Range Report 308 Win, 220gr SMK, RL17

M

MontanaMarine

MGySgt, Ret.
Full Member
Minuteman
Dec 9, 2001
2,237
520
63
Canyon Ferry, MT
#1
Did a chrono ladder today to see what kind of velocity I might find before excess pressure appeared. Accuracy testing will follow.

I only fired two rounds of each charge to get an idea of velocity/pressure.

Rem700 308
20.5" factory bbl, 1/12 twist
Win brass (58.0gr H2O capacity)
220gr SMK, moly'd
OAL 2.82" (fits in magazine, .11" jump to lands)
CCI 200 primer

Reloder 17
46gr - 2368, 2401 (velocities 30 feet from muzzle)
47gr - 2402, 2448
48gr - 2484, 2463
49gr - 2535, 2532

The 46-48gr loads were sooting the necks, the 49gr load was lightly sooted. Primers and bolt lift were good. 47-49gr are compressed, but not enough to mark the bullet with the seater.

I know it's a small sample, but the velocity spread really tightened up as I got up to 49gr. I'm going to load up some with 49gr for accuracy testing. Conventional opinion may be against the 1/12 twist bbl, but these 220s are actually .05" shorter overall than the 208 AMax.

P9130010.jpg



<div class="ubbcode-block"><div class="ubbcode-header">Code:</div><div class="ubbcode-body ubbcode-pre" ><pre>
Gun / Ammunition : .308 Win, 20.5" Rem Varmint bbl, 1/12. Win brass
Bullet : .308, 220, Sierra HP MatchK 2240, moly'd
Bullet weight : 220 grains or 14.26 Grams
Muzzle velocity : 2545 fps
-------------------------------------------------------------------------------------
Range Velo Time of Energy Path Deflection Total Sight correction Target
city flight to at crosswind drop for setting new lead
LOS of 10.0 Mph zero range 33 fps
-------------------------------------------------------------------------------------
·Yards fps s ft.lbs. in. in. MOA in. Clicks MOA yds ·
-------------------------------------------------------------------------------------
| 0 2545 0.0000 3165 -2.0 0.0 ----- 0.0 ------ ----- 0.00
X 100 2426 0.1197 2877 0.0 0.3 0.30 2.7 0.0 0.00 1.31
| 200 2311 0.2465 2610 -3.9 1.9 0.90 11.4 +5.5 +1.89 2.70
| 300 2199 0.3802 2363 -14.4 4.7 1.49 26.6 +13.4 +4.61 4.16
| 400 2090 0.5203 2134 -32.1 8.6 2.05 49.0 +22.3 +7.69 5.69
| 500 1983 0.6659 1921 -57.3 13.5 2.57 78.9 +31.9 +10.96 7.28
| 600 1879 0.8204 1725 -91.4 19.9 3.17 117.7 +42.3 +14.57 8.97
| 700 1780 0.9860 1547 -136.1 28.3 3.86 167.2 +54.0 +18.59 10.78
| 800 1684 1.1615 1385 -192.3 38.4 4.59 228.0 +66.8 +22.97 12.70
| 900 1590 1.3457 1236 -260.3 50.1 5.32 300.7 +80.3 +27.64 14.72
| 1000 1501 1.5379 1101 -340.9 63.2 6.03 386.0 +94.7 +32.57 16.82
| 1100 1417 1.7428 981 -437.7 78.5 6.82 487.5 +110.5 +38.01 19.06
| 1200 1340 1.9617 878 -553.3 96.3 7.66 607.9 +128.1 +44.05 21.45
| 1300 1270 2.1912 788 -687.8 116.0 8.52 747.1 +146.9 +50.54 23.96
| 1400 1207 2.4337 711 -844.9 137.9 9.40 908.9 +167.6 +57.64 26.62
| 1500 1152 2.6883 648 -1026.6 162.0 10.31 1095.3 +190.0 +65.36 29.40
| 1600 1104 2.9545 596 -1235.1 188.0 11.22 1308.5 +214.3 +73.72 32.31
| 1700 1064 3.2314 553 -1472.4 216.0 12.13 1550.5 +240.4 +82.71 35.34
| 1760 1043 3.4021 532 -1629.0 233.6 12.68 1710.0 +256.9 +88.39 37.21

</pre></div></div>
 
#5
Re: 308 Win, 220gr SMK, RL17

Watching with interest Shane...

