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johngarnett

Terminal velocity

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This is a question for F'ers, FTR'ers and TR'ers!

What muzzle velocity will still be supersonic and stable at 1000yds in 308 using 190 SMK please?

I have an idea from the various calculators available but I wonder if anyone has real info and data please?

(12T 30" barrel, Powder prob Vit150)

Thank you

JohnG

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Hi John. 

I've just been running some numbers for you here and it looks like you will need to get the 190's up to, at the very least, 2700 fps to be just on the edge of supersonic / transonic (c. 1300 fps) at 1K, but I think you will hit a bit of a problem with bullet stability as the speed drops off.                                         The stability calculators seem to indicate that even at that muzzle velocity, you're only getting a S. G. of just over 1.4, so its going to be marginal from the beginning. By the time you've lost several hundred fps over that distance I think they'll start tumbling. 

I've personally only used these bullets once before, about 20 or so years back, in a 1:12 twist barrel and they weren't that great, and I have since been told they really need a 1:11 or, better still, a 1:10.

In addition to that, to get to those muzzle velocities using N150 you will need a compressed charge in the case (even if you seat the bullets long) and will most likely get some very high chamber pressures - somewhere in the region of high 50's / low 60's thousand psi 

Please don't take this as gospel, and if anyone can chip in and correct what I've said, then please do - as I'll have learned something new as well.

All the best.

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I know some FTR shooters that use the 190gr TMKs and there very good.not sure on there loads but they will be using 30 odd inch 1 in 10 barrels i think, they would be stiffish loads.

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Thank you for the replies. I was reckoning on just over 2700fps as mv for the 190s.

I have been using TR140 & RS50 and 155 Lapuas for many years quite successfully but then tried N150 and 190s and turned to one hole groups at 100yds so hopefully good at 1k!

Thanks again

JohnG

 

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Don't worry about it and forget what some literature stipulates.  The smk 190 behaves VERY well through the transonic region and I've consistently shot these at moa to 1000 yds when launched at 2600fps.  They perform equally well as TMK175's shot at 100fps faster and I have on occasion matched my 6.5CM 139 Scenar loads (well above transonic at 1000yds) shooting the venerable old smk190 from my .308.  It's a great jump and transonic tolerant bullet.

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I’ve shot the SMK 190s out if my (now sold) Sako TRG22. They reached 1000 yards ok but the accuracy wasn’t there. I put that down to tge 26”barrel limitations.

It’s a great bullet to tune. As VarmLR says they are very jump and transonic tolerant but they have the BC of a nail. Because of this I didn’t know any F TR or F Open guys who use them. Some of us are having success with the newer 195 TMK but even that doesn’t have a good BC compared to most 200 grain bullets.

Having said that, the 190 SMK is still popular with some Match Rifle ( MR ) shooters but they push them hard.

They need at least a 1:11 twist barrel though.

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