Cartridge for 18" barrel?

[ImBillT]

For hunting I don't put enough rounds done field per year to worry about brass life - just safety.

Then hotrod away.

on an aside though, another reason not to base an entire build on cartridge that must operate near 100% of its capabilities to meet your requirements is related to tuning. You may find that the cartridge can hit the velocity you’re looking for, but the accuracy node is below your velocity goal, and you’re unable to hit the next node above it. With a 280AI, you’ll like have multiple accuracy nodes above your minimum muzzle velocity. The same can be said of seating depth. You may be able to meet your velocity goals with a smaller cartridge if you seat the bullet long to spare case capacity, but find that your bullet shoots best with more jump, and thus lose your ability to put enough powder in the case.

 

[ImBillT]

JBM has me at 420yds 2165fps 1500ftlbs with 144gn Hammer Hunter (G2=.230) @ 2850fps and 3500ft elevation. At 450yds it gives me 2120fps and 1440ftbls - close enough for govt. work as they say. So for my purposes, it sounds like 7x57AI, 7SAUM and 280AI can get me there on paper.

That’s why I was suggesting reducing your target range a tad in earlier posts. A 7-08 will hit your velocity and energy targets much more comfortably at 400yds than at 450yds.

This entire thread is loaded with reasons why I have a 7mm barrel and 280AI reamer sitting in a shop down the road just waiting for a bored gunsmith to go to work.

 

[VikingsGuy]

Then hotrod away.

on an aside though, another reason not to base an entire build on cartridge that must operate near 100% of its capabilities to meet your requirements is related to tuning. You may find that the cartridge can hit the velocity you’re looking for, but the accuracy node is below your velocity goal, and you’re unable to hit the next node above it. With a 280AI, you’ll like have multiple accuracy nodes above your minimum muzzle velocity. The same can be said of seating depth. You may be able to meet your velocity goals with a smaller cartridge if you seat the bullet long to spare case capacity, but find that your bullet shoots best with more jump, and thus lose your ability to put enough powder in the case.

I typically get an average max charge from a couple of reliable reloading books/mfg websites and then drop down about 10% and work up from there. I usually find a few nodes along the way. In my experience, it seems the top load below the max seems to be the best one, but that may just be good luck. I typically never exceed max book load as I don't water weigh fired brass to calculate capacity for my particular rifle and I value my life over a fast round (or as I say, life is short, no reason to make it shorter). The hammers make this trickier as they don't seem to create pressure signs at the point I would typically expect and my 7mm08 has about a grain more powder than I would typically have considered max with more traditional monos.

 

[winmag]

Had a friend do a quick test with his 24” barrel 7 Rem Mag; suppressed vs non-suppressed. Only picked up 15fps with the suppressor. I suspect an 18” barrel would pick up more. And I suspect a suppressor baffled for a 7mm would pick up more too (his has 30 caliber baffles so he can switch it between rifles).

 

[ImBillT]

I typically get an average max charge from a couple of reliable reloading books/mfg websites and then drop down about 10% and work up from there. I usually find a few nodes along the way. In my experience, it seems the top load below the max seems to be the best one, but that may just be good luck. I typically never exceed max book load as I don't water weigh fired brass to calculate capacity for my particular rifle and I value my life over a fast round (or as I say, life is short, no reason to make it shorter). The hammers make this trickier as they don't seem to create pressure signs at the point I would typically expect and my 7mm08 has about a grain more powder than I would typically have considered max with more traditional monos.

The point is that if it requires a max load to reach the target MV, then you don’t have any room to tune the load. The load just is what it is. On the other hand, if you pick a cartridge that will substantially exceed your target MV, then you have lots of room to tune seating depth and powder charge while remaining above the minimum MV target. If a 7-08 barely gets there, then you’ll either have to accept the load however it shoots, or tune, and accept that you fell below the target.

A 7-08 will barely get you there with a 168 lead bullet. A mono might make it tough. A 7-08AI or 7x57 would probably give you a little room to tune with the top few powders. A 7x57AI, 280, 284, or 280AI should all leave you plenty of room to tune with just about any powder that’s suitable for them.

A Lilja 3-groove can be worth some extra velocity.

 

[ImBillT]

Had a friend do a quick test with his 24” barrel 7 Rem Mag; suppressed vs non-suppressed. Only picked up 15fps with the suppressor. I suspect an 18” barrel would pick up more. And I suspect a suppressor baffled for a 7mm would pick up more too (his has 30 caliber baffles so he can switch it between rifles).

How many shots with each? 15fps is well within most extreme spreads, and even within a single standard deviation for a lot of loads.

How quiet is a suppressed 7mag? An 18” 280AI would probably be at least as loud, if not louder.

 

[winmag]

How many shots with each?

5 each. I’ve seen it as high as +100fps with short barrels.

