Critique My Rifle Build

[hunter399]

Run an ar10 in 308 or creed .
16 or 18 in barrel.
Yes its heavy ,but also suppresser ready.
Very fast follow up shots ,shoot till it's down.
My ar10 average about 2700 fps in 308 with an 18 in barrel.
308 uses a faster burn powder and can still get decent velocity in a short barrel ,down to 16 in.

[James]

When I first came up with this wacky idea years ago, I assumed like many of you that the velocity would be so low it wouldn’t work. And to be fair all the non mag cartridges I have looked at (like the 308) this doesn’t work. Velocities are just too low.

I knew bullet acceleration though the length of a barrel isn’t linear, but it wasn’t until I dug into it that I got some hope that something like a 300 wsm could work.

Take a look at the pressure, velocity, and distance graphs.  Now these are for a .270 win, but from what I can tell on reloading software this trend holds true for most modern rifle calibers.

The bullet velocity curve has an inflection point at about 5” of barrel length, meaning the acceleration of the bullet is less and less after 5” of barrel. The real heavy lifting gets done very early on, and I think we know that all instinctually.  Adding 2” of barrel length to 16” rifle generally results in a larger increase in velocity than adding 2” of barrel to a 28” rifle (everything else being equal).







Now the big question, is this all correct? I Don’t know, but the three different ways I have estimated muzzle velocity were all in the same ballpark (2800 ft/sec), so that’s a good sign.  I should prob see how the savage striker, savage 110 PCS, Remington XP-100, T/C Encore, etc crowd is doing their thing.

[James]

Here is a question to the guys suggesting other calibers.

I totally understand and can see value of using a big bore handgun or lever gun for this application.  You guys might be totally right that is the best call.

But the guys recommending  things like 308, 358 win, etc. How are you guys deriving your muzzle velocities and what are you getting for an 8-10" barrel?  When I run the numbers I can't get anything high enough to work for this application. Only calibers like 300 wsm, 270 wsm, 300 wm, etc. seem to put out numbers that make this project worthwhile.

I would like to understand how we are getting such opposite results.

[yorketransport]

This is the first interesting topic I've seen here in a while! 

The only issue I see with your plan has nothing to do with the gun itself, just with the factory ammo requirement. In order for your plan to work effectively, you need to think outside the box (literally I suppose). You'd like to use monometal bullets if possible, which is already going to limit your options for factory loads. The problem you'll have next is finding factory loads using the appropriate bullet to accomplish your goal. You'll actually want a bullet in the 130gr range to help keep your velocity up. You're looking to use it at moderate ranges (inside 350), so BC isn't a big deal. What you really need is a lighter bullet at a higher velocity to make sure the bullet performs on impact. Some of the ammo for places like DoubleTap and Copper Creek might have something that would work for you.

Working within the parameters you initially put out here, the only thing you need to do is locate an ammo company that either currently loads lightweight bullets for the 300 WSM, or is willing to custom load the ammo for you. You could check with some of the custom ammo shops about loading ammo using the lightweight bullet from Barnes, Cutting Edge, or Hammer. A 125-130gr copper bullet with a muzzle velocity of around 2500 fps should be possible from a 10" barrel without too much effort.

Here's where I'll completely change your plan and suggest what I'd do to accomplish the same goal. 

Unlike everyone who's telling you to go with a smaller chambering, I'd go bigger and look at something like the 30 Nosler or 300 PRC. The only way to maintain velocity while taking away barrel length is to add powder. If you go too big though you'll have a hard time getting a good case fill when using lightweight bullets with an appropriate powder. It can still work, I just don't like getting down into the 80% case fill range. Powder choice is influenced more by bullet weight than barrel length, so that isn't even a consideration for me.

The barrel length would have a lot to do with how I wanted the gun to balance. The really short barrel is going to make the gun balance in a weird spot. I'd look at a 12" barrel so that it comes in around 18" with your suppressor on there. I just don't like guns with too much weight in the buttstock.

I'm not a suppressor guy, so I can't provide any intelligent or informed information on that aspect. I would assume that it's going to be tough to find a suppressor that's rated for a very short barreled 300 mag (in any form). That's a lot of muzzle pressure to contain and I'm not sure how many suppressors can handle that.

[dreadi]

Do it. Have fun. Kill elk.


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[b23]

What weight bullet are you thinking about using if you were to go 300 WSM?

FWIW, running a 300WSM with a 10in tube and 200gr bullet through QL it says RL26 will be the best powder for velocity and at max chamber pressure 2265 fps. 

Running the same build spec and bullet but chambered in 308 QL says CFE223 is the best powder and at max pressure 2085 fps.

BUT, to get that extra 180fps with the 300 WSM you'll be using 25.3 grains more powder.

If I were insistent on building such a short barreled setup I think I'd look at doing a .338 maybe something like the 338 Ruger Compact Mag or even necking up the 308 to 338.

QL says a 10in 338 RCM with 200gr bullet will go 2300 using 63gr CFE223 and a 338-308 will go 2210 burning 46.7gr powder.  IMO, either one of those, in such a short build, would be a better choice than the 300 WSM.

[hunter399]

There is a reason that with most magnum calibers ,you won't hit peak velocity till 24 in of barrel.
You may think most of the magic happens at the first five inch of barrel. But with slow burn powders,which most magnum calibers use ,that bullet is picking up speed till it hits the end of the muzzle. Basically pressure and burning powder are pushing the bullet.
Even if all the powder burns in 5 in of barrel all the pressure will be lost at 10 in or at the end of the barrel.
That's why let's say my ar10 ,I can stick the same rounds in my bolt gun ,2850 velocity,stick them in my ar10 ,2700 or less ,some of that pressure is delivered back to the action.
18 in barrel ,gas system,vs,bolt action with 22in barrel.

