread in the bolt gun section. People didn’t seem to be interested in the reloading mechanics. 25 GT thread
On the reloading side the only problem I’m having is with the match master seating die. The 6mm stem is giving me a little variation in CBTO but it’s not really hurting groups or SD’s so I’m slowly working on it.

I have a little over 550 rounds on it so far. Throat erosion looks good so far at .001-.002. The brass is on its second firing and has straitened out. Run out is down to less than .002 total run out. The gun consistently puts down .5 MOA groups. Smallest .3 largest .6. Last time I ran it over the magneto speed es of 5 SD 2.2. First 4 shots were the exact same speed.
The final load I settled on was 36.7 of H4350 cci 450 .005 off the lands. 2800 FPS.
We ended up running it to 1500 yards and it was pretty easy to hit our 3x4 foot steel, in a shifty 11-1 o’clock 5 mph wind. At 1940 yards I went 1/9 and the group looked pretty big. That was about 100-150 yards past transonic. So I’m pretty sure the bullets didn’t like the transition but that’s along way and like I said that shifty off the nose wind makes some big movements in a 3.4 second bullet flight.
I’m really happy with it. Recoil has been great I’m seeing trace for the first time through the scope. (Prone) and seeing splash and hits off barricades past 250 or so.
Love this. Really want to try one of these out. Running the blackjacks at 2800fps with little recoil would be money.
 
With the powder crunch I decided to run a ladder on what’s available. Tried Vihta
vuori N540. Starting from scratch on a wild cat I apparently started way to low. I normally try and run 10-12 shots with about 1% steps on a ladder. This was done in two separate runs. Other than 2 very slow nodes it is about 20fps per .3 grains. Recoil was equal to the H4350 and N540 metered exceptionally well. I’ll probably load up five at 33.6 and see how they do.

N540
28.5-2365
28.8-2365
29.1-2384
29.4-2419
29.7-2419
30.0-2443
30.3-2476
30.6-2474
30.9-2508
31.2-2521
31.5-2541
31.8-2558
—————-
31.2-2587
31.5-2610
31.8-2625
32.1-2647
32.4-2699
32.7-2712
33.0-2737
33.3-2757
33.6-2779
33.9-2798
34.2-2815
34.5-2841 ejector mark heavy lift
 
So I have a friend who just chambered a new rifle in 25GT. He has a large stash of IMR 4451. His rifle is using the same bartlien 5R heavy varmint and was chambered with my reamer. if it’s like mine it’ll probably speed up 50-60 FPS.
With the Ace 131

36.0 -2679
36.2 -2690
36.4 -2701
36.6 -2757
36.8 -2742
37.0 -2752
37.2 -2795
37.4 -2833

it also threw down a .388 MOA group at 100 with a random break in load.
 
Update. Ran out of blackjacks, barrel was pulled and put away for now. But just got 1000 of the Berger 135. My friend still has his together so I’ll post the results of those when they get in.
In the meantime here is my friend’s 1000 yard group recorded on a shot marker system. This was shot in high mirage (mid afternoon in New Mexico) his gun is now settled in and shooting at 2810 FPS.
Remember when looking at the velocity and SD/ES that is at 1000.
779B4376-51D4-4504-9074-3F2D70A2E6E3.jpeg
 
who did your barrel work, and who made the reamer?

The barrel work was done by a local smith but he’s not currently taking anymore work. The reamer was done by Manson. You can contact Manson he has the reamer specs. I used a .155 freebore. The specs on the original print specified a .320. Make sure to ask for the 155. Ask for the 25GT Ace.
 
I've read both of your threads.... this has got me really interested in the 25gt. One question...how do you think this would compare to say a 250 Savage? The 250 savage is an old-school case, but I was thinking that if I could get 25GT- like performance without having to go wildcat, maybe that would work better for my needs. I know nothing about the Savage either, so maybe it is not as easy to tune or not as efficient, etc.

Thanks in advance.
 
