What caliber is this rifle?

[Xtracrispy]

So a while back my friend picked up a Springfield 1903A3 barreled receiver that was supposed to be chambered in 25-06. He bought a box of 25-06 Remington and after shooting it was quickly determined that it was not 25-06 Rem.

What does it look like? After some research it looks like maybe 25 Gibbs, But there also seems to be a 6mm Gibbs and 6.5 Gibbs. A loaded 25-06 falls into the chamber so far the extractor won't grab it(because of the different shoulder), so I'm assuming it's not a 6mm.

Obviously we would need to measure the actual barrel diameter to know for sure what size bullet it is, but are we on the right track?

[LynnJr]

Looks like a Gibbs maybe an Ackley Improved.
Measure the fired rounds neck and that will tell you the caliber. Harbor freight calipers run $15 and will work good enough for this purpose.
To avoid the casehead separations you can fireform using red dot or unique and Cream of Wheat breakfast cereal.
Start at 12 grains.

[scamp62]

+1 on AI

[ar15barrels]

That is NOT a 25.06 AI.
That fired case has a much shorter neck and the neck-shoulder junction looks forward quite a bit as evidenced by the case failure.
A proper 25-06 AI would fire standard 25-06 ammo with no headspace or case failure issues.

[ElvenSoul]

25 Remington the long forgotten

http://www.chuckhawks.com/25_remington.htm

[ElvenSoul]

The only other .25's are

.257 Roberts
250-3000 Savage
257 Weatherby

[ar15barrels]

25 Remington the long forgotten

http://www.chuckhawks.com/25_remington.htm

You are so far off base that you are not even on the same kind of playing field.
Take that volleyball and get off the football field..

[LynnJr]

The 25 Remington had a long neck and doesn't look like that case in the picture.
And they make a 25 WSM and a 25/284 and about 60 other wildcats as well.
25 Ackley Krag
25 BR Spencer
25 Gibbs
25 IHMSA
25 Krag
25 MRC
25 STW
25 WSM
25 x 257
250-3000 Ackley
25-06 Ackley
25-06 Mashburn Improved
25-270
25-270 ICL
25-275 Hoffman
25-284 Winchester
25-6.5 Remington Magnum
257 Ackley .284 neck
257 Banshee
257 Brotherton
257 Roberts Ackley
257 Roberts Ackley .284 neck
257 TCU
6.35 x 59mm
25 RUSM
25/300 Ultra Mag
.25/26 Nosler

[SonofWWIIDI]

Perhaps you might consider casting the chamber?

[kblack583]

This looks close.

http://stevespages.com/jpg/cd25gibbs.jpg

[Horrendo Revolver]

You are actually looking for the cartridge the rifle is chambered for, not just the caliber.

[Pofoo]

Perhaps you might consider casting the chamber?

This video give a pretty good over all process, but, there are a few things to be aware of. Primarily, don't over fill the action into the locking lug recess. You wouldn't be able to pop out the casting.

[FLIGHT762]

Look at the bolt face. See if it has been opened up from a standard face to a magnum case head.

[Xtracrispy]

Thanks for the input. Seems to confirm our fears that it's a wildcat. We knew it was a long shot but were hoping someone would chime in and say "That's definitely an xyz commercialy produced round". After talking to him it sounds like he is going to sell it and get a 30-06 barreled action. If it's any of the cartridges it seems like it is, they are too rare and expensive for him and his cheap range toy.

I might mess around with it some more for some closure, but I don't know that it matters too much exactly what it is at this point.

[NapalmCheese]

And they make a 25 WSM

25 WSSM

https://en.wikipedia.org/wiki/.25_Winchester_Super_Short_Magnum

Apparently 25 WSM had/has pressure issues while 25 WSSM was better behaved; thus winchester only produced the WSSM.