I do thinks it's a great idea,if you have the money to burn.
I agree with dreadi ,build it,kill elk.
There are lots of other calibers that would reach the same velocity like a ,45/70,30-30,300 blk,308 loaded with a 200 grain bullet. You could get a 30-06 right out the box loaded with factory 220 grain bullet and be in the same boat or better.

I think you would end up with similar results as these.

[Alchase]

You wanted Critique here it is . 1st you need a $200 tax stamp for the SBR , then another $200 stamp for the Suppressor  , then your going to have to pin and weld a $1000+ Suppressor to the rifle . Which can are you looking at ? Is it even rated for your 300WSM  and the pressure ? If you go through all the above what's the decibel benefit making a 300 Wsm sound like a 30.06 ? Kinda defeats the purpose of a can . No way would I tie up one of my $1000+ Suppressors to one gun .
Probably be better off like others have suggested and just get a lever action..

 

Except, if you have an SBR stamp, no need to pin weld.

If you filed today for your Tax stamp and Suppressor, you would be extremely lucky to have them within six months.

Somethings to think about, first you are building a short barrelled rifle for hunting thick cover, but you require 300 yard accuracy. 

If I was to build a short barreled rifle, I would start with a caliber designed for short barrelled rifles. The 300 Blackout was specifically designed for this purpose. A 300 blk with a 100 yard zero, would have roughly a 2 ft. drop at 300 yards.  Inside 200 yards it is would be optimal.
If going this way, I would choose a 9" barrel, the optimum length for the 300blk, on a AR platform.

Then again, if you just want to build a short barrelled rifle with a high caliber bullet just for kicks, literally  , there are a couple guys on here that have built exactly what you want.

[huntandjeep]

You wanted Critique here it is . 1st you need a $200 tax stamp for the SBR , then another $200 stamp for the Suppressor  , then your going to have to pin and weld a $1000+ Suppressor to the rifle . Which can are you looking at ? Is it even rated for your 300WSM  and the pressure ? If you go through all the above what's the decibel benefit making a 300 Wsm sound like a 30.06 ? Kinda defeats the purpose of a can . No way would I tie up one of my $1000+ Suppressors to one gun .
Probably be better off like others have suggested and just get a lever action..

 

Except, if you have an SBR stamp, no need to pin weld.

Yeah not sure what I was thinking last night about the pin / weld combo.

[Caseknife]

Don't think anyone makes a suppressor rated for a 10" barreled 300 mag.  The shortest are 20" for the 300 mags and up, 10" for the 223/5.56 capacity cartridges.

Get a Ruger Ranch in 450 Bushmaster, short barrel and lots of thump.

I know this isn't politically correct, but I have been hunting for over 40 years and killed plenty of elk and deer in the timber with all sorts of firearms and NEVER have used hearing protection.  I can still hear.  Have I lost hearing acuity, yes, but is it not from the many years of using 1/2" impact wrenches and air die grinders?  I always use hearing protection at the range, but with only one shot or two while hunting, I don't think that is going to destroy your hearing any more than walking around with ear buds in listening to music blasting as we see all the time.

That said, build away, have fun.

[MeatMissile]

You may think most of the magic happens at the first five inch of barrel....

I read an article in COSMO that a majority of American women under 30 believe a longer barrel is necessary for any real magic.

[fly-by]

10" Barrel
.300 WSM
Suppressed

Pick 2

This package is very handy and a lot less money/effort.

[dreadi]

Don't think anyone makes a suppressor rated for a 10" barreled 300 mag.  The shortest are 20" for the 300 mags and up, 10" for the 223/5.56 capacity cartridges.

That’s not true.

https://deadairsilencers.com/products/sandman-k/





https://deadairsilencers.com/products/sandman-s/





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[hunter399]

You may think most of the magic happens at the first five inch of barrel....

I read an article in COSMO that a majority of American women under 30 believe a longer barrel is necessary for any real magic.

 
What do most woman over 30 believe.
Sometimes you gotta make due with what God gave ya.

[kselkhunter]

If you have the money and want to do a fun build have at it and enjoy.  We all love fun gun projects.  Yorke has posted alot of such fun short barrel/pistol projects on here over the years and it's fun to follow along.


I guess my issue is with the physics of the plan.   The best suppressors reduce roughly 23-26db (based on actual testing not marketing claims).  Rifles in standard barrel lengths range from 150db-175db depending on chosen cartridge, and will vary from there based on how short you make the barrel.   And unsuppressed 308 with 24" barrel is 156db, and with 20" barrel is 170db.  A 10" barreled 300WSM hasn't been officially measured, but you're likely going to be pushing 180db-200db in that setup.  140db is the pain threshold level for hearing, and what suppressors are designed to get you below.  In your desired setup, you're likely going to be in the 150-170db range with suppressor.   


Plus with 10" barrel a portion of your powder isn't going to burn in a factory ammo cartridge, it's going to blow through the suppressor and out the barrel.   Factory ammo isn't likely to perform like you think it will.  You'd need to hand load and experiment with different powders to optimize velocity and powder burn. 


I would call the suppressor company you're thinking of and asking them about the rating for 300WSM barrel specifically in 10" barrel.  The cans will be in the 5-10" long range depending on company.  So cutting your barrel and adding a can is going to put you back into the 16-20" barrel+suppressor length range.


Yes I realize the suppressor also helps calm recoil....but again you're creating excessive recoil by shooting a 300WSM in a 10" barrel and putting a suppressor on it to end up at the same recoil level (or higher) than you'd be at with a different cartridge choice. 


Again, it sounds like a fun new gun project.  But just make sure you understand the physics of it so you're not disappointed when your suppressed SBR is shooting at 160db ratings.