Minimum muzzle diameters in bigger 7mm's for carry & target work.

[VaniB]

Ok guys, I've taken quite a bit of notes and numbers in trying to determine which is the minimum muzzle diameter that should be considered for a 284 Winchester rifle, (and other bigger 7’s for that matter) that is to be used as a carry rifle, but mostly to be used for target off of the bench at the 100 yard range. I need your input here! The question is; Starting from a cold 26” barrel, can I get a single ½” MOA group (or better) from out of a .805” diameter barrel?
I have observed and taken the measurements of the following factory rifles for which we can use to help us make or break the case in determining the minimum muzzle diameter required;


Remington Varmint Fluted VSSF; .223 = .805"
Remington Varmint Fluted 17 Fireball =.805
Remington Varmint BDL, 1970’s .222 = .827”
Remington Varmint HS stock .220 Swift = .835”
Remington .270 Sendero = .833”
Remington VLS 22-250, Varmint Laminted = .836
Remington Police 300Win Mag Sendero = .825
Remington Police 308 Win HS stock .308 = .825
Remington 7mm-08 SPS = .838
Remington 7mmMag SPORTER acrylic BDL, = .644”
Remingtom 300Mag SPORTER acrylic BDL = .663


Savage Model 12 “Low Profile” .204 Ruger =.812”
TC 7mm-08 =.815
TC 300Mag =.810
Winchester model 70 Coyote, Laminated .308Win =.753
Winchester 70 Coyote, Laminated 22-250 =.748


Being I have no experience with shooting big bore, I can't be sure what minimum barrel diameter I should rely on to help provide for a single 1/2" MOA 5 shot group (or better) over a single 30 minute relay. I’m hoping that I can go with a .805-.810 barrel diameter in the Sendero contour. That's my objective and the kind of shooting I wish to do with my custom 26” Brux .284 Winchester barrel. Obviously heat dissipation will be a big consideration. If you follow Remington’s lead, they seem to use .805” in their 26” barrels for the small bore calibers, and .825-.830” for the larger bores. Winchester goes down to a .748 diameter in their 24” fluted and none-fluted Model 70 varmint rifles to help me make the case that perhaps a .805 is all the barrel thickness I will need. (and not need the .830”)

Now granted, a 284 Winchester shooting 162 Amax at 2800-2900fps is hot. But if just seeking a single 5 shot ½” MOA group ….. can I pull it off with an .805” barrel?

 

[Fordnutter]

I had your dilemma but for for a dual purpose varminter / F Class rig. I settled on a Palma contour - enough barrel to not be affected by long shot strings & trim enough even when carrying short distances in the field.

 

[Preacher]

.025 difference in barrel diameter will not make a barrel shoot better than it will at any other diameter..
Lots of small diameter barrels will shoot lights out...
If your .805 barrel is a good one and has been chambered carefully it should shoot good for you, but so would a .830...........
On any barrels you just pay the money and hope for the best, no real way of knowing for sure till you shoot em...

 

[VaniB]

Preacher and Fornutter,
I thank you two gents for your opinion, but the heavier Palma is not what I'd care for, and I need to feel like 5 shots will do 1/2" MOA.






Not to confuse issues w/ this equation, let's focus on the question of barrel diameter & heat dissipation effects on accuracy only. (not barrel quality, smithing, etc)

Reading the archives would lead us to believe that accuracy cannot be expected beyond 3 shots before barrel heat-up and shot dispersion. HOWEVER, I don't believe such an assertion can be reached without knowing the barrel diameter, cartridge size (ie; not 7Mag) , and frequency of the shots fired. (not "F class") This is why as an example I mentioned a cold .805" barrel firing five .284 Win cartridges from the bench over a 15 minute period.

I'm inclined to feel safe duplicating the .830" Sendero barrel configuration. Do you concur? But I really prefer the looks and lighter heft of a .805" diameter .223 VSSF style Remington barrel. I just don't know if I'm near the border line with having a .284 bore in that size barrel compared to the itzy bitzy .223 bore that has all that metal surrounding it. Then again, I only want 5 slow fire shots. Maybe the .805" diameter will be enough metal and heat absorption for a single tight group???