One of the things I'll be curious to see, is the performance in wind vs. the 208. My 208's are getting just over 1/2 the wind correction called for by JBM, where my buddies 200 SMK's are *really* close. This is where I've found the 208 to really shine.

So, if you can do some back-to-back testing in the same wind conditions, I'd be interested in that data.

(now I know why you didn't answer my PM about the 208's
grin.gif
)

John
 
#6
Re: 308 Win, 220gr SMK, RL17

For wind, the 208 at 2600 fps and .648 BC should beat the 220 SMK at 2545 fps and .629 BC, but the difference shouldn't be a whole bunch.

QuickTarget calcs 5.5 moa vs 6.0 moa at 1K, 10 mph full value, in favor of the 208 AMax.

 
#7
Re: 308 Win, 220gr SMK, RL17

Interesting post Shane, I'd not considered anything heavier than a 200 SMK from a 1:12 to be honest.
I've been using the 208's and 220's in a 300WM and the results of the 208's have been exceptional. However with the 208's being like rocking horse shit to get hold of I've not bothered trying them in 308. I do however have plenty of the 220's to hand so very much looking forward to see the results of your accuracy testing.

Ed
 
#10
Re: 308 Win, 220gr SMK, RL17

I'm trying the 220 on a whim, because I happen to have a box of them onhand. The way the bullet is shaped, it's easier to fit it in the mag. The tangent ogive puts more mass forward, less in the case. That leaves more powder room too.

I have some test loads loaded up, mag length (2.82" oal), 49.0gr RL17, 2545 fps.

Should have some range results posted up this week.
 
#11
Re: 308 Win, 220gr SMK, RL17

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hill billy</div><div class="ubbcode-body">Curious why you picked the 220 over the 210 with a BC of .645 if I remember right? </div></div>

The 210 makes more sense on paper, but Sierra is rather proud of them, apparently. I know no one that's shooting them due to their ridiculous cost. They're more than Bergers and JLK's. Stupid.


John
 
#12
Re: 308 Win, 220gr SMK, RL17

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jrob300</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hill billy</div><div class="ubbcode-body">Curious why you picked the 220 over the 210 with a BC of .645 if I remember right? </div></div>

The 210 makes more sense on paper, but Sierra is rather proud of them, apparently. I know no one that's shooting them due to their ridiculous cost. They're more than Bergers and JLK's. Stupid.


John </div></div>I can't argue with that. When I got the first box I ordered, I had to double check the site I ordered them from to make sure I didn't get something wrong. Double the cost of the 220's, sheesh.

I seem to have no trouble with my 10 twist 308 but I was wondering how a 12 would handle them. I guess this thread answers that.
 
#13
Re: 308 Win, 220gr SMK, RL17

The 220 SMK's are very stable, especially when going transonic. Kind of like comparing a B-52 (220 grain SMK's) verses an F-15 (210 grain SMK's). The 210's fly faster and flatter but become squirely when going from supersonic to subsonic. the big fat 220's just rumble along like big fat flying salami.

Besides, read the Navy report on why they choose the 220's over the 210's for the new 300 Win Mag cartridge. It's around here on the Hide, somewhere.
 
#15
Re: 308 Win, 220gr SMK, RL17

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ranger1183</div><div class="ubbcode-body">The 220 SMK's are very stable, especially when going transonic. Kind of like comparing a B-52 (220 grain SMK's) verses an F-15 (210 grain SMK's). The 210's fly faster and flatter but become squirely when going from supersonic to subsonic. the big fat 220's just rumble along like big fat flying salami.

Besides, read the Navy report on why they choose the 220's over the 210's for the new 300 Win Mag cartridge. It's around here on the Hide, somewhere. </div></div>

The 208 Amax seems to be equally stable going transonic. Both MM and I have shot them well through TS and they continue to group very well and fall nose first.

It would seem that the most compelling argument made for the 220 SMK by the military is that they are more forgiving with regard to same loading across different rifles, much like the 190 SMK. The secant ogive of the 210, although as mentioned is better in wind and flatter trajectory, can be a little finicky with regard to loading off the lands. It is possible that transonic performance was also a factor.

