short barrel on a valmet Petra .308

[Petra308]

Hello all,

I' am looking for expert advice regarding short .308 barrel in a semi auto rifle.

I have a Finnish Valmet Petra .308, it had damaged wood parts so I replaced the butt stock with an ATI stock and removed the front part to install 2 picatinny rails, not winning any beauty contest but it does the job on wild pigs at dusk with implacable regularity and the rifle is very reliable, I seldom miss using iron sight only.
I only hunt at short distance, 100 yards max. I fitted a Finnish Jaki suppressor to the rifle and it is now way too long to be practical and handy in thick bush, I therefore plan to shorten the barrel and re-crown it myself and leave the suppressor on permanently, due to the expected increase in muzzle blast. What would the be the minimal barrel length I should consider? I am not worried about losing fps but other parameter will need to be taken into consideration.
The barrel is 20'' and there is 8.8'' of it from muzzle to gas block, so in theory I could cut at least 6'' out of 8'' and leave 2'' enough for the threading, but is 14'' too short for .308? Should I expect a variation of aim using the iron sight (the fore sight is on the gas block) and would the 308 (I usually use Hornady American gunner rounds) stabilize correctly out of a 14'' barrel? will the semi auto cycling be affected by the shorter barrel despite the suppressor?
The norm for short barrel in .308 seems to be 16.25'' or 16.50'' but not sure if this is for legal or ballistic reasons, thank you to give me your opinion.

Thank you and best regards,

Fred

 

[SC45-70]

Hello all,

I' am looking for expert advice regarding short .308 barrel in a semi auto rifle.

I have a Finnish Valmet Petra .308, it had damaged wood parts so I replaced the butt stock with an ATI stock and removed the front part to install 2 picatinny rails, not winning any beauty contest but it does the job on wild pigs at dusk with implacable regularity and the rifle is very reliable, I seldom miss using iron sight only.
I only hunt at short distance, 100 yards max. I fitted a Finnish Jaki suppressor to the rifle and it is now way too long to be practical and handy in thick bush, I therefore plan to shorten the barrel and re-crown it myself and leave the suppressor on permanently, due to the expected increase in muzzle blast. What would the be the minimal barrel length I should consider? I am not worried about losing fps but other parameter will need to be taken into consideration.
The barrel is 20'' and there is 8.8'' of it from muzzle to gas block, so in theory I could cut at least 6'' out of 8'' and leave 2'' enough for the threading, but is 14'' too short for .308? Should I expect a variation of aim using the iron sight (the fore sight is on the gas block) and would the 308 (I usually use Hornady American gunner rounds) stabilize correctly out of a 14'' barrel? will the semi auto cycling be affected by the shorter barrel despite the suppressor?
The norm for short barrel in .308 seems to be 16.25'' or 16.50'' but not sure if this is for legal or ballistic reasons, thank you to give me your opinion.

Thank you and best regards,

Fred

If you live in the USA, to be legal the barrel must be at least 16 inches, unless you plan on filing a form 1 for a short barreled rifle.
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[Petra308]

Hello, I am not in the USA, no restriction on barrel length, so is 14'' OK in terms of ballistic and semi auto cycling, if the fps loss is not an issue?

thanks a lot,

fred

 

[edwardware]

Ballistics by the Inch doesn't have a .308Win dataset, but you can look at .223 for an analog. You can also extrapolate from other data, limited to >16" for legal reasons.

 

[Blue68f100]

This being a gas operated AR, You need a min of 5-6" past the gas block port for the gun to function. Don't know how the can will impact this. I know it does play with the gas pressure though.

 

[SC45-70]

I don't know about a 308, but a 16 inch .556 cut to 11 inches on an AR works fine with a suppressor attached. I have not tried it without the suppressor.
I think you could shorten a 308 2 inches and still have it work fine.
Worst case scenario, if you shorten it and it doesn't work without the suppressor attached, you can open the gas port and install an adjustable gas block.

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