@Wapitiaddict
I really don’t know much about the 250 savage either but, I think the GT case would be easier to tune, steeper shoulder straiter walls, I would also think that you’d have a better selection of quality brass.
The 250 might also take a little wild catting for the reamer. I wonder if the saami spec reamers are short throated for the lighter shorter traditional 25 cal bullets. You could have to have the throat reamed or you might end up stuffing more bullet into the case.
In my opinion the thing about the GT case is it being close to 100% fill at the sweet spot of recoil/velocity for the heavy 25 cal billets. So I guess the bog unknown here is what I’d the H20 capacity of the savage case.
 
So correct me if I am dumb please. The 6.5 CM and all following cases were derived from the 22-250 case. Some modernizing like shoulder angle and barrel twists etc we’re done. Ultimate Reloader had a really good video/article on this. It more has to do with barrel twist. Any .250 Savage (parent case of 22-250) is likely going to be twisted way to slow. But add a modern twist and it will likely fall between the two of these.

As a newbie. Am I way off base?
 
So correct me if I am dumb please. The 6.5 CM and all following cases were derived from the 22-250 case. Some modernizing like shoulder angle and barrel twists etc we’re done. Ultimate Reloader had a really good video/article on this. It more has to do with barrel twist. Any .250 Savage (parent case of 22-250) is likely going to be twisted way to slow. But add a modern twist and it will likely fall between the two of these.

As a newbie. Am I way off base?
Yes you are sorta off base. The 6.5 creed is not from the 22-250, it’s parent case is a 30 tc.

And yes, steeper shoulder are a bit more efficient in combustion and the faster twist is needed to stabilize the longer higher bc bullets.
 
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Yes you are sorta off base. The 6.5 creed is not from the 22-250, it’s parent case is a 30 tc.

And yes, steeper shoulder are a bit more efficient in combustion and the faster twist is needed to stabilize the longer higher bc bullets.
Did the 30TC come from the 22-250? I swear I read that in a gun mag somewhere. But alas I also may be way wrong.
 
Did the 30TC come from the 22-250? I swear I read that in a gun mag somewhere. But alas I also may be way wrong.
Yeah sorta in broad strokes but there have been some divergences and optimizations over time so it’s not exactly a straight line to it sorta deal. They are all from the 8x57 depending on how far we stretch the relation thing.
 
Put the 25 GT barrel back on the the Impact last week. The 6 CM finally gave up. I’ve been looking forward to trying the new bergers out.

Most of the reports I’ve seen on the bergers versus the Ace have shown they are nearly twins and loads are within .2-.4 grains. I started out with a shot ladder just to get velocity, and ended up needing to go up .1 grain to get my velocity back where i was.
H4350
36.12738
36.32761
36.52776
36.72778
36.92797
37.12820
37.32821 stiff bolt

After that i ran 2, 5 round test groups, to check where it wanted to be seated. I tried .005 off, and .020 off. Much deeper than that it starts to impact case capacity. It seemed to like the .020 depth more. Ran a drop test on it and the BC came out to .340 G7. Gun is shooting right around .5 MOA with me on it. In nasty cold conditions.

Shot groups at 36.8
.8 MOA at .005 jump
.6 MOA at .020 jump (4 touching 1 flyer)
16 shots
Avg speed 2781
SD 6.5 ES 21


Bullet differences. 131 v 135
weight. 131 / 135
OAL. 1.442 / 1.415
OTB. .695 / .687
Boat tail length. .228 / .238 (approximately)

For more details on the gun and match performance check out 25GT thread.
 
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Been a while since I updated. I’ve put another 500 through the rifle in the last couple of months.
First of all the Berger 135s have been super consistent base of ogive, and not to bad on OAL. Weight has also been super consistent.
Bad news they seem to to create more pressure and to get my old speed of 2800 I’m running probably about .5 under max. I’m using the same jump. It’s not really bad but I’m not sure they would be safe in the rain with wet cases. I did have some problems with pressure shooting on moon dust last week. They run fine until the chamber or cartridges get dirty, dusty, or wet. Then stiff bolt lift and ejector swipes.

