SVT able to handle 308 pressures?

H Wally

H Wally

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Basic question: Is there any past evidence of the SVT being successfully rechambered to 308? Any past evidence of it taking the pressures involved? Any past evidence of max pressure testing on the SVT similar to Julian Hatcher and Ackley's destructive tests on various rifles.

Complex question: I want to rebarrel an SVT to 308. The gun will have a new barrel, gas system, and have a refitted bolt face and extractor. I'm able to cope with most other issues in the build, however I don't have the info on the SVT's maximum pressures - the x54r cartridge being far lower than the 308, but the action also being overbuilt for the 54r. My main concern is the narrow long bolt of the SVT and the smallish recoil lug on the SVT. The FAL's bolt is slightly larger in diameter and definitely shorter, and likely of better metallurgical quality. In this case, I'm concerned headspace would quickly go out of spec and the gun would end up either with case failures or a bent bolt. Before putting the energy into building the setup to test the idea I'm asking in case anyone out there has any knowledge on the subject, or might know of a source.
 
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I can't remember where I read this , but it was a magazine article comparing several of the semi auto's of the mid 40's to the mid 50's .
what I came away from it was this , the svt40 was basicly just beating its self to death as it could barely handle the pressure of the 7.62x54 round . ..... now thinking about it , was it a matter of too much chamber pressure , or too much pressure in the gas system beating the action to death by a "gun writer" who didn't know any better ?

the case is straighter with much less case taper on the 308 , which would equal less backthrust at the same chamber pressure .
what about the bolt face ?
 
Bolt thrust is a product of casehead diameter and chamber pressure. Bolt thrust will be less with the 308 at equal pressures. Gas port pressure is a product of pressure at the port and it's size and shape, all of which can be modified.

It's doable.
 
gewehr76 said:
Enjoy SVT40 for what it is, a historical first generation semi auto rifle that fought blodiest war in human history to date. Making a phazer out of it will not change anything. It still going to be old SVT40 with all its positives and negatives present.
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I hear and support what you say. However, the op seems to be willing to "experiment" for the benefit of us all.

As for me, I'm keeping my SVT-40 "as is" and will continue to fire off 7.62 x 54r milsurp rounds.

Speaking of phasers...

"There are two settings: stun and kill. It would be best not to confuse them."

Malcolm Reed, Enterprise
 
burnt_servo said:
I can't remember where I read this , but it was a magazine article comparing several of the semi auto's of the mid 40's to the mid 50's .
what I came away from it was this , the svt40 was basicly just beating its self to death as it could barely handle the pressure of the 7.62x54 round . ..... now thinking about it , was it a matter of too much chamber pressure , or too much pressure in the gas system beating the action to death by a "gun writer" who didn't know any better ?

the case is straighter with much less case taper on the 308 , which would equal less backthrust at the same chamber pressure .
what about the bolt face ?
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Hmm - I was under the impression thrust was also related to surface area of the base of the cartridge (or internal base area?), in which case the x54r has larger base surface area. I haven't crunched the numbers so I suspect you're likely correct that the 308 might generate less thrust. I think there was an Ackley article demonstrating that with a suitable cartridge the bolt primarily supports the cartridge from failing at pressure rather than holding it in place, as a dry cartridge and chamber create enough friction to largely stay put.

For the bolt face I was thinking of fitting a ring to make up the difference in rim diameter and center the cartridge and a longer extractor claw.

MattRidge said:
AFAIK, there has been more or lees successfull attempt to convert SVT-40 to 303-British.
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Yep - though it's my understanding that 303 is more similar to x54r in thrust, pressure and case taper than 308.

burnt_servo said:
did some googling and found a couple references to svt40's rechambered to 308 , no real info ...... then I started daydreaming ...... what about 45-70 ?
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Hahah - I thought about that too, though for my purposes 45-70 doesn't fit :p Unless I get a second parts gun :p

desporterizer said:
How do you figure max pressure on the 54 is way lower than .308?
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I was basing it off max pressures listed in a couple of my reloading books and what I've found online, but for the most part I'm piecing things together. I also see that I may have found some sources using PSI and some using CUP, so that might be where my error was. If I solely use Hodgdon's data and the fact they only provide CUP data for x54r then they cite 46 400 CUP as max for x54r while 308 is given 51 400 CUP as max for 308. It's imperfect, but at least it's one source so there shouldn't be too many discrepancies.

