.338 Whisper #2 in HK91 platform?

[avenger15]

Do you think it's feasible? I'm debating whether to go this route or buy an AR-10 conversion from SSK. However, I am not knowledgeable enough about the HK operating system to know whether it would be doomed from the start.

I'd love to have something like an HK51SD, but in a Whisper caliber.

[THE DOCTOR]

I doubt you could generate sufficient pressure in a 91 platform to make the rollers unlock with a subsonic cartridge(not sure but i assume that is what you are going for) maybe with a lightened mainspring maybe......?

Would be easier to do this project not that it would be easy on an HK anyway on a HK 93 that way you wouldn't have to weld the bolt face up to make it 338 whisper #2 that has the 221 fireball or 223 shortened the 93 would already be the right diameter.

Would be cheaper and easier on the ar platform for sure

but more unique on the HK

only you can decide if it is worth the hassle.

[avenger15]

I see what you are saying there about the 93, I was originally considering .300 Whisper through a Vector 53 clone I own, and might still go with that project for simplicity's sake.

[THE DOCTOR]

anything is possible if money is no object. do you want to integrally suppress it like the one in your picture or just put a can on the end of a 30 cal rebarreled 53?

[avenger15]

Doc, I already own a detachable 9mm can from an HK-94 converted by Ceiner into an MP5SD. I've been in contact with a guy over at HKPro.com who built his own 53SD, so maybe that project will pan out. From there, it would be relatively simple (I hope) to convert to .300 Whisper and then to expiriment with the right load for the round.

[THE DOCTOR]

in theory it should be simple but getting a fluted chamber like the 93 for a 338 will likely be difficult and achieving enough pressure to unlock the rollers will be a big hill to climb. trimming the mainspring can only go so far because it will not want to rechamber a new round just like the ar

i am running a wolff lightened spring on my ar and it works great

You might get wolff to make you a custom spring nice guy there would be worth a try

again I wish you lots of luck

[avenger15]

I wonder if I should just get a ported barrel and fire nearly full-power rounds through it and let the ports retard the fps.

[JFettig]

Avenger, the ports will not effect the thrust from the case when the bullet is in the case up until the ports. Your best bet would be to figure out what the case pressure should be, the timing of that pressure then try to duplicate it(nearly impossible in a completely different cartridge).

You might be able to make a new locking piece.

Jon

[THE DOCTOR]

You might be able to port the barrel enough somewhere between full power and subsonic using a fast pistol powder so the pressure builds fast then drops fast. Like I said it will be an uphill pull and obviously far easier on an ar platform.

You have to ask yourself is getting 60 grain heavier bullet 30 cal 240 SMK .685~ bc vs 338 300 SMK .750~ bc and a little better bc worth all this extra effort.

Another option to get the power you are looking for in the 338 cartridge would be to run the powdered tungsten bullets This company makes the best powdered Tungsten bullets out there.

http://www.drtammo.com/products.html

DRT makes a 124 grain 223 bullet you might try to get some of those and run it through your 93 and see if it would cycle subsonic with that heavy a bullet. Or you might buy some powdered tungsten 308 bullets they make a 280gr PT bullet that is the same footprint as a 208 amax awesome bullets but very expensive like 3-4 bucks apiece but compared to buying a custom barrel or having custom locking pieces built then finding out it wont' work after all and you have a very expensive straight pull bolt action.

You might try to take a 91 and run subsonic 308s through it and see if you can get it to cycle with a lighter mainspring and different locking piece before you start spending a lot of money on a custom barrel.


Just some ideas and Options

[JFettig]

Just to give you an idea of pressures of subsonic .223:
69gr SMK with 4.2gr of pistol powder(non comercial- around titegroup burn rate)
average velocity: 1038fps
Average Pressure: 16,200psi.

Thats no where near normal pressures, I can't imagine that subsonic .308 has much higher pressure, no where near enough to cycle.

Jon