I’ve heard a ton of different high powered rifle calibers (223 through 338 Lapua) with suppressors and they all just sound like a loud crack without much bang. I’m sure you could measure a few decibels difference here or there but all the suppressed hunting rifles I’ve heard sound about the same.

 

[ImBillT]

5 each. I’ve seen it as high as +100fps with short barrels.

I’ve heard a ton of different high powered rifle calibers (223 through 338 Lapua) with suppressors and they all just sound like a loud crack without much bang. I’m sure you could measure a few decibels difference here or there but all the suppressed hunting rifles I’ve heard sound about the same.

It certainly makes sense that a can would increase velocity, but have never heard actual numbers. Obviously it would be a lot less than adding the same length barrel. I never knew if it was a meaningful amount or not. 15fps really isn’t meaningful. 100fps would be.

If there’s not a substantial difference in loudness, then I see no reason for VikingsGuy not to go straight to a 280AI at a minimum.

 

[winmag]

The more overbore the cartridge and the shorter the barrel, the more the suppressor adds. The +100fps I mentioned was an 18” barrel 243.

 

[ImBillT]

Because I have an illogical aversion to magnums I have not looked into them very much. I just realized that a 7SAUM and 280AI should be essentially equal in terms of performance.

 

[brockel]

Because I have an illogical aversion to magnums I have not looked into them very much. I just realized that a 7SAUM and 280AI should be essentially equal in terms of performance.

The 7mm saum just fits the tikka action better in my experience

 

[ImBillT]

Std7mag is claiming 2840ish with a 140 from a 7mm-08AI. He didn’t mention barrel length. 2840fps with a 140gr is attainable from a standard 7mm-08. The standard 308Win and other cases based on it have limited body taper already, and aren’t terribly long. Turning them into an AIs adds very little.

 

[Wind Gypsy]

Tikka actions are a great platform for SAUM or 284! 300 WSM, SAUM, or RCM would all be good too.

I think 280AI is ballistics twin of 7SAUM, any reason to prefer one over the other in a suppressed 18" barrel? I ask as I already have brass and dies for the 280AI.

Main thing is you can't seat bullets as long in a 280ai and fit in a tikka mag and you lose close to a half inch of bore length with the same length barrel. Not deal breakers.

 

[Curvebow]

What about the new 6.8 Western cartridge? Supposed to be really potent! (Apologies if already mentioned; I only read part of page 1.)

 

[tzone]

.308, 7-08, 6.5CM

 

[CForest]

I'm getting close to finally starting a very similar tikka/carbon six build, also suppressed. As of now I think I have myself convinced to do a 20" 7saum throated for 180s, likely with the intentions of the 172 absolutes even though the bc isn't overly exciting. I still have some decisions to make, but I'll probably start with the carbon six barrel since they are currently on sale....

 

[std7mag]

I was getting 2,832 fps from my 7mm-08AI from a 22" barrel with H414, PP2000MR, IMR 4350 and 140gr Berger VLD Hunting bullets.
The hotrod was 2,916 fps with RL17.

Vikingguys parameters seem to me best for the 6.5 Grendel.

History teaches the lessons we forget.
Remington came out with their 6.5mm Rem Mag coupled with their 350 Rem Mag in the Model 600, Model 660.
The cartridges were fine.
The short barreled rifles, not so much.
Recoil & muzzle blast were a major part of the demise of those 2 cartridges.

Velocity comes from pressure & barrel length.
So for the 7mm-08 at 2,800 fps from a 22" barrel take off about 25 fps per inch less.

The comment on page 1 about a big bore bears some thought.
Perhaps a 450 Bushmaster?
Or 358 Win.

 

[Idahoarcheryhunter]

Can’t go wrong with 308 IMO.

 

[JohnCushman]

The Army is going to a 6.5 PRC in a carbine size urban sniper rifle according to Guns and Ammo TV.

 

[ImBillT]

I was getting 2,832 fps from my 7mm-08AI from a 22" barrel with H414, PP2000MR, IMR 4350 and 140gr Berger VLD Hunting bullets.
The hotrod was 2,916 fps with RL17.

Vikingguys parameters seem to me best for the 6.5 Grendel.

Not sure you read the parameters. The 6.5 Grendel won’t come remotely close to meeting his velocity and energy desires at 450yds.

Small case volumes for bore diameter loose less velocity from shorter barrels than larger cartridges do, and therefore have less disadvantage compared large cartridges, while maintaining all their normal advantages, thus, they more commonly used when barrels are short BUT the question was not “I’m using an 18” barrel, is it worth using a 26Nosler instead of 6.5CM?” The question was “what cartridge will meet these criteria even from an 18” barrel?” Hitting a certain goal for the velocity/energy combination actually requires a larger cartridge the shorter the barrel gets.