I just recently went to a new keg of H4350. Bad news is it is slower, good news is is also appears to be less pressure. 200+ rounds and no pressure signs. My buddy is still running at 2800 with his 4451, and no pressure.

I really think the aces were better for the experiment, but for now it’ll have to be the bergers. Maybe somebody from Hornady will see this and do a 128gr A-tip?

Current load is 36.8 H4350, cci450, gap brass, @ 2755.

Got to compare it to a full race 6gt. The recoil of the 25 is higher than the 6. But not unmanageable. I’lol measure the erosion when I get the chance and update.
 
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Been a while since I updated. I’ve put another 500 through the rifle in the last couple of months.
First of all the Berger 135s have been super consistent base of ogive, and not to bad on OAL. Weight has also been super consistent.
Bad news they seem to to create more pressure and to get my old speed of 2800 I’m running probably about .5 under max. I’m using the same jump. It’s not really bad but I’m not sure they would be safe in the rain with wet cases. I did have some problems with pressure shooting on moon dust last week. They run fine until the chamber or cartridges get dirty, dusty, or wet. Then stiff bolt lift and ejector swipes.

I just recently went to a new keg of H4350. Bad news is it is slower, good news is is also appears to be less pressure. 200+ rounds and no pressure signs. My buddy is still running at 2800 with his 4451, and no pressure.

I really think the aces were better for the experiment, but for now it’ll have to be the bergers. Maybe somebody from Hornady will see this and do a 128gr A-tip?

Current load is 36.8 H4350, cci450, gap brass, @ 2755.

Got to compare it to a full race 6gt. The recoil of the 25 is higher than the 6. But not unmanageable. I’lol measure the erosion when I get the chance and update.
I observed the same thing with the 135 berger in my creedmoor.
 
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Kenny from Eagle Eye Shooting Had some of the same issues, but 133's seemed to work much better for him in 25 Creedmoor. Might be worth looking at if you can get your hands on some.
I havent tried the 133’s yet but i have them on the shelf. Took some careful measurements and they are 100% identical in shape to my 135’s. Just thought it was interesting.
 
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(Copied from the thread in the Bolt gun Forum)

So bad news on the 25 GT front. Me and the cartridge are on the outs. Ever since I have switched to the Berger 135s I have been fighting pressure signs. Stiff bolt lift, ejector swipe, the works. I have downloaded it to 2750 fps, the bc has dropped to .320 G7. So the advantage of the slow high bc bullet over the 6mm’s is gone. There is a chance i have developed a carbon ring, and am planning on checking the throat soon. The barrrel is currently sitting at 2,073 rounds. Of which about are 800 have been working the bedgers.

my current load: 36.8 H4350, Berger 135, gap brass (5x fired annealed after 4), cci 450, .007 off the lands. impact Action, BartLein barrel.

My buddy is still having no problems with his load, i think he is 36.5 +/- IMR4451, Berger 135, cci 450, .010 jam, gap brass (3x fired annealed every load. Kelbly action bartlein barrel

I have another friend that built one. His was cut with a different reamer and smith, but the same specs from Manson. He is having problems with multiple loads and with his 200 shot round count can’t get Past 2730 without pressure signs, regardless of powder. Impact action bartlein barrel.

this weekend at the match my buddy with the Kelbly’s shot my rounds through his rifle for the whole match. His zero didn’t change and they were running at the same speed as his loads. (30 fps faster than mine: 2780). He had a little pressure but only at the end of the stage at 8+ rounds, a little stiff bolt lift. He did report that they felt a little spicier. (Perhaps that is just the different powder making a sharper pulse?)

