7mm-08 and a 20" barrel


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Ardent
January 21, 2005, 02:47 AM
How fast can I get a 162gr AMAX or a 175gr Sierra MK (preferably) going in a 20" barrel?

I'm putting together a tactical remington 700 short action with a 20" long 1" diameter barrel and an accuracy international stock in either .243, .260, or 7mm-08. Right now I'm trying to decide on the cartridge out of those three. For those who would mention it, I've ruled out the .308 based on the ballistic coefficients of the practical bullet weight choices for a barrel of this length, plus, I'd like something other than a run of the mill .308.

If you know what a 7mm-08 will do out of a 20" barrel with these bullet weights I would be much obliged, as well, I'd like to know what the .260 would be capable of in this length with 140gr and 155gr, if you can help, thanks again!

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rbernie
January 21, 2005, 09:27 AM
Lyman's book is the most optimistic - they claim 2600fps for a Hornady 162gr BTSP #2845 and 2500fps for a Speer GrandSlam 175gr #1643 out of their 24" universal receiver/barrel. These velocities are about 100fps faster than most other manuals. You also have to bear in mind that you'll likely lose 150fps-200fps when you lop off 4" of barrel length - these sample velocities were all reached by using relatively slow powders (RE19, 4350) that really want a longer barrel.

Sounds like you're trying to run a pretty heavy bullet in a small capacity case and out of a pretty short barrel.

Ardent
January 21, 2005, 02:29 PM
Yeah, that's my problem, I think I will end up going 6mm to get decent velocities. I've managed 3000fps out of a 20" barrel with a 100gr .243, so this is the route I really should be going. I will still consider the 6.5mm.

Thanks for the info.

kimbernut
January 21, 2005, 04:07 PM
This fellow mixes 'em a little hot for me but an interesting site.

http://members.tripod.com/sed88/rem7/

dakotasin
January 21, 2005, 06:00 PM
there is far more to exterior velocities than launch speed... for what you describe, i would be inclined to go either 7-08 or 260, preference to the 7-08...

as far as velocity, i don't have a 20" barrelled 7-08, so i can't say for a fact what it would be...

rbernie
January 22, 2005, 04:16 PM
Why not consider a 140gr .284 bullet? For example, the 7mm/08 will comfortably push a 140gr SPBT (BC .415) @ 2800+ fps. The same round with a 168gr MK drops 200fps in exchange for a BC of .488.

When I plug this into PointBlank, it tells me that the 140gr bullet will have less drop from the muzzle to past 500 yards. In other words, the extra velocity more than made up for the minor delta in BC.

So I guess I've gotta ask - what are you trying to do with the rifle? Is this going to be used for hunting, medium range (100-400 yard) target work, or long range target work?

Ardent
January 23, 2005, 02:07 AM
Reason for the 162gr is the AMAX has a BC of .625 which is quite astounding really.

The rifle will be for punching paper and varmints out to and past 600 yards or more when the distance is known. It will also serve as a walk around precision coyote rifle and for calling.

I'm really starting to like the 6.5mm in 139-142gr with BC's as high as .595.

I realize I'm handicapping myself with the 20" barrel for this but I have a thing for short, fat, stiff barrels. I also appreciate carrying them in the field :)

I will either go one way or the other, by that I mean I will go 26" or 20", I am still considering that one.

Art Eatman
January 23, 2005, 11:14 AM
I follow the notions of what you're trying to do, but the heavier bullets in that short case sorta handicap the deal.

I've had good results with Sierra's BT bullets in .30 at 500 yards. 150, 165 and 180 all provide about the same groupings.

I'd play "cut and try" in 7mm08, starting with a 139 or 140 BT. Then try the heavier weights and see what happens.

My 7mm08 is the 700Ti. 22" barrel. It seems handy enough to carry. I haven't gotten serious about tailored loads, but since inside one MOA is more than adequate as a hunting-only deal, I haven't really tried.

All the .308 series cartridges were designed around a shorter barrel than such as the '06. They don't lose as much velocity per inch of shortening. My .243 is a 19" barrel Sako Forester, and the results of the 85-grain Sierra HPBT are astounding. Gotta be around or above 3,000.

