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Which 20" barrel magnum

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Slowshot18

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Aug 8, 2018
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Houston, TX
I want to preface with yes, I know short barreled magnums are dumb, you don't burn all the powder unless your barrel is 40" long, might as well get a 308 based cartridge, blah blah blah. I had a short 308 and it was boring.
Here is what I'm looking for:
I hunt primarily in Texas where we traditionally hunt out of box blinds. I take a lot of clients hunting for work. Some of those clients are not great shots and I like to finish off those animals quickly. The animals range from whitetail, nilgai, eland, etc (please don't add commentary on the ethics of high fenced hunting, heard it before).
Having my 27" 300wm with a can or my 26" 28 nosler with a can is not real practical in a blind. I've done it plenty of times. I have a 20" 6.5 CM and its real handy to shoot but I want something with more ass behind it. This has led me to a 20" barreled magnum.

Constraints:
  • Will be on an origin LA so no normas or lapuas
  • 20" length will keep within the range of the Thunder Beast's parameters for the 338 ultra can that will live on this gun
  • No wildcats. Must be able to purchase ammo from common shops or custom reloaders such as unknown, copper creek etc. (I do not want to load for another cartridge at the moment).
  • No weatherbys
  • If I can run a ~200-ish grain bullet in the neighborhood of 2700 fps+, that would be great.

So what would you recommend? Do you have any data with shorter barrels?
I was wanting to potentially try a 300 PRC due to the factory loaded ammo with the heavies, but have yet to find much data on those with shorter barrels. Or I could go real dumb with a 300 rum.
 
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I cut down an extra 300wm barrel I had to somewhere around 20-21”. It was a 9 twist X caliber pre-fit. I also have a 26” Bartlein, 9 twist with whatever 300wm Straight Jacket Armory was using at the time they cut my barrel and the difference between the two is somewhere around 75-80fps or so with the same loads.
I shoot 220gr Berger’s around 2850 ish with RL26 out of the shorter barrel. 208’s were slightly above 2900 with H1000.

It’s been awhile but I did shoot some older ABM 300wm with 215gr Hybrids and from what I recall they were in the upper 2800’s.
 
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Bandit31 said:
I cut down an extra 300wm barrel I had to somewhere around 20-21”. It was a 9 twist X caliber pre-fit. I also have a 26” Bartlein, 9 twist with whatever 300wm Straight Jacket Armory was using at the time they cut my barrel and the difference between the two is somewhere around 75-80fps or so with the same loads.
I shoot 220gr Berger’s around 2850 ish with RL26 out of the shorter barrel. 208’s were slightly above 2900 with H1000.

It’s been awhile but I did shoot some older ABM 300wm with 215gr Hybrids and from what I recall they were in the upper 2800’s.
Click to expand...
@Bandit31 Trusty 300wm coming in clutch! I appreciate the speed info. This something I was definitely considering since I already have the infrastructure to reload if I wanted to down the road.

b6graham said:
30SM or 338SM no questions asked

buy 300PRC Mayhem ammo from Unknown and eventually, you'll have fire formed brass to last a life time or sell it
Click to expand...
@b6graham got any speed data on the shorter barrel spectrum? The 30SM is a candidate because I don’t have to immediately load for it but the 338SM is out, although probably one of the best candidates.
 
Slowshot18 said:
@Bandit31 Trusty 300wm coming in clutch! I appreciate the speed info. This something I was definitely considering since I already have the infrastructure to reload if I wanted to down the road.


@b6graham got any speed data on the shorter barrel spectrum? The 30SM is a candidate because I don’t have to immediately load for it but the 338SM is out, although probably one of the best candidates.
Click to expand...
check the Sherman Website. he has links to the LRH thread. also his FB group is very active

Unknown will load for 338SM (338PRC in reality) afaik but pricey (it all is)
 
I like your style! Some good advice please keep us posted.

I started a similar creation years back with a 300 Ruger Compact Magnum. Sadly the project went down in flames. Long story short I bought two new M77 all weathers for short barrel/suppressor hunting but both were horribly inaccurate.

Now, I've got a new, old stock Rem 700 WSM that's taunting me to give it another go!
 
I know you want to stick with your action, but I purchased a T/C Encore specifically to hunt a particular small box blind. I think a 20"-22" 300WSM would be real handy. Won't break the bank either. Just something to think about.
 
im not a big fan of them but if you want short with a long barrel get a DTA

they shoot great and you can still have proper barrel length
 
I've thought about setting up a 300 WSM or 7mm WSM/SAUM similarly. I can get 190gr ABLRs up to ~2,640 fps in my 18.5" .30-06, so your velocity goals would seem to be pretty easily achievable in a WSM. With the long action I guess you could load the WSM out a bit, I'd probably stick with bullets on the heavier end of the spectrum as you OP suggests, IME they tend to lose less velocity in shorter barrels. I'm sure any number of Wildcats could do the same thing, but what's the point if the reasonably common WSM gets you there?
 