John
 
#16
Re: 308 Win, 220gr SMK, RL17

Shot this load today.

308 Win
220gr SMK, moly'd
Win brass
CCI 200
2.82" OAL
49gr RL17
20.5", 1/12 twist bbl
2545 fps

Conditions: 51F, 25.4 Hg, 60% Humidity, wind steady, 10 mph from west.

Shot at three distances. 200 yards, 1200 yards, 1760 yards.

200 yards: fired 10 rounds. had f/v wind. Shot on paper, All ten went right at 1 moa. more windage dispersion than elevation. All the holes were clean and round. Stabilization looked to be fine.

1200 yards: Fired five rounds. changed direction of fire to put wind at my back. Shot at a rock about 1 moa in size. JBM calc'd 44 moa at 70F. first round was low about 1 moa. Went to 45 moa and the next four rounds hit at about 1 moa accuracy, on and near the rock I was aiming on.

1760 yards: Fired five rounds. Wind at my back. Aiming at a small sagebush about 1 moa in size. Used the GenII Mildot reticle to hold 15 mils (about 51.5 moa), and dialed an additional 40 moa, for a total of about 91.5 moa. First round was low about one mil. i dialed in three more moa on the erector, for a total of 94.5 moa. Next round was elevation correct and about 1 mil left (wind). Dialed right 3.5 moa wind, and the next three hit right at the base of the sage I was aiming on. I would estimate all within 1 moa of each other.

Stabilization seemed to be fine in this atmo. And accuracy was 1 moa or so, at all distances.

My cases looked good. Very sooty at the necks though, which I read as low pressure. Primers and bolt lift showed no indications of excess pressure.



CopyofP9220052.jpg
 
#22
Re: 308 Win, 220gr SMK, RL17

Very interesting. MM, I'm assuming you are running a factory Remington barrel/chamber? This would give you a longer throat allowing you to seat the bullets out further. I wonder how this would work with a custom barrel chambered for 175 SMKs. I've been running this setup in Laupa brass, so it may not work so well. Any thoughts?
 
#23
Re: 308 Win, 220gr SMK, RL17

John, yes I'm shooting the factory bbl/chamber/throat.

I found these 220 SMKs kiss lands at 2.93" in my chamber. I was curious as to how they might perform at magazine length, but they could certainly be loaded longer in my rifle.

Not sure how much difference it would make pressure wise to be kissing lands, ala chamber cut for 175s at 2.80" oal.

Another factor is I'm moly coating them.

I may load up a few at 2.93" (kissing lands in my rifle) and see how it goes. I would easily have space for another 1-2gr of powder, if pressure allows it.
 
#24
Re: 308 Win, 220gr SMK, RL17

Intresting post, heavy slow bullets in 308.

Many years ago I looked at some swiss 7,5x55 match ammo that apparantly fired a 220+gr lubed jacketed bullet at something like 2300fps. The really interesting part was that claimed barrellife was 20000+ rounds. If there are any swiss shooters at the hide maybe they can inform us about this.
 
#25
Re: 308 Win, 220gr SMK, RL17

MM, great posting I loaded some 220 smk's a while ago using RL-15 but did no serious testing, just shot for group size at 2 & 300 yards. After reading all the posts on the 208 AMax and RL-17, I did a little more research and read a little more of Bryan Litz's book.After reading this article
http://www.longrangehunting.com/articles/30-caliber-1.php
it really seems that heavier is the way to go. Decide to try the 210 boattail variety from Berger, Sierra and Swampy with RL-17 and see what sort of reaults I can come up with.
 
#29
Re: 308 Win, 220gr SMK, RL17

I was able to try the 220 SMK with RL17 yester with good results. Note I stil have to adjust the OAL to my rifle. This is with Lapua brass.

10-2-10_220SMK_RL17_480.jpg


My rifle is a Savage Model 10 w/26" barrel, 1 in 10" twist, Chote stock, and Bushnell 3200 5-15 w/tactical turrets
 
#32
Re: 308 Win, 220gr SMK, RL17

I'm going to chrony in a few weeks. There were too many last minute deer hunters signing in their rifles so I wasn't able to set up.
 
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