Art

GooseGestapo
January 27, 2005, 10:19 AM
RE: 20" bbl w/7mm-08.........

Funny you should ask!!!

I've been playing with a Rem M-7 w/20" bbl lately. Just yesterday I took it to the range and tried it out after glass- bedding it over the weekend. Excellent improvement. (Has laminated-nutmeg stock).

I'm getting only perhaps 40fps below what the manuals are showing for 24" bbls, with same bullets/powders/brass. About what most manuals call for. Expect 80-140fps less with 18.5" bbl. This is what I saw back in '91-92 while working up loads for a friends rifle then. (a 788 w/18.5"bbl) Because of the high effiency of this cartridge, it dosen't lose as much velocity as I expected. Suprised Me!

I haven't tried anything heavier than 150gr Nosler B.T. but results are very promising. With my first trials of H-380, I'm indeed getting best accuracy to date, with higher than anticipated velocities, just like the Lyman manual stated and the Nosler manual infered. According to my observations, 2,650fps is certainly possible, and 2,700fps perhaps possible with the 162gr bullet. Your barrel may be different. Mine is tight and fast. Factory PMC w/139gr Hornady SpirePts. chamber "hard", and show pressure marks after firing (bright smears on headstamp, and occasional impression from ejector-plunger hole. I used these as my "referrence" for pressure determintions. None of my loads produce this much pressure except for 47.5gr of IMR-4350, which I consider over-max for my rifle w/140gr bullets.

Best Loads and chrono'd vel's. and group sizes:
(vels. @15")

139gr PMC factory load:
2,800 avg. es-47fps, sd.21fps (2,840 advertised, 24"bbl)
1.8" groups (wanted to shoot with 3~1/2", two flyers)

140gr Rem. Cor-Lokt
Reloader 15; @2.800"oal. (2.830" to lands)
41.0gr 2,730fps (2.1" five shots before bedding, 1.2", 4-.85" after)
43.0gr 2,835fps (2.3" before; 1.2" after)
H-4350
46.5gr 2,775fps (2.0" before)
48.0gr 2,885fps (2.2" before) (max. my gun, but "OK"!)
IMR-4350
46.5gr 2,780fps (max my gun, this lot#) one deer killed w/this load/bullet. very good bullet performance!
47.5gr (first shot- sticky extraction, ejector-plunger mark- too hot!) single shot fired @ 2,920fps.
H-414 (dissapointing! my lot# seems "faster burning than previous lot#'s I used in .257Robt. and .30/06, and seems even faster than current lot of H-380)
46.0gr 2,725fps, 47.0gr may be max this gun, accuracy was poor at >2.5" five shots. didn't pursue further)
48.0gr (over max. 2,840fps, single shot fired)
H-380
46.0gr 2,783fps (14fps es!, 6fps sd!) 1.6" group before bedding
47.3 2,877fps (100fps faster than some manuals w/24"bbl!)
(this is max load my gun and per Hod. 2003 manual)
1.1" after bedding, 4 @ .55"! single "flyer" showed a 50fps variation, ruining a 21fps es and 15fps sd of other 4), suspect an out of spec. bullet, or possibly primer (WinLR).7

140gr Sierra BoatTail S.P. (2.775" oal. 2.795" to lands)
RL-15
41.0gr 2,740fps (.870", best group before bedding. 2min between shots, seated to 2.795", New, unfired brass!)
42.5gr 2,820fps (1.7", 4 @ .90")
(killed three deer w/3-shots with this load!) Preferred hunting load before using H-380 or H-4350
H-4350
47.5gr 2,870fps 1.95" before bedding)(anticipate possibly using this w/140gr Nosler Part. for elk load next season)
48.0gr 2,890fps (consider over max. for my rifle,this bullet) two shots ran over 2,900fps) avg is 2,900fps corrected to muzzle.