I run a 20” 30 Sherman Mag, Proof CF Bbl. I shoot 215 bergers at 2950fps with N570. Not running it hot either. It also shoots factory 300 PRC 212 ELD-X ammo at 2750fps
AA6375C1-51AD-4696-BC8E-680CB55A984A.jpeg

C74A3A78-DB8A-40F9-B886-E92DF33E69C6.jpeg
 
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I did a 28 Nosler 22" on a Gunwerks action and the customer was shooting 180s exceptionally well. I think he was getting around 3000, I can't remember exactly. The barrel was a McGowan 8 twist. He also sent me some video of impacts on steel at 1200 some yards. I was quite impressed with what he was able to get out of that short barrel.
 
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@Gtscotty That is impressive velocities out of an 06'.

@CA48 thats a sexy build! I'm really impressed with the speeds of the factory 300PRC in the Sherman chamber. Do you think there would be much velocity boost in a standard PRC chamber as energy might not be wasted on pushing out the shoulders in the 300SM chamber for factory PRC ammo? And were those numbers based off of your barrel before or after it sped up?

@FisherT&C I already own a 28 and I love it! 3200+fps with 180 eldms, n570, adg in 26" proof. With your customer breaking 3k in a 22", that is a logical choice to suite my needs. Thanks for the info
 
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300 WSM or 325 WSM should do the trick for you. You could also do a long action caliber and just tolerate the muzzle blast and loss of velocity. It’ll still be greater than a 308. Since you’ve got a long action, you could also do 338 win mag
 
Slowshot18, those velocities were after the barrel sped up. I don’t think you would see much difference in velocity with a standard 300 PRC maybe 10 or 15 fps.
I also have a 16” 30-06 with a long throat that runs 215s at 2580fps with RL17.
 
Gunwerks did a podcast discussing shorter barrels and for the 300 PRC and a 215gr Berger they had a 200 fps swing from 18” to 24”.
 
b6graham said:
Factory or reloaded with better powder (RL26 H1000 VVN5xx)?
Click to expand...

Most likely either their in-house ammo or handloads. They said the velocity was 2650 to 2850 so I’d guess H1000.
 
Welp, I decided on a 20” 300 PRC. I love my proof’s but they didn’t offer a blank in 20” with anything faster than a 1:10 twist.
Called up carbonsix, spoke to them for a while, and they seem like a decent value.
Ordered a 20” 1:8 twist prefit from Carbonsix in 300 PRC. Should have it in 3-4 months. Soon enough I’ll have my magnum chode ready to go!
 
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I'm 2 months in on my wait for my carbon 6. They're hard to beat for price and all the options they have. Plus everytime I've called, ive gotten someone very knowledgeable.
 
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I run Berger 245s @ 2750 from my 20” 300 PRC.

Also, not sure if Proof changed their offerings but I have a 1-8 twist 20” proof carbon barrel.
 
@Jlknights61 that’s impressive! What powder/brass combo are you using?
In regards to the proof: I searched their website and a few vendors with no cigar. I know some of their offerings have changed on the prefit side of things (discontinued 28 nosler for a lot of actions) within the last 6 months, not sure about their blanks.
 
Using Hornady Brass for now though hoping to get my hands on some Lapua in the future. I’m loading 90.6 gr of RL50.
 
I'm running a 20" 7ss, 175 Berger's at 2850fps with RL26. I could probably push it faster, never ran into pressure in my ladder test, but my last load in my ladder shot 2850 with a 2.5sd so I just stuck with it. Short barrel makes it really nice with suppressor to get around, in and out of vehicles and blinds.
 
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I may not know shit from shinola, but I recently spent some time on the YO Ranch. The Ranch Manager had a .300 Win Mag (Mesa from Christensen Arms) cut back to 20” and wearing a Silencerco Harvester. That’s a work gun for him, seems to do all right. He’s got a lot of big critters to contend with and loads 180 grain Accubonds at 2950 fps (basically just the advertised factory load dialed in for his rifle). FWIW.

Seems to me you could just borrow his rifle or build one near the same and be equally pleased with the results.
 
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Sounds like a fun build me I’m doing a 20 inch 6.5 prc with an ultra 7 on it for the reasons you listed as far as length goes
 
Having a 22” 300wm hunting rifle being built as we speak. You know what gets my vote.
 
@DJL2 the YO is a nice place. Haven’t been there in a really long time. I’m glad to hear the manager is running a shorty 300wm. He probably has to finish a myriad of game all year long. Hearing this confirms my choice of going with the shorty 300 prc since I don’t want to lose for another barrel at the moment.
@2c1fr a shorty 6.5 prc was close on my list. This past season I used a 20” 6.5 cm with 140 eldms and it was a hammer on sub 200lb game.
@rope 300wm is always a solid choice!
 
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This will be my third 300wm, first was a 26” barrel, then a 24” and now a 22”.
 
My 21” 300prc is currently running 3 grains under max with rl26, 215 berger @ 2850

Granted that velocity reading was taken at 30 rounds so it may be faster now
 
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