Andy said:
Bolt thrust is a product of casehead diameter and chamber pressure. Bolt thrust will be less with the 308 at equal pressures. Gas port pressure is a product of pressure at the port and it's size and shape, all of which can be modified.

It's doable.
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Yep - it would need a new gas system entirely so I'm hoping that would help.

desporterizer said:
It would be interesting to see how well a conversion would feed from a svt mag.
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Yep - I dicked around with some 3006 cases as I didn't have any 308 and they fitted and held well, though the 3006 were too long to feed properly, so I've got hope for the 308

gewehr76 said:
Enjoy SVT40 for what it is, a historical first generation semi auto rifle that fought blodiest war in human history to date. Making a phazer out of it will not change anything. It still going to be old SVT40 with all its positives and negatives present.
Click to expand...

In this case the SVT in question has a wrecked chamber and is missing a lot of parts, so it's got no historical value, at least until they become rarer. It will also indeed still be an SVT 40, which is part of the goal since we can't have SVD's, it's going to be a lookalike externally.

lalunette said:
I hear and support what you say. However, the op seems to be willing to "experiment" for the benefit of us all.
As for me, I'm keeping my SVT-40 "as is" and will continue to fire off 7.62 x 54r milsurp rounds.

Speaking of phasers...
"There are two settings: stun and kill. It would be best not to confuse them."
Malcolm Reed, Enterprise
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Haha - yep, I enjoy tinkering when it doesn't damage a historical piece. Since this one requires a rebarrel regardless of intent, I figured I'd see if I could have some fun with it :p
 
Dsiwy said:
308 max chamber pressure is 62,000 and 7.62x54r is 52,000

so I would tread carefully
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Agreed - that's largely what's leading my train of thought. I'm hoping to get a fairly solid idea of whether it's feasible in concept and how likely the gun is to survive longterm in that chambering. Ideally an already converted SVT would be the best since it would have already dealt with the whole concept and come out the other side.

For my knowledge - where were you getting those specs from? I'm finding enough variation in Max specs between cartridges that it's tough to tell exactly how much the 308 is pushing the design. 308 is definitely hotter, but how much so is pretty murky.
 
Dsiwy said:
308 max chamber pressure is 62,000 and 7.62x54r is 52,000

so I would tread carefully
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The thing is these are just numbers there no unit of measure and how they were measured. Even if they are bith PSI they might be messure differently so who know the actual difference.
 
Caleb314 said:
The thing is these are just numbers there no unit of measure and how they were measured. Even if they are bith PSI they might be messure differently so who know the actual difference.
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There is, it is "SAAMI PSI standard" and its done in a lab setting by people much smarter then us :p
 
Dsiwy said:
There is, it is "SAAMI PSI standard" and its done in a lab setting by people much smarter then us :p
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Do you think they bothered to measure milsurp ammo? In the real world, I would bet there is very little difference between the working pressure of the two cartridges.
 
It would be interesting to compare the critical dimensions of the SAFN-49 bolt and the bearing insert with those of the SVT-40, which it resembles quite closely. My general impression is that the '49 is more heavily built, in general, but that's just a qualitative impression. The '49, of course, handled 7.92X57 and 30-06, etc. With regard to .308/ 7.62X51, there has been discussion in the past about whether owners of Ishapore 2A/2A1 Lee-Enfields should use only NATO spec ball and avoid .308 spec. The implication is that the military spec 7.62 is safer (ie. lower pressure?) but, as with most interweb debates, I could never find a full resolution of the question. I do, however, stick to the mil-spec ammo with my own 2A1.

Milsurpo
 
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