Nosler 150gr Part. 2.830" oal (max for my mag. length- 2.880" to lands!)
40.0gr RL-15 2,690fps
42.0gr RL-15 2,750fps (strung vertically 1.5" prompted bedding rifle stock)
H-380
44.0gr (no vel.) 1.1" before bedding, verticle stringing,w 3 touching!
45.5gr (2,766fps, too hot my gun- 5-shots at .9", 4 at .5" second best groups w/this rifle)

As these velocities indicate, I'm getting approx. 40fps on average below what most current manuals show for 24" bbl. My 1984 Sierra manual shows some powders and 140gr bullet at over 2,900fps, but I consider them "suspect", due to available pressure testing technology then available. Charges are also higher than I will attempt. I also didn't see anywhere near Lymans 2,900+fps with Win748. Identical max. charge gave 2,838fps for single shot fired/tried.

I also didn't include my RL-19 data, as my lot# is way off on velocities. I burned up most of the 1lb I had testing with an '06 w/24" bbl. I couldn't get but 2,690fps w/180gr bullet at 59.0gr book max. Same gun gets 2,800fps w/RL-22 @ 61.0g and simular pressures. A 22"bbl Rem742 showed 2,650fps @58.5 and caused bolt to stick/jam open. Further testing was suspened with that load/gun!
W/7mm-08 the single 5rd string of 140gr Cor-lokts at 52.0g (Alliant's max) ran 2,830fps, about same vel's and pressures as RL-15 at 10gr less powder. At 48.5gr they were in low 2,600fps range with Sierra 140gr bullets. (starting load)

I expect some 150gr Cor-lokts in Monday or Tuesday, and will try them out with the H-380. I also have some 139gr Horn. SST's coming too.

Depending on how the 150s' go, I may try some 160gr Sierra's and the H-4350, for possible elk fodder later with 160gr Nosler Part's.

Like the other poster related, the 140's seem to hold their velocity/trajectory advantage even against heavier bullets with significantly better b.c.'s

I really like this gun/cartridge. I originally got it to use in deferrence to my 9.5lb MkX in .338/06 for "self guided" elk hunts in the high country of Colorado. This was because I felt the feather.wt. .257Robt. might be a little "too light" caliber wise for elk.

I've ended up liking this rifle so much, I killed the last 6 deer this season with it. Two with factory load, one w/cor-lokt handload, and three with Sierra BTSP. One of these Sierra's was very destructive w/6" exit wound on 100lb doe (weighed) shot at a measured 176yds. My impression is it's too soft for anything bigger than deer. Hornady and Remington C-L seem to be a bit tougher constructed.

And this was to be the "big brother" to my Rem M-7 in .223 I used to kill the #2,#3 and #6 deer I took with gun this year! (first one with cross bow in archery season). I just couldn't put the "Little 7 in 7" down. Plus, it's an incredibly "lucky" gun. My brother, the LasVegas poker dealer says it's in the "numbers"! It has to be Lucky! Upon seeing it at a recent visit and holding up one of the Nosler loaded rds, he pronounced it: "now THAT'S an ELK RIFLE for the mountains"
(he uses a pre-64 mod.70 F.W. in .308wcf and 150gr Nosler part's. 3shots, 3elk; and "numerous" mule and w.t.deer.

It wears a Leupold vari-X III 2.5-8x, and weighs 7.2lbs after I drilled two 3/4"x5.5" holes in the butt-stock (it felt butt-heavy compared to the .223- denser lamiated stock) and 5rds. About the same as the Mod-7 in .223 with 18.5"bbl and 2x-8x Tasco W.C.compact scope. Both wear Leupold bases and rings.
I still prefer the shorter .223 for hunting from shooting houses where the shorter barrel is easier to swing and manuver into shooting position without clubbing the structure like a did once with the 20"bbl!. Don't even think about swinging the 24" bbl'd Mauser's! Slide them up into position!

Sorry for the LOOOOONG post. The "little" rifle just does that to me!

Ardent
January 30, 2005, 01:38 PM
Fantastic!

I can't believe my luck, that is exact;y what I'm after, I'll have to come back to it when I have more time to read it, I have to run to work right now, but on skimming it looks like exactly what I'm after, thanks!

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