Older .25 Sumatra

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JamesD.

JamesD.

Member
Dec 9, 2015
2,566
308
NE PA, United States
I have an older Sumatra coming. I never realized this but they are listed as 1:18 RH twist, whereas everyone else went with 1:16 like .22LR

The gun in question I'm told LOVES a discontinued Air Venturi 50 grain .25 that came in a blue plastic case. Any info as to what these older ones liked besides these?

He may have stumbled upon the best thing he could have as it is said to be putting those 50 grain .25's in a 1/4" @ 40 yards. They're spire point ones. I see some casters have some similar ones; but I'll have to mic the ammo, swage barrel, do all the testing. Found a quick disconnect for $20.00

So, what you guys using as I don't need to buy 20 types to test. 

Also, what's anyone seen as far as tunes for these? Full out power shots & a medium say 50ftlb bell curve. What can I expect between those 2 on shot counts, 500cc.

I owned one before, had an adapter, nice LDC. I don't need it where I live, & it makes it long but I like quiet.
 
James,

The JSB's did well in mine. A couple years ago I had one and here is the "notes" from my tuning. Mine was a single tune carbine and I tuned it for 12 shots.



Well I picked up 2 different size springs at McMaster. One is the same diameter wire as stock (.054") and the other is smaller at .047".

When I initially got the gun I fired fulls mags of JSB King Heavies (33.95g)starting at 3K on different wheel settings.

Highest - 965,941,928,902,882,865 70FPE declining to 56FPE
Lower - 948,938,928,918,884 68FPE declining to 59FPE
Lower - 916,910,892,883,879,853 63FPE declining to 55FPE
Lowest - 763,762,758,745,741,736 43.9FPE declining to 41FPE

Only the lowest setting kept the speed w/i 4% for the 6 rounds.

I did some testing with both springs in different lengths and wound up with the below strings.

.047 spring 4.75" long
Wheel set 9 clicks down from max
Fill Pressure - 2500psi
JSB Kings -25.4g
12 shots (2 mags)
48FPE Avg
906
919
934
934
931
931
937
928
925
915
911
903

.054 spring 3.5"
Wheel set 8 clicks down from max
Fill Pressure - 3000psi
JSB King Heavy -33.95g
12 shots (2 mags)
58FPE Avg
861
866
877
887
887
891
892
892
886
879
876
871

So I was able to tune the gun to 2 full mags at each of the power settings. Changing between the 2 is very simple. Two screws on top of receiver. Remove spring pin from hammer guide, remove and replace spring. Move power wheel 1 click. Fill to appropriate setting.

The benefits are a much more consistent string. 12 shots is plenty for hunting. Easier cocking and MUCH easier trigger pull. Lower noise. My Roy Kasten addition does a fantastic job, but it is even quieter when not wasting as much air.
 
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Guys, thank you SO much. I don't have a chrony or money to waste testing so this saves me a ton of time & $. The wire dimensions are what I was after, thank you.

The mold company looks GREAT, but a little confusing. That link didn't seem to work so I just went to it. Between Gene at PA, Will Piatt, Mr. Hollow Point, this company you showed as I do have tons of lead to cast, I think I'll get a custom mold made once I swage & mic it. I'll try to find close to 50 grain spires, & Bob has some. 1/4 @ 40 is beyond good enough. Just to find new supply or have them make a mold around the 30 I have left.

110ftlbs is hot. If it could do that for 10 consistent shots, I'd have no need to buy a 16 shot regulated RAW .357, LOL. I'm going to tune her down to your 48ftlb ave tune or even a little less. My old AZ Rapid was spitting 25.43 Kings at 880. I may be able to get the 22 shots PA claims at that level. Hey, the fun is in trying but it's helpful to know where to start. Thanks so much guys & a HUGE thank you to Lefty Craig.


 
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Got some more info for any who care. Sumatra barrels are NOT choked. They're usually right at .251". They are perfect for cast slugs, though I'm not so sure 1:18 is better than most average 1:16 barrels for .22, .25 diameters & weights. poop, we've got .177's from under 6 grains to 29. We have .22's from alloy light 10 grains to 33.95 pellets & slugs to 55 grains & .524" long. That BC will shame a JSB 33.95. It'll shame an Eley Match .22LR. We have .25's from 16 grains to 105 grain slugs, but those are for specialty breeches, guns. the more common ones are 35-73 grains & the lengths are .361 to .651" so some of these hot valved small bores can out perform the dogs of the big bore world.

These custom slugs have me seriously guessing if I really want a RAW .357 as it's 130ftlb 16 regulated shots with 81 grain JSB's that retain 30.5+ftlbs at 300 yards & only have 23.6' of drop. There's custom .257's out there that would dog those specs; but are there ANY that can come close to 16 regulated shots at the given power or more? I don't think so unless I build a custom backpack frame, (flamethrower style) to hold 2 Great White 4500psi tanks from Joe Brancato, tethered to my custom Doug Noble Air Force .257

I'm just going to play with my new Sumatra while I save for a Bauer for sure. I'll decide later with what long range rifle to go with. New things at every shot show. Prices coming down. Custom builders getting their works perfected.
 
