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View Full Version : Your input please for minimal muzzle diameter with a Krieger barrel and the 7mmMag?



VaniB
12-01-2010, 03:23 PM
Gentlemen, while I don't participate in actual Benchrest shooting, I still use very much the same equipment and hand tailored loads for my rifle, and seek premium accuracy from my rigs. Not sure if I should call them Varmint or Target Rifles, but I always seek 1/4" 5 shot groups if possible. I'm getting ready to order a 7mmMag barrel and a match grade reamer. I'd like to keep this rifle at 11-12 pounds with the scope if possible. Therefore, I want the minimum weight barrel that will be sufficient for a single tight 5 shot group at 100 yards starting from a cold barrel. That is my goal.

Choices;

A)The Krieger Remington Sendero sporter contour barrel is 26" and .830" @ the muzzle and aprox 4.5 lbs.

B) The Krieger tapered #8 "Varmint & Match contour" barrel is 26" and .820 @ the muzzle, and aprox 6lbs.

Question:

If I only shot a single 5 shot group out of the Rem 7mmMag cold barrel, will either one of these barrel contours allow a single sub-1/2" 5 shot group before the barrel overheats? (ie; will accuracy degrade after the first 3 or 4 shots?)

VaniB
12-02-2010, 01:54 AM
Oh Lord grant me patience. The dreaded one-liner! And this one ain't even funny.

(Pardon me folks.....just thinking aloud as I wait)

John Kielly
12-02-2010, 01:59 AM
Here's another one liner:

You might have better results on the 1000 yard benchrest forum as they are more likely to shoot in the manner you've stated with a calibre like you plan using.

VaniB
12-02-2010, 04:36 PM
Here's another one liner:

You might have better results on the 1000 yard benchrest forum as they are more likely to shoot in the manner you've stated with a calibre like you plan using.

John,

My past experince with the 600 and 1,000 yard guys is that they often shoot prone and will talk about their 4" to 9" groups. It's a different language and translates poorly with my goal to shoot 1/4" 5 shot 100 yard targets.

No John....I really think the problem is that those really experienced shooters on BRC and this forum who DO know the answers, just don't to care to participate in the thread of this PIA long-winded novice shooter and outsider who doesn't participate in organized competition...... but who sure does ask a whole lotta questions. But John, that's OK......because they are usually polite when and if they do participate in my threads. I have learned more about precision shooting in the last 5 years from these guys, then what I knew in my first 30 years of shooting and handloading.

Mike Bryant
12-02-2010, 06:24 PM
Either contour should work for 5 shot groups with no degradation in accuracy. If accuracy starts opening up as the barrel heats up with five shot groups then the barrel probably has a stress relief problem. I consider either of the two contours that you listed as being heavy contour barrels. When you get into light weight barrels #3 or smaller then they become more prone for group sizes to open up as the barrel heats up. Some barrels will shoot to a different place on a first shot after cleaning. Whether this is caused by the first shot in a clean barrel or whether it's caused by some solvent left in the barrel, I don't know.

VaniB
12-03-2010, 01:31 AM
Either contour should work for 5 shot groups with no degradation in accuracy. If accuracy starts opening up as the barrel heats up with five shot groups then the barrel probably has a stress relief problem. I consider either of the two contours that you listed as being heavy contour barrels. When you get into light weight barrels #3 or smaller then they become more prone for group sizes to open up as the barrel heats up. Some barrels will shoot to a different place on a first shot after cleaning. Whether this is caused by the first shot in a clean barrel or whether it's caused by some solvent left in the barrel, I don't know.

Thanks Mike. That's good info and reassuring too when it's coming from you.......never mind the thrill for me to return here to see a first real reply in 2 days. LOL

It seems I've heard some guys on these forums and elswhere mention that it is practically a given to expect the POI to wander after 3 shots due to excess heat from these larger cartridges. While we aren't there to witness the barrel contour they are using, or know all the circumstances leading to such poor shooting, all I knew was I didn't want to set out building a $2,000 target rifle that couldn't put 5 rounds out of a cold barrel into .5" group. I have little experience shooting the larger cartridges and thought it would be wise for me to investigate this a bit further with people that know. You're that "people". :o Hopefully I will not be the unlucky guy that gets stuck with a barrel that has "stress relief" problems. Appreciate your help.

