6.5mm SMK - 140g vs 142g

[NealWright]

Hello, I'm trying to find some information here. We've always shot 100yds, and am now working out on 300yds ... I have a Savage 6.5x284 coming (kind of wish it was a 6br), but am curious on bullets.

Obviously, it seems that 142SMK's are the "it" bullet ... and subsequently, are sold out most everywhere. My questions, is how different can the 140SMK be? Is it a completely different profile, or just slightly shorter?

Thanks, Neal

 

[Rust]

A few years back when first starting off with 6.5 X 284 I did a little initial load testing with the 140 gr SMK. It proved slightly more accurate at short ranges than the 142 SMK.

The difference between the two is the shape, with the 142 having a higher BC for long range shooting. The 140 won't be giving up anything at 300 yards. At long range BC rules though.

I can't say I recommend a 6.5 X 284 for a short range plinking rifle as it burns out barrels at a pretty ferocious rate. If you are not shooting it in competition where long strings are required, don't let the barrel get hot.

And the 139 Scenars shoot very well too, as do the Bergers.

 

[MLC]

A moderate load with the 107 Sierras will likely hammer at 300 and be easier on your bore.

 

[camac]

I agree with these guys - chasing the very high BC for short range shooting might be very disadvantageous. If I ever use my 6.5*284 at 300 (ALMOST NEVER) I have a 120gr SMK load which hands down beats for accuracy anything I can get out of the 142's (>0.15 MOA difference). In low wind I use this load out to 600. But as wind picks up I switch to the 142's. At 300 the extra pace and accuracy you can get will make up for the BC advantage.

The BC of 140 to 142 is also very significant but this really only comes into play beyond 300 and the 140 should be more accurate as well. As a rule of thumb the really high BC, low drag bullets can be "finicky" but some rifles love them.

As these guys pointed out. Using a 6.5x284 for plinking or 300 shooting will be costly in the long run. Especially by the time you build up 2 loads (e.g. 142's and (140's, 120's or 107's)) you probably have already made a significant dent on your barrel life.

That being said - personally I would recommend you grab the 142's (or Berger 140's or Scenar's if you can't get the SMK'142's) and have a go at the longer range stuff. You should be pleasantly surprised and to be quite honest - more competitive at 600 than 300 with the 6.5 x 284. What you have to learn going from 100-300 is basically the same as 100-600 but you have the rifle for it.

 

[Rust]

Well, if you want to minimize barrel wear while working up a load there are two powders, H4831 and H4350 for the heavier bullets and with a 30" barrel go with the H4831 first. At 300 yards primer choice between Federal and CCI won't make a bit of difference. Work up in .5 grain charge weight increments. Do NOT let the barrel get hot so no more than six shots in a string taking your time at that. At 100 a good handload should shoot at or under 1/2".

Once you have a load that shoots, stop messing around with load development. You can use up half the barrel life chasing a load.

There is a really good 6.5 X 284 cartidge section on this site, read it.

 

[camac]

I totally agree with Rust there is some excellent info on the page. Also totally agree on keep it simple. BUT the page doesn't give much load data on the lighter pills. Same two powders do very well though.
I ran some figures quickly on JBM. The 123 SMK at 3120fps (my accuracy load for 120's) and 142 at 2950fps. at 300 yds the difference in windage at 10 knots is <0.1moa (5.3 inches to 4.9 inches net 0.4). Therefore even if you misjudged the wind by up to 10 knots it would not make up for a decrease in accuracy of 0.15moa (e.g 0.5moa vs 0.35 moa). For 300 you should put preference on accuracy over BC....(to a point). This is why the 6BR is so great at 300 - very accurate with reasonable BC.
At 600 the same two loads will be around 0.2 moa different which starts to make a difference but most guys can judge much better than a 10 knot gust.