So to make a long story endless, i need to concentrate on the rest of my season, and have decided to run a 6cm for the rest of the year. The death of the ACE bullet has lead to a pause of the cartridge. Perhaps this fall i will try some 133s and see if they help. But i am afraid the project may be shelved until the Ace comes back (not looking good) or someone else comes up with another heavy 25.
 
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(Copied from the thread in the Bolt gun Forum)

So bad news on the 25 GT front. Me and the cartridge are on the outs. Ever since I have switched to the Berger 135s I have been fighting pressure signs. Stiff bolt lift, ejector swipe, the works. I have downloaded it to 2750 fps, the bc has dropped to .320 G7. So the advantage of the slow high bc bullet over the 6mm’s is gone. There is a chance i have developed a carbon ring, and am planning on checking the throat soon. The barrrel is currently sitting at 2,073 rounds. Of which about are 800 have been working the bedgers.

my current load: 36.8 H4350, Berger 135, gap brass (5x fired annealed after 4), cci 450, .007 off the lands. impact Action, BartLein barrel.

My buddy is still having no problems with his load, i think he is 36.5 +/- IMR4451, Berger 135, cci 450, .010 jam, gap brass (3x fired annealed every load. Kelbly action bartlein barrel

I have another friend that built one. His was cut with a different reamer and smith, but the same specs from Manson. He is having problems with multiple loads and with his 200 shot round count can’t get Past 2730 without pressure signs, regardless of powder. Impact action bartlein barrel.

this weekend at the match my buddy with the Kelbly’s shot my rounds through his rifle for the whole match. His zero didn’t change and they were running at the same speed as his loads. (30 fps faster than mine: 2780). He had a little pressure but only at the end of the stage at 8+ rounds, a little stiff bolt lift. He did report that they felt a little spicier. (Perhaps that is just the different powder making a sharper pulse?)

So to make a long story endless, i need to concentrate on the rest of my season, and have decided to run a 6cm for the rest of the year. The death of the ACE bullet has lead to a pause of the cartridge. Perhaps this fall i will try some 133s and see if they help. But i am afraid the project may be shelved until the Ace comes back (not looking good) or someone else comes up with another heavy 25.
What length barrels? All those mid/high 2700 velocities seem fast to me, and the charges seem large. My 26” 25 CM is only going 2795 with 39.7 gr in Lapua brass.


You definitely cant just use 131 BJ load data with the 135.
 
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What length barrels? All those mid 2700 velocities seem fast to me, and the charges seem large. My 26” 25 CM is only going 2795 with 39.7 gr in Lapua brass.


You definitely cant just use 131 BJ load data with the 135
All the guns in question are running 28” 5r bartlien.
i agree With not just using the same data. I did an initial ladder and it looked like max was about 2800. ive Backed it down to the point I’d be better off with a 6mm dasher or GT. That’s why I’m taking a break from it. The cartridge really shines at 2800. But with the Bergers and 2700 fps it’s just not worth the recoil.
im Still thinking irs the bearing surface length. I’ve heard a lot of the 25 creed guys say the same as you. that they had to slow down with the Bergers. Another thing I might experiment with is running the freebore out for more jump or a slow h1000 speed powder. Just out of curiosity.
 
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What length barrels? All those mid/high 2700 velocities seem fast to me, and the charges seem large. My 26” 25 CM is only going 2795 with 39.7 gr in Lapua brass.


You definitely cant just use 131 BJ load data with the 135.
My 24" light Palma 25C & 135's is running 2851 with 42.1 H4350 in Alpha brass & no pressure signs. I have however been struggling to get a good load for the 135's. The aces were easy @ 2899 with 44.4 N555.

@High Desert duck - You may want to give the PVA 120 Seneca's a try. They're shooting great for me at 3000 in a 7.5T (PVA recommends 7.25T). Probably need the 7.25T + if your under 2900.
They're long as hell, but you've got plenty of mag room with a GT. I'm jamming the drive band .010 & cant even feel it when closing the bolt.
The Senecas are $$ though. G1 = .640 & G7 is .310
IMG_6416.jpg
 
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