Randall

Octopus
12-09-2010, 07:56 AM
My experience is the 26" barrel is short for the Rem 7MM Mag case. A longer barrel is needed to utilize so much powder. With so much powder in a 7mm bore the muzzle pressure is high. That is the pressure behind the bullet when it exits the barrel is usually sufficient to de-stablize the bullet. The bullet leaves the barrel coning. Coning bullets drop more and are more subject to side winds. With a boat tail bullet the coning condition is increased. The boat tail bullet then goes down range in a spiral and does not go to sleep till it passes 200 or even 300 yards.

I would suggest the 7-08 AI would be better at short ranges and even out to 600 yards.

Mostly what you get with the added powder is more muzzle blast.

VaniB
12-09-2010, 11:13 PM
My experience is the 26" barrel is short for the Rem 7MM Mag case. A longer barrel is needed to utilize so much powder. With so much powder in a 7mm bore the muzzle pressure is high. That is the pressure behind the bullet when it exits the barrel is usually sufficient to de-stablize the bullet. The bullet leaves the barrel coning. Coning bullets drop more and are more subject to side winds. With a boat tail bullet the coning condition is increased. The boat tail bullet then goes down range in a spiral and does not go to sleep till it passes 200 or even 300 yards.

I would suggest the 7-08 AI would be better at short ranges and even out to 600 yards.

Mostly what you get with the added powder is more muzzle blast.



Along the lines of what barrel length were you thinking?


The 7mmMag is a done deal. I only need to order the barrel. I dont want an excessively long and heavy bench based rifle. I was thinking something more along the lines of the long time proven Remington 700 police/sniper rifle in 300Win Mag. I've so far decided on a 26" barrel with an .850" diameter muzzle and an 1 1/4" Hollands brake beng contoured to the barrel. (total 27 1/4" long barrel)

I carefully studied all cartridges and ballistics before settling on the Rem 7mmMag. I've concluded that nothing can shoot a 162 grain bullet at 3,000FPS so far and so flat......not a 300 Win Mag or any 264 based cartridge. The 7mm stainless 700 action, cases, and reloading tools are plentifull and inexpensive. This is why I chose it over the new WSM style cases. Barrel wear and recoil are reasonable for a cartridge of this power. (especially with a brake)

Your input is welcome.

Jbordi
12-14-2010, 10:43 PM
Interesting article on barrel length.

www.tacticaloperations.com/SWATbarrel/

Donald
12-15-2010, 02:38 AM
Not that I would build a rifle like this but I would figure the weight of all the other components and then go with the heaviest barrel I could stand. Maybe go a bit heavy and have it fluted back to a bit lighter weight.

JerrySharrett
12-15-2010, 08:54 AM
Some barrels will shoot to a different place on a first shot after cleaning. Whether this is caused by the first shot in a clean barrel or whether it's caused by some solvent left in the barrel, I don't know.

A chronograph will give a good part of the answer about a different POI for the first shot on a just-cleaned barrel. A just-cleaned barrel will chrono 75-150 fps slower on the first shot than it will on subsequent shots.

VaniB
12-16-2010, 01:58 AM
Interesting article on barrel length.

www.tacticaloperations.com/SWATbarrel/


Thanks for that link.

While I have heard similar style studies done on the 22LR rimfire and the .223/5.56 cartridge with final conclusions that favor shorter 20" length barrels, I don't recall reading such studies for the larger 308 and 300win Mag cartridges. I personally just don't care for the looks of a short and stout 20" barrel on a bolt action centerfire. But if anything, this article reinforces the premise that my choice of a 26" barrel should be maximum length (and not longer). And so too should my choice of an .850 muzzle also prevent barrel "whip".

Yes gents, agreed that the first one or two shots out of any cleaned barrel should be "fouler shots" (.....no matter what the scientific reason for why they will often stray.)

Nodak7mm
12-16-2010, 11:58 AM
VaniB,

I like the way you think... I too love the 7RM

27", Brux #5 w/interrupted fluting & a SSG Brake. Rig weighs 10.5lbs as you see it. I run the 162 Amax around 3070.
Barrel is awesome and scary accurate. It shoots far better than I am capable of.

Rod


http://i531.photobucket.com/albums/dd357/nodak7mm/IMG_2696.jpg