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" 110ftlbs is hot. If it could do that for 10 consistent shots, I'd have no need to buy a " 

Not a chance. Had a career 707II that would hit 99fpe for one shot. Have tried Sumatras ( okay back when they had 3 power settings but anything is tunable) .

Those korean power house rigs have a radical cliff shot curve.

With no reg 6 shots at 60fpe would be very well balanced and with a reg something under 30 shots at an even 50fpe is normal.

If wanting max power get used to 2-3 shots & refill.



John


 
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Yes Tom, thank you. The rifle is arriving this weekend according to tracking.

I've noticed a few things, and now I guess they all changed 10yrs ago. The flip up too low peep sight was replaced with a v blade in front of breech.

I don't believe the cheek piece is adjustable any longer.

The new Sumatras have clear mags, and a quick disconnect. I can switch the probe fitting out in 5 minutes for a $20.00 quick disconnect.

So, I'm assuming I'm receiving a .253 groove, .251 land 1:18 twist barrel. It is the 500cc full size. I don't plan on 2-3 shots. I'll have it set for at least 6 to 12, and owning an older one myself 8-10 years ago, There's plenty more shots but yes they drop off. Either adjust the wheel or hold over for given distance. Given how many ways one could tune this rifle with different springs & TP wheel restrictor.

Spysir, if I get a reg installed by Will Piatt when he reseals my Rainstorm, rebuilds that reg, I'll be thrilled if he gets 5 full mags or more at 40-50ftlbs. Depends on what the barrel likes in head size, weight. 

A very good long time friend from another forum sent this rifle before payment for me to inspect. He just asked I pay shipping if not happy. At his asking price, there's no way on Earth I won't be happy. I may even need to buy another new one. One regulated for pellets somewhere between 40-50ftlbs, and one for sized slugs & retaining some wallop out to 200 yards. For this rig, if it retains 12-30ftlbs at 200 I'm happy, even if only 6 consistent shots.
 
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The only clear mags I've seen or heard about were .22. I believe Will Piatt o-rings the .25 magazines to retain the .251's better. If you lathe your own o-ring slots, cut until it just touches the chambers and then use a narrow file to finish. Before I had a lathe a neighbor did mine and went too deep by about .020" so I had to remove the o-rings to load bullets and then put them back on. The o-ring should only intrude about .005" or so into the chamber so as to not catch on the bullet. Regards, Tom
 
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JamesD, once upon a time I had two of the most highly tuned and most powerful .25 Sumatra 2500's. The most accurate slugs out of the factory barrels are the Hunters Supply 49 grain flat nose slugs sized to .251...my Sumatra would push them at around 1050 ft/s. At 50 yards I would get a very concentric group about the size of a dime. The Hunter Supply hollow points and round nosed slugs were never as accurate as the flat nose were. I shot every slug in .25 cal slug available at the time and even some custom boat tails Bob Sterne sent me to try, but the very best of all were the Hunters Supply 49 grain flat nose. As for pellets? The Benjamin .25 cal. pellets worked the very best even on highest power settings above and beyond every other .25 cal. pellet on the market. Try both of these... you will be very happy you did.
 
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JamesD, once upon a time I had two of the most highly tuned and most powerful .25 Sumatra 2500's. The most accurate slugs out of the factory barrels are the Hunters Supply 49 grain flat nose slugs sized to .251...my Sumatra would push them at around 1050 ft/s. At 50 yards I would get a very concentric group about the size of a dime. The Hunter Supply hollow points and round nosed slugs were never as accurate as the flat nose were. I shot every slug in .25 cal slug available at the time and even some custom boat tails Bob Sterne sent me to try, but the very best of all were the Hunters Supply 49 grain flat nose. As for pellets? The Benjamin .25 cal. pellets worked the very best even on highest power settings above and beyond every other .25 cal. pellet on the market. Try both of these... you will be very happy you did.
Click to expand...

Thank you tons Chuck. I've been playing with it spitting JSB 25.43's & 33.95's, what it came with. It's a very interesting rifle as it has power in spades. I can plink with the 25.43's at 32 yards even on the 2nd power setting and there's drop, but it's still flattening them out against a steel 55 gallon drum lid. Send those on anything well setting 4 or above and pellets just go through the first lid and disintegrate. depending on angle of lids, you may find flattened fully petaled pellets, or too fast and they've fragmented into super tiny pieces. 

I'm definitely taking your advice and ordering both of your suggestions. I had about 30 50 grain solid core slugs. Even on high power. full fill, they might do great at long range but I'm not sure the lead is hard enough to make use of all that power. It goes through the first lid almost punching a clean hole as a .22LR would, but then is about spent and crushed flat. Probably great for hunting but I'm really just a mid to long range plinker shooting groups for my own enjoyment. I'll see how well the 2 you mentioned fly.
 
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