Your thoughts?

 

[jo191145]

FWIW I have a Kreiger 308W Palma barrel chopped down to 26". It measures .835" at the muzzle.

Beyond that I totally agree with Preacher.

Heres a thought.
If I had what I consider a thin barrel prone to heat distortion and I wanted to shoot one group in 30 minutes.
I'd pick the upstart of a condition and run them five down range as fast as possible. Sit back, have some water and watch the show.
Should be able to get em all out BEFORE all that heat has eminated throughout the entire barrel.
If you need to wait for target setters I quess my idea bites ;D

 

[Glenn Powell]

First time I have ever heard a 7mm referred to as a big bore : just had to chime in with absolutely nothing else to offer. Good luck! ;D

 

[VaniB]

Heres a thought.
If I had what I consider a thin barrel prone to heat distortion and I wanted to shoot one group in 30 minutes.
I'd pick the upstart of a condition and run them five down range as fast as possible. Sit back, have some water and watch the show.
Should be able to get em all out BEFORE all that heat has eminated throughout the entire barrel.
If you need to wait for target setters I quess my idea bites


Like many 100 yard public ranges out there, the relays each last about 20-25 minutes. This gives me plenty of time to comfortably position my rifle on the Hart rest, eyeball my flags, and take my time to TRY and pull off five well placed sub 1/2" MOA shots in about 10-15 minutes. The rifle goes back on the rack for the remaining 5-10 minutes when the cease fire is called and the folks go out to change their targets for another 15 minutes. And if I've chosen the right contour barrel, (say maybe about .805" at the muzzle) the rifle barrel will have plenty time to cool off. But I'd hate to have to rush through 5 shots.

 

[nastynatesfish]

I had a .705 or .735 on my 7mag savage rifle and it was a great shooter. 26" long it was my deer rig. But just because you have some meat on your gun doesn't mean it's going to shoot .5 MOA groups. Accuracy is an expensive game and most my 7mm bullets are more accurate at 2500-400 yards than at 100yds.

 

[VaniB]

Nastynate,

What you say has a lot of validity, and lots of folks have advised the same about expecting better accuracy in the distance with a 284 rather then at 100 yards.

So.....I wasn't expecting the best accuracy with my intent on shooting a 284 Winchester with a 26" barrel at 100 yards..... AND THEN I found this page at accuratereloading .com.... where just that is being done;
-------------------------------------------------------------------

http://www.accuratereloading.com/284win.html

-------------------------------------------------------------------

If you can believe it, that's a slew of incredible groups in the 1's, 2's, 3's, and 4's !!


Granted, it's a custom rifle with a Hall Action. But, it makes the case that PLENTY of very tight 5 shot groups can be expected if you have the right stuff and know how to shoot. A Hart "Varmint Weight Barrel" is mentioned...whatever diameter that may be, they don't define.

 

[nastynatesfish]

Here a group from mine at 100yds with 162gr amax.

I can hold a 1.5" group at 400yds. The bottom was a bad adjustment, it was suppose to go3clicks right and I went left.

Here's the rifle in subject rifle

 

[VaniB]

Nice shooting there. Yes, those 4 shots look to be a 5 /16" to 3/8" MOA group and what I'd very much like myself. Do you still own that Remington to put a caliper on the muzzle for me?

I got off the phone with Ken at Brux barrel. While he wasn't keen on knowing the particular Remington diameters off of the top of his head, he doubted that I would see any difference in group size from doing a Sendero barrel in .805 diameter instead of the factory .830

He said the fact that it's only intended to be 5 shots during a single relay is the key, and if I had been intending a larger cartridge like a 7mmMag it may be a different story.

 

[nastynatesfish]

It's .780 at muzzle. It's a 26" ershaw barrel with their helical fluting that I finish reamed and installed. There barrels are are the only ones I use. I've got 4on rifles that I have, one on the way and one that I ruined. This is my deer rifle. It weighs in